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The geomorphology and permafrost conditions of Garry Island, N.W.T. Kerfoot, Denis Edward 1969

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THE  GEOMORPHOLOGY  AND  GARRY  PERMAFROST  CONDITIONS OF  ISLAND, N.W.T. by  DENIS EDWARD KERFOOT B.Sc. , King's C o l l e g e , U n i v e r s i t y of London, 1961 M,A», U n i v e r s i t y of B r i t i s h Columbia, 1964 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY In the Department of Geography  We accept t h i s thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA August, 1969  In p r e s e n t i n g t h i s  thesis  an advanced degree at  in p a r t i a l  f u l f i l m e n t of the requirements f o r  the U n i v e r s i t y of B r i t i s h  the L i b r a r y s h a l l make i t  freely available  Columbia,  I agree  that  f o r r e f e r e n c e and Study.  I f u r t h e r agree that p e r m i s s i o n f o r e x t e n s i v e copying of t h i s  thesis  f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . of  this  It  thesis for f i n a n c i a l  is understood that copying or p u b l i c a t i o n gain s h a l l  written permission.  Department of  CSgo&fefifiV^V-  The U n i v e r s i t y of B r i t i s h Vancouver 8, Canada Date  Ho>i«.rr V)ejp ^ . k  Columbia  A^kT.  not be allowed without my  ii ABSTRACT Garry I s l a n d , approximately 11 kilometres (7 miles) long and 0.8 to 3.2 kilometres (0.5 to 3.2 miles) wide, i s located at about l a t i t ude 69° 28'N and longitude 135° 42'W  i n the southern part of the Beaufort  Sea. The stratigraphy consists mainly of unconsolidated sands, s i l t s , clays and stony clays which have been i n t e n s i v e l y deformed by the thrusting action of g l a c i e r - i c e moving from the south.  The deformed sed-  iments are l o c a l l y o v e r l a i n by undisturbed sands and gravels containing marine f o s s i l s dated at>42,000 years.  The absence of any evidence of  g l a c i a l t i l l on top of the sands suggests that Garry Island lay beyond the northwestern l i m i t s of the Laurentide ice sheet during the late-Wisconsin glaciation.  Elevated s t r a n d - l i n e s , which may be of great a n t i q u i t y and  occur at approximately 7.5 metre (25 feet) i n t e r v a l s to an a l t i t u d e of almost 46 metres (150 f e e t ) , indicate the extent of Pleistocene f l u c t u a tions of sea l e v e l and the drowning of a pre-existing topography.  The  development of tundra polygons, i n small f l a t s behind sandspits or bars b u i l t across the drowned v a l l e y s i n association with the former sea l e v e l s , has imparted a d i s t i n c t i v e , stepped l o n g i t u d i n a l p r o f i l e to the stream courses. The tundra vegetation of Garry Island i s c l a s s i f i e d into ten major habitats which are p r i m a r i l y r e l a t e d to drainage conditions and type of geomorphic a c t i v i t y .  The i s l a n d i s underlain by permafrost and the  thickness of the active layer i s greatest, and ground temperatures i n t h i s layer are highest, beneath unvegetated surfaces and where the substrate i s composed predominantly of mineral s o i l .  iii S t r a t i g r a p h i c , geomorphic and h i s t o r i c evidence i n d i c a t e s considerable recession of the c o a s t l i n e i n recent times.  Current rates of  r e t r e a t , reaching maxima of 10.5 metres (35 feet) per annum, are p r i m a r i l y r e l a t e d to the composition of the permafrost, being greatest i n areas of f i n e - g r a i n e d sediments, containing high i c e contents, w i t h a southerly exposure.  Thermal erosion of the permafrost  i s the dominant process i n -  f l u e n c i n g c l i f f r e t r e a t and the primary r o l e of wave a c t i o n , on a short term b a s i s , i s i n the removal of thawed debris from the base of the c l i f f s . Observations exposure of segregated  of three h i g h l y a c t i v e mudslumps, created by the  ground i c e , show that the r a t e of headwall recession  i s strongly c o r r e l a t e d w i t h ambient a i r temperatures. occurs  Maximum recession  where the i c e content i s high and the slumped debris i s frequently  removed from the base of the scarp. system on the i c e face i s described.  The c y c l i c development of a g u l l y The longevity of mudslump a c t i v i t y  i s prolonged where strong mudflows carry the thawed m a t e r i a l away from the foot of the headwall, thus preventing the progressive b u r i a l of the scarp face.  Mudflow v e l o c i t i e s r e v e a l a rhythmic p u l s a t i o n r e l a t e d to p e r i o d i c  b l o c k i n g of t h e i r channels.  Mud: levees, bordering the mudflows, r e s u l t  from the progressive bleeding of moisture from, and subsequent stagnation of,  the mud rather than as r e s i d u a l features pushed aside by the advancing  mudflow. Patterned ground on Garry I s l a n d i s p r i m a r i l y r e s t r i c t e d to non-sorted  types.  Angular i n t e r s e c t i o n s of thermal c o n t r a c t i o n cracks,  representing the i n c i p i e n t stages of tundra polygons, e x h i b i t a preferred tendency toward s l i g h t l y - o r i e n t e d , orthogonal systems.  The i n i t i a l micro-  r e l i e f of earth hummocks i s believed to o r i g i n a t e through the accentuation of a miniature d e s i c c a t i o n / f r o s t - crack pattern.  F o l l o w i n g the  e s t a b l i s h m e n t of a v e g e t a t i o n c o v e r , t h e i r subsequent growth further  d i f f e r e n t i a l f r o s t a c t i o n and s o l i f l u c t i o n .  show t h a t  involves  Statistical  tests  the h e i g h t , s i z e and shape of e a r t h hummocks a r e c l o s e l y  to t h e i r p o s i t i o n on the s l o p e p r o f i l e .  related  V  ACKNOWLEDGMENTS It i s impossible to give f u l l c r e d i t to a l l the people who gave assistance i n the preparation of t h i s thesis. p a r t i c u l a r thanks are:-  Singled out f o r  Dr. J . Ross Mackay, my advisor, whose teaching  stimulated ray interests i n the Canadian A r c t i c and who has been a constant source of i n s p i r a t i o n i n the classroom and i n the f i e l d ;  Dr. J . K.  Stager f o r h i s assistance i n the f i e l d and encouragement and advice i n the preparation of the text;  Dr. H. 0. Slaymaker and Dr. W. H. Mathews  for their advice and comments on the text;  Dr. M. A. Melton and my fellow  graduate students f o r seminar discussions which enabled me to test and c l a r i f y my thoughts;  Dr. J . D. Ives and the s t a f f of the former  Geographical Branch, Ottawa, f o r the generous support of the f i e l d programme through the provision of funds, equipment, laboratory f a c i l i t i e s and a base map of Garry Island;  Dr. J„ G. F y l e s , of the Geological Survey  of Canada, f o r advice i n the f i e l d , radiocarbon dates and, with h i s colleague Dr. F. J . E. Wagner, i d e n t i f i c a t i o n of the f o s s i l Dr. E„ Hulten and Dr. H  e  specimens;  Personn of the Naturhistoriska Riksmusset,  Stockholm, f o r i d e n t i f i c a t i o n s of the plant species; Mr. R. M. H i l l and the s t a f f of the Inuvik Research Laboratory f o r their u n f a i l i n g support i n the f i e l d area;  Mr. R. Reynolds and the staff of the P r i n t Shop, Brock  University, f o r their assistance i n the p r i n t i n g of the thesis;  Mr. P. J .  Tighe and Mr. W. B. Windjack of the Audio V i s u a l and Photographic Department, Brock University, f o r their assistance with the photographic illustrations;  and l a s t , but by no means l e a s t , to my wife, Helen, f o r  the innumerable occasions that I was able to depend on her i n the roles of  f i e l d a s s i s t a n t , geographer, cartographer and secretary.  August, 1969.  Denis E. Kerfoot.  vii  TABLE OF CONTENTS CHAPTER I.  PAGE INTRODUCTION  1  The Scope of the Study Current Geomorphic Processes  4  The Role of Permafrost  7  Geomorphological H i s t o r y  8  The Study Area  II.  10  H i s t o r i c a l Significance  12,  Climate  14  STRATIGRAPHY  22  Areas of Deformed Sediments  24  Sand Headland Areas  29  The Extent of the Marine Submergence  35  L o n g i t u d i n a l Stream P r o f i l e s  50  Summary  III.  4  61  VEGETATION  63  Vegetation Types  65  I.  Dryas-Hummock Type  65  II.  Alnus c r i s p a Type  70  III.  Cassiope Snowpatch Type  71  IV.  Eriophorum Tussock Type  71  Hummock-Tussock T r a n s i t i o n Type  73  Stream Course Willow Thickets  73  V. VI.  viii CHAPTER  PAGE VII. VIII. IX. X.  Sedge-Moss F l a t s  75  Mudslump Communities  75  Strand Communities  78  Polygonal Ground  83  Summary  IV.  84  PERMAFROST CONDITIONS Depth of Thaw Measurements Earth Hummock Experiments Ground Temperature Measurements Freeze-Back i n the A c t i v e Layer, 1964 Summary  V.  88 90 100 108 118 122  GEOMORPHOLOGICAL PROCESSES  125  Coastal Recession  125  Evidence of Coastal Recession  126  Coastal Stake Measurements  131  Relevance of the P r o f i l e Studies to other Coastal Areas Processes at work i n Coastal Recession Muds lumps Rates of Retreat A b l a t i o n Studies  144 145 149 154 163  The Recession Process and E v o l u t i o n of the Gully System The Mudslump Cycle  171 178  ix CHAPTER  PAGE Mudflows  184  Rates, of Movement  .  Mud Levees Patterned Ground Tundra Polygons  191 201 203 204  I n c i p i e n t F r o s t Crack Patterns  206  Low-Centred Polygons  217  High-Centred Polygons  225  Thermokarst Features  228  Earth Hummocks  232  The Structure of Earth Hummocks  234  The Size and Form of Earth Hummocks  254  The O r i g i n and Development of Earth Hummocks Summary  VI.  272 277  SOME OBSERVATIONS ON THE GE0M0RPH0L0GICAL EVOLUTION OF GARRY ISLAND  282  Pleistocene Deposits and G l a c i a t i o n  282  The Extent of the Marine Transgression  289  Current Geomorphological Processes  293  The Concept of a P e r i g l a c i a l Morphogenetic Region  BIBLIOGRAPHY  296  299  X  APPENDIX I  305 A.  L i s t of vascular  species found on Garry  Island B.  L i s t of Bryophytes found on Garry Island  305 308  xi  LIST OF TABLES TABLE I.  PAGE Mean Daily Temperatures f o r A k l a v i k , Inuvik, Tuktoyaktuk, Shingle Point and Nicholson Peninsula (Degrees Centigrade).  II.  Mean Monthly P r e c i p i t a t i o n T o t a l s f o r A k l a v i k , Inuvik, Tuktoyaktuk, Shingle Point and Nicholson Peninsula (Cms.)  III.  . .  1, 1964  X. XI.  141  Mudslumps - Rates of Retreat (Metres)  156  Rates of Recession at selected stake p o s i t i o n s i n Slump B 177  Ice Contents (Weight of Ice to Dry S o i l ) of samples taken from exposure of ground i c e i n Slump B  XIII.  112  Sand Headland P r o f i l e Changes  (Metres) XII.  106  Ground Temperatures recorded at d i f f e r e n t depths i n Mud, B o i l , Earth Hummock and Inter-Hummock Depressions (°C)  IX.  102  Earth Hummock watering experiment, Garry I s l a n d , J u l y 26 - August 30, 1965  VIII.  92  Depths of Thaw beneath Earth Hummocks on Garry I s l a n d , J u l y 19 - August 30, 1965  VII.  55  Depths of Thaw beneath the major vegetation types, Garry I s l a n d , September  VI.  20  Elevations of the breaks of slope on the l o n g i t u d i n a l p r o f i l e s of Garry I s l a n d streams  V.  18  Comparisons of Temperature and P r e c i p i t a t i o n Data i n the Delta area f o r the months of July-August, 1964-1966 . . . .  IV.  16  C o e f f i c i e n t of V i s c o s i t y of a Garry I s l a n d Mudflow  183 199  xii TABLE XIV.  PAGE A n a l y s i s of Garry Island Earth Hummock Data Heights (Cms.)  XV.  263-264  A n a l y s i s of Garry I s l a n d Earth Hummock Data Sizes (Cms.)  266-267  xiii  LIST OF FIGURES FIGURE  PAGE  1.  Garry Island:  Topography  11  2.  Garry Island:  Stratigraphy  23  3.  Logarithmic Grain. S i z e D i s t r i b u t i o n Diagrams  4.  Grain Size D i s t r i b u t i o n f o r s o i l samples taken from the  27  Sand Headlands and areas of Deformed Sediments 5.  Garry Island:  6.  S t r a t i g r a p h i c section exposed i n c o a s t a l b l u f f s along  32  Raised Shoreline Features  43  northwest coast of Garry I s l a n d  47  7.  L o n g i t u d i n a l Stream P r o f i l e s (1)  52  8.  L o n g i t u d i n a l Stream P r o f i l e s (2)  53  9.  Cross-Valley P r o f i l e s - Stream 'G'  59  10.  Garry Island:  Vegetation Types  11.  Vegetation P l o t :  .  Surface Contours above datum and  Vegetation Types 12.  Vegetation P l o t :  95 P o s i t i o n of the F r o s t Table August 1  and September 1, 1964  97  13.  Vegetation P l o t :  14.  Mean Ground Temperatures and Ground Temperature F l u c t u a t i o n s  15.  Ground Temperature patterns i n an. Earth Hummock and  Depth of Thaw P r o f i l e s  adjacent Depression (°C)  .....  16.  Ground Temperature patterns i n a Mud B o i l  17.  Coastal Recession Features: Island  18.  66  Sand Headland P r o f i l e s (1)  98 111  115 116  Northwest coast of Garry 130 138  xiv FIGURE  PAGE  19.  Sand  Headland P r o f i l e s  20.  Garry  21.  Mudslump:  22.  Relationship  Island:  (2)  139  Distribution  Slump  Mudslumps  151  B  157  between  degree-days  of  for  rate  three  of  retreat  Garry  and number  Island  of  thawing  Mudslumps  159  23.  Ablation  Studies  i n Slump  B  -  Profile  I  166  24.  Ablation  Studies  i n Slump  B  -  Profile  II  167  25.  Relationship  between  degree-hours Island  ablation  i n Slump  26.  Garry  27.  Recession  28.  A  29.  Mudflow  -  Rates  of  30.  Incipient  Frost  Crack  31.  Diagrammatic  32.  Surface  Garry  Diagram  Island  of  a  Contours  Garry  Mudslump,  1964-1966  .  Kendall  of  Crack  Frost  and C r o s s - S e c t i o n a l  Island,  N.W.T.  intersection Profile  of  a  .  patterns  Low-Centred  Polygon  Network  35.  Surface  on Sand  Headlands Profile  223 of  a  typical  Polygon  Contours  Types  227 on upper  part  and S t r u c t u r a l  located  214  221  and C r o s s - S e c t i o n a l  located  211  219  34.  High-Centred  .  typical  Polygon  Contours  180  193  Pattern,  Network  Vegetation  Island  179  Movement  Polygon  E a r t h Hummock  1964-1966  189  Low-Centred  37.  thawing 170  33.  Surface  of  Mudflow  sketches  E a r t h Hummock  a n d number  B  Mudslump P r o f i l e ,  Low-Centred  36.  rates  on upper  of  slope  profile:  Profiles  part  of  slope  236 profile: 237  XV  FIGURE 38.  PAGE Earth Hummock located on middle part of slope p r o f i l e : Surface Contours and S t r u c t u r a l P r o f i l e s  39.  Earth Hummock located on middle part of slope p r o f i l e : Vegetation Types  40.  242  Earth Hummock located on lower part of slope p r o f i l e : Surface Contours and S t r u c t u r a l P r o f i l e s  41.  244  Earth Hummock located on lower part of slope p r o f i l e : Vegetation Types  42.  241  245  S t r u c t u r a l P r o f i l e of an Earth Hummock located at the foot of a slope  246  43.  Mud B o i l :  Surface Contours  246  44.  Mud B o i l :  Vegetation Types  248  45.  Earth Hummock S t r i p e s :  Surface Contours and S t r u c t u r a l  Profiles  250  46.  Earth Hummock S t r i p e s :  Vegetation Types  47.  Slope p r o f i l e s showing l o c a t i o n s of Earth Hummock sampling s t a t i o n s  251  256  48.  Histograms of Hummock Heights - P r o f i l e I  258  49.  Histograms of Hummock Heights - P r o f i l e I I  259  50.  Histograms of Hummock Heights - P r o f i l e I I I  260  51.  Histograms of Hummock Heights - P r o f i l e IV  261  52.  Histograms of Hummock Heights - P r o f i l e V  262  xvi  LIST OF PLATES PLATE I.  PAGE Stratigraphy  25  . II.  Raised Shoreline.Features  40  III.  Vegetation Types  67  IV.  Vegetation Types  74  V.  Vegetation Types  81  VI.  Coastal Recession  128  VII.  Coastal Recession  133  Sand Headland P r o f i l e Studies  136  IX.  Mudslumps  152  X.  Mudslumps  164  A Garry I s l a n d Mudflow  190  Mudflow:  195  VIII.  XI. XII. XIII. XIV. XV. XVI. XVII.  Surge Phenomena  I n c i p i e n t F r o s t Crack Patterns.  208  Low-Centred Polygons  220  High-Centred Polygon andThermokarst Features  226  Earth Hummocks  238  Earth Hummock S t r i p e s  252  CHAPTER I  INTRODUCTION  The attracted  arctic  the a t t e n t i o n of s c i e n t i s t s  t h e S e c o n d W o r l d War. to these  Prior  remote n o r t h e r n  strategic  o f Canada have i n c r e a s i n g l y  i n t h e i n t e r v a l s i n c e t h e end o f  t o 1945, r e l a t i v e l y  little  a t t e n t i o n was p a i d  l a n d s , b u t the post-war r e a l i z a t i o n of t h e i r  s i g n i f i c a n c e a n d a t t e m p t s t o e s t a b l i s h and d e v e l o p  economic r e s o u r c e aspects  and s u b a r c t i c r e g i o n s  their  p o t e n t i a l , have c o n t r i b u t e d g r e a t l y t o s t i m u l a t e a l l  of research  i n these  high  latitudes.  Much v a l u a b l e d a t a h a s b e e n  obtained  as a ' b y - p r o d u c t ' o f t h e c o n s t r u c t i o n a n d o p e r a t i o n o f t h e  military  installations  potential mineral data  and t h e e x p l o r a t o r y s u r v e y s  deposits.  i s that considerable  geomorphology d u r i n g This  to locate  One c o n s e q u e n c e o f t h e a v a i l a b i l i t y  progress  the past  seeking  h a s b e e n made i n t h e f i e l d  of this  of a r c t i c  few decades.  same t i m e i n t e r v a l , s i n c e 1 9 4 5 , h a s a l s o w i t n e s s e d t h e  g r o w t h and c o n s o l i d a t i o n o f a number o f new a p p r o a c h e s t o t h e s u b j e c t o f geomorphology.  T r a d i t i o n a l l y , geomorphological  d e v e l o p m e n t have r e l i e d descriptions culminating  h e a v i l y on q u a l i t a t i v e d e s c r i p t i o n .  formed t h e b a s i s o f geomorphology d u r i n g i n the c y c l i c  two t o t h r e e  the f i r s t  half of this  Such  the 19th century,  concepts of W i l l i a m Morris Davis,  the s t u d i e s undertaken d u r i n g past  s t u d i e s of landscape  and most o f  century.  Inthe  d e c a d e s however , a t t e m p t s h a v e b e e n made t o e s t a b l i s h  t h e s u b j e c t o n a more p r e c i s e , o b j e c t i v e f o u n d a t i o n  by s u b s t i t u t i n g  q u a n t i t a t i v e measurements f o r v e r b a l d e s c r i p t i o n s .  Although  the adoption  2 of t h i s q u a n t i t a t i v e approach to Landform studies i s s t i l l i n i t s infancy, a number of p r i n c i p a l avenues of research can be i d e n t i f i e d .  These  include the compilation and t a b u l a t i o n of data r e l a t i n g to the scale and shape of landforms;  i n v e s t i g a t i o n s of the mode of operation and  inter-  r e l a t i o n s h i p s between degradational and aggradational f o r c e s , i n c l u d i n g t h e i r expression i n the forms of models, graphs or formulae;  and  measurements of the a c t u a l rates at which geomorphic processes are opera t i n g on various parts of the earth's surface today.  To date, most,  though not a l l , of the success achieved by the employment of these methods has been i n the humid temperate regions of the world, and i n the f i e l d of f l u v i a l geomorphology where the drainage basin forms a  convenient  u n i t study area. The adoption of the q u a n t i t a t i v e approach to  geomorphological  studies r e f l e c t e d , i n p a r t , a growing d i s s a t i s f a c t i o n w i t h the s u b j e c t i v e , g e n e t i c a l l y - o r i e n t e d Davisian model of landscape development and the scant a t t e n t i o n paid to process studies i n t h i s model.  A d d i t i o n a l reactions  against the Davisian approach to the subject have a l s o r e s u l t e d i n increasing a t t e n t i o n being paid to a l t e r n a t i v e theories of landscape development.  Thus, objections to the long period of c r u s t a l s t a b i l i t y  required f o r the production of a peneplain, have led to a r e v i v a l of the ideas of Penck and an emphasis on the s i g n i f i c a n c e of c r u s t a l m o b i l i t y i n the formation of landforms.  Other geomorphologists have concentrated  on  the r o l e of c l i m a t e , and the b e l i e f that the r a t e of operation of geomorphological processes v a r i e s considerably from one c l i m a t i c region to another. A considerable amount of i n t e r e s t i n a r c t i c geomorphology has been generated by the development and elaboration of t h i s concept of  3 c l i m a t i c geomorphology.  1  In t h i s concept i t i s postulated that there i s a  very close r e l a t i o n s h i p between climate and geomorphology, to the extent that under a given set of c l i m a t i c conditions c e r t a i n geomorphic processes w i l l predominate, and these i n turn w i l l lead to the development of a c h a r a c t e r i s t i c assemblage of landforms.  On the basis of these p o s t u l a t e s ,  some proponents of the concept have further suggested that the influence of climate i s such that a s e r i e s of morphogenetic regions can be i d e n t i f i e d i n which the topographic c h a r a c t e r i s t i c s of an area can be d i f f e r e n t i a t e d from those of other areas developed under contrasting c l i m a t i c regimes. In North America, the concept of c l i m a t i c geomorphology was developed by P e l t i e r who t e n t a t i v e l y i d e n t i f i e d nine morphogenetic 2 regions.  For one of these regions he adopted the term p e r i g l a c i a l , to  describe those parts of the earth's surface which have an annual temperature range of 5-30°F and an average annual r a i n f a l l range of 5-55 inches, and i n which the geomorphic processes are characterized by strong mass movement, moderate to strong wind a c t i o n and a weak e f f e c t of running 3  water.  Although the p e r i g l a c i a l environment i s c u r r e n t l y r e s t r i c t e d to  polar l a t i t u d e s and high a l t i t u d e s , i t has attracted wide a t t e n t i o n because many f e a t u r e s , which have been described from more temperate  lat-  i t u d e s , have t e n t a t i v e l y been interpreted as evidence of a s i m i l a r , more widespread environment during the Pleistocene period. B i r d , J . B r i a n (1967) The Physiography of A r c t i c Canada, The Johns Hopkins P r e s s , B a l t i m o r e , Maryland, p. 158. 2 P e l t i e r L„C. (1950) "The geographical cycle i n p e r i g l a c i a l regions as i t i s r e l a t e d to c l i m a t i c geomorphology", Ann. Assoc. Amer. Geog., V o l . 40, pp. 214-236. 9  3  I b i d . , p. 215.  4 One of the major shortcomings of P e l t i e r ' s paper was that i t was construed w i t h i n the framework of the t r a d i t i o n a l Davisian approach to geomorphology.  As such, and as P e l t i e r himself r e a l i z e d , i t was r e s t r i c t e d  to q u a l i t a t i v e d e s c r i p t i o n and was based on inadequate data. Further discussion of the v a l i d i t y and l i m i t a t i o n s of the concept of morphogenetic regions need not be debated here, save to mention that before i t can be given a d d i t i o n a l credence i t w i l l have to be established on a q u a n t i t a t i v e basis through d e t a i l e d geomorphic process studies.  As y e t , however, there  has been only l i m i t e d research i n t o the p e r i g l a c i a l processes operating i n 4 northern Canada.  The number of process studies i s s t e a d i l y i n c r e a s i n g ,  but many more are needed before a r c t i c geomorphology can be f u l l y i n t e r preted, and only as a r e s u l t of such i n v e s t i g a t i o n s can the proper r o l e of v a r i a t i o n s i n the c l i m a t i c regime be evaluated. The Scope of the Study. The aims of t h i s t h e s i s are to make a threefold c o n t r i b u t i o n to the general f i e l d of a r c t i c geomorphology: 1.  To study some of the geomorphic processes c u r r e n t l y operating i n an a r c t i c environment on Garry I s l a n d , N.W.T.  2.  To examine the r o l e of permafrost i n the operation of these geomorphic processes.  3.  To attempt to decipher the complex geomorphological h i s t o r y of the outer Mackenzie Delta area i n g l a c i a l and p o s t - g l a c i a l times. Current Geomorphic Processes.  The s p e c i f i c geomorphic pro-  cesses investigated were those involved i n c o a s t a l r e c e s s i o n , mudslumps  B i r d , J . B r i a n (1967) op. c i t . , p. 157.  5  and associated mudflows, and the genesis of certain types of patterned ground.  This l i s t i s by no means exhaustive of a l l the contemporary  processes operating on Garry Island.  The most obvious omission i s the  process of s o l i f l u c t i o n which i s undoubtedly one of the most f a m i l i a r and widespread agencies moulding the landscape i n a r c t i c latitudes and has been more intensively investigated than most of the other geomorphic processes.  For this reason, an examination of the comprehensive aspects of  s o l i f l u c t i o n was excluded from the programme of studies on Garry Island. Observations of the rate of coastal recession were made on approximately 2.5 kilometres (1.5 miles) of coastline along which stakes were i n s t a l l e d during the summer of 1964.  Most of these stakes were  located along the exposed northwest coast of the i s l a n d , and measurements of the amount of recession that had taken place were made at the beginning and end of each of the f i e l d seasons.  To supplement these observations,  and provide additional data on the processes involved i n c l i f f four p r o f i l e stations were established on the prominent sand along the north coast of the i s l a n d .  retreat,  headlands  At each of these stations wooden  stakes were driven into the c l i f f face, normal to the surface, and these were surveyed p e r i o d i c a l l y throughout one of the field^seasons to detect p r o f i l e changes. Mudslumps are created by the melting out of large bodies of ground i c e , and the fine-grained sediments, containing substantial masses of segregated i c e , which underlie much of Garry Island provide favourable s i t e s for the development of these features. A series of stakes was i n s t a l l e d around three highly active mudslumps, and measurements of the amount of retreat were made throughout each of the f i e l d seasons. programme of ablation studies was also carried out on the ice face  A  6 exposed i n the headwall of one of the mudslumps. three weeks, a number of stakes was  At intervals of two to  i n s t a l l e d normal to the ice face and  the amount of ablation was measured d a i l y for f i v e or s i x consecutive days each time.  Attempts were made to correlate the data on the rates of  headwall retreat and rates of ablation with meteorological observations recorded at a small weather s t a t i o n established on the i s l a n d .  Further  observations on the manner i n which a mudslump headwall retreats were obtained through investigations of the seasonal evolution of a d i s t i n c t i v e gully system which, while i t e x i s t s , imparts a miniature 'badland' raphy to the i c e face.  topog-  These process studies were combined with  observations on mudflows to describe a model of the c y c l i c development of mudslumps and the factors which influence the longevity of this cycle. Mudflows are the most e f f e c t i v e agents by which thawed debris i s removed from the foot of an a c t i v e l y r e t r e a t i n g mudslump headwall.  An  active mudflow was surveyed i n d e t a i l , and markers were i n s t a l l e d on i t s surface to determine pattern.  the rate of movement and the nature of the flow  Samples of mud were collected to t r y to correlate variations i n  the v e l o c i t y of the mudflow with changes i n the v i s c o s i t y of the Detailed measurements and excavations of the mud  mud.  levees bordering both old  and active mudflows were made to determine variations l n the height, slope, symmetry, composition and mode of o r i g i n of these features. The studies of patterned ground were r e s t r i c t e d to i n v e s t i g ations of some of the more controversial aspects of the development of tundra polygons and earth hummocks.  P a r t i c u l a r attention was  paid i n the  tundra polygon studies to the i n c i p i e n t f r o s t crack stage, and the nature of the angular intersections of the cracks which can only be measured with any r e l i a b l e degree of accuracy at this stage.  Several areas of polygonal  7  ground were also surveyed i n d e t a i l to examine some of the factors i n fluencing the size and spacing of the polygonal units and the t r a n s i t i o n from low- to high-centred forms. Most of the l i t e r a t u r e pertaining to earth hummocks consists of very generalized, descriptive statements concerning their shape and s i z e , and a part of the f i e l d programme was aimed at replacing these qualitative statements with quantitative data.  Preliminary observations  of the hummocks on Garry Island suggested that their size and spacing were related to their position on the slope p r o f i l e .  Five slope p r o f i l e s  were surveyed and a series of s i x survey lines was established from each p r o f i l e running p a r a l l e l to the contours.  Using a horizontal sight l i n e ,  the height and spacing of each hummock and depression on each of the survey l i n e s were recorded, and s u f f i c i e n t l y large samples were obtained so that any differences i n the calculated means could be tested s t a t i s t i c ally.  At the same time observations were made r e l a t i n g to the alignment  and p r o f i l e s of the hummocks, and these were combined with a series of excavations to determine the structure and mode of o r i g i n of these micror e l i e f features. The Role of Permafrost.  The second contribution of the thesis  i s c l o s e l y a l l i e d to the f i r s t and i s related to the concept of c l i m a t i c geomorphology and, i n p a r t i c u l a r , the r o l e of the permafrost conditions. The various geomorphic processes operating i n a r c t i c regions today may be peculiar to the northlands, or they may simply d i f f e r i n degree from those shaping the landscape i n more southerly l a t i t u d e s .  Any such differences,  either i n kind or degree, may possibly be related to the presence of permafrost, the r o l e of which i s imperfectly understood.  The thickness  and composition of the permafrost, and p a r t i c u l a r l y the presence or  8 absence of large bodies of segregated ground i c e , have a d e f i n i t e influence on the occurrence or non-occurrence and the r a t e s of operation of c e r t a i n geomorphic processes.  Of p a r t i c u l a r s i g n i f i c a n c e to the genesis of some of  the m i c r o r e l i e f features i n high l a t i t u d e s are the conditions i n the active layer.  This i s the l a y e r , extending from the ground surface down to the  permafrost t a b l e , which undergoes seasonal thawing during the summer months.  A knowledge of the changes i n the thermal regime of t h i s active  layer i s r e l e v a n t to a l l attempts to develop the economic p o t e n t i a l of the northlands, as w e l l as to a f u l l e r understanding of a r c t i c ; geomorphology. To date, however, r e l a t i v e l y few measurements of ground  temperature  patterns i n the a c t i v e layer have been recorded i n northern Canada. A c c o r d i n g l y , the second aim of t h i s thesis i s to examine the influence of the composition of the permafrost on the rates of operation of the geomorphic processes, and some of the f a c t o r s which contribute to v a r i a t i o n s i n the o v e r a l l thickness and thermal regime of the active layer. Geomorphological H i s t o r y .  The t h i r d c o n t r i b u t i o n of the t h e s i s  i s an attempt t o decipher the complex geomorphological h i s t o r y of the outer Mackenzie D e l t a area i n g l a c i a l and p o s t - g l a c i a l times.  This l a t e s t epoch  of g e o l o g i c a l time witnessed immense expansions of g l a c i e r s i n middle and high l a t i t u d e s , the extent of which f l u c t u a t e d i n response to c l i m a t i c changes.  The waxing and waning of the i c e sheets was accompanied by  profound o s c i l l a t i o n s i n the l e v e l of the sea.  Large t r a c t s of the earth's  crust were depressed by the weight of these i c e masses, and the subsequent melting of the i c e contributed t o r i s i n g sea l e v e l s and an extensive submergence of the c o a s t a l lowlands.  At a l a t e r date these same lowlands  emerged from beneath the sea as the earth's crust slowly responded to the  9 removal of the r e c e n t l y melted i c e cover. The number of g l a c i a l and i n t e r g l a c i a l episodes, and  their  orderly arrangement i n t o a chronological sequence, i s s t i l l imperfectly understood i n the a r c t i c regions of Canada.  There i s no doubt that the  area i n the v i c i n i t y of the Beaufort Sea was a f f e c t e d by g l a c i e r s advancing from the south, but there are differences of opinion as to the number of advances that a f f e c t e d the area and t h e i r r e l a t i o n s h i p to the c l a s s i c a l Pleistocene sequence established f o r more southerly l a t i t u d e s . S i m i l a r controversies e x i s t i n the i n t e r p r e t a t i o n of evidence i n d i c a t i v e of changing patterns of land-sea r e l a t i o n s h i p s and the extent of the postg l a c i a l marine transgression.  The i d e n t i f i c a t i o n and i n t e r p r e t a t i o n of  t h i s evidence, and an attempt to arrange the sequence of events i n t o a chronological order, c o n s t i t u t e s the t h i r d aim of t h i s t h e s i s . The s e l e c t i o n of Garry I s l a n d as a f i e l d study area was at the advice of Dr. J . Ross Mackay, my a d v i s o r , on the basis of h i s extensive knowledge of the Mackenzie Delta area.  The f i e l d work was c a r r i e d out  during the periods June 25 - September 8, 1964, June 22 - September 13, 1965 and J u l y 26 - August 29, 1966.  I am deeply indebted to the former  Geographical Branch, Department of Mines and Technical Surveys, Ottawa, for the generous p r o v i s i o n of funds and equipment i n support of each of the f i e l d seasons.  I a l s o g r a t e f u l l y acknowledge support f o r the f i e l d  programme which was received by Dr. J . Ross Mackay from the Department of Northern A f f a i r s and N a t i o n a l Resources, by way  of the Committee on A r c t i c  and A l p i n e Research, the U n i v e r s i t y of B r i t i s h Columbia, and from research funds of the U n i v e r s i t y of B r i t i s h Columbia.  10  THE STUDY AREA Garry Island i s centred at l a t i t u d e 69° 28' N and longitude 135° 42' W i n the southern part of the Beaufort Sea (Figure 1). at the d i s t a l end of the Mackenzie Delta;  a low, f l a t area  It lies  approximately  80 kilometres (50 miles) wide and 160 kilometres (100 miles) long."  5  The  modern d e l t a i s characterized by a myriad of i n t e r l a c i n g channels and small l a k e s , and Garry Island forms part of an arcuate chain of i s l a n d s which represent the seaward remnants of a formerly more extensive P l e i s t ocene, or e a r l i e r , ancestor of the modern d e l t a . The i s l a n d i s approximately oriented i n a northwest-southeast  11 kilometres (7 miles) long,  d i r e c t i o n , 0.8  to 3.2 kilometres (0.5 to  2 miles) wide, and reaches e l e v a t i o n s exceeding 46 metres (150 feet) above sea l e v e l .  These e l e v a t i o n s , and those of adjacent i s l a n d s , are consider-  ably higher than the heights found i n the modern d e l t a of the Mackenzie R i v e r , and they owe t h e i r a l t i t u d e to the development of i c e - t h r u s t features and the growth of s u b s t a n t i a l bodies of segregated ground i c e . The major topographic features of Garry I s l a n d , which may be described as 6 gently r o l l i n g , are shown i n Figure 1.  Extensive f l a t summit areas are  l a c k i n g and the higher ground i s characterized by smooth slopes seldom The metric standard of measurement i s used i n t h i s t h e s i s . However, on some of the maps, i f the f i e l d surveys were done using B r i t i s h measures, the B r i t i s h u n i t s are used. The topographic map of Garry I s l a n d shown i n Figure 1 was compiled from a e r i a l photographs by the former Geographical Branch, Department of Mines and Technical Surveys, Ottawa. Although t h i s map accurately portrays the general features of the topography, and has therefore been reproduced w i t h only minor m o d i f i c a t i o n s , the absence of any accurate ground height c o n t r o l implies that the p o s i t i o n s o f , and the numerical values assigned t o , the form l i n e s are only estimates.  12 exceeding 5-10 degrees.  The high ground i s broken by a series of shallow  v a l l e y s and depressions, the sides of which may have slopes of 25-35 degrees.  On the north side of the i s l a n d , three prominent aprons of  coarse sand produce f l a t to g e n t l y - s l o p i n g surfaces ranging from 7.5-15.0 metres (25-50 feet) above sea l e v e l . Drainage conditions over much of the i s l a n d are poor and r e f l e c t the presence of permafrost at shallow depths beneath the ground surface.  Despite the presence of a number of f a i r l y w e l l - d e f i n e d stream  courses, integrated drainage patterns are poorly developed.  The present  channels serve p r i m a r i l y as conduits f o r surface runoff derived from melting snow and the thawing of the a c t i v e layer during the spring and early summer.  Throughout the r e s t of the summer these channels are kept  moist by seepage from the thawing ground, but surface runoff i s generally l a c k i n g except f o r a short time f o l l o w i n g e x c e p t i o n a l l y prolonged periods of heavy r a i n f a l l .  The f l o o r s of the depressions, p a r t i c u l a r l y at lower  e l e v a t i o n s , and parts of the stream courses are f u r t h e r characterized by the  development of polygonal ground w i t h associated pond and marsh areas.  H i s t o r i c a l Significance. Despite i t s small s i z e , Garry I s l a n d has played a controvers i a l r o l e i n the h i s t o r y of the e x p l o r a t i o n and mapping of t h i s northwestern section of the Canadian A r c t i c .  I n 1789, Alexander Mackenzie  completed h i s epic voyage down the Grand R i v e r , ^ subsequently renamed i n his honour, at a small i s l a n d which he named 'Whale I s l a n d ' a f t e r the numerous beluga, or white whales, which he observed i n the surrounding  Stager, J.K. (1965) "Alexander Mackenzie's e x p l o r a t i o n of the Grand R i v e r " , Geographical B u l l e t i n , V o l . 7, pp. 213-241.  waters.  8  In 1825, S i r John F r a n k l i n journeyed down the same r i v e r and  named the s i t e of h i s most n o r t h e r l y camp i n the d e l t a Garry Island i n 9 honour of h i s f r i e n d the Deputy Governor of the Hudson's Bay Company. F r a n k l i n included a map of the d e l t a i n the account of h i s voyage and although he d i d not see 'Whale I s l a n d ' , he located i t on h i s map using Mackenzie's l a t i t u d i n a l and l o n g i t u d i n a l o b s e r v a t i o n s . ^ Consequently, 1  for more than a century, Garry I s l a n d and 'Whale I s l a n d ' appeared adjacent to one another on Canadian topographic maps of the Mackenzie Delta area u n t i l the f i r s t accurate maps were produced from photographs taken during a e r i a l reconnaissances of the d e l t a flown during the Second World War.  11  Since these maps f a i l e d to r e v e a l any presence of land at the p o s i t i o n described by Mackenzie, the name 'Whale I s l a n d ' was rescinded by the Can12 adian Board on Geographical Names i n 1960. There are s t r i k i n g s i m i l a r i t i e s i n the respective explorers' d e s c r i p t i o n s of 'Whale I s l a n d ' and Garry Island w i t h respect to t h e i r s i z e , e l e v a t i o n above sea l e v e l and panoramic v i s t a s of adjacent islands 8 Mackenzie, A. (1801) Voyages from Montreal on the River S t . Laurence through the continent of North America to the Frozen and P a c i f i c Oceans i n the years 1789 and 1793, T. C a d e l l , Jun. and W. Davies, Strand; Cobbett and Morgan, P a l l M a l l ; and W. Creech at Edinburgh. Reprinted e d i t i o n (1966) i n March of America Facsimile S e r i e s , Number 52, U n i v e r s i t y M i c r o f i l m s I n c . , Ann Arbor, Michigan, pp. 64-65. 9 F r a n k l i n , S i r John (1828) N a r r a t i v e of a^ second expedition to the shores of the P o l a r Sea i n the years 1825, 1826 and 1827, Carey, Lea and Carey, P h i l a d e l p h i a , p. 49. 10 I b i d . , Map F r o n t i s p i e c e . 11 B r e d i n , T.F. (1962) "'Whale I s l a n d ' and the Mackenzie Delta: charted errors and unmapped d i s c o v e r i e s , 1789 to 1850", A r c t i c , V o l . 15, p. 52. 12 Anon. (1960) "Geographical Names i n the Canadian North", A r c t i c , V o l . 13, p. 143.  14 i n the d e l t a and the f r o n t of the Richardson Mountains.  The major d i s -  crepancies are i n the l a t i t u d i n a l p o s i t i o n s of the two i s l a n d s , and the compass d i r e c t i o n s of the topographic features i n the panoramas.  In  attempting to reconstruct the o r i g i n a l route of Mackenzie's voyage through the d e l t a to the coast, Bredin discovered a number of e r r o r s i n the d i s tances and d i r e c t i o n s as reported by Mackenzie.  The most s i g n i f i c a n t of  these errors are a consistent recording of the l a t i t u d e s south of t h e i r a c t u a l p o s i t i o n s , and recorded compass d i r e c t i o n s of t r a v e l always more westerly than h i s true d i r e c t i o n s , even a l l o w i n g f o r magnetic v a r i a t i o n s .  1  I f due consideration i s taken of these f a c t o r s , the r e v i s e d l o c a t i o n of 'Whale I s l a n d ' c o i n c i d e s , almost i d e n t i c a l l y , w i t h that of Garry I s l a n d . A s i m i l a r conclusion, using somewhat d i f f e r i n g c r i t e r i a , was also reached by Mackay, by combining Mackenzie's d e s c r i p t i o n s of n a t u r a l features w i t h 14 h i s own d e t a i l e d knowledge of the conditions i n the d e l t a .  Thus, the  enigma of 'Whale I s l a n d ' has been solved, f o r there i s l i t t l e doubt that the 'Whale I s l a n d ' of S i r Alexander Mackenzie and the Garry I s l a n d of S i r John F r a n k l i n are one and the same i s l a n d . Climate. There are f i v e operating meteorological s t a t i o n s i n the v i c i n i t y of the Mackenzie D e l t a , but few of these have records which extend back over a large number of years.  F a i r l y continuous records are  a v a i l a b l e f o r the town of A k l a v i k , from 1926 onwards, but, w i t h the establishment of Inuvik, they were terminated i n 1959.  Bredin, T.F. 14  Data f o r the Inuvik  (1962) op. c i t . , pp. 52-53.  Mackay, J , Ross (1963) "The Mackenzie Delta area, N.W.T.", Geographical Branch Memoir, No. 8, p. 6.  15 a i r p o r t are a v a i l a b l e from 1958.  The most continuous records of the  e x i s t i n g meteorological s t a t i o n s , dating from 1948, are those of Tuktoyaktuk.  With the establishment of the Distant E a r l y Warning (DEW  line)  system, a d d i t i o n a l weather-recording s i t e s were provided at Shingle P o i n t , i n the Yukon T e r r i t o r y to the west;  Tununuk, at the southern end of  Richards I s l a n d ; Atkinson Point and Nicholson Peninsula, approximately  80  and 160 kilometres (50 and 100 miles) northeast of Tuktoyaktuk respecti v e l y . 1^  The s i t e s at Tununuk and Atkinson Point have subsequently been  abandoned, and the records f o r Shingle P o i n t and Nicholson Peninsula date back to the summer of  1957.  With the lone exception of Inuvik, the published observations at each of the meteorological s t a t i o n s are r e s t r i c t e d to p r e c i p i t a t i o n t o t a l s and temperature extremes.  The lengths of the records are, i n most  cases, too short to provide t r u l y r e l i a b l e means and, consequently, the values presented i n the f o l l o w i n g tables should be i n t e r p r e t e d accordingly. Furthermore,  there i s the problem of the v a r i a b l e length of the records at  each of the s t a t i o n s :  31 years at A k l a v i k , 21 years at Tuktoyaktuk,  11 years at Inuvik, Shingle P o i n t and Nicholson Peninsula.  and  These two  f a c t o r s , lack of r e l i a b i l i t y and non-comparability of the means, are fundamental to any d i s c u s s i o n of the r e g i o n a l climate. The mean d a i l y temperatures f o r each of the meteorological s t a t i o n s i n the Mackenzie Delta area are shown i n Table I .  Mean d a i l y  temperatures are below f r e e z i n g f o r eight months of the year.  January i s  the coldest month f o r most of the s t a t i o n s , except f o r Tuktoyaktuk  and  - For l o c a t i o n s of the place-names see the World A e r o n a u t i c a l Chart, I.C.A.O., 1:1,000,000. Sheet 2062, F i r t h River (1967) included at the back of the t h e s i s . >  16 TABLE I MEAN  DAILY  SHINGLE  TEMPERATURES  POINT  AND  FOR  NICHOLSON  AKLAVIK, PENINSULA  INUVIK, TUKTOYAKTUK, (Degrees Centigrade).  Aklavik  Inuvik  Tuktoyaktuk  Jan.  -27.7  -30.9  -28.1  -26.1  -25.9*(3)  Feb.  -27.1  -27.5  -29.2  -24.3*(3)  -27.9*(2)  Mar.  -22.7  -23.9  -26.4  -26.1  -25.8*(4)  Apr.  -13.0  -13.3  -18.6  -17.5  -.18.8  May  -  -  -  -  -  0.5  0.8  5.2  Shingle Point  4.1  Nicholson Peninsula  6.0  June  9.4  10.2  5.0  5.1  4.2  July  13.6  13.9  10.1  10.3  7.1  Aug.  10.1  10.4'  9.2  8.8  7.4  3.4  3.1  1.8  1.7  0.4  Sept. Oct.  -  Nov.  -19.4  -20.8  -21.3  -20.3  -21.1  Dec.  -26.9  -28.2  -25.6  -23.8  -25.9  6.8  -  7.6  -  7.2  -  7.7  -  7.8  * Unfortunately the mean d a i l y temperatures are only i n t e r m i t t e n t l y reported f o r these months, and the means are of correspondingly less value. The f i g u r e s i n brackets i n d i c a t e the number of years records on which these means are based.  Source:  Canada, Department of Transport, M e t e o r o l o g i c a l Branch, Monthly Record(s): Meteorological Observations i n Canada, Queen's P r i n t e r , Ottawa.  17 possibly Nicholson Peninsula, where the average February temperatures are colder.  The t r a n s i t i o n from winter to summer temperatures i s quite r a p i d .  As Table I shows, mean d a i l y temperatures increase by 26-28°C between A p r i l and J u l y , which i s u s u a l l y the warmest month.  Using a c l i m a t i c  d e f i n i t i o n of the a r c t i c , the mean J u l y temperatures of approximately 10°C (50°F) f o r the warmest month at Tuktoyaktuk and Shingle P o i n t i n d i c ate a l o c a t i o n on the boundary between a r c t i c and subarctic climates despite t h e i r l o c a t i o n s w e l l to the north of the t r e e - l i n e .  The trans-  i t i o n from summer to winter temperatures i s as r a p i d , w i t h the onset of sub-freezing temperatures again i n late-September or early-October. The mean monthly p r e c i p i t a t i o n t o t a l s f o r these same s t a t i o n s are shown i n Table I I .  Annual t o t a l p r e c i p i t a t i o n i s low, averaging  14-19 cms. (5-7 inches) at the c o a s t a l l o c a t i o n s and i n c r e a s i n g to 25-28 cms. (10-11 inches) f u r t h e r i n l a n d .  Each of the s t a t i o n s records a  summer maximum, i n the form of r a i n , during J u l y and August,, and t h i s maximum i s more pronounced at the coast w i t h 40-50 per cent of the annual t o t a l occurring i n these two months, compared to less than 30 per cent further inland.  Approximately one-half of the p r e c i p i t a t i o n i s i n the  form of snow. Garry I s l a n d , occupying an intermediate p o s i t i o n between Tuktoyaktuk and Shingle P o i n t , probably has an annual temperature and p r e c i p i t a t i o n pattern s i m i l a r to these s t a t i o n s , w i t h the coldest month being January or February and below-freezing temperatures f o r eight months of the year.  L i g h t snowfalls were encountered during August and September  i n 1964 and 1965, but the snow d i d not p e r s i s t f o r any length of time. T o t a l snowfall i s probably quite l i g h t , and the thickness of the cover i s r e l a t e d to the a c t i o n of the wind.  Much of the snow i s swept from the  18  TABLE I I MEAN  MONTHLY  PRECIPITATION TOTALS  TUKTOYAKTUK, SHINGLE  POINT  FOR AKLAVIK, INUVIK,  AND NICHOLSON  PENINSULA  (Cms.)-  Aklavik  Inuvik  Tuktoyaktuk  Shingle Point  Nicholson Peninsula  Jan.  1.68  2.39  3.45  0.64  0.18  Feb.  1.50  1.42  1.02  0.18  0.25  Mar.  1.12  1.35  0.23  0.15  0.25  Apr.  1.52  2.16  0.91  0.66  0.43  May  1.40  1.30  0.84  0.51  0.48  June  2.13  2.18  1.30  2.49  1.88  July  3.53  4.60  3.33  4.65  2.64  Aug.  3.66  2.97  4.09  3.25  4.14  Sept.  2.39  1.78  1.30  1.37  1.45  Oct.  2.46  3.71  0.99  3.81  1.45  Nov.  2.21  1.96  0.61  0.71  0.41  Dec.  1.22  1.80  0.56  0.18  0.25  24.82  27.62  18.63  18.60  13.81  Total  Source;  Canada, Department of Transport, M e t e o r o l o g i c a l Branch, Monthly Record(s): M e t e o r o l o g i c a l Observations i n Canada, Queen's P r i n t e r , Ottawa.  19 exposed slopes and summit areas and i t i s p i l e d i n t o t h i c k d r i f t s i n the depressions and against the c o a s t a l b l u f f s . A climate s t a t i o n was established on Garry I s l a n d , f o r the duration of each f i e l d season,, i n conjunction w i t h observations on vari a t i o n s i n the r a t e and depth of thaw of the a c t i v e layer a t selected s i t e s on the i s l a n d .  M e t e o r o l o g i c a l records from t h i s s t a t i o n permit the  only v a l i d comparisons w i t h the published records of the other s t a t i o n s i n the d e l t a area.  The r e s u l t s of these comparisons are shown i n Table I I I .  The temperature data contained i n Table I I I demonstrate the modifying e f f e c t of proximity to the Beaufort Sea. Mean temperature values f o r each of the summer months on Garry I s l a n d were c o n s i s t e n t l y 2-3°C cooler than those experienced a t Inuvik. The f a c t that the Garry I s l a n d temperatures a l s o averaged 1-2°C cooler than those at Tuktoyaktuk and Shingle P o i n t probably r e f l e c t s i t s i n s u l a r character. A comparison of the temperature extremes recorded during the same time period e x h i b i t s the same features.  Although there was l i t t l e or no d i s c e r n i b l e pattern i n  the recorded minima, the maximum temperatures f o r each month at Inuvik were c o n s i s t e n t l y 2-4°C warmer than those recorded on Garry I s l a n d .  The  values f o r the monthly p r e c i p i t a t i o n t o t a l s do not r e v e a l much of a pattern though, w i t h the exception of Shingle P o i n t , the amounts recorded at the c o a s t a l s t a t i o n s were less than f u r t h e r i n l a n d at Inuvik. The number of hours of b r i g h t sunshine was a l s o recorded on Garry I s l a n d during the 1964^ and 1965 f i e l d seasons.  An average of 321  hours of b r i g h t sunshine was recorded i n the month of J u l y and 197 hours i n August.  These t o t a l s were 7 and 22 hours less than Inuvik r e s p e c t i v e l y .  Although each s t a t i o n averaged four days without sunshine i n the month of J u l y , the corresponding f i g u r e s f o r August f o r Garry I s l a n d and Inuvik  20 TABLE I I I COMPARISONS OF TEMPERATURE. AND PRECIPITATION DATA IN THE DELTA AREA FOR THE MONTHS OF JULY - AUGUST, 1964 - 1966. Mean Daily Temperatures (Degrees Centigrade) 1964 J u l y Aug. Garry I s l a n d Tuktoyaktuk Nicholson Pen. Shingle Point Inuvik  9.0 8.3 5.7 8.8 11.6  7.3 8.2 5.8 8.2 10.2  1965 J u l y Aug.  1966 J u l y Aug.  9.3 11.6 9.5 9.8 13.9  9.7 11.1 8.5 11.7 14.3  7.3 9.9 8.2 9.2 10.7  5.9 7.1 5.3 7.1 9.6  1964-66 J u l y Aug. 9.3 10.3 7.9 10.1 13.3  6.8 8.4 6.4 8.2 10.2  Daily Temperature Extremes (Degrees Centigrade) 1964 J u l y Aug. Garry I s l a n d  Max. Min. Tuktoyaktuk Max. Min. Nicholson Pen, Max. Min. Shingle P o i n t Max. Min. Inuvik Max. Min.  26.7 -3.3 26.7 -1.7 27.2 -7.8 27.8 -3.9 28.9 -2.2  22.5 -1.1 22,8 -0.6 22.2 -4.4 21.7 0.0 23.9 3.9  1965 J u l y Aug.  1966 J u l y Aug.  24.6 1.9 23.3 1.7 25.0 0.0 26.1 2.2 27.2 -1.1  26.7 20.0 -0.6 -0.6 25.0 . 20.6 1.1 -0.6 25.6 18.9 -1.1 -3.3 27.8 21.1 1.1 -1.7 29.4 23.9 -3.3 -6.1  20.0 -2.8 21.1 0.6 19.4 0.0 23.9 -4.4 24.4 -1.7  Monthly P r e c i p i t a t i o n Totals (Cms.) 1964 J u l y Aug. Garry I s l a n d Tuktoyaktuk Nicholson Pen. Shingle P o i n t Inuvik Source:  0.6 2.9 0.4 7.3 6.2  1.3 1.7 •2.5 1.5 1.9  1965 J u l y Aug. _  3.1 T 3.5 4.6  _  4.4 2.4 5.9 9.0  1966 J u l y Aug. 0.7 0.6 0.7 2.2 3.3  1964-66 J u l y Aug.  0.2 . _ 2.2 1.1 0.4 1.6 2.2 4.3 1.4 4.7  _  2.4 2.2 3.2 4.1  Data f o r Tuktoyaktuk, Nicholson Peninsula, Shingle P o i n t and Inuvik taken from Monthly Record(s): M e t e o r o l o g i c a l Observations i n Canada, Queen's P r i n t e r , Ottawa,,  21 were nine and three days r e s p e c t i v e l y . Comparisons of wind speeds and d i r e c t i o n s showed that the dominant winds during each of the summer months on Garry I s l a n d were from the northwest and east, the same as Inuvik.  Periods of calm were r e l a t -  i v e l y r a r e on the i s l a n d however, and the mean wind v e l o c i t i e s f o r each month, 8-10 m.p.h., were c o n s i s t e n t l y 2-3 m.p.h. higher than those recorded at the inland s t a t i o n .  CHAPTER I I STRATIGRAPHY  The purpose of t h i s chapter i s to describe the major s t r a t i graphic u n i t s occurring on Garry I s l a n d and the evidence f o r changes i n the former r e l a t i v e p o s i t i o n s of land and sea.  This m a t e r i a l w i l l then  be used, i n the f i n a l chapter, i n an attempt to decipher the geomorphol o g i c a l h i s t o r y of the i s l a n d i n l a t e - and p o s t - g l a c i a l times. Garry I s l a n d i s the westernmost member of an arcuate chain of i s l a n d s , which includes adjacent P e l l y , K e n d a l l , Hooper and P u l l e n I s l a n d s , located i n the outer part of the Mackenzie D e l t a .  These i s l a n d s , together  w i t h most of Richards I s l a n d , the Tuktoyaktuk P e n i n s u l a , a c o a s t a l f r i n g e along the south side of the Eskimo Lakes, and an area s t r e t c h i n g north and northeast of the Caribou H i l l s , represent the discontinuous remnants of one or more deltas constructed by a P l e i s t o c e n e , or e a r l i e r , ancestor 1 of the modern Mackenzie R i v e r .  The s t r a t i g r a p h y c o n s i s t s e n t i r e l y of a  sequence of unconsolidated sands, g r a v e l s , s i l t s , c l a y s and stony-clays, cemented by i c e , i n which many of the beds have been deformed from t h e i r original position.  Figure 2 i s a map  features of Garry I s l a n d . This map  showing the major s t r a t i g r a p h i c  i s based on a l i m i t e d number of clean  exposures, mainly i n wave-cut b l u f f s , which have not been obscured by the combined e f f e c t s of s o l i f l u c t i o n processes and slumping, or mantled beneath a t h i n veneer of g l a c i a l  till.  1 Mackay, J . Ross (1956) "Mackenzie Deltas - A Progress Report", The Canadian Geographer, No. 7, pp. 3-7.  Figure 2  GARRY  ISLAND  -  STRATIGRAPHY  24 Areas of Deformed Sediments. The oldest sediments found on Garry Island are those represented i n a s e r i e s of discontinuous exposures i n a number of mudslumps and c o a s t a l b l u f f s along the south and west coasts of the i s l a n d . The f o l l o w i n g d e s c r i p t i o n o u t l i n e s the major s t r a t i g r a p h i c and s t r u c t u r a l features observed i n a s e r i e s of transects along the l a t t e r c o a s t l i n e where active slumping and c o a s t a l recession have r e s u l t e d i n the greatest number of clean exposures.  The f i r s t transect A-B (see i n s e t , Figure 2 ) ,  includes approximately 900 metres (3,000 feet) of c o a s t l i n e i n which a sequence of sands, s i l t s and clays has been uncovered i n a number of active mudslumps.  The clays contain large q u a n t i t i e s of segregated  ground i c e which has a d i s t i n c t i v e banded appearance caused by an a l t e r n a t i o n of bands of frozen ground, w i t h a high s i l t and clay content, and c l e a r ice*  These sediments, which dominate the s t r a t i g r a p h i c  sequence, are i n t e r c a l a t e d w i t h beds of f i n e sand, 4.5-9.0 metres (15-30 feet) t h i c k , containing an abundance of twigs, washed wood, bone fragments and s h e l l s .  Most of the s h e l l s have been severely crushed  during deformation of the s t r a t a , but two complete specimens, i n d i c a t i n g a marine d e p o s i t i o n a l environment, were i d e n t i f i e d as species of P o r t l a n d i a a r c t i c a (Gr ay) Canada.  by Dr. F.J.E. Wagner of the Geological Survey of  A l l the sediments i n t h i s transect have been deformed ( P l a t e I.-A) ,  and measurements taken from both the segregated i c e bands and the sand beds show a remarkable degree of consistency i n t h e i r a t t i t u d e , being t i l t e d to the southwest at angles ranging from 30-75 degrees. The transect B-C traverses a series of high b l u f f s reaching maximum heights of approximately 29 metres (95 feet) above sea l e v e l . Samples were taken s y s t e m a t i c a l l y from each of the major s t r a t i g r a p h i c  25 Plate I STRATIGRAPHY  A. Deformed body of s e g r e g a t e d ground i c e . Banded s t r u c t u r e s d i p to the southwest at a n g l e s of 60-65 d e g r e e s .  C. G r a n i t i c g l a c i a l e r r a t i c at an e l e v a t i o n o f a p p r o x i m a t e l y 85 f e e t above s e a l e v e l on the south s i d e of Garry I s l a n d .  B. Shear p l a n e d e v e l o p e d i n silty-clay.  D. S t r u c t u r a l ( ? ) r i d g e at an e l e v a t i o n of 60-65 f e e t above sea l e v e l on the s o u t h s i d e of Garry I s l a n d .  26 units exposed i n these b l u f f s , w i t h the exception of those occurring i n the mudslumps near C, and were analysed to determine t h e i r granulometric composition.  The r e s u l t s are i l l u s t r a t e d g r a p h i c a l l y i n Figure 3A.  The  sediments are p r i m a r i l y s i l t s and s i l t y - c l a y s , w i t h occasional beds of s a n d y - s i l t and, l i k e the sediments i n the previous t r a n s e c t , they e x h i b i t many signs of i n t e n s i v e deformation.  Bedding planes, where preserved,  are t i l t e d and o c c a s i o n a l l y contorted into a s e r i e s of gentle f o l d s .  The  most s a l i e n t feature of the deformation however i s the occurrence of large shear planes w i t h well-preserved s l i c k e n s i d e d surfaces which cut o b l i q u e l y across, and l o c a l l y o f f s e t , many of the o r i g i n a l bedding structures ( P l a t e I-B).  These shear planes, spaced at i n t e r v a l s ranging  from a few centimetres to s e v e r a l metres, are frequently concave up and i n places extend almost to the top of the b l u f f s .  Their presence  produces a much more complex pattern of deformation than that described i n the previous t r a n s e c t , and the a t t i t u d e of the i n d i v i d u a l beds often changes r a p i d l y over very short distances.  Further evidence of the  complexity of the s t r a t i g r a p h i c r e l a t i o n s h i p s i n t h i s s e c t i o n was  found  i n the s e q u e n t i a l examinations of constantly changing exposures at the same l o c a t i o n as a r e s u l t of continued marine erosion and  slumping.  Seldom, i f ever, d i d these new exposures repeat i d e n t i c a l l y the pattern which had been observed at an e a r l i e r date.  Nevertheless, the general  pattern of deformation i s s i m i l a r t o , a l b e i t less consistent than, that found i n the p r e v i o u s l y described t r a n s e c t , w i t h the s t r a t a maintaining dips approximately to the southwest.  Where the shear planes are concave,  the o r i e n t a t i o n of the concavity i s a l s o towards the  southwest.  The deformed sediments are buried i n the s e c t i o n C-D (Figure 2) beneath a s e r i e s of beach and l a c u s t r i n e d e p o s i t s , the  Figure 3 LOGARITHMIC  B.  GRAIN  SAND  SIZE  HEADLANDS  DISTRIBUTION  DIAGRAMS  28 s i g n i f i c a n c e of which w i l l be discussed below.  The deformed sediments  reappear again f u r t h e r along the coast but most of the exposures are obscured by s u r f i c i a l slump deposits.  Two measurements were recorded i n  deformed ground i c e bodies, exposed i n a large mudslump, where i t appears that the beds have a north or northwesterly dip of 20-30 degrees. Exposures i n the high b l u f f s along the south coast of the i s l a n d are very l i m i t e d due to the r e s t r i c t e d active r e c e s s i o n of the c l u f f s and t h e i r mantling by d e b r i s . Two observations made i n deformed beds of s i l t and c l a y , and one i n a small exposure of ground i c e , indicate a generally n o r t h e a s t e r l y dip of 15-25 degrees.  Only one  exposure of deformed sediments was recorded along the whole of the north coast, where a band of v e i n ice i n a mudslump appears to be gently folded and plunges almost due north at an angle of about 9 degrees. Direct evidence of deformation over the remainder of the i s l a n d i s l a c k i n g , but a e r i a l photographs r e v e a l the presence of a few marked l i n e a t i o n features which may be s t r u c t u r a l l y c o n t r o l l e d .  Ground checks  of these features however f a i l e d to confirm whether or not they were d e f i n i t e l y r e l a t e d to any underlying s t r u c t u r e s . S i m i l a r deformation of P l e i s t o c e n e or e a r l i e r sediments has been recorded along adjacent sections of the mainland coast, from Herschel I s l a n d i n the west to the Nicholson Peninsula i n the east; a 2 distance exceeding 485 kilometres (300 m i l e s ) .  Three possible  mechanisms - slumping, t e c t o n i c disturbance and i c e t h r u s t i n g - were ^Mackay, J . Ross (1956) "Deformation by G l a c i e r Ice at Nicholson P e n i n s u l a , N.W.T., Canada", A r c t i c , V o l . 9, pp. 219-228. Mackay, J . Ross (1960) "Glacier Ice Thrust features of the Yukon Coast", Geographical B u l l e t i n , No. 13, pp. 5-21.  presented  to e x p l a i n the deformation  patterns.  Although the conditions  on Garry I s l a n d are often very conducive to mudslump development, the scale of the deformation, the r e g u l a r i t y of the pattern and the presence of deformation  features.; i n areas where there i s no sign of past or  present slump a c t i v i t y , are considered to be s u f f i c i e n t c r i t e r i a for e l i m i n a t i n g t h i s mechanism as a s a t i s f a c t o r y explanation of the deformat i o n pattern. The most s a t i s f a c t o r y i n t e r p r e t a t i o n of the  deformation  pattern i s that i t i s the r e s u l t of the o v e r r i d i n g a c t i o n of g l a c i e r - i c e ; the same mechanism which produced the disturbed features on the mainland.  adjacent  D i r e c t evidence of the g l a c i a t i o n of Garry I s l a n d i s d i f f i c u l t  to assess, but the stony nature of the a c t i v e layer suggests that many slopes are mantled by a t h i n veneer of g l a c i a l t i l l .  Glacial erratics  found on the slopes, i n s o l i f l u c t i o n deposits and along the beaches include g r a n i t e s , gneisses, q u a r t z i t e s , sandstones and slabs of f o s s i l i ferous (Devonian ?) limestone.  Large e r r a t i c s , up to 3 metres (10 feet)  across, are found close to the highest summits of the i s l a n d ( P l a t e I-C),, but since the whole i s l a n d l i e s below the upper marine l i m i t (see below), the p o s s i b i l i t y that they may have been i c e - r a f t e d cannot be  excluded.  Sand Headland Areas. Exposures on the north coast of the i s l a n d (Figure 2) are dominated by t h i c k deposits of sand which terminate 6-11  metres (20-35 feet) high.  i n coastal bluffs  The precise a r e a l extent and thickness of  the sands are d i f f i c u l t to determine since very few contacts w i t h the  •^Mackay, J . Ross (1960) " G l a c i e r Ice Thrust features of the Yukon Coast", Geographical B u l l e t i n , No. 13, p. 5.  30 underlying sediments are exposed.  The headland surfaces are gently  sloping and devoid of any major r e l i e f features, and they contrast markedly with the more rugged topography of the area of deformed sediments to the south.  This change i n the character of the l o c a l r e l i e f occurs at  elevations of approximately 12-15 level.  metres (40-50 feet) above present sea  The sands are brown i n c o l o u r , h o r i z o n t a l l y s t r a t i f i e d w i t h  occasional signs of current bedding, and consist mainly of sands i n the medium- to f i n e - g r a i n s i z e category (Figure 3B) w i t h i n c l u s i o n s of gravel lenses.  The sands are not deformed, except for l o c a l upturning  along  the  l i n e s of the more prominent ice-wedges, and there i s no evidence of any g l a c i a l deposition on any of the headland surfaces. The sands contain i r o n - s t a i n e d twig fragments and an abundant marine molluscan fauna.  The f o l l o w i n g species were i d e n t i f i e d by  Dr. Wagner: A s t a r t e b o r e a l i s Schumacher Astarte montagui (Dillwyn) Astarte montagui (Dillwyn) forma t y p i c a Astarte montagui var. s t r i a t a (Leach) Astarte montagui var. warhami Macoma calcarea Gmelin My a truncata Linnl" Trachoma b a l t h i c a Linne Tachyrhyncus sp. probably T. erosum T r i c h a t r o p i s sp. A sample of these f o s s i l s submitted for radiocarbon dating y i e l d e d an of >42,600 years (G.S.C.- 562).  age  Many of these s h e l l s are i n an e x c e l l e n t  state of preservation and frequently have t h e i r outer valve cover (periostracum)  intact.  Consequently, although no hinged specimens of the  s h e l l s were found, and despite the f a c t that the sands also contain many broken s h e l l fragments, the f o s s i l s probably have not been reworked from e a r l i e r deposits, and the above date i s therefore interpreted to be a  31 r e l i a b l e i n d i c a t o r of the minimum time of sand deposition. The t e x t u r a l s i m i l a r i t y of a l l the sand exposures (Figure 3B) may i n d i c a t e that they represent the discontinuous remnants of a formerly much more extensive sand p l a i n formed when the r e l a t i v e l e v e l of the sea was 12-15 metres (40-50 feet) higher than at present. The d i s c o n t i n u i t y of the bodies of sand may be p a r t i a l l y inherent, r e f l e c t i n g i r r e g u l a r d e p o s i t i o n , or i t may be e n t i r e l y r e l a t e d to the e f f e c t s of marine erosion subsequent to deposition.  I n e i t h e r case, the main problem  concerns the o r i g i n a l source of the sand-size m a t e r i a l and, i n p a r t i c u l a r , whether i t was derived l o c a l l y or had an extraneous o r i g i n . One possible mode of o r i g i n f o r the sands, implying a l o c a l source, i s that they represent the r e s i d u a l accumulations of coarse m a t e r i a l r e s u l t i n g from long-continued marine erosion of the i s l a n d .  The  c o a s t l i n e of Garry Island i s c u r r e n t l y undergoing r a p i d recession i n many places, and there i s evidence that the shoreline has retreated a considerable distance during the past.  A comparison of the two g r a i n s i z e  d i s t r i b u t i o n diagrams i l l u s t r a t e d i n Figure 3 i s shown i n the t r i a n g u l a r graph of Figure 4, i n d i c a t i n g r e l a t i v e percentages of m a t e r i a l of sand-, s i l t - and c l a y - s i z e p a r t i c l e s of samples taken from both the sand headlands and the areas of deformed sediments.  The l a t t e r have an average  sand content of only 7 per cent, and only one per cent i s i n the medium and coarse sand f r a c t i o n s (<0.50 mm.)-  The major exception to these  f i g u r e s i s the f o s s i l i f e r o u s sand beds described i n transect A-B which have an average sand content of 91 per cent, 10 per cent of which i s i n the medium sand or coarser range.  These values contrast w i t h the average  of 91 per cent sand-size m a t e r i a l i n samples taken from the sand headlands and an average of 26 per cent of m a t e r i a l w i t h a g r a i n s i z e greater  32  Figure 4 GRAIN  SIZE  TAKEN  DISTRIBUTION  FROM  AREAS  THE OF  FOR  SAND  SOIL  SAMPLES  HEADLANDS  DEFORMED  AND  SEDIMENTS  C L A Y (<0.004mm.) 100 %  SAND (>0.06 mm.)  SILT (0.06 to 0.004mm.)  o Samples  from  Sand  •  from  Deformed  Samples  Headlands Sediments  33 than 0.50 mm. Whilst the number of samples upon which these f i g u r e s are based i s s m a l l , they do i n d i c a t e that the volume of coarse m a t e r i a l i n the deformed sediments i s quite minor and, i f the sands are to be i n t e r preted as a r e s i d u a l accumulation produced by long periods of marine erosion of the i s l a n d , they must r e f l e c t the disappearance of very extensive t r a c t s of older sediments.  Some of the sand and g r a v e l , of  course, may have been derived i n a s i m i l a r manner through erosion of the s u r f i c i a l mantle of g l a c i a l t i l l and the stony-clays, containing the segregated ice bodies, exposed i n the mudslumps.  A l t e r n a t i v e l y , the sand  headland m a t e r i a l may represent the r e s i d u a l deposits r e s u l t i n g from the erosion of s t r a t i g r a p h i c u n i t s which are poorly represented ing succession.  i n the e x i s t -  I f the land, which has subsequently been eroded away by  the sea, contained greater q u a n t i t i e s of the f i n e sands described i n the transect A-B, or was mantled by a greater thickness of g l a c i a l d e p o s i t s , i n c l u d i n g t i l l and/or outwash m a t e r i a l l a i d down f o l l o w i n g the r e t r e a t of the g l a c i e r ( s ) , the problem of a source m a t e r i a l would be g r e a t l y alleviated. As a c o r o l l a r y to t h i s mode of o r i g i n , which i n t e r p r e t s the sands as beach or s p i t d e p o s i t s , i t i s i n t e r e s t i n g to note the d i s t r i b u t i o n of lakes on the i s l a n d .  As Figure 2 shows, some of them occur along the  contact zone of the sand bodies and the older, deformed sediments. The lakes may thus have o r i g i n a t e d as lagoon features on the landward sides of the sandspits, i n much the same way as lagoons are c u r r e n t l y being formed i n a s s o c i a t i o n w i t h the present day sandspits. encountered w i t h t h i s hypothesis averaging  The major d i f f i c u l t y  i s that the present lagoons are shallow,  1.5-2.0 metres (5-6 feet) i n depth, whereas the lake bottoms are  34 as much as 12-15 metres (40-50 feet) below the surfaces of the sand headlands.  P a r t of t h i s d i f f e r e n t i a l may p o s s i b l y be explained by the thermo-  karst or warming action of the lake water on the underlying sediments, since the thawing of any ice contained i n these materials could have r e s u l t e d i n a s e t t l i n g of the lake f l o o r . An a l t e r n a t i v e mode of o r i g i n for the sands, i n f e r r i n g an extraneous rather than a l o c a l source, i s that they represent  coarse  m a t e r i a l brought down by streams f o l l o w i n g the r e t r e a t of the i c e . These deposits may have been l a i d down under marine conditions when the r e l a t i v e l e v e l of the sea was 12-15 metres (40-50 feet) higher than at present, or i t may be that the marine f o s s i l s represent a post-depositional phase during which the sands were reworked.  Such an o r i g i n seems more probable  than the above-mentioned l o c a l source on the basis of comparisons of the compositions  of the sand headlands and the present day beach deposits.  The l a t t e r contain abundant cobbles and boulders, derived from erosion of the g l a c i a l t i l l , whereas s i m i l a r m a t e r i a l forms a very minor constituent i n the rather uniform composition of the sand headlands. Since much of the sand m a t e r i a l may have been l a i d down under the influence of wave action and moulded into large s p i t s , some of the lakes may s t i l l have o r i g i n a t e d as lagoon features.  A l t e r n a t i v e l y , the  lakes may represent deeper parts of the former r i v e r channels as i n the case of the lake s i t u a t e d immediately south of the sand headland o u t l i e r on the northwest coast of the i s l a n d .  Yet another o r i g i n may be postulated  for the deep, steep-sided lake incorporated w i t h i n one of the headlands, which p o s s i b l y may be interpreted as a k e t t l e feature.  Unfortunately,  there are no good exposures of sand around the shores of t h i s lake to check t h i s hypothesis.  35 THE EXTENT OF THE MARINE SUBMERGENCE The c o a s t a l lowlands of a r c t i c Canada were i n f l u e n c e d , to varying degrees, by the f l u c t u a t i o n s i n sea l e v e l produced by the waxing and waning of the i c e sheets.  Attempts have been made to determine the precise  l i m i t s of the extent of the marine transgression using the four c r i t e r i a of:  (1) the highest a l t i t u d e at which marine s h e l l s occur; (2) the highest  a l t i t u d e at which s t r a n d - l i n e s are preserved; (3) the lowest a l t i t u d e at which undisturbed ground moraines can be recognized; and (4) the lowest 4 a l t i t u d e at which perched boulders are found.  As a r e s u l t of research  conducted along these l i n e s , enough evidence has been accumulated to provide an overview of the p a t t e r n and extent of the p o s t - g l a c i a l marine transgression i n northern Canada. Reference to the G l a c i a l Map of Canada reveals that the area affected by the p o s t - g l a c i a l marine transgression was much less extensive i n the v i c i n i t y of the Beaufort Sea than i n other sectors of the Canadian arctic.  This undoubtedly r e f l e c t s the f a c t that much of the eastern  a r c t i c was, i n general,'an area of t h i c k i c e cover, whereas the Mackenzie Delta area, being at or close to the northern l i m i t of i c e advance, was blanketed by a much thinner i c e sheet.  I t may also r e f l e c t the f a c t that  the eastern a r c t i c has been more i n t e n s i v e l y i n v e s t i g a t e d and thus there i s a r e l a t i v e paucity of observations from the west.  A l s o of s i g n i f i c a n c e  Sim, V.W. (1960) "Maximum p o s t - g l a c i a l marine submergence i n northern M e l v i l l e P e n i n s u l a " , A r c t i c , V o l . 13, p. 180. ^Geological Survey of Canada (1968) G l a c i a l Map of Canada. Farrand, W.R. and Gajda, R.T. (1962) "Isobases on the Wisconsin marine l i m i t i n Canada", Geographical B u l l e t i n , No. 17, pp. 5-22.  36 may be the f a c t that the evidence of a marine transgression i n t h i s westernmost sector of the Canadian a r c t i c i s by no means as obvious as i n i t s eastern and c e n t r a l counterparts.  The d i s t i n c t i v e f l i g h t s of strand-  l i n e s , which form prominent features i n the landscape of the c e n t r a l and eastern a r c t i c , are generally l a c k i n g i n the Beaufort Sea area. the s t r a t i g r a p h y c o n s i s t s of unconsolidated  Most of  s i l t s and c l a y s : materials  which are e a s i l y eroded but are not conducive to. the development of prominent and p e r s i s t e n t wave-cut b l u f f s .  The l a c k of persistence  r e f l e c t s the high s u s c e p t i b i l i t y of these same sediments to f r o s t a c t i o n and mass movement, e s p e c i a l l y s o l i f l u c t i o n , and the operation of these processes, throughout at l e a s t p o s t - g l a c i a l time, has tended to obscure much of the evidence of former submergence and emergence, i f indeed i t ever occurred.  Intimately associated w i t h t h i s tendency i s the evidence  which suggests that the area i n the v i c i n i t y of the Beaufort Sea was not g l a c i a t e d during the late-Wisconsin, or most recent, stage of the Pleistocene p e r i o d , thus presenting a longer time i n t e r v a l during which the traces of former sea l e v e l s could be o b l i t e r a t e d . Even when the evidence for a marine transgression has been deciphered, there are further problems involved i n e s t a b l i s h i n g a chronological sequence i n the Mackenzie Delta area.  This sequence must take i n t o consideration the complex i n t e r -  a c t i o n of an o v e r a l l p o s t - g l a c i a l r i s e i n sea l e v e l which may p o s s i b l y be coupled w i t h two opposing forces i n the earth's c r u s t ; an upward or p o s i t i v e movement representing a response to the removal of the weight of the i c e , and a downward or negative movement representing c r u s t a l depression i n response to the weight of the accumulating brought down by the Mackenzie River i n recent  d e l t a i c sediments  times.  Because the conditions that favour the development and  37 preservation of d e f i n i t e evidence of a marine transgression are so poor, and the i n t e r p r e t a t i o n of t h i s evidence i s so complex, i t i s d i f f i c u l t to determine, w i t h any r e a l degree of p r e c i s i o n , how extensive i t was.  This  i s r e f l e c t e d i n the e x i s t i n g l i t e r a t u r e which contains a number of widelycontrasting opinions.  Richards claimed that there was no evidence of any 6  p o s t - g l a c i a l marine beaches i n the v i c i n i t y of the Mackenzie D e l t a . Mackay, on the other hand, has described a number of extensive estuarine r i v e r terraces which suggest a r e l a t i v e submergence of approximately 15 metres (50 feet) when the c o a s t a l area f i r s t became free of ice.'' The emergence of the land i n the subsequent period may have been reversed more r e c e n t l y to be replaced by a period of submergence 3-6 metres (10-20 f e e t ) .  i n the order of  8  The magnitude of these apparent changes i n the land-sea r e l a t i o n s h i p s i s quite small compared to the evidence, a l b e i t more dubious, reported from the area l y i n g to the west of the d e l t a .  O'Neill  reported that the f i n d i n g of marine f o s s i l s i n h i g h - l e v e l g l a c i a l deposits, and high terraces on the mountains f a c i n g the A r c t i c Ocean, indicated that g l a c i a l or p o s t - g l a c i a l submergence of the A r c t i c coast 9 extended at l e a s t to 152 metres (500 feet) above sea l e v e l . Richards, H.G. (1950) " P o s t g l a c i a l marine submergence of A r c t i c North America with s p e c i a l reference to the Mackenzie D e l t a " , Amer. P h i l . Soc. Proc. , V o l . 94, p. 36. Mackay, J . Ross (1963) The Mackenzie Delta area, N.W.T., Geographical Branch Memoir, No. 8, p. 39. 7  8  I b i d . , p. 47.  0 ' N e i l l , J . J . (1924) "Geology of the A r c t i c coast of Canada, west of the Kent Peninsula", Report of the Canadian A r c t i c Expedition, 1913-1918, V o l . X I , Geology and Geography, P a r t A, p. 18A. 9  38 More recent i n v e s t i g a t i o n s , using f o s s i l evidence and the mechanical properties of sediments found i n excavations at the Engigstciak. a r c h e o l o g i c a l s i t e , near the mouth of the F i r t h R i v e r , suggest an a l t e r n a t i v e explanation f o r evidence of such h i g h - l e v e l submergence.^ Although marine clays at t h i s s i t e are found at an a l t i t u d e of 207 metres (680 f e e t ) , and f o s s i l s i n these sediments i n d i c a t e that they l i v e d i n water depths of more than 30 metres (100 f e e t ) , i t i s believed that the clays were transported to t h e i r present e l e v a t i o n by the t h r u s t i n g a c t i o n of glacxer-xce. East of the Mackenzie Delta there a l s o appears to be evidence of a more extensive marine transgression than i s found i n the immediate v i c i n i t y of the d e l t a . Mackay has described a s e r i e s of elevated beaches and gravel terraces r i s i n g to 61 metres (200 f e e t ) , and O ' N e i l l observed s i m i l a r features at elevations reaching 67 metres (220 feet) above sea 12 level.  Further north, the evidence of a marine transgression on Banks  I s l a n d has been found at a number of l o c a l i t i e s i n the neighbourhood of 177-183 metres (580-600 f e e t ) .  1 3  10 Mackay, J . Ross, Mathews, W.H. and MacNeish, R.S. (1961) "Geology of the Engigstciak a r c h e o l o g i c a l s i t e , Yukon T e r r i t o r y " , A r c t i c , V o l . 14, pp. 25-52. 1 1  I b i d . , p. 47.  Mackay, J . Ross (1958) "The Anderson River map area, N.W.T.", Geographical Branch Memoir, No. 5, p. 38. 12  O ' N e i l l , J . J . (1924) o£. c i t . , p. 33A. P o r s i l d , A.E. (1955) "The vascular plants of the Western Canadian A r c t i c Archipelago", Nat. Mus. Can. B u l l . , No. 146, p. 188. 1 3  Manning, T.H. (1956) "Narrative of a Second Defense Research Board Expedition to Banks I s l a n d , w i t h notes on the country and i t s h i s t o r y " , A r c t i c , V o l . 9, pp. 3-77.  39 The i d e n t i f i c a t i o n and i n t e r p r e t a t i o n of evidence i n d i c a t i n g changes i n the pattern of land-sea r e l a t i o n s h i p s was part of the f i e l d study programme on Garry I s l a n d .  However, few of the afore-mentioned  c r i t e r i a f o r d e l i m i t i n g the extent of a marine transgression are r e a d i l y a p p l i c a b l e to the conditions on Garry I s l a n d . to employ the c r i t e r i o n of undisturbed that the whole i s l a n d was  It is virtually  impossible  ground moraine, since i t appears  a f f e c t e d by submergence, and therefore  one  cannot use a comparative i n v e s t i g a t i o n of disturbed and undisturbed  till  deposits to determine the upper l i m i t of the marine transgression.  No  evidence was found i n the form of perched boulders but, again, i f the i s l a n d were completely  submerged i n the past i t i s u n l i k e l y that any of  these would have survived. The use of marine f o s s i l s as evidence of a marine invasion of the land i s also extremely l i m i t e d .  Even where t h i s c r i t e r i o n has been  adopted i n other areas, there are problems i n determining whether the f o s s i l s are ' i n situ'  1  or whether they were transported to t h e i r present  elevations as '.shelly d r i f t ' by the t h r u s t i n g a c t i o n of g l a c i e r - i c e . Insomuch as there i s abundant evidence that the l a t t e r process has  pro-  foundly a f f e c t e d the s t r a t a on Garry I s l a n d , i t would r e q u i r e c a r e f u l consideration.  However, due to the f a c t that the late-Wisconsin i c e  sheet d i d not cover the i s l a n d , the long period of s u b a e r i a l exposure has probably r e s u l t e d i n the d e s t r u c t i o n of much of the f o s s i l i f e r o u s evidence by weathering processes.  In any case, the only marine f o s s i l s found i n  a s s o c i a t i o n with the r a i s e d shorelines were r e s t r i c t e d to elevations around 7.5-10.5 metres (25-35 feet) above sea l e v e l . The presence of r a i s e d shoreline features affords the most d i r e c t evidence of a former submergence of the i s l a n d .  Unfortunately,  40 however, the conditions on Garry I s l a n d are s i m i l a r to those found i n other parts of the d e l t a , and were generally unfavourable to the formation and preservation of these features.  Most of the s t r a n d - l i n e s were e i t h e r  only weakly developed, or evidence of t h e i r presence has been obscured, or even o b l i t e r a t e d , by the operation of p e r i g l a c i a l geomorphic processes i n the i n t e r v a l since the withdrawal of the sea.  As a general r u l e , the  r a i s e d shorelines do not e x h i b i t strong topographic  expressions  and seldom  are they backed by prominent wave-cut b l u f f s ( P l a t e II.-A). .In.fact, the only surface expression of many of the s t r a n d - l i n e s c o n s i s t s of a f a i n t bevel, or break of slope, the presence of which might go completely undetected i f i t were not accentuated by contrasts i n the vegetation pattern. Since most of the s t r a t i g r a p h i c u n i t s on Garry I s l a n d are composed of r e l a t i v e l y f i n e - g r a i n e d s i l t s and c l a y s , the r a i s e d shoreline features are r a r e l y characterized by impressive shingle or boulder r i d g e s . Where these are developed they c o n s t i t u t e the exception rather than the rule.  Mechanical probing of the a c t i v e l a y e r , however, frequently revealed  concentrations of coarse sand, gravel and well-rounded, i r o n - s t a i n e d , pebbles at depths ranging from 30-60 cms. (1-2 feet) below the ground surface.  These deposits, found i n a s s o c i a t i o n with the f a i n t breaks of slope  on the topographic  p r o f i l e , can often be traced quite extensively along the  contours, but f o r distances of only a few metres i n e i t h e r an upslope or downslope d i r e c t i o n . They are i n t e r p r e t e d as r e s i d u a l beach deposits buried beneath a mantle of s o l i f l u c t e d m a t e r i a l .  The l o c a t i o n s of the s t r a n d - l i n e s are often marked by the development of a vegetation a s s o c i a t i o n which includes the t u s s o c k - l i k e forms of the Sheathed Cotton-grass (Eriophorum vaginatum).  Plate I I  RAISED  SHORELINE  FEATURES  A. Wave-cut b l u f f a t an e l e v a t i o n of a p p r o x i m a t e l y 75 f e e t above sea l e v e l .  B. Sandspit associated with the 25 f o o t r a i s e d s t r a n d line .  C. Peat a c c u m u l a t i o n damming the o u t l e t of a l a k e at an e l e v a t i o n of 120-125 f e e t above sea l e v e l .  D. I n t e r r u p t i o n i n the l o n g i t u d i n a l p r o f i l e of Stream 'B' a t an e l e v a t i o n of 100 f e e t above sea l e v e l .  42 The d i s t r i b u t i o n of these r a i s e d shoreline features i s shown i n F i g u r e 5.  Although many of them can be traced f o r considerable d i s t a n -  ces, the incompleteness of the pattern r e f l e c t s : observations made;  (1) the number of  (2) the degree to which the s t r a n d - l i n e s have been  destroyed by the combined a c t i o n of mudslump development and c o a s t a l r e cession associated w i t h lower sea l e v e l s than those at which they were formed;  (3) the depth to which the evidence has been buried by s o l i f l u c -  t i o n deposits; developed.  and (4) the type of sediment i n which the shorelines were  The. importance of the. f i r s t f a c t o r i s revealed i n F i g u r e 5  where only a l i m i t e d number of observations was made i n the c e n t r a l part of the i s l a n d .  A s i m i l a r paucity of evidence along the south coast of the  i s l a n d can l a r g e l y be a t t r i b u t e d to i t s o b l i t e r a t i o n by slumping and c o a s t a l recession.  The s i g n i f i c a n c e of the l a t t e r two f a c t o r s i s r e l a t e d  to the thickness and composition of the a c t i v e l a y e r .  I f the r e s i d u a l  accumulations of sand and pebbles l i e at depths greater than the thickness of the a c t i v e l a y e r , t h e i r presence can only be determined by d r i l l i n g i n t o the permafrost beneath.  Furthermore, i f the composition of the sub-  s t r a t e c o n s i s t s of coarse-grained sediments, i t i s d i f f i c u l t to d i f f e r e n t i a t e between the parent m a t e r i a l and possible r e s i d u a l beach deposits. I t i s f o r t h i s reason that l i t t l e evidence of r a i s e d s t r a n d - l i n e f e a t u r e s , i f indeed they e x i s t , i s shown on the surfaces of the sand headlands. As F i g u r e 5 i n d i c a t e s , the evidence suggests the presence of a series of r a i s e d s t r a n d - l i n e s , at approximately 7.5 metre (25 foot) i n t e r v a l s , reaching to heights of 46 metres (150 feet) above sea l e v e l .  The  approximate elevations of the s t r a n d - l i n e s were determined using a t e l e s c o p i c alidade and an a l t i m e t e r .  Because; of the weak topographic  expression of the r a i s e d s h o r e l i n e s , the degree to which the m a j o r i t y of  Figure 5  44 them have been obscured by s o l i f l u c t i o n deposits and the v i r t u a l impossi b i l i t y of l o c a t i n g the o r i g i n a l breaks of slope beneath t h i s m a t e r i a l , and i n the absence of a f i x e d datum f o r mean sea l e v e l r e s u l t i n g i n an error of 0.3-0.6 metres (1-2 feet) produced by t i d a l f l u c t u a t i o n s , i t i s almost impossible to determine the precise elevations of the s t r a n d - l i n e s . The heights assigned to the r a i s e d shoreline features must consequently be regarded as approximations, and the ' r e g u l a r i t y ' of t h e i r spacing  should  be i n t e r p r e t e d as apparent rather than r e a l . The highest s t r a n d - l i n e s , at the '46' metre (150 foot) and '38' metre (125 foot) l e v e l s , are the l e a s t extensively developed since few of the summit areas reach these e l e v a t i o n s . est topographic  They a l s o have the weak-  expression, and t h i s i s undoubtedly r e l a t e d to t h e i r  greater a n t i q u i t y and t h e i r exposure to the modifying  influences of p e r i -  g l a c i a l or other geomorphic processes f o r longer periods of time.  One  noticeable aspect of the d i s t r i b u t i o n a l pattern of these highest shorel i n e s , and to some extent that of the '30.5' metre (100 foot) s h o r e l i n e , i s t h e i r r e l a t i o n s h i p to the major topographic  features of,the i s l a n d .  A r e c o n s t r u c t i o n of the c o n f i g u r a t i o n of Garry I s l a n d when the r e l a t i v e l e v e l of the sea was  38 metres (125 feet) higher than at present, shows  that i t would a c t u a l l y c o n s i s t of nine small i s l a n d s separated by open stretches of water.  The manner i n which the elevated s t r a n d - l i n e s can  traced on both the north and south sides of the i s l a n d , and along the c o l s i n the summit areas, suggests that the main topographic  be low  features of  Garry I s l a n d are of considerable a n t i q u i t y , and that the e f f e c t s of submergence and subsequent emergence have had l i t t l e e f f e c t i n the remoulding of the landscape. Almost a l l the s t r a n d - l i n e s developed at and below the  45 30.5 metre (100 foot) contour l e v e l have some topographic expression, and can be traced much more e x t e n s i v e l y along the length of the i s l a n d .  Each  shoreline i s r e a d i l y detectable around the i n t e r f l u v e areas, but seldom i s i t possible to trace them across the l i n e s of the v a l l e y reentrants. The possible reason for t h i s w i l l be discussed more f u l l y below.  Just to  the east of Stream 'K' i s a l a r g e , steep-sided depression across which there i s a prominent r i d g e , the e l e v a t i o n of which i s  approximately  18.5-20 metres (60-65 feet) above sea l e v e l ( P l a t e I-D)... This ridge cannot be l i n k e d w i t h any of the adjacent s t r a n d - l i n e features and i t i s composed of r e l a t i v e l y f i n e sands with few pebbles or boulders.  Although  no conclusive evidence could be found, the ridge i s interpreted to be a s t r u c t u r a l feature i n the deformed sediments behind which a small lake may  have temporarily been ponded. Between the '15' metre (50 foot) and  '23' metre (75 foot)  s t r a n d - l i n e s are a number of i s o l a t e d boulder accumulations developed at the 17-18  metre (55-60 foot) l e v e l .  These are p a r t i c u l a r l y noticeable on  the north side of the i s l a n d , to the east of Stream 'B', and on the west side of the open v a l l e y above the head of Stream ' I . Their 1  c o n s i s t i n g of l a r g e , well-rounded, 30 cms.  composition,  iron-stained boulders, often exceeding  i n length, and t h e i r prominence contrasts markedly w i t h the minor  accumulations of beach deposits found i n a s s o c i a t i o n with the s e r i e s of strand-lines.  They appear to be much older features and may be i s o l a t e d  remnants of an e a r l i e r p o s i t i o n of the sea r e l a t e d to the time of deposition of the m a t e r i a l i n the sand headlands. The evidence of s t r a n d - l i n e development at the 7.5 metre (25 foot) l e v e l , where preserved, i s the most pronounced of a l l the elevated s h o r e l i n e s , but i t s l i m i t e d occurrence bears witness to the  46 extent of c o a s t a l recession i n recent times.  V i r t u a l l y nowhere along the  south coast of the i s l a n d i s there any i n d i c a t i o n of i t s presence, and i t i s best developed around the margins of b a y - l i k e depressions between the sand headlands on the north side of the i s l a n d .  Here the old shoreline  feature can be traced quite r e a d i l y around the l a t e r a l margins of the sand headlands and i t s development i n the coarse-grained  sediments probably  accounts for i t s prominence and preservation, since the sands are less susceptible to slumping and s o l i f l u c t i o n than the s i l t s and c l a y s . Although, as mentioned p r e v i o u s l y , i t i s d i f f i c u l t to apply the c r i t e r i o n of r e s i d u a l beach deposits at depth to the sand headland areas, there appears to be no doubt that the '7.5' metre (25 foot) s t r a n d - l i n e d e f i n i t e l y post-dates The  their  formation.  '7.5' metre (25 foot) r a i s e d s t r a n d - l i n e i s also  developed around the edge of another large depression on the northwest coast of the i s l a n d (Figure 5).  In t h i s l o c a l i t y , the r e t r e a t of the  present c o a s t l i n e i s also responsible f o r i t s . l i m i t e d occurrence, but the s t r a t i g r a p h i c sequences exposed i n the c o a s t a l b l u f f s provide e x c e l l e n t cross-section of the structure of the depression. of t h i s c r o s s - s e c t i o n c o n s t i t u t e the p r o f i l e C-D  an The  details  shown i n Figure 6.  The depression i s developed i n the deformed clay sediments which occur i n the large mudslump, where they also contain bodies of ground i c e , at the northeastern end of the transect B-C  (Figure 2).  These clays are only exposed i n the extreme southwestern part of the cross-section and elsewhere they are buried beneath 5.5-6.0 metres (18-20 feet) of pebbly-gravel. i s approximately  The a l t i t u d e of the top of these gravels  7.5 metres (25 feet) above sea l e v e l at point C; the  same e l e v a t i o n as that of the shoreline feature found around the edge of  Figure 6  S T R A T I GRAPHIC  SECTION  NORTHWEST  For l o c a t i o n of s e c t i o n  see  Inset  EXPOSED COAST  Figure 2  OF  IN  COASTAL  GARRY  BLUFFS  ALONG  ISLAND  Solifluction  Material  Peat Pebbly Horizontal  Scale  Gravel  1 inch = 350 feet  Lacustrine  1 inch =  Beach  Vertical  Scale  Vertical  Exaggeration  xlO  35 feet  Pebbly  Sediments  Gravels Clay  48 the depression.  From t h i s point the surface of the gravels slopes gently  toward the centre of the b a s i n , r i s i n g again to a height of 7.3 metres (24 feet) i n a well-defined r i d g e .  This ridge can also be traced across  the f l o o r of the depression, where the gravels appear at the surface, and i t represents an old s p i t or bar associated with the '7.5' metre (25 foot) s t r a n d - l i n e ( P l a t e II-B).  Beyond the s p i t the thickness of the gravels  decreases u n t i l they disappear  completely  i n the centre of the s e c t i o n .  The gravels reappear again beyond the area of polygonal ground and increase to a thickness of 4 metres (13 feet) again at point D. The gravels i n turn are o v e r l a i n by a sequence of o r g a n i c - r i c h clays which l o c a l l y e x h i b i t a v a r v e - l i k e banding.  These clays contain an  abundant c o l l e c t i o n of gastropods, i d e n t i f i e d by Dr. F.J.E. Wagner as Lymnaea species, and these f o s s i l s i n d i c a t e that the clays were deposited i n freshwater  conditions.  The thickness of the l a c u s t r i n e sediments, on  both sides of the depression, increases towards the centre where they t h i n again and are replaced by t h i c k accumulations of peat i n the form of a number of high-centred tundra polygons.  These polygons have been  dissected by deep trenches created by melting along the l i n e s of former positions of the intervening ice-wedges.  A specimen of peat from one of  these polygons, taken from the c o a s t a l b l u f f at a depth of 1.5 metres (5 feet) below the surface, was y i e l d e d an age of 4120  submitted for radiocarbon dating and  - 130 years (G.S.C. - 513).  A s i m i l a r sequence of l a c u s t r i n e sediments was  deposited i n  the smaller marginal basin created by the formation of the gravel s p i t . A peat sample, c o l l e c t e d by Dr. J.G. F y l e s , taken from the basal layer of t h i s sequence near point C indicated an age of 10,330 ^ 150 years (G.S.C. - 517).  At t h i s same l o c a t i o n , however, the lake sediments are  49 also buried beneath a f u r t h e r 1.5-1.8 metres (5-6 feet) of pebbly-gravel followed by an a d d i t i o n a l 0.6-1.2 metres (2-4 f e e t ) . o f peat.  This g r a v e l ,  the upper surface of which i s at a height of 10.5 metres (35 feet) above sea l e v e l , contains a number of i r o n - s t a i n e d twigs and wood fragments and a sample of these, a l s o c o l l e c t e d by Dr. F y l e s , provided a f u r t h e r r a d i o carbon date of 9730 "r 160 years (G.S.C. - 575).  The  interstratification  of the gravels and organic m a t e r i a l i s the only evidence found which suggests that the changing pattern of land-sea r e l a t i o n s h i p s on Garry Island was not a simple, progressive emergence of the land or withdrawal of the sea. The d e t a i l s of t h i s s t r a t i g r a p h i c c r o s s - s e c t i o n provide an i n s i g h t into the mode of formation of the elevated s t r a n d - l i n e features on Garry I s l a n d . The c o n f i g u r a t i o n of the '7.5' metre (25 foot) s t r a n d - l i n e i s h i g h l y suggestive of the submergence of a p r e - e x i s t i n g topography, and the submergence of the depressions i n the topography created a s e r i e s of embayments i n the c o a s t l i n e .  Residual deposits of sand and g r a v e l ,  derived from the erosion of the adjacent sections of the coast, accumulated along the shoreline and on the f l o o r s of the depressions.  Locally  t h i s m a t e r i a l was concentrated i n t o sandspits or bars developed across the mouths of the embayments c r e a t i n g a number of lagoons on t h e i r sides.  landward  As the bars extended completely across the mouths of the bays, the  lagoons were transformed into freshwater lakes. which were gradually i n f i l l e d by the deposition of l a c u s t r i n e sediments.  The f i n a l stages of  t h i s i n f i l l i n g were accompanied by the development of tundra polygons. Although s t r a t i g r a p h i c evidence of t h i s sequential development can only be demonstrated c o n c l u s i v e l y at the one l o c a t i o n on the northwest coast of the i s l a n d , i t i s believed that the b a y - l i k e depressions on the north side  50 of the i s l a n d represent a s i m i l a r sequence of events, although the bays may not have been converted into freshwater lakes. The large b a y - l i k e depressions are p a r t i c u l a r l y  well-developed  i n a s s o c i a t i o n with the '7.5' metre (25 foot) s t r a n d - l i n e . I n v e s t i g a t i o n s of the l o n g i t u d i n a l p r o f i l e s of some of the main stream courses i n d i c a t e that s i m i l a r features were formed, a l b e i t u s u a l l y on a much smaller s c a l e , i n a s s o c i a t i o n w i t h the other r a i s e d s h o r e l i n e s . . L o n g i t u d i n a l Stream P r o f i l e s . Under favourable circumstances  the l o n g i t u d i n a l and cross-  v a l l e y p r o f i l e s of major r i v e r v a l l e y s may record the evidence of r e l a t i v e changes i n base l e v e l .  A negative or downward movement of the base l e v e l  causes a rejuvenation of a stream at i t s mouth and a regrading of the stream towards i t s new base l e v e l .  Such rejuvenation may r e s u l t i n the  production of an interrupted or stepped p r o f i l e , w i t h the breaks of slope, or n i c k p o i n t s , representing the headward extent of the regrading  process.  The l o n g i t u d i n a l breaks i n the p r o f i l e can also often be c o r r e l a t e d w i t h 'valley i n v a l l e y  1  forms i n which r i v e r t e r r a c e s , or simpler v a l l e y - s i d e  f a c e t s , mark the former l e v e l s of the v a l l e y f l o o r s .  The existence of  s i m i l a r terraces i n the estuarine sections of some of the main r i v e r s on 15 the adjacent mainland has already  been.discussed.,  There are no large perennial streams on Garry I s l a n d .  Indeed,  the present watercourses carry only a very i n t e r m i t t e n t surface runoff during the spring and e a r l y summer when they receive water from the melting of the snow cover.  Throughout the r e s t of the summer months,  Mackay, J . Ross (1958) op_. c i t . , p. 38.  51 these channels r e c e i v e m o i s t u r e seepage,  produced  l a y e r on the a d j o i n i n g v a l l e y s i d e s , and t h i s  by thawing  i s seldom  of t h e a c t i v e  s u f f i c i e n t to  m a i n t a i n s u r f a c e r u n o f f except when combined w i t h the e f f e c t s of a prolonged p e r i o d of heavy r a i n f a l l . demonstrated  The i n e f f i c i e n c y of stream e r o s i o n i s  by s t u d i e s o f the stream c h a n n e l s .  Over most o f t h e i r l e n g t h  the s u r f a c e s o f these channels are aggrading by the growth and a c c u m u l a t i o n of  organic material.  i l l - d e f i n e d and t h e i r tion pattern.  As a r e s u l t o f t h i s p r o c e s s most o f the channels are l i n e s can b e s t be t r a c e d by c o n t r a s t s i n the v e g e t a -  I n the absence  of a w e l l - d e f i n e d c h a n n e l , s u r f a c e r u n o f f ,  when i t o c c u r s , i s e a s i l y d i v e r t e d strated 1965  i n the case o f Stream  field  t o other r o u t e s .  T h i s was amply demon-  'D' ( s e e F i g u r e 5) a t the b e g i n n i n g o f the  season, where snow meltwater  no l o n g e r f o l l o w e d the stream  c o u r s e , but had been d i v e r t e d a l o n g the l i n e o f a w e l l - t r o d d e n path between the base camp and the beach.  Attempts  t o lower a r t i f i c i a l l y the  l e v e l s o f two l a k e s on the i s l a n d , by means o f d i t c h e s , p r o v i d e d y e t another example o f the weak e r o s i v e power of r u n n i n g water.  The d i t c h e s  were c u t through peat and g r a v e l b a r r i e r s a t the o u t l e t s o f the l a k e s ( P l a t e II-C).  I t was hoped t h a t , once e s t a b l i s h e d , these channels would be  excavated f u r t h e r by the f l o w of water d r a i n i n g from the l a k e s . the l a k e s , however, i t was soon demonstrated to  excavate  t h a t the f l o w was  A t one of insufficient  the u n d e r l y i n g p e a t , g r a v e l and c l a y , and the channel c o u l d  o n l y be m a i n t a i n e d by c o n s t a n t d i g g i n g . The  l o n g i t u d i n a l p r o f i l e s o f f o u r t e e n Garry I s l a n d  stream  courses were surveyed and the r e s u l t s are shown i n F i g u r e s 7 and 8. at  Only  t h e i r mouths, where they c u t through the c o a s t a l b l u f f s , do these  streams  possess a w e l l - d e f i n e d channel bordered by steep banks a p p r o x i -  mately one metre (3-4 f e e t ) h i g h .  Over most of t h e i r  l e n g t h s , as  Figure 7 LONGITUDINAL  STREAM  Profile  Horizontal  Scale  1 0 0 0 feet  1 inch  2 0 0 feet  Scale  Vertical  Exaggeration  Cross-Valley  D  1 inch  Vertical  I-VI  PROFILES  x5  Profile  Locations  (I)  Figure 8 LONGITUDINAL  Horizontal  Scale  STREAM  1 inch = 1 0 0 0 feet  Vertical  Scale  1 inch = 2 0 0 feet  Vertical  Exaggeration  x5  PROFILES  (2)  54 mentioned  i n the previous paragraph, the channels have been f i l l e d by the  accumulation of organic m a t e r i a l , and t h e i r p o s i t i o n s are marked by contrasts i n the vegetation pattern where the higher moisture content of 16  the substrate favours the growth of w i l l o w s , sedges and moss. The lack of d e f i n i t i o n of the stream courses becomes i n c r e a s i n g l y apparent towards the higher e l e v a t i o n s .  Each of the streams  has an i l l - d e f i n e d source area i n e'ither one of the steep-sided depressions or f l a t - f l o o r e d cols i n the summit areas.  From these  i n d e f i n i t e beginnings, as Figures 7 and 8 i n d i c a t e , the descent to the c o a s t l i n e i s not a smooth curve but e x h i b i t s a c h a r a c t e r i s t i c s t e p - l i k e form ( P l a t e II-p_).  Where best developed, the. i n t e r r u p t i o n s on the l o n g i -  t u d i n a l p r o f i l e are marked by the occurrence of small lakes o r , more commonly, areas of tundra polygons on the v a l l e y f l o o r .  Elsewhere, the  breaks i n slope are less prominent but are accompanied by a widening of the v a l l e y f l o o r , as indicated by the vegetation p a t t e r n , to 2-3 times the normal width. The d i s t r i b u t i o n of the elevations of these i n t e r r u p t i o n s i n the l o n g i t u d i n a l p r o f i l e s of the fourteen streams i s shown i n Table IV. The heights have been grouped into selected height-range i n t e r v a l s to see i f there i s any c o r r e l a t i o n between the e l e v a t i o n s of the breaks i n slope and those of the elevated s t r a n d - l i n e s .  The a l t i t u d e s i n parentheses  i n d i c a t e those which f a l l outside the selected height-range i n t e r v a l s . As Table IV shows, eight of the fourteen streams have ani n f l e c t i o n point on t h e i r l o n g i t u d i n a l p r o f i l e s at an e l e v a t i o n of Further d e t a i l s on the vegetation patterns of the stream courses are included i n the f o l l o w i n g chapter.  TABLE ELEVATIONS  OF  THE  BREAKS OF  OF  GARRY  SLOPE  ON  THE  LONGITUDINAL  PROFILES  ISLAND STREAMS  Elevation at Source (Metres)  6-9  A  25.3  7.6  B  49.4  C  33.2  D  22.9  E  29.9  7.9  F  28.3  7.6 (11.6)  21.9  G  39.9  7.6  21.6  H  24.7  I  28.0  7.9 ( 9.8) 15.5  J  48.5  7.9  K  44.8  L  47.9  M N  S tream  IV  Selected Height Ranges (Metres) 14-17  21-24  36-39  44-47  30.2  36.9  45.7  23.5 (11.3)  (1.2)  29-32  7.6  15.5 (12.2)  (11.0)  31.1  16.8  22.6  14.3 (18.6)  22.9  29.6  38.1  15.2 24.1 (26.5)  15.5 14.6  24.1  31.1  16.2  22.9  29.9 (33.8)  41.1  14.3  22.6  25.9  16.5  23.2  7.9  37.2 45.4 38.1  approximately 7.5 metres (25 feet) above sea l e v e l .  Of the s i x streams  which do not, three d r a i n toward the south coast and one to the west coast where, i n each case, they terminate i n high c o a s t a l b l u f f s which have undergone considerable recession.  As a r e s u l t of t h i s r e c e s s i o n , the  lower courses of these streams have become deeply entrenched and they reach the present shoreline through narrow 'V-shaped v a l l e y s . Interruptions i n the l o n g i t u d i n a l p r o f i l e s at a l t i t u d e s of both approximately 15 and 23 metres (50 and 75 f e e t ) , are represented i n ten of the fourteen stream courses, but the evidence of s i m i l a r breaks of slope at a l t i t u d e s exceeding 30.5 metres (100 feet) above sea l e v e l i s more restricted.  Thus the numbers of i n f l e c t i o n points i n the p r o f i l e s  occurring at the 30.5, 38 and 46 metre (100, 125 and 150 foot) l e v e l s are only f i v e , four and two r e s p e c t i v e l y .  The l i m i t e d number of i n t e r r u p t i o n s  i n the p r o f i l e s at these l e v e l s can r e a d i l y be explained by the f a c t that progressively fewer of the streams o r i g i n a t e at these higher elevations (Table I V ) . For example, only eight of the fourteen streams shown i n Figures 7 and 8 o r i g i n a t e at elevations of more than 30.5 metres (100 feet) above sea l e v e l ; s i m i l a r figures f o r a l t i t u d e s of 38 and 46 metres (125 and 150 feet) are s i x and three streams r e s p e c t i v e l y . I n a l l , Table IV l i s t s a t o t a l of 48 e l e v a t i o n s , each of which represents a point of i n f l e c t i o n on a l o n g i t u d i n a l stream p r o f i l e .  Of  t h i s t o t a l , no fewer than 39, or more than eighty per cent, occur w i t h i n the selected height-ranges.  There may be some s i g n i f i c a n c e , however, to  the f a c t that of the breaks i n slope which do not occur w i t h i n these height ranges, more than one-half are developed at an e l e v a t i o n of approximately 10.5 metres (35 feet) above sea l e v e l . The evidence from the surveyed stream courses suggests that  57 there i s a c o r r e l a t i o n between the a l t i t u d e s of the i n f l e c t i o n points on the l o n g i t u d i n a l p r o f i l e s of these streams and the elevations of the r a i s e d shoreline features.  I t i s p o s t u l a t e d that the two sets of features  are c l o s e l y i n t e r r e l a t e d and that both are associated w i t h former p o s i t i o n s of the sea. When the r e l a t i v e l e v e l of the sea stood at each of the positions indicated by the s t r a n d - l i n e s , i t i s postulated that the l i n e s of the v a l l e y s formed small indentations or bays i n the s h o r e l i n e . Residual accumulations of coarse sand and g r a v e l , produced by the erosion of the coastal b l u f f s , were deposited at the s h o r e l i n e , and l o c a l l y these were concentrated into small s p i t s or bars, extending across the mouths of the bays.  The lagoons, created by the formation of these bars, may  eventually have been sealed o f f from the open sea and transformed into shallow, freshwater lakes.  Some of these lakes may have been drained  immediately when the r e l a t i v e l e v e l of the sea was lowered but many were l e f t occupying p o s i t i o n s i n the newly-exposed  valley floors.  The larger  and deeper lakes have p e r s i s t e d through to the present time, but many of the s m a l l e r , shallower ones have subsequently been f i l l e d by the accumul a t i o n of organic m a t e r i a l and become the l o c i f o r tundra polygon development.  The r e p e t i t i o n of t h i s sequence of events i s offered as an  explanation of the stepped p r o f i l e so c h a r a c t e r i s t i c of the stream courses on Garry I s l a n d . The s e q u e n t i a l stages of development, offered to account f o r the d i s t r i b u t i o n and formation of the areas of polygonal ground, i s s i m i l a r , a l b e i t on a much smaller s c a l e , to that proposed f o r the o r i g i n of the exposures of l a c u s t r i n e sediments found along the northwest coast of the i s l a n d .  The hypothesis gains a c e r t a i n c r e d i b i l i t y from two  58 aspects of studies of the contemporary s h o r e l i n e .  Firstly,  practically  a l l of the present streams have t h e i r o u t l e t s blocked by accumulations of g r a v e l , driftwood and peat.  Even during periods of r e l a t i v e l y strong  r u n o f f , the streams are only temporarily able to e s t a b l i s h a channel through these materials to the sea.  Such channels are very ephemeral  f e a t u r e s , however, and are soon choked by wave a c t i o n .  The second l i n e of  support comes from the f a c t that polygonal ground i s c u r r e n t l y developing around the margins of lagoons enclosed by the construction of the modern sandspits. In an attempt to e s t a b l i s h further the v a l i d i t y of t h i s hypothesis a number of c r o s s - v a l l e y p r o f i l e s was along Stream 'G'.  surveyed at s t r a t e g i c points  These p r o f i l e s are shown i n Figure 9.  At each of these  points a s e r i e s of d r i l l holes was made across the stream course to determine the nature of the substrate and, i f p o s s i b l e , locate the presence of the buried gravel ridges required to support the hypothesis.  The depths  at which gravels were encountered i n these d r i l l holes are also recorded i n Figure 9.  C r o s s - p r o f i l e I was  located at an e l e v a t i o n of  approximately  4.5 metres (15 feet) above sea l e v e l where the stream course traverses the large b a y - l i k e reentrant i n the '7.5' metre (25 foot) s t r a n d - l i n e .  The  i l l - d e f i n e d nature of the channel i s immediately apparent and the d r i l l i n g operations revealed no s i g n of gravels^ at l e a s t to depths of 2 metres (6 f e e t ) .  C r o s s - p r o f i l e s I I , I I I and IV were located at elevations of  approximately  7.5, 15 and 23 metres (25, 50 and 75 feet) above sea l e v e l .  As Figure 9 shows each of these l o c a t i o n s was  characterized by the  presence of a f a i r l y prominent gravel ridge at depths of up to 1.5 metres (5 feet) below the surface.  The d e t a i l s of one of these ridges were  p a r t i c u l a r l y we11-developed at an a l t i t u d e of 23 metres (75 feet) above  Figure 9 C R O S S - V A L L E Y  PROFILES  -  STREAM  'G  Profile I  Horizontal  Scale  1 inch = 100 feet  Vertical  Scale  Vertical  Exaggeration  1 inch = 2 0 f e e t x5  Buried  gravel  w  Willows  s  Sedge/Moss  1  60 sea l e v e l where they could be traced l a t e r a l l y to prominent ridges on the side of the v a l l e y .  C r o s s - p r o f i l e V was  metres (90 feet) above sea l e v e l .  located at an e l e v a t i o n of  27.5  Although gravels were encountered  beneath the stream course i t s e l f , they could not be detected at a l l on the sides of the v a l l e y .  The f i n a l c r o s s - p r o f i l e was  located j u s t below  an area of weakly-developed tundra polygons at an a l t i t u d e of 38 metres (125 feet) above sea l e v e l .  As the p r o f i l e shows, gravels were encounter-  ed at shallow depths beneath the channel and for considerable distances either side.  on  Thus, although the subsurface p r o f i l e s were only determined  at s t r a t e g i c points along one of the streams, the l i m i t e d evidence provided by these p r o f i l e s i s i n accordance w i t h the hypothetical sequence o u t l i n e d above. The studies of the l o n g i t u d i n a l and c r o s s - v a l l e y p r o f i l e s of the stream courses corroborate  the opinion that a s e r i e s of elevated  s t r a n d - l i n e s , spaced at i n t e r v a l s of approximately 7.5 metres (25 feet) and reaching elevations of 46 metres (150 feet) above sea l e v e l , can be i d e n t i f i e d on Garry I s l a n d .  In the absence of d e f i n i t i v e f o s s i l evidence,  however, i t i s reasonable to question the v a l i d i t y of a further conclusion that these s t r a n d - l i n e s mark the p o s i t i o n s of former l e v e l s of the sea. The prime reason for s t a t i n g that these shorelines are marine features i s based e n t i r e l y on the apparent uniformity of t h e i r elevations on a l l sides of the i s l a n d . I r r e s p e c t i v e of the aspect of the slope on which they are developed, the shorelines seem to e x h i b i t a strong degree of w i t h respect to t h e i r e l e v a t i o n above sea l e v e l . i n keeping w i t h a hypothesis of p r o g l a c i a l lakes.  consistency  Such consistency i s not  that they were developed around the margins  Moreover, the conditions on Garry I s l a n d were r a r e l y  s u i t a b l e for the development of these lakes.  They could have only  61 developed, to any r e a l extent, along the south side of the i s l a n d where meltwater may temporarily have been ponded between the c o a s t l i n e and the ice front as i t retreated to the south. also considered,  A further hypothesis, which was  i s that some of the shorelines were developed around  lakes which were ponded by s t r u c t u r a l deformation features. existence of one such lake was r e f e r r e d to previously.  The possible  The absence of  any marked anomalies i n the heights of the shoreline features would appear to i n d i c a t e that neither of these possible modes of o r i g i n was more than of l o c a l s i g n i f i c a n c e , i f any at a l l .  SUMMARY The s t r a t i g r a p h y of Garry Island consists of a sequence of sands, s i l t s , c l a y s , and stony-clays, cemented by i c e , which have been i n t e n s i v e l y deformed by the t h r u s t i n g action of g l a c i e r - i c e moving from the south.  The deformed sediments are l o c a l l y o v e r l a i n by sands and  g r a v e l s , probably brought down by streams f o l l o w i n g the r e t r e a t of the ice.  These materials are undisturbed  > 42,000 years.  and contain marine f o s s i l s dated at  The absence of any signs of g l a c i a l t i l l on top of the  sands suggests that Garry Island lay beyond the northwest l i m i t s of the Laurentide  ice sheet during the late-Wisconsin  glaciation.  Attempts to determine the extent of changes i n the former r e l a t i v e p o s i t i o n s of land and sea are complicated by the weak topographic expression of r a i s e d shoreline f e a t u r e s , and the degree to which they have been obscured, or even t o t a l l y o b l i t e r a t e d , by subsequent geomorphic a c t i v i t y .  I n addition to these d i f f i c u l t i e s , the absence of a  f i x e d datum for mean sea l e v e l prevents a completely r e l i a b l e determina-  62 t i o n of the precise a l t i t u d e s of the shorelines.  Despite these l i m i t a -  t i o n s , the evidence suggests the existence of a series of elevated strand-lines which occur at approximately 7.5 metre (25 feet) i n t e r v a l s to an a l t i t u d e of 46 metres (150 f e e t ) .  Some a d d i t i o n a l support for t h i s  view comes from surveys of the l o n g i t u d i n a l p r o f i l e s of 14 stream courses on the i s l a n d .  These p r o f i l e s are c h a r a c t e r i s t i c a l l y s t e p - l i k e , and the  a l t i t u d e s of the i n f l e c t i o n points on the thalwegs e x h i b i t a strong degree of s i m i l a r i t y to the elevations of the r a i s e d shoreline  features.  Further comments on the o v e r a l l s i g n i f i c a n c e of these s t r a t i graphic observations and t h e i r incorporation  into a possible  sequence w i l l be discussed i n the f i n a l chapter of the t h e s i s .  chronological  CHAPTER I I I VEGETATION  Garry Island i s located wholly beyond the northern l i m i t of trees which presently l i e s approximately 65-80 kilometres (40-50 miles), to the. south i n the modern d e l t a of the Mackenzie R i v e r .  The t r e e l e s s  character of the i s l a n d places i t i n the a r c t i c tundra region and  the  vegetation i s composed p r i m a r i l y of dwarf shrubs, herbs, mosses and lichens.  The objective of t h i s chapter i s to describe the major vegeta-  t i o n types which occur on Garry Island and to examine the i n t e r r e l a t i o n ships between the vegetation patterns and types of geomorphic a c t i v i t y . Attempts to define tundra vegetation communities on the basis of t h e i r plant composition are complicated  by the f a c t that there are not  always d i s t i n c t i v e , or diagnostic species i n each of the plant a s s o c i a t i o n s . Many species have a broad tolerance of environmental c o n d i t i o n s , and therefore occur i n a wide v a r i e t y of h a b i t a t s .  This fundamental inadequacy  of a c l a s s i f i c a t i o n of a r c t i c vegetation on the basis of physiognomy or f l o r a l composition has been recognized by numerous b o t a n i s t s , as i s exemplified by the f o l l o w i n g quotations: "In the a r c t i c , differences are merely q u a n t i t a t i v e . The habitat preferences of the i n d i v i d u a l species f i n d expression merely i n increased or decreased abundance i n more or less favourable h a b i t a t s rather than by presence here or absence there.... A r c t i c vegetation must be described by reference to the p h y s i c a l conditions of the habitat rather than by an attempt to discover and deal w i t h  habitat preferences of the species present." Accordingly, the major purpose of the vegetation study was  to  examine the various f a c t o r s c o n t r i b u t i n g to the p h y s i c a l character of the plant habitats and, i n p a r t i c u l a r , the r e l a t i o n s h i p s of the vegetation pattern to geomorphic a c t i v i t y .  Subsurface conditions were also checked,  w i t h s p e c i f i c reference to the r e l a t i v e amounts of the organic m a t e r i a l and mineral s o i l f r a c t i o n s , and the depth of the active layer was  recorded  at various times throughout the summer for each of the h a b i t a t s . A d i s cussion of t h i s data i s contained i n the f o l l o w i n g chapter. The vegetation was mapped i n the f i e l d on a scale of approximately 1:25,000 and the d e l i n e a t i o n of the types was checked through subsequent studies of a e r i a l photographs and coloured transparencies.  For  each of the major h a b i t a t s i d e n t i f i e d , an attempt was made to estimate the r e l a t i v e percentages  of the area occupied by the dominant species.  Since  the emphasis was on the p h y s i c a l character of the h a b i t a t , however, t h i s was done by v i s u a l estimation rather than by the employment of the more rigorous quadrat sampling technique.  For completeness, and for readers  having i n t e r e s t s i n botany, the various species i d e n t i f i e d have been l i s t e d under each of the vegetation types, i n which they occur.  Although  i t i s not claimed to be exhaustive, Appendix I contains a summary of t h i s information and l i s t s a t o t a l of 106 vascular species and 17  bryophytes  Griggs, R. F. (1936) "The Vegetation of the Katmai D i s t r i c t " , Ecology, V o l . 17, pp. 381-382.  65 c o l l e c t e d and i d e n t i f i e d on Garry I s l a n d .  VEGETATION TYPES Figure 10 shows the a r e a l extent and d i s t r i b u t i o n of the p r i n c i p a l vegetation types found on Garry I s l a n d . The c l a s s i f i c a t i o n i s based p r i m a r i l y on the p h y s i c a l character of the h a b i t a t , but i t also includes the names of the s p e c i f i c plant species wherever they tend to dominate the p a r t i c u l a r vegetation type. I.  Dryas-Hummock Type. Most of the d r i e r tundra s i t e s are characterized by an  i r r e g u l a r surface where the ground i s covered by numerous, rounded earth hummocks, the s i z e and spacing of which vary according to t h e i r p o s i t i o n on the topographic p r o f i l e .  These m i c r o r e l i e f forms are found on a l l  summit areas and v a l l e y - s i d e slopes with moderate to good drainage cond i t i o n s . ( P l a t e III-A).  Hummock p r o f i l e s c o n s i s t of a surface layer of t u r f  and organic m a t e r i a l , beneath which there i s a domed core of mineral s o i l , but there i s l i t t l e or no s o i l beneath the intervening depressions which are the s i t e s of organic  accumulation.  The vegetation i s composed p r i m a r i l y of low matted, woody shrubs together w i t h lichens and mosses.  This vegetation type i s the most  An attempt was made i n the f i e l d " to i d e n t i f y the vascular plants using N. V. Polunin's book,, Circumpolar A r c t i c F l o r a , Clarendon P r e s s , Oxford, 1959, and the format of Appendix I i s based on t h i s t e x t . I am indebted however, to Dr. E r i c Hulten of the N a t u r h i s t o r i s k a Riksmusset, Stockholm, for h i s precise i d e n t i f i c a t i o n of the species l i s t e d . I am s i m i l a r l y indebted to Dr. Herman Personn, of the same i n s t i t u t e , for the i d e n t i f i c a t i o n s of the bryophytes. Unfortunately i t was not possible to i d e n t i f y the l i c h e n s .  Figure  G A R R Y VEGETATION  Dryas  Hummocks  Cassiope Alnus  Snowpatches  crispa  Eriophorum  Tussocks  Hummock - T u s s o c k Stream Sedge  Course - Moss  Mudslump Strand  Transition  Willow  Thickets  Flats  Communities  Communities  - Gravel  Bars  - Marsh - Lagoon Polygons  -  Low  Centred  -  High  Centred  [  Scale  I A p p r o x t m ate) 1  10  I S L A N D TYPES  Plate I I I  VEGETATION  A.  DRYAS  HUMMOCK.  Hummock i n c e n t r e dominated by l i c h e n s , A r c t i c Avens, and B i g e l o w ' s Sedge. Darker c o l o u r of t h e inter-hummock d e p r e s s i o n s i s due t o t h e dominance o f t h e A r c t i c White B e l l - h e a t h e r and mosses.  C.  CASSIOPE  SNOWPATCH.  Typical vegetation association found i n areas o f l a t e - l y i n g snowpatches. The dominant s p e c i e s a r e t h e A r c t i c White B e l l - h e a t h e r and w i l l o w s .  TYPES  B.  ALNUS  CRISPA.  A l m o s t pure stands o f t h e M o u n t a i n A l d e r growing i n a shallow, sheltered depression on t h e n o r t h s i d e o f G a r r y Island.  D.  ERIOPHORUM  TUSSOCKS.  C h a r a c t e r i s t i c t u s s o c k forms o f the Sheathed C o t t o n - g r a s s . The i n t e r - t u s s o c k a r e a s a r e dominated by mosses and t h e A r c t i c White Be11-heather.  68  extensive found on the i s l a n d and i t i s also the most d i v e r s i f i e d i n terms of i t s f l o r i s t i c composition.  On the f l a t summit areas, the hummocks are  quite subdued i n form, but the m i c r o r e l i e f factor i s s t i l l s u f f i c i e n t to produce two d i s t i n c t plant h a b i t a t s .  The d r i e r , elevated hummock centres  are dominated by the A r c t i c Avens (Dryas i n t e g r i f o l i a ) , after which the vegetation type i s named, together w i t h mosses ( c h i e f l y  Pieranum,  C i n c l i d i u m and Bryum species) and lichens (the so-called 'reindeer moss'). C o l l e c t i v e l y these plants may account f o r 50-60 per cent of the vegetation cover on the hummock surface. Other major species found on the hummocks include Bigelow's Sedge (Carex b i g e l o w i i ) , A r c t i c Blueberry (Vaccinium uliginosum var. alpinum), Mountain Cranberry (Vaccinium v i t i s - i d a e a ) , Common Crowberry (Empetrum nigrum), and the Glandular B i r c h (Betula glandulosa).  On the more sheltered flanks of the hummocks there i s an  increase i n the percentage cover of these s p e c i e s , and a corresponding decrease i n the cover of avens and l i c h e n s .  Small willows ( S a l i x  r e t i c u l a t a , S_. glauca var. niphoclada) , rooted i n the hummocks, and the Narrow-leafed Labrador-tea (Ledum palustre ssp. decumbens) are also found on the sides of the hummocks. Less common species encountered growing on the hummock centres include the A r c t i c Wintergreen (P y r o l a g r a n d i f l o r a ) , A r c t i c Meadow Grass (Poa a r c t i c a ) , Capitate Lousewort  (Pedicularis  c a p i t a t a ) , A l p i n e Bearberry (Arctostaphylos r u b r a ) , Veiny-leafed Willow (Salex phlebophylla) , Northern Wood-rush (Luzula confusa), Woolly Lousewort ( P e d i c u l a r i s 1anata), Long-stalked S t i t c h w o r t ( S t e l l a r i a l o n g i p e s ) , Mountain Meadow B i s t o r t (Polygonum b i s t o r t a ) , Narrow-leafed Saussurea (S aussurea a n g u s t i f o l i a ) , A l p i n e B i s t o r t (Polygonum viviparum) , Lapland Rose-bay (Rhododendron lapponicum) and the Lake Louise A r n i c a (Arnica louiseana f r i g i d a ) .  69 The inter-hummock depressions are s i t e s of snow accumulation during the winter months and the organic substrate remains much moister than the more exposed hummock centres. These depressions support an e n t i r e l y d i f f e r e n t and less d i v e r s i f i e d plant assemblage.  Mosses  ( c h i e f l y Aulacomnium, Hylocomnium and Sphagnum species) and the A r c t i c White Bell-heather (Cassiope tetragona) are the dominant constituents of the f l o r a , and c o l l e c t i v e l y account for 60-70 per cent of the vegetation cover.  Other u b i q u i t o u s , though minor, species found i n the depressions  include the Lapland Butterbur ( P e t a s i t e s f r i g i d u s ) , Sudetan Lousewort ( P e d i c u l a r i s s u d e t i c a ) , F r a g i l e Sedge (Carex membranacea), Sheathed Sedge (£. vaginata) , Radiate Saxifrage (Saxifraga r a d i a t a ) , Lapland Reedgrass (Calamagrostis. lapponica), A l p i n e Hedysarum (Hedysarum alpinum americanum) , Alpine F o x t a i l (Alopecurus alpinus) and the Naked-stemmed Parrya (Parrya nudicaulis). The above d e s c r i p t i o n s pertain to c h a r a c t e r i s t i c plant assemblages of hummocks and depressions on the upland surfaces. Changes i n these plant compositions appear to be most markedly affected by the degree of exposure and the moisture supply.  On exposed, windswept slopes the  hummocks are even more subdued than on the f l a t summit areas, the vegetat i o n cover i s t h i n n e r , and there i s patchy development of bare ground. The most noticeable e f f e c t of these conditions i s an increase i n the cover of the A r c t i c Avens, to a point where they are almost the only species found on the hummock surface.  Contrasts i n the moisture conditions of the  hummock centres and the depressions are less pronounced and the avens are frequently found growing on dry moss pads i n the l a t t e r areas. plants which appear to t h r i v e i n t h i s exposed environment  Other  include the  Veiny-leafed Willow, Woolly Lousewort, Northern Wood-rush and the A r c t i c  70 Lupin (Lupinus arcticus) . Between the upland summit areas and the lower e l e v a t i o n s there i s a gradual, but progressive, increase i n the s i z e of the hummocks. Coincident w i t h t h i s increase i n the m i c r o r e l i e f , the vegetation contrasts between the hummocks and depressions become more pronounced.  This i s  p a r t i c u l a r l y noticeable on the upper slopes, but towards the foot of the slope there are d i s t i n c t changes i n the vegetation cover on the hummocks. The l i c h e n s disappear almost completely and the A r c t i c Avens become only a minor constituent of the f l o r a .  Mosses, Sedges, the Common Crowberry,  A r c t i c Blueberry and Labrador-tea achieve much greater prominence and the A r c t i c White Bell-heather i s also found on the hummocks.  The most notable  change i n the depressions i s an increase i n the amount of the moss cover. I t i s not s u r p r i s i n g that the vegetation type which has the greatest areal extent, and the most d i v e r s i f i e d f l o r i s t i c  composition,  lends i t s e l f to the p o s s i b l e r e c o g n i t i o n of abundant sub-types.  Some of  these have already been alluded to w i t h reference to the e f f e c t s of exposure, moisture c o n d i t i o n s , e t c .  The problem of d i f f e r e n t i a t i n g  between a sub-type and a separate type i s not an easy one, but i n two cases the vegetation a s s o c i a t i o n that was produced was so d i s t i n c t i v e the Alnus c r i s p a and the Cassiope Snowpatch types - that separate  vegeta-  t i o n types were recognized. II.  Alnus c r i s p a Type. In a very few sheltered l o c a t i o n s , w i t h a moderate to good  moisture supply, the vegetation i s l o c a l l y dominated by pure stands of the Mountain Alder (Alnus c r i s p a ) .  The l a r g e s t stand of Alder was found  on a north-facing slope and was composed of low bushes approximately one  71 metre (3 feet) high ( P l a t e III-B).  Each bush has a l a t e r a l spread of  almost 2 metres (6.5 f e e t ) , and t h i s e f f e c t i v e l y shades out the underl y i n g ground surface which i s consequently devoid of any further plant cover and mantled by a l i t t e r of dead leaves.  The stand of Mountain Alder  shown i n P l a t e 3JXL-B i s the only s u b s t a n t i a l one on the i s l a n d , although i n a number of i s o l a t e d , favourable spots i n d i v i d u a l bushes were noted. III.  Cassiope Snowpatch Type. In the s e c t i o n on the Dryas-Hummock vegetation type, downslope  changes i n the f l o r a l composition were t e n t a t i v e l y r e l a t e d to changes i n the moisture conditions of the s o i l .  L o c a l l y , i n a d d i t i o n to the increase  i n moss cover, the hummocks and depressions a l i k e are blanketed by a dense, almost pure cover of the A r c t i c White Bell-heather (Cassiope tetragona)  and  willows ( P l a t e III-C). This vegetation pattern gives a d i s t i n c t i v e dark c o l o u r a t i o n to the ground surface which i s r e a d i l y detectable on a e r i a l photographs.  The lower slopes receive water seepage, derived from the  thawing of the a c t i v e l a y e r , from the upper parts of the slopes, and are also the s i t e s of l a t e - l y i n g snow patches.  These e f f e c t s are most pro-  nounced i n the larger sheltered depressions and on northeast-facing slopes where the snow may remain on the ground w e l l i n t o the summer before i t disappears. IV.  Eriophorum Tussock Type. Wet  tundra h a b i t a t s occur i n areas where the slopes are only  of the order of 1-2 degrees and the r e s u l t i n g poorly developed  drainage  conditions are r e f l e c t e d i n a water table which i s close to the ground surface.  This vegetation type i s found p r i m a r i l y on the f l o o r s of the  major depressions and on the surfaces of the sand headlands, but i t also  72 occurs l o c a l l y along f l a t s associated w i t h the r a i s e d beach l i n e s and around the margins of some areas of polygonal ground.  I n these s i t e s the  underlying s o i l s are t y p i c a l l y c o l d , grey s i l t s or c l a y s , and the surface, i s mantled w i t h a l i t t e r of raw humus. The vegetation of these areas i s dominated by plants of the sedge (Cyperaceae)  family and the Sheathed Cotton-grass or 'Niggerhead'  (Eriophorum vaginatum) i n p a r t i c u l a r .  This plant e x h i b i t s a c h a r a c t e r i s -  t i c tussock form ( P l a t e III-D), up to 35-40 centimetres (14.0-15.5 ins.) high and as much as 30-35 centimetres (12-14 ins.) across at the crown. Each tussock i s a s i n g l e plant and consists of a mass of dead and l i v i n g organic m a t e r i a l overlying a small plug of mineral s o i l .  The roots form a  t i g h t l y woven mat penetrating down i n t o t h i s mineral s o i l .  The spacing of  the tussocks i s v a r i a b l e and they are separated by shallow troughs ranging in width from 10-75 centimetres (4.0-29.5 i n s . ) .  Where best developed, on  slopes of 1-2 degrees, the tussocks occur i n close j u x t a p o s i t i o n and account f o r as much as 90 per cent of the vegetation cover.  The f l o o r s of  the intervening troughs may be occupied by small pools of standing water, raw organic debris or saturated pads of moss ( c h i e f l y Sphagnum and Hypnum species).  Other plants of minor importance found w i t h i n t h i s same h a b i t a t ,  and p a r t i c u l a r l y i n the s l i g h t l y d r i e r s i t e s such as elevated moss polders or the sides of the i n d i v i d u a l tussocks, include the A r c t i c White B e l l heather (Cassiope tetragona) , Narrow-leafed Labrador-tea (Ledum palustre ssp. decumbens), Glandular B i r c h ( B e t u l a glandulosa), Common Crowberry (Empetrum nigrum), A r c t i c Wintergreen ( P y r o l a g r a n d i f l o r a ) , and the willows ( S a l i x pulchra, S_. r e t i c u l a t a ) .  73 V.  Hummock-Tussock T r a n s i t i o n Type. Whereas the major extent of both the Dryas-Hummock and  Eriophorum-Tussock vegetation types i s e a s i l y i d e n t i f i a b l e , the margins are frequently b l u r r e d by extensive t r a n s i t i o n zones i n v o l v i n g considerable i n t e r d i g i t a t i o n w i t h each other.  On slopes of 2-4 degrees the  tussocks become smaller and f u r t h e r apart, accounting f o r only 20-40 per cent of the plant cover.  The i n t e r - t u s s o c k areas become less moist, and  there i s an increase i n the number and v a r i e t y of other species and Cassiope tetragona i n p a r t i c u l a r .  Large earth hummocks, w i t h f l o r i s t i c  associations s i m i l a r to those described i n the Dryas-Hummock type, and bare mud b o i l s are intermingled w i t h the tussock forms.  F i n a l l y , on  slopes above 4 degrees the tussocks are gradually eliminated and the vegetation becomes of the Dryas-Hummock type. VI.  Stream Course Willow Thickets. The majority of the stream courses are occupied by narrow  s t r i p s of w i l l o w growing i n a substratum of moist organic m a t e r i a l and o c c a s i o n a l l y sandy-gravel ( P l a t e IV-A).  Such s i t e s are nearly always  amply supplied w i t h water, r e c e i v i n g runoff from the melting snow i n the spring and e a r l y summer, and are kept moist throughout the r e s t of the summer by seepage from the thawing ground.  The t y p i c a l vegetation  a s s o c i a t i o n c o n s i s t s of a f a i r l y dense t h i c k e t of w i l l o w s , c h i e f l y the Diamond-Leaf Willow ( S a l i x pulchra) and the Northern Willow (S. glauca var. niphoclada), ranging from 0.5 to 1 metre (1.5 to 3.0 feet) high. The s t r i p i s commonly l e s s than 5 metres (16 feet) wide, although i t frequently expands to many times t h i s f i g u r e at stream junctions and at the intakes and o u t l e t s of some of the lakes.  I n these l o c a t i o n s , the  P l a t e IV  VEGETATION  A.  STREAM COURSE WILLOW THICKETS.  Stream c o u r s e marked by a narrow ribbon of w i l l o w s p e c i e s . Darker p a t c h e s on the s l o p e s i n the c e n t r e of the photograph a l s o show the C a s s i o p e Snowpatch v e g e t a t i o n t y p e .  C.  MUDSLUMP  COMMUNITIES .  Dark a r e a on the upper r i g h t s i d e o f the p h o t o g r a p h r e p r e s e n t s an a c t i v e mudslump. The f o r e g r o u n d i s dominated by almost pure s t a n d s o f the Marsh F l e a w o r t . The s c a r of a former mudslump, dominated by g r a s s e s , can be seen i n the c e n t r e background.  TYPES  B.  SEDGE - MOSS  FLATS.  Typical vegetation association found on the f l o o r s o f the l a r g e r d e p r e s s i o n s , c o n s i s t i n g o f an almost f e a t u r e l e s s mat o f mosses t o g e t h e r w i t h the C r e e p i n g Sedge, A r c t i c Marsh W i l l o w and A l p i n e Bearberry.  D.  MUDSLUMP  COMMUNITIES .  The v e g e t a t e d f l o o r o f a former mudslump dominated by g r a s s e s . The o l d h e a d w a l l i n the background has been c o l o n i z e d by the Dryas Hummock v e g e t a t i o n .  75 willows may reach heights of as much as 2 metres (6.5 f e e t ) .  Beneath the  w i l l o w s , the ground cover consists p r i m a r i l y of mosses ( c h i e f l y Sphagnum sp.) together w i t h the Common H o r s e t a i l (Equisetum arvense) and the occasional 'niggerhead' tussock (Eriophorum vaginatum).  Other species  found i n t h i s same h a b i t a t , but of minor importance, include the Lapland Reedgrass (Calamagrostis lapponica) , Lowly Fleabane (Erigeron h u m i l i s ) , Alpine F o x t a i l (Alopecurus alpinus) and the Northern Anemone (Anemone p a r v i f l o r a ) and Richardson's Anemone (A. r i c h a r d s o n i i ) . VII.  Sedge-Moss F l a t s . Sedge-moss f l a t s are developed i n areas of impeded drainage  as found on the f l o o r s of the larger depressions, around the margins of areas of polygonal ground, and bordering the w i l l o w t h i c k e t s of the stream courses.  In the upper portions of the stream p r o f i l e s , t h i s vegetation  a s s o c i a t i o n frequently replaces the w i l l o w t h i c k e t type.  The  substratum  i s composed e n t i r e l y of organic m a t e r i a l which i s u s u a l l y saturated. Spongy mosses (Sphagnum squarosum, S_. warnstorfianum, Tomenthypnum nitens and Hypnum callichroum) are the dominant c o n s t i t u e n t s of the f l o r a and l o c a l l y they may be the only plants present.  U s u a l l y , however, they are  found i n a s s o c i a t i o n w i t h the Creeping Sedge (Carex chordorrhiza) and the A r c t i c Marsh Willow ( S a l i x arctophila) ( P l a t e IV»B). Minor l o c a l r e l i e f i n t h i s habitat i s provided by the growth of elevated moss polders, and these s l i g h t l y d r i e r s i t e s support more extensive covers of the Alpine Bearberry (Arctostaphylos r u b r a ) , together w i t h the A r c t i c Wintergreen ( P y r o l a g r a n d i f l o r a) and the A r c t i c Blueberry (Vaccinium uliginosum). VIII.  Mudslump Communities. Mudslumps are large amphitheatre-like depressions formed by  76 the melting out of tabular bodies of segregated ground i c e . Since c o a s t a l recession i s the major agency responsible f o r the exposure of these i c e bodies, the vegetation type associated w i t h these features i s l a r g e l y conf i n e d to c o a s t a l l o c a t i o n s . Because of the high i c e to mineral s o i l r a t i o i n these exposures, melting produces large q u a n t i t i e s of excess water and very l i t t l e debris to accumulate on the f l o o r of the slump.  Prominent  headwalls formed i n the slump p e r s i s t f o r long periods a f t e r i t becomes i n a c t i v e , so that a precise d e l i n e a t i o n of the h a b i t a t i s often a simple procedure.  Vegetation a s s o c i a t i o n s i n these mudslumps appear to be  r e l a t e d to c o l o n i z a t i o n stages once the slump has become i n a c t i v e , and they can be subdivided i n t o a number of sequential types. A c t i v e mudslumps.are characterized by large q u a n t i t i e s of i c e exposed i n the headwall, and the f l o o r of the slump i s covered to varying degrees, w i t h a mobile layer of f l u i d mud.  Most of the-surface i s bare  except f o r the presence of clumps of vegetation, hummocks and w i l l o w s , which have been detached i n t a c t from the r i m of the slump. ice  face, the l i q u i d mud  and the. l e s s active, mud  Away from the  i s generally r e s t r i c t e d , to w e l l - d e f i n e d mudflows, surfaces are r a p i d l y colonized by almost pure  stands of yellow Marsh Fleawort  (Senecio congestus) ( P l a t e IV-C).  species grows gregariously even i n places where f r e s h mud  and s i l t  This are  c o n t i n u a l l y being deposited by streams of water coming from the a c t i v e slump face.  Other plants found i n t h i s moist environment include the  A r c t i c Butterbur ( P e t a s i t e s a r c t i c u s ) , Langsdorf's Lousewort ( P e d i c u l a r i s l a n g s d o r f i i ) , Marsh Felwort (Lomatogonicum rotatum), A r c t i c  Cotton-grass  (Eriophorum scheuchzeri), Scentless Mayweed ( M a t r i c a r i a ambigua) and Black-tipped Groundsel (Senecio lugens).  the  In s l i g h t l y d r i e r areas, though  s t i l l moist, the above species are gradually replaced by the A l p i n e  77 Hedysarum (Hedysarum alpinum americanum), A r c t i c Dock (Rumex a r c t i c u s ) , T i l e s i u s ' s Wormwood (Artemesia t i l e s i i ) , Tawny A r c t o p h i l a ( A r c t o p h i l a fulva) , Kotzebue's Grass of Parnassus (Parnassus kotzebuei) and  Anderson's  A l k a l i Grass. ( P u c c i n e l l i a a n d e r s o n i i ) . The next stage of the c o l o n i z a t i o n process develops when the f l o o r of the mudslump i s no longer subjected to mudflows or to deposition by running water. . The surface of the mud becomes extremely hard and dry, and i s often traversed.by networks of d e s i c c a t i o n cracks. S o i l conditions are t y p i c a l of the disturbed nature of the h a b i t a t , c o n s i s t i n g p r i m a r i l y of mineral s o i l w i t h patches of organic m a t e r i a l i r r e g u l a r l y d i s t r i b u t e d at depth.  The percentage of bare ground ranges from 20-50 per cent, being  l e a s t where the surface has been i n a c t i v e f o r longer periods of time. Where the mudslump as a whole i s no longer a c t i v e , the o l d headwall may  be  p a r t i a l l y covered by Dryas-Hummock vegetation s l i d i n g down from the surface above.  The. t y p i c a l vegetation of these areas i s a dense cover of  grasses (Plate IV-D), of which the f o l l o w i n g species were the most prominent:  V i o l e t Wheat Grass (Agropyron l a t i g l u m e ) , Spiked Trisetum  (Trisetum spicatum), American Hare's Ear (Bupleurum americanum), Smoothing Whitlow Grass (Draba g l a b e l l a ) , A r c t a g r o s t i s ( A r c t a g r o s t i s l a t j f o l i a ) and the Sheathed A l k a l i Grass ( P u c c i n e l l i a vaginata).  Other species found i n  the same h i b i t a t include the Northern Asphodel ( T o f i e l d i a coccinea), A r c t i c Lychnis (Melandrium a f f i n e ) , Macoun's Poppy (Papaver k e e l e i ) , Pale Paint. Brush ( C a s t i l l e j a p a l l i d a ssp. elegans), Maydell's Oxytrope (Oxytropis maydeliana), A l p i n e M i l k - v e t c h (Astragalus a l p i n u s ) , Longstalked Stitchwort ( S t e l l a r i a longipes), Fingered B u t t e r c r e s s (Cardamine d i g i t a t a ) , Low Northern Rockcress (Braya humilis.ssp. a r c t i c a ) , Northern Tansy-mustard  ( D e s c u i r a i n i a sophioides), Mackenzie's Hedysarum (Hedysarum  78 mackenzii),  B e r i n g i a n Chickweed (Cerastium beeringianum), Dawson Hemlock  P a r s l e y (Conlosellnum c n i d i l f o l i u m ) , A c u t i s h Jacob's Ladder (Polemonium acutiflorurn), Reddish Sandwort ( A r e n a r i a r u b e l l a ) and the M i l f o i l (Achillea borealis). Following even greater periods of s t a b i l i t y the ground supports a continuous cover of vegetation and the o l d headwall i s s i m i l a r l y mantled w i t h Dryas-Hummocks. S o i l conditions s t i l l show the e f f e c t s of the disturbed nature of the h a b i t a t , but they tend to be moister and there i s a t h i n organic accumulation at the surface. The grass vegetation i s eventually replaced by dense w i l l o w t h i c k e t s composed mainly of the Northern Willow ( S a l i x glauca var. niphoclada), Alaskan or Felt-leaf Willow (S_. alaxensis) and the Net-veined Willow (S_. r e t i c u l a t a ) . Beneath, and between, these willows i s a scant ground cover comprised mainly of mosses together w i t h the Common H o r s e t a i l (Equisetum and the A r c t i c Lupin (Lupinus a r c t i c u s ) .  arvense)  This type of vegetation associa-  t i o n i s also widely d i s t r i b u t e d along many of the s t a b i l i z e d b l u f f s , many of which formerly underwent a c t i v e r e c e s s i o n by a process s i m i l a r to that operating i n active mudslumps. IX.  Strand Communities. Strand communities  also c o n s t i t u t e one of the most d i s t i n c t i v e  vegetation types and, l i k e the mudslumps, are e a s i l y i d e n t i f i a b l e on a e r i a l photographs.  They are also r e l a t i v e l y simple to d e l i n e a t e since  they generally abut quite sharply against the other vegetation types w i t h l i t t l e or no t r a n s i t i o n zone i n between.  Four sub-types, two major and  two minor, make up the strand communities. The minor sub-types, too small to be shown e f f e c t i v e l y on  79 Figure 10, include the a c t i v e beaches and c o a s t a l b l u f f s ; two l o c a t i o n s which, together w i t h the active mudslumps, account for most of the unvegetated areas on the i s l a n d .  A c t i v e beaches, composed of coarse sands,  gravels and boulders are well-drained and subjected to ice scouring i n the f a l l and winter months and wave abrasion during the summer. They also may be the s i t e s of deep snow accumulation where i t i s p i l e d i n d r i f t s against the b l u f f s .  The net e f f e c t of these adverse environmental  conditions i s  to keep the beaches almost completely devoid of any plant growth except for a few i s o l a t e d clumps at the base of some of the c l i f f s . ing  Actively retreat-  sections of the c o a s t l i n e are also vegetation free except for i s o l a t e d  clumps detached from the c l i f f edge during the r e t r e a t process.  Stabilized  c l i f f s , u s u a l l y r e s u l t i n g from the formation of p r o t e c t i v e sandspits at the foot of the c l i f f , support a vegetation cover proportionate to t h e i r period of s t a b i l i t y .  The c l i f f s  composed of fine-grained sediments, containing  abundant ground i c e , have already been discussed under the heading of mudslump communities.  On the sand headlands, sections of the c o a s t l i n e that  were a c t i v e l y r e t r e a t i n g u n t i l r e l a t i v e l y recent times, s t i l l have 40-50 per cent of the c l i f f face bare of any vegetation cover.  The  remaining  surface supports a l i g h t cover of mosses ( c h i e f l y P s i l o p i l u m cavifolium) together w i t h the Radiate Saxifrage (S a x i f r a g a r a d i a t a ) , A r c t i c Avens (Dryas i n t e g r i f o l i a ) and the Sudeten Lousewort ( P e d i c u l a r i s s u d e t i c a ) . B l u f f s which are also the s i t e s of l a t e - l y i n g snowpatches, e s p e c i a l l y on northeast-facing exposures, are characterized by the appearance of such a d d i t i o n a l species as the Lowly Fleabane (Erigeron humilis) and the Smallflowered P r a i r i e Rocket (Erysimum inconspicuum). portions of these same c l i f f s  Towards the upper  the vegetation i s dominated by the Diamond-  leaf Willow ( S a l i x pulchra) which appears to colonize the c l i f f s  from the  headland surface above.  C l i f f s which have been protected from erosion f o r  much longer periods of time are covered by dense w i l l o w t h i c k e t s s i m i l a r in composition  to those found i n the f i n a l c o l o n i z a t i o n of the mudslumps.  The greatest a r e a l extent of the strand communities, i s developed i n the v i c i n i t y of the large sandspits (Figure 10) where two major h a b i t a t s can be d i s t i n g u i s h e d : (Plates V-A,  V-B).  gravel bars and marsh-lagoons  The seaward margins of the sandspits have the same.un-  favourable environment as the a c t i v e beaches, and are subject to the same d i u r n a l and seasonal f l u c t u a t i o n s of ice-scouring and wave abrasion. the higher, l e s s - a c t i v e portions of the gravel accumulations, 90 per cent of the surface may cover.  On  as much as  s t i l l be devoid of any form of vegetation  Among the f i r s t plants to colonize these surfaces i s the Lyme  Grass (Elymus arenarius ssp. m o l l i s ) , the fibrous roots of which penetrate deeply i n t o the well-drained substratum.  Other c h a r a c t e r i s t i c species i n  t h i s environment, and commonly forming prostrate mats on patches of f i n e r material or r a f t s of washed organic m a t e r i a l eroded from the  adjacent  sections of the c o a s t l i n e , include the Sea-beach Sandwort (Arenaria peploides), Low Chickweed ( S t e l l a r i a humifusa), B e r i n g i a n Chickweed (Cerastium beeringianum), Common Scurvy Grass (Cochlearia o f f i c i n a l i s ) and the Alpine M i l k - v e t c h (Astragalus a l p i n u s ) . On the inner margins of the sandspit, bordering the marsh-lagoon, the percentage of bare ground decreases, and there i s an increase i n the number and v a r i e t y of the plant species.  The habitat i s s t i l l subject to p e r i o d i c f l o o d i n g during  storm surges, but the sands are f i n e r , moister and frequently contain admixtures of organic m a t e r i a l .  Lyme Grass i s less prominent i n these  areas i n which the most common species are the A r c t i c Marsh Willow ( S a l i x a r c t o p h i l a ) , Creeping Sedge (Carex chordorrhiza), Beach Pea  Plate V  VEGETATION  A.  STRAND  COMMUNITIES.  S t e r i l e s u r f a c e o f the s a n d s p i t i s l o c a l l y c o l o n i z e d by t u f t s o f Lyme Grass and r a f t s o f t h e Sea-beach Sandwort. The marsh-lagoon h a b i t a t o c c u r s between the s a n d s p i t and the s t a b i l i z e d c o a s t a l b l u f f s i n the background.  C.  LOW-CENTRED  POLYGON.  The margins o f t h e c e n t r a l d e p r e s s i o n , o f t e n o c c u p i e d by w a t e r , and the i s l a n d s o f v e g e t a t i o n i n the c e n t r e a r e composed o f A q u a t i c Sedge and F i s h e r ' s D u p o n t i a . The r a i s e d edge o f t h e p o l y g o n i s c h a r a c t e r i z e d by l i c h e n s and mosses.  TYPES  B.  STRAND  COMMUNITIES .  The v e g e t a t i o n cover i n c r e a s e s on the f i n e r sands a l o n g the i n n e r margins o f the s a n d s p i t , and the s p e c i e s i n t e r d i g i t a t e w i t h those of t h e lagoon-marsh h a b i t a t .  D.  HIGH-CENTRED  POLYGON.  Convex p o l y g o n c e n t r e i s c o v e r e d by m a r b e l o i d hummocks o f l i c h e n and moss t o g e t h e r w i t h the G l a n d u l a r B i r c h and w i l l o w s p e c i e s . The wedge a r e a i n t h e f o r e g r o u n d i s almost c o m p l e t e l y overgrown w i t h sedges, mosses and w i l l o w s .  82 (Lathyrus maritimus), Alpine Hedysarum (Hedysarum alpinum amer i c anum), Scentless Mayweed ( M a t r i c a r i a ambigua), Dawson Hemlock Parsley (Conioselinum c n i d i i f o l i u m ) , Pale Paint Brush ( C a s t i l l e j ; a p a l l i d a ssp. elegans), Seaside Crowfoot (Ranunculus cymbalaria var. a l p i n u s ) , A r c t i c Fireweed (Epilobium l a t i f o l i u m ) , Roseroot (Sedum rosea ssp. i n t e g r i f o l i u m ) , Gentian (Gentiana arctophila) and the Greenland Primrose (Primula egaliksensis).  L o c a l l y , the junction between the sandspit and the  c o a s t a l b l u f f i s marked by the growth of t a l l stands of the Alaskan or F e l t - l e a f Willow ( S a l i x alaxensis) as much as 3-4 metres (9-12 feet) t a l l . The other major habitat w i t h i n the strand communities includes the  marsh-lagoons enclosed behind the gravel bars.  These s i t e s , which  are  also subject to p e r i o d i c f l o o d i n g , have numerous bodies of shallow,  open water which may or may not be connected to the sea.  The s o i l , which  i s almost always saturated, contains abundant organic m a t e r i a l , p a r t l y due to the n a t u r a l accretion of vegetation d e b r i s , and p a r t l y as a r e s u l t of the  accumulation of waterborne m a t e r i a l eroded from the c o a s t a l b l u f f s .  Many of the plants bordering the moist sand areas are also found along the  periphery of the lagoons but they are gradually replaced by a f l o r a  i n which the most c h a r a c t e r i s t i c species are the Lowly Fleabane (Erigeron h u m i l i s ) , Common H o r s e t a i l (Equisetum arvense), H a i r - g r a s s - l i k e Reedgrass (Calamagrostis deschampsioides), A r c t i c Rush (Juncus a l p i n u s ) , A l k a l i Grasses ( P u c c i n e l l i a ander s o n i i , P . phryganodes , P_. v agin at a) , Common Mare's t a i l (Hippuris v u l g a r i s ) , Marsh C i n q u e f o i l ( P o t e n t i l l a p a l u s t r i s ) , Sea-Pink (Armeria maritima ssp. a r c t i c a ) , Yellow Marsh Saxifrage (Saxifraga h i r c u l i s ) , Nodding Saxifrage (S_. cernua) , P a l l a s ' s Buttercup (Ranunculus p a l l a s i i ) and F i s h e r ' s Dupontia (Dupontia f i s h e r i ) .  83  X.  Polygonal Ground. The plant communities associated w i t h polygonal ground are  i n t i m a t e l y r e l a t e d to the stage of development of these features and can be c l a s s i f i e d accordingly. The e a r l i e s t stage w i t h which a d i s t i n c t i v e vegetation pattern can be linked i s the low-centred type ( P l a t e V-G), c h a r a c t e r i s t i c form of which consists of a c e n t r a l depression by a r a i s e d rim of v a r i a b l e width and height.  the  surrounded  In many polygons of t h i s  type, the c e n t r a l depression may be occupied by a shallow body of open water which may be completely devoid of any vegetation.  This water  frequently has a d i s t i n c t i v e golden-brown colour due to c e r t a i n algae, the accumulated remains of which form a layer of s o f t , oozy m a t e r i a l on the f l o o r of the pool.  O c c a s i o n a l l y , i s o l a t e d t u f t s of the Aquatic Sedge  (Carex a q u a t i l i s ) and Fisher's Dupontia (Dupontia f i s h e r i ) occur as small islands of vegetation i n the water bodies.  Around the shallower margins  of the pool the vegetation i s dominated by the Tawny A r c t o p h i l a ( A r c t o p h i l a fulva) together w i t h the Aquatic Sedge and Fisher's Dupontia. The surrounding ridges are composed of peat, and t h i s d r i e r h a b i t a t i s r e f l e c t e d i n a completely d i f f e r e n t f l o r a l assemblage dominated by mosses and l i c h e n s .  The major vascular species growing on the ridges include the  Veiny-leafed Willow (S a l i x phlebophylla) , Alpine Bearberry (Arctostaphylos r u b r a ) , Cloudberry (Rubus chamaemorus), A r c t i c Blueberry (Vaccinium Uliginosum var. alpinum), Mountain Cranberry (Vaccinium v i t i s - i d a e a ) , Narrow-leafed Labrador-tea (Ledum palustre ssp. decumbens), Glandular B i r c h (Betula glandulosa), A r c t i c Avens (Dryas i n t e g r i f o l i a ) and the A r c t i c White Bell-heather (Cassiope tetragona). The troughs o v e r l y i n g the ice-wedges between the polygons also contain bodies of open water which may be p a r t i a l l y f i l l e d with a shallow  84 blanket of Sphagnum and sedge.  I n t h i s aquatic h a b i t a t , the f l o r a i s  s i m i l a r to that found i n the c e n t r a l pools, together w i t h the Gmelin's Buttercup (Ranunculus g m e l i n i i ) , Marsh Marigold (Caltha p a l u s t r i s ssp. a r c t i c a ) , Richardson's Anemone (Anemone r i c h a r d s o n i i ) , Meadow B i t t e r c r e s s (Cardamine p r a t e n s i s ) , Nodding Saxifrage (Saxifraga cernua) and the Common Cotton-grass (Eriophorum angustifolium). With increasing passage of time the c e n t r a l pools of the lowcentred polygons become progressively shallower and they are gradually colonized by the plants growing around t h e i r margins.  The accumulation of  vegetable d e b r i s , c h i e f l y the Aquatic Sedge and F i s h e r ' s Dupontia, r a i s e s the l e v e l of the c e n t r a l area u n t i l i t i s f l a t and equal i n height to the surrounding ridges.  At the same time, there i s a l a t e r a l spreading of the  species from the dry ridges onto the c e n t r a l area, and t h i s a s s o c i a t i o n gradually replaces the sedges.  Further accumulation of peat i n t e n s i f i e s  the dry nature of the h a b i t a t , and may eventually give the polygon the convex form of the high-centred type (Plate V-D).  SUMMARY The a r c t i c tundra vegetation of Garry Island can be c l a s s i f i e d into ten major types which can be r e l a t e d to v a r i a t i o n s i n the physical character of the h a b i t a t s .  Drainage conditions and geomorphic a c t i v i t y ,  acting s i n g l y o r , more often i n combination, appear to afford the best c r i t e r i a f o r the d e l i n e a t i o n of the h a b i t a t s , with the possible exception of the 'Alnus c r i s p a ' type where shelter may be the most important f a c t o r . Seven of the h a b i t a t s , corresponding to the 'Dryas-Hummocks', 'Cassiope Snowpatch', 'Eriophorum Tussock',  'Hummock-Tussock T r a n s i t i o n , 1  85  'Stream Course Willow T h i c k e t s ' , and 'Sedge-Moss F l a t s ' vegetation types, are recognized p r i m a r i l y on the basis of v a r i a t i o n s i n the moisture cond i t i o n s of the h a b i t a t .  The influence of geomorphic a c t i v i t y i s also  evident i n each of these types however.  Hummocks and tussocks are  generally regarded as products of f r o s t a c t i o n , and the m i c r o r e l i e f produced by the development of these features i s s u f f i c i e n t to produce wet and dry habitats w i t h i n the same vegetation type.  In the case of the  hummocks, the influence of the m i c r o r e l i e f f a c t o r becomes less pronounced towards the lower, moister sections of the slopes, and i t v i r t u a l l y d i s appears, as i n the 'Cassiope Snowpatch' type, i n the s i t e s of l a t e - l y i n g snow patches.  The 'Stream Course Willow T h i c k e t s ' and the 'Sedge-Moss  F l a t s ' , vegetation types are found along the f l o o r s of the v a l l e y s and depressions into which i n t e r m i t t e n t runoff and moisture seepage are channelled throughout the summer months. I n the 'Strand Communities', 'Mudslump Communities' areas of 'Polygonal Ground', the p h y s i c a l character of the habitat i s determined p r i m a r i l y by geomorphic a c t i v i t y .  Within the 'Strand Communities' two  contrasting habitats can be i d e n t i f i e d :  these are the g r a v e l bars, which  are subject to d i u r n a l and seasonal f l u c t u a t i o n s of wave-abrasion and i c e - s c o u r i n g , and the marsh-lagoon areas, enclosed and protected by the bars, where the conditions are r e l a t i v e l y quiescent.  Differences i n the  vegetation patterns of these two environments may also be r e l a t e d to v a r i a t i o n s i n the moisture conditions of the substrate. In the 'Mudslump Communities' there appears to be a d i s t i n c t i v e sequence of plant c o l o n i z a t i o n r e l a t e d to the length of time that the mudslump has been i n a c t i v e .  Thus the vegetated sections of active mudslumps are  dominated by almost pure stands of the Marsh Fleawort (Senecio lugens).  Once the f l o o r of the mudslump i s no longer subjected to mudflows or deposition by running water, the surface becomes colonized by a cover of grasses and, f o l l o w i n g even greater periods of s t a b i l i t y , t h i s grass veget a t i o n i s eventually replaced by w i l l o w t h i c k e t s .  In the areas of poly-  gonal ground, the growth of ice-wedges a l s o r e s u l t s i n the production of wet and dry h a b i t a t s , and another d i s t i n c t i v e plant c o l o n i z a t i o n sequence can be i d e n t i f i e d through which the polygons are transformed from lowcentred to high-centred types. The s t a t i s t i c a l v a l i d i t y of the percentages for the dominant plant species i n each vegetation type i s l i m i t e d due to the subjective method of v i s u a l estimation employed.  Despite the crude nature of these  percentages however, i t was possible to recognize four species, Dryas i n t e g r i f o l i a , Alnus c r i s p a , Cassiope tetragona and Eriphorum vaginatum, as being d i a g n o s t i c of s p e c i f i c vegetation types on the basis of t h e i r dominance of the plant composition.  Though not dominated by a s i n g l e  species, the 'Strand Communities' were a l s o characterized by a d i s t i n c t i v e f l o r a l assemblage probably due to the s t r i c t e r tolerance conditions produced by the presence of s a l i n e or b r a c k i s h water.  Furthermore,  little  d i f f i c u l t y was encountered  i n determining the areal extent of the  communities i n the f i e l d .  Even where the c l a s s i f i c a t i o n was based on  changes i n the drainage conditions of the h a b i t a t , i t was found that the contacts between adjacent vegetation types were quite d i s t i n c t .  Only  where the lower slopes were g e n t l e , and drainage conditions changed g r a d u a l l y , were there extensive t r a n s i t i o n zones n e c e s s i t a t i n g the r e c o g n i t i o n of the 'Hummock-Tussock T r a n s i t i o n ' type.  Where the h a b i t a t  was determined p r i m a r i l y by geomorphic a c t i v i t y , the vegetation type u s u a l l y formed a d i s t i n c t unit and there was no problem i n determining the  87 precise a r e a l extent of the plant community.  CHAPTER IV  PERMAFROST CONDITIONS  The term permafrost, or permanently frozen ground, i s used to describe a thickness of s o i l or other s u p e r f i c i a l deposit, or even of bedrock, at a v a r i a b l e depth beneath the surface of the earth i n which a temperature below f r e e z i n g has e x i s t e d c o n t i n u a l l y f o r a long time (from two to tens of thousands of years).''' This thermal c o n d i t i o n may  be  wholly contemporaneous w i t h the e x i s t i n g climate, or i t may be a r e l i c feature which was  i n i t i a l l y developed during an e a r l i e r , colder climate  and has been preserved under the negative mean annual temperatures of the present climate. Approximately  o n e - f i f t h of the land area of the world, and as  much as one-half of the area of Canada, i s underlain by permafrost  in  2 e i t h e r a continuous or discontinuous d i s t r i b u t i o n .  W h i l s t the a r e a l  extent of the p e r e n n i a l l y frozen ground i s reasonably w e l l e s t a b l i s h e d i n Canada, only a l i m i t e d amount of data i s a v a i l a b l e r e l a t i n g to i t s v e r t i c a l thickness.  Largely as a r e s u l t of townsite i n v e s t i g a t i o n s and  o i l e x p l o r a t i o n d r i l l i n g programmes, more i s known about the thickness of ^Muller, S.W. (1947) Permafrost or permanently frozen ground and r e l a t e d engineering problems, J.W. Edwards, Inc., Ann Arbor, Michigan, p. 3. 2 Jenness, J.L. (1949) "Permafrost  i n Canada", A r c t i c , V o l . 2,  p. 13. Geological Survey of Canada (1967) Permafrost 1246A, F i r s t E d i t i o n , Scale 1: 7,603,000.  i n Canada, Map  89 the frozen ground i n the Mackenzie Delta area than i n other parts of the Canadian A r c t i c .  Brown has reported permafrost to depths of 76-91 metres  (250-300 feet) i n the v i c i n i t y of Inuvik, and Mackay thicknesses of 3 107-122 metres (350-400 feet) near A r c t i c Red River and F o r t McPherson. Temperature data from a d r i l l hole near Tununuk on Richards I s l a n d r e v e a l 4 that permafrost occurs to a depth of 366 metres (1200 f e e t ) .  Thus,  although no information i s a v a i l a b l e concerning the thickness of permaf r o s t on Garry I s l a n d , i t may w e l l be that the frozen ground extends to a depth of 305 metres (1000 feet) or more beneath the centre of the i s l a n d . The precise thickness of the frozen ground i s of r e l a t i v e l y minor importance to the geomorphic processes operating i n permafrost areas.  Of greater s i g n i f i c a n c e i s the a c t i v e layer which thaws during  the summer months and i s subject to a l t e r n a t e f r e e z i n g and thawing during successive seasons.  The thickness of t h i s a c t i v e layer i s quite v a r i a b l e  and i s r e l a t e d to d i f f e r e n c e s i n slope, n a t u r a l drainage, aspect, type of vegetation cover and the nature of the m a t e r i a l beneath the surface vegetation. The purpose of t h i s chapter i s to describe a number of i n v e s t i g a t i o n s made on Garry I s l a n d designed to:  (1) determine the r a t e  and depth of thaw i n the active layer under varying slope, exposure, Brown, R.J.E. (1966) " R e l a t i o n between mean annual a i r and ground temperatures i n the permafrost region of Canada", Proc: Permafrost I n t e r n a t i o n a l Conference, L a f a y e t t e , Indiana, November, 1963 Nat. Acad, of Sciences - Nat. Research C o u n c i l , Washington P u b l i c a t i o n , No. 1287, p. 243. J  Mackay, J . Ross (196 7) "Permafrost depths, Lower Mackenzie V a l l e y , Northwest T e r r i t o r i e s " , A r c t i c , V o l . 20, pp. 21-26. 4 Mackay, J . Ross.  Personal communication, October, 1968.  90 vegetation, moisture and m i c r o r e l i e f conditions; and (2) measure the ground temperatures at selected s i t e s i n t h i s a c t i v e layer i n order to better understand the processes involved i n the development of earth hummocks. These studies were accomplished p r i m a r i l y by making comparat i v e i n v e s t i g a t i o n s of the depths of thaw, at various times throughout the summer, beneath each of the major vegetation types i d e n t i f i e d i n Chapter III.  The depth to the f r o s t t a b l e was determined by using a metal rod as  a probe.  S i m i l a r measurements, though using a network of wooden stakes  and on a d a i l y b a s i s , were a l s o made to examine changes i n the configurat i o n of the f r o s t table beneath the surface of a small vegetation p l o t 5.6 square metres (60 square f e e t ) i n area.  To complement these  observa-  t i o n s , excavations were made to determine the nature of the substrate. F i v e s t r i n g s of thermistor cables were also i n s t a l l e d to d i f f e r e n t depths beneath the centres of an earth hummock, two inter-hummock depressions, and a mud b o i l and adjacent depression, i n an attempt to detect v a r i a t i o n s i n the thermal regime of the seasonally thawed l a y e r .  DEPTH OF THAW MEASUREMENTS A number of authors have i n v e s t i g a t e d and documented the e f f e c t s of a vegetation cover on the thermal regime of the underlying  91 ground."'  These i n v e s t i g a t i o n s have shown that the influences of the  vegetation cover on permafrost are exceedingly complex, and that quantitat i v e evaluations of these influences are extremely d i f f i c u l t to obtain. One of the most r e a d i l y measurable c h a r a c t e r i s t i c s of these r e l a t i o n s h i p s i s the v a r i a t i o n i n the thickness of the active layer beneath contrasting surface covers.  The data presented i n Table V show  some of the v a r i a t i o n s i n the thickness of the active layer beneath the major vegetation types on Garry I s l a n d as they were recorded at the end of the 1964 f i e l d season.  As the table shows, the greatest depths of thaw  were encountered i n areas having- l i t t l e or no vegetation cover, as exemplified by the bare ground of some of the mudslumps and a c t i v e sandspits.  I n both these type l o c a l i t i e s , the p o s i t i o n of the f r o s t table  was i n excess of one metre (3 feet) below the ground surface and, i n the case of the sandspit areas, could not be detected by probing.  The  influence of the type of mineral s o i l i n the substrate may also be r e f l e c t e d i n the greater depth of thaw i n the coarse sands and gravels of the strand areas compared w i t h the s i l t - and c l a y - s i z e d m a t e r i a l found on the f l o o r s of the mudslumps. Comparisons of the thickness of the active layer beneath the  Benninghof, W.S. (1952) " I n t e r a c t i o n of Vegetation and S o i l Frost Phenomena", A r c t i c , V o l . 5, pp. 34-44. T y r t i k o v , A.P. (1959) " P e r e n n i a l l y Frozen Ground and Vegetation", P r i n c i p l e s of Geocryology, (Permafrost S t u d i e s ) , P a r t I , General Geocryology, Acad. S c i . U.S.S.R., Moscow, pp. 399-421. T r a n s l a t i o n by R.J.E. Brown, N a t i o n a l Research Council of Canada, Technical T r a n s l a t i o n 1163, 1964, pp. 1-34. Brown, R.J.E. (1966) "Influence of Vegetation on Permafrost", Proc: Permafrost I n t e r n a t i o n a l Conference, L a f a y e t t e , Indiana, op_. c i t . , pp. 20-25.  TABLE  V  DEPTHS OF THAW BENEATH THE MAJOR VEGETATION TYPES, GARRY ISLAND, SEPTEMBER 1, 1964.  Depth of Thaw (Cms.)  Vegetation Type Dryas-Hummock  Hummocks Depressions Mud B o i l  Eriophorum Tussocks Tussocks Depressions Sedge-Moss F l a t s Stream Course ) Willow Thickets Mudslump Communities  Strand Communities  45 22 70  65 30 75  45 - 60 18 - 25 18  22  25  30  Bare Ground  > 100  Grass Cover  45 - 50  Sandspits Lagoon F l a t s  > 100 40 - 50  93 vegetated surfaces show that the amount of thawing was greatest beneath the domed centres of the Dryas-Hummocks and tussock-Like forms of the Sheathed Cotton-grass (Eriophorum vaginatum).  In actual f a c t , i t i s  extremely d i f f i c u l t to provide a meaningful average for these l o c a l i t i e s , and t h i s i s i l l u s t r a t e d by the wide ranges i n d i c a t e d i n Table V.  The  depth of thaw i s influenced considerably by the m i c r o r e l i e f f a c t o r and, i n general, the larger the hummocks and the more prominent the tussocks, the greater the depth of thaw.  Because of the v a r i a t i o n s introduced by  t h i s m i c r o r e l i e f f a c t o r , i t i s , however, v i r t u a l l y impossible, using simple probing techniques, to evaluate p r e c i s e l y the r e l a t i v e e f f e c t s of the various vegetation types on the thermal regime of the underlying ground. One noticeable aspect of Table V i s the uniformly lower depths of thaw recorded beneath vegetation associations w i t h a considerable percentage of moss i n t h e i r f l o r a l composition.  As described i n the previous  chapter, the shallow depressions between the earth hummocks are f r e quently dominated by mosses and accumulations  of organic debris.  Such  l o c a l i t i e s were characterized by depths of thaw which were frequently less than one-half of those recorded i n the r a i s e d centres of the hummocks.  This r e l a t i o n s h i p was also observable on the summit areas  and  on south-facing slopes where the hummocks were'often more subdued i n form and, consequently, the m i c r o r e l i e f f a c t o r was of r e l a t i v e l y less importance.  A s i m i l a r pattern was  also observed i n the Eriophorum-  Tussock communities where the i n t e r - t u s s o c k depressions were again characterized by depths of thaw which were u s u a l l y less than one-half of those measured i n the adjacent tussocks.  Further evidence of the insu-  l a t i n g property of a moss cover on the underlying ground was demonstrated  94 by the f a c t that the average depth of thaw beneath the major vegetation types was lowest, 18-22 cms. (7.0-8.5 i n s . ) , beneath the f e a t u r e l e s s surfaces of the sedge-moss f l a t s . The f i g u r e s presented  i n Table V, despite t h e i r l i m i t a t i o n s ,  corroborate the f i n d i n g s of other i n v e s t i g a t o r s and.demonstrate that the thickness of the active layer i s greatest beneath bare ground surfaces, and that a cover of mosses allows l e s s heat to penetrate to greater depths i n the underlying ground than does a vegetation cover dominated by vascular p l a n t s . The above d e s c r i p t i o n s are r e l a t e d to measurements of the thickness of the a c t i v e layer at a number of s e l e c t e d , i s o l a t e d points. To complement these observations, a vegetation p l o t was established during the 1964 f i e l d season, to examine the influences of some of these same f a c t o r s on the c o n f i g u r a t i o n of the f r o s t table over a small contiguous area.  The dimensions of t h i s p l o t were approximately  0.9 metres by  6.1 metres (3 feet by 20 feet) , and i t was located on the lower part of the west-facing slope of a v a l l e y , close to the j u n c t i o n with the v a l l e y floor.  A s e r i e s of wooden stakes, graduated i n centimetres and spaced at  30 cm. (1 foot) i n t e r v a l s , were i n s t a l l e d i n the p l o t and were driven into the ground u n t i l they were halted by the f r o s t t a b l e , at which point the depth of penetration was recorded.  This procedure was repeated on a  d a i l y basis over the period J u l y 9 - August 28, 1964. Figure 11 i l l u s t r a t e s the surface contours and the vegetation  The vegetation p l o t c o n s t i t u t e d part of the f i e l d study programme of Dr. J . Ross Mackay and Dr. J.K. Stager, of the U n i v e r s i t y of B r i t i s h Columbia, and I am most g r a t e f u l to them f o r permission to r e f e r to t h e i r studies i n t h i s t h e s i s .  Figure 11  VEGETATION  PLOT  96 cover of t h i s p l o t .  Most of the surface was dominated by the dwarf shrubs  of the Ericaceae or Heath Family including the A l p i n e Bearberry (Arctostaphylos r u b r a ) , A r c t i c White Bell-heather (Cassiope tetragona), Narrow-leafed Labrador-tea (Ledum palustre ssp. decumbens), A r c t i c Blueberry (Vaccinium uliginosum var. alpinum), and Mountain Cranberry (Vaccinium v i t i s - i d a e a ) , together with minor quantities of l i c h e n s and A r c t i c Avens (Dryas i n t e g r i f o l i a ) .  This f l o r a covered a number of sub-  dued earth hummock forms, s i m i l a r to those described i n the previous chapter, the c e n t r a l portions of which were elevated by 20-30 cms. (8-12 ins.) above the surrounding depressions.  The plant associations  occurring i n these depressions were composed p r i n c i p a l l y of mosses and the A r c t i c White B e l l - h e a t h e r . The other p r i n c i p a l constituent of the f l o r a of the vegetation plot was the d i s t i n c t i v e t u s s o c k - l i k e forms of Sheathed Cotton-grass (Eriophorum vaginatum). p l o t was dominated by the unvegetated  The c e n t r a l part of the  surface of a prominent mud b o i l .  The depth of thaw measurements are shown i n Figure 12, showing the c o n f i g u r a t i o n of the f r o s t table at the beginning of August and September, 22 and 53 days a f t e r the i n s t a l l a t i o n of the stakes respectively.  The i s o l i n e s on these maps represent the depth of the  f r o s t table beneath the ground s u r f a c e , and the higher values thus correspond to depressions i n the f r o s t t a b l e .  The greater d e t a i l shown  i n the map for August 1, r e f l e c t s the number of observations made at intermediate points between the stakes, whereas the map for September 1 was based s o l e l y on the data obtained i n the excavations of the p r o f i l e s shown i n Figure 13. Reference to Figure 12 reveals that the depth of thaw was quite v a r i a b l e and imparted an i r r e g u l a r topography to the top of the  ;  97  Figure 12  VEGETATION POSITION  OF  FROST  TABLE  (DEPTH  Aug. 1, 1964  Contour  Interval  BELOW  PLOT GROUND  SURFACE  IN  Sept. 1, 1964  5 cms.  Scale 0  20  40  60  80 Cm».  CMS.)  98 Figure 13  VEGETATION DEPTH  OF  THAW  Mineral  PLOT PROFILES  Soil Scale 0  For locations  of  profiles  see  Figure 11  i  20  40  60  80  i •4  Cms.  99 frozen ground.  Comparison with Figure 11 shows that the contours of the  f r o s t table do not p a r a l l e l the c o n f i g u r a t i o n of the ground surface. I n general, the upper surface of the frozen ground occurs at greater depths where the ground surface i s highest, and i t l i e s at shallower depths where the ground surface i s lowest.  Thus the f r o s t table i s frequently  deeper beneath the earth hummocks and tussocks than beneath the i n t e r vening  depressions. The inverse r e l a t i o n s h i p between the configurations of the  ground surface and the permafrost  surface undoubtedly r e f l e c t , at least  in p a r t , the s i g n i f i c a n c e of the m i c r o r e l i e f f a c t o r .  The elevated  nature of the earth hummocks and tussocks allows heat to penetrate the ground l a t e r a l l y from t h e i r s i d e s , as w e l l as v e r t i c a l l y from the t o p , thus c o n t r i b u t i n g to a greater r a t e of thawing.  The undulations i n the  f r o s t table cannot, however, be a t t r i b u t e d s o l e l y to the influence of v a r i a t i o n s i n the m i c r o r e l i e f .  The r a t e and t o t a l depth of thaw are  also influenced by the type of m a t e r i a l occurring i n the substrate. Figure 13 shows a t o t a l of 21 c r o s s - s e c t i o n a l p r o f i l e s i n the vegetation p l o t which were excavated  at the beginning of September, 1964, when the  p o s i t i o n of the f r o s t table was approximately surface of the p e r e n n i a l l y frozen ground.  coincident w i t h the Upper  As these p r o f i l e s i l l u s t r a t e ,  there i s apparently also an inverse r e l a t i o n s h i p between the t o t a l depth of thaw and the thickness of organic m a t e r i a l i n the p r o f i l e .  Thus the  greatest depth of thaw, i n excess of 75 cms. (29.5 ins.) was recorded beneath the surface of the mud b o i l where the substrate was composed e n t i r e l y of mineral s o i l , and the next greatest depths of thaw were recorded beneath the earth hummocks which were also composed predominantly  of mineral s o i l .  As the r a t i o of organic m a t e r i a l to mineral  100 s o i l i n the p r o f i l e s increased, the depth of thaw decreased accordingly, and the elevated parts of the permafrost s u r f a c e , corresponding  to the  lowest depths of thaw i n Figure 12, occurred beneath the accumulations of organic m a t e r i a l occupying the depressions  i n the ground surface.  Earth Hummock Experiments. In the preceding paragraphs the d i s c u s s i o n was centred on v a r i a t i o n s i n the t o t a l depth of thaw beneath each of the major vegetation associations found on Garry I s l a n d .  These v a r i a t i o n s , w h i l s t providing an  i n d i c a t o r of the e f f e c t s of contrasts i n the f l o r i s t i c composition, must equally r e f l e c t the numerous other c l i m a t i c and t e r r a i n f e a t u r e s , which also combine to influence the depth of thaw from the ground surface to the permafrost t a b l e . A number of experiments was undertaken during the 1965 f i e l d season to i n v e s t i g a t e some of the f a c t o r s i n f l u e n c i n g the rate and depth of thaw beneath the centre of a t y p i c a l earth hummock. S p e c i f i c a l l y experiments were designed cover, l i v i n g  these  to examine the influence of the vegetation  and dead, and the a d d i t i o n of c o n t r o l l e d q u a n t i t i e s of water  on the thickness of the thawed l a y e r . The f i r s t set of experiments was designed of the vegetation cover alone.  to examine the r o l e  An attempt was also made to d i f f e r e n t i a t e  between the e f f e c t s of the surface mat of l i v i n g vegetation and the underl y i n g accumulation  of dead organic m a t e r i a l which frequently o v e r l i e s the  domed core of mineral s o i l i n a t y p i c a l earth hummock. The success i n making t h i s d i s t i n c t i o n was r e s t r i c t e d by the f a c t t h a t , as others have noted, i t i s extremely d i f f i c u l t to delineate the boundary between these  101 l i v i n g and dead components of the organic layer.'' S i x hummocks were selected for these s t u d i e s , each of which occupied a s i m i l a r p o s i t i o n w i t h respect to aspect and general l o c a t i o n on the topographic slope p r o f i l e . ' I n a d d i t i o n , to eliminate the possible influence of v a r i a t i o n s produced by the m i c r o r e l i e f f a c t o r , each of the hummocks was of very s i m i l a r dimensions, being about 70 cms. (27.5 ins.) i n length, 55 cms. (21.5 ins.) i n width and having a r a i s e d centre which projected about 35 cms. (14 ins.) above the l e v e l of the adjacent i n t e r hummock depressions.  From two of these hummocks, the surface vegetation  l a y e r , averaging 7 cms. (3 ins.) i n thickness, was removed leaving the r a i s e d centre s t i l l covered by a layer of 4-5 cms. (1.5-2.0 ins.) of peat material.  From two of the other hummocks the complete organic cover of  l i v i n g vegetation and peat was removed, exposing the mineral s o i l core. The remaining two hummocks were l e f t i n t a c t to act as c o n t r o l s . The depth from the ground surface to the f r o s t table was recorded at weekly i n t e r v a l s over a six-week period and the r e s u l t s are shown i n Table VI.  I n t h i s t a b l e , the values given for the hummocks from  which the organic layer was e i t h e r p a r t i a l l y or completely removed do not include the thicknesses of the removed l a y e r s . As the f i g u r e s i n Table VI i n d i c a t e the response to the p a r t i a l or complete removal of the organic m a t e r i a l was quite r a p i d . During the f i r s t week of the experiment,  although characterized by only  Brown, R.J.E. (1966) "Influence of Vegetation on Permafrost", op. c i t . , p. 20.  102  TABLE V I  DEPTHS OF THAW BENEATH EARTH.HUMMOCKS ON GARRY ISLAND, JULY 19 - AUGUST 30, 1965.  Type of Cover  Depth of Thaw (Cms.) July  (a) N a t u r a l  (b) L i v i n g V e g e t a t i o n Removed  (c) Complete O r g a n i c L a y e r Removed  August  Total Change  19  26  2  9  16  23  30  51  54  55  58  59  60  61  + 10  52  54  54  57  58  60  62  + 10  40  49  51  55  56  59  60  +20  39  48  50  53  55  57  58  +19  37  47  51  55  57  59  61  +24  36  47  50  54  55  58  59  +23  103  g 85 thawing degree-days,  the l e v e l of the f r o s t table i n the c o n t r o l  hummocks was lowered by 2-3 cms. (1 i n c h ) , whereas i n the hummocks from which the organic layer was either p a r t i a l l y or completely removed the corresponding values were 9 cms. (3.5 ins.) and 10-11 cms. (4.0-4.5 ins.) respectively.  Over the remainder of the observation period the  d i f f e r e n t i a l rates were not always as marked, though they remained quite significant.  The depth of thaw beneath the centres of the c o n t r o l  hummocks increased by an average of 10 cms. (4 ins.) during the six-week period i n response to a t o t a l of 560 degree-days of thawing.  The removal  of the surface mat of l i v i n g vegetation r e s u l t e d , however, i n a lowering of the f r o s t table by an average of 19.5 cms. (7.5 i n s . ) , w h i l s t the complete removal of the e n t i r e organic layer produced an average increase i n the depth of thaw of 23.5 cms. (9.5 ins.) over the same time span. Assuming that the subsurface c o n d i t i o n s . i n each of the hummocks were the same, w i t h respect to the type of mineral s o i l and frozen moisture content, these figures demonstrate, quite c o n c l u s i v e l y , the important influence which a s u r f i c i a l layer of organic m a t e r i a l exerts on the thermal regime of the underlying ground.  The complete  removal of t h i s i n s u l a t i n g layer of vegetation increased the depth of thaw by 135 per cent over that recorded i n the c o n t r o l hummocks.  Even  where t h i s layer was only p a r t i a l l y removed, the corresponding increase i n the depth of thaw was 95 per cent.  Due to the afore-mentioned problem  Thompson, H.A. (1963) "Freezing and Thawing Indices i n Northern Canada" , Proc. of the F i r s t Canadian Conference on Permafrost, Ottawa, A p r i l 17-18, 1962, p. 21. The number of degree-days f o r any one day i s the d i f f e r e n c e between the average d a i l y a i r temperature and 32°F and thawing degree-days occur when the former exceeds 32°F.  104 of d i s t i n g u i s h i n g accurately the boundary between the l i v i n g and dead components of the organic m a t e r i a l , i t cannot be stated a f f i r m a t i v e l y that the d i f f e r e n t i a l between the two percentage increases can be a t t r i b u ted  s o l e l y to the r e l a t i v e influences of these two constituents.  I t does  i n d i c a t e , however, that a t h i n layer of peat, 4-5 cms. (1.5-2.0 ins.) i n thickness, had s u f f i c i e n t i n s u l a t i n g e f f e c t to r e s u l t i n a depth of thaw which was almost 17 per cent less than that recorded i n the hummock from which the organic layer was removed e n t i r e l y . The second part of the experiment was designed to examine the influences of aspect and moisture, s i n g l y and i n combination, on the depth of thaw.  A t o t a l of twenty earth hummocks was used f o r these i n v e s t i g a -  tions and again, i n an attempt to achieve as much uniformity i n the other v a r i a b l e s as p o s s i b l e , each hummock was of approximately the same dimensions and occupied a s i m i l a r p o s i t i o n on the topographic slope p r o f i l e . Nine of these hummocks were located on the southwest-facing slope of a v a l l e y , and another nine were located on the opposing northeast-facing slope.  Three of the hummocks i n each of these groupings were s p r i n k l e d  w i t h one l i t r e of water d a i l y , another three received two l i t r e s of water each day w h i l s t the remaining t h r e e , l e f t unwatered,were used as c o n t r o l s . In a d d i t i o n , two hummocks, also located on the southwest-facing s l o p e , were p a r t i a l l y or completely stripped of t h e i r vegetation cover, as described i n the previous experiment, and were sprinkled w i t h one l i t r e of water d a i l y .  The temperature of the water was recorded before i t was  applied to the hummock surfaces. These observations were continued over a five-week p e r i o d , and the depths of thaw were measured at weekly intervals.  One a d d i t i o n a l problem was introduced by these measurements,  insomuch as the i n s e r t i o n of the metal probe to the f r o s t table might  105 leave an open conduit presenting easy penetration of the water.  An  attempt was made to prevent t h i s by plugging the hole at the surface w i t h a length of wooden dowelling, but i t cannot be claimed that these precautions were completely s u c c e s s f u l . The r e s u l t s of t h i s project are presented i n Table V I I , and as the  figures show the experiments y i e l d e d inconclusive r e s u l t s .  Comparisons  of the measurements i n the c o n t r o l hummocks on the two opposing slopes reveal no influence of aspect as the average lowering of the f r o s t t a b l e , 8.67 cms. (3.5 ins.) was i d e n t i c a l on both sides of the v a l l e y . the  Similarly,  a d d i t i o n of water to the hummock surfaces appeared to have few con-  t r a s t i n g e f f e c t s on the two sides of the v a l l e y .  On the southwest-facing  slope the a p p l i c a t i o n of one l i t r e of water d a i l y r e s u l t e d i n a s l i g h t increase i n the amount of lowering of the f r o s t t a b l e , whereas a doubling of the quantity of water applied produced a s l i g h t decrease.  I n each case  the  d i f f e r e n c e s represented a d e v i a t i o n of less than one centimetre from  the  value recorded i n the c o n t r o l hummock.  the  hummocks on the northeast-facing slope r e s u l t e d i n s l i g h t decreases  The a p p l i c a t i o n of water to  i n the depth of thaw i r r e s p e c t i v e of the quantity of water added, though, once again the differences from the c o n t r o l value involved a maximum of one centimetre. Although the magnitude of the changes i s s m a l l , i t appears that the a p p l i c a t i o n of one l i t r e of water to the hummocks on the northeast-facing slope produced a larger reduction i n the depth of thaw than the a p p l i c a t i o n of two l i t r e s . Comparisons of Tables VI and VII give some i n d i c a t i o n of the e f f e c t s of adding water to the surfaces of earth hummocks from which the vegetation cover had been e i t h e r p a r t i a l l y or completely removed. hummock from which only the surface layer of l i v i n g vegetation was  I n the  106 TABLE VII EARTH  HUMMOCK WATERING  EXPERIMENT,  GARRY ISLAND,  JULY 26 - AUGUST 30, 1965. Type of Treatment  Depth of Thaw (Cms.) July  August  26  2  9  16  23  30  Net Changi  50 53 52  51 55 53  53 58 57  55 60 56  57 61 58  58 62 61  + 8 + 9 + 9  (b) 1 L i t r e of water added d a i l y  48 50 52  49 52 53  52 53 55  54 54 56  56 56 58  57 58 62  + 9 + 8 +10  (c) 2 L i t r e s of water added d a i l y  48 50 55  50 51 56  50 51 59  52 53 60  53 55 63  55 58 64  + 7 + 8 + 9  (d) Surface vegetation removed. 1 l i t r e added d a i l y .  43  45  49  50  52  52  + 9  (e) Complete organic layer removed. 1 l i t r e added d a i l y .  44  45  48  51  53  54  +10  (f) Control  52 49 49  52 51 51  55 55 52  56 56 53  60 58 55  60 59 57  + 8 +10 + 8  (g) 1 L i t r e of water added d a i l y  50 50 55  52 52 57  53 55 59  55 55 59  57 58 61  58 59 61  + 8 + 9 + 6  (h) 2 L i t r e s of water added d a i l y  55 56 55  57 58 56  60 60 58  61 60 60  64 64 63  65 63 63  +10 + 7 + 8  A. Southwest-facing Slope (a)  Control  B. Northeast-facing Slope  107 s t r i p p e d , the observed lowering of the f r o s t table amounted to 9 cms. (3.5 i n s . ) , whereas the removal of the e n t i r e organic material r e s u l t e d in a corresponding f i g u r e of 10 cms. (4 i n s . ) .  I n each case these were  1.5 and 3.0 cms. (0.5 and 1.0 ins.) less than those recorded over the same time period i n the i d e n t i c a l l y prepared hummocks to which no water was added. The a p p l i c a t i o n of 35 or 70 l i t r e s of water r e s p e c t i v e l y , w i t h an average temperature of 8.25°C, to the two groups of hummocks over the five-week period represented a considerable p o t e n t i a l source of heat to the underlying ground.  Unfortunately, i t i s impossible to i n f e r  whether t h i s water was able to penetrate into the mineral s o i l core of the  hummock, or whether i t was absorbed by the s u p e r f i c i a l mantle of  organic m a t e r i a l .  I n the case of the hummock from which the vegetation  cover was removed completely, i t was r e a d i l y observed t h a t , despite the l i g h t s p r i n k l i n g nature of the a p p l i c a t i o n , some of the water was l o s t by surface runoff.  The e f f e c t of any water which was able to penetrate the  organic layer would also depend on the e x i s t i n g moisture content of the soil.  The replacement of the a i r i n the pores of the s o i l by water would  have the e f f e c t of increasing the heat capacity of the s o i l , thereby reducing the amount of heat a v a i l a b l e to warm the s o i l at greater depths. I t seems reasonable to i n f e r , however, that most of the water was probably absorbed by the layers of organic material and was subsequently l o s t by evaporation, including evapotranspiration.  Since the  evaporation process requires heat, which may be drawn from the surrounding atmosphere, vegetation or s o i l , T y r t i k o v has postulated that t h i s may r e s u l t i n a lowering of the a i r temperature near the ground surface and  108 consequently  a reduction i n the warming of the s o i l .  Whether or not t h i s  postulate can be applied to such a small area as the surface of a hummock i s debatable, but, i f v a l i d , i t may  account f o r the s l i g h t cooling e f f e c t  of the water applied to the hummocks.  GROUND TEMPERATURE MEASUREMENTS The preceding d i s c u s s i o n has been based on observations made i n the r a t e and t o t a l depth of thaw beneath each of the vegetation types.  A  s e r i e s of observations was a l s o made to determine more p r e c i s e l y the v a r i a t i o n s i n the thermal regime of the thawed layer above the and the uppermost parts of the  permafrost  permafrost.  Five s i t e s were selected for these measurements to evaluate the s p e c i f i c e f f e c t s of c e r t a i n types of surface cover.  Three of the s i t e s  were i n one of the t y p i c a l hummock-depression associations found i n the Dryas-Hummock vegetation type.  The r a i s e d centre of the earth hummock,  almost c i r c u l a r i n plan and 60-70 cms.  (23.5-27.5 ins.) i n diameter,  reached e l e v a t i o n s of 30-35 cms. (12-14 ins.) above the l e v e l of the surrounding depressions, and supported a surface cover dominated by A r c t i c Avens, Narrow-leafed Labrador-tea, A r c t i c White B e l l - h e a t h e r , together w i t h a few lichens and dry moss pads. layer of 10-15  This vegetation was rooted i n a s u r f i c i a l  cms. (4-6 ins.) of organic m a t e r i a l o v e r l y i n g a prominent  domed core of mineral s o i l extending down to the f r o s t t a b l e .  The  adjacent  depressions, 50-60 cms. (19.5-23.5 ins.) i n length and 20-40 cms« (8.0-15.5 ins.) across, were dominated by the growth of sphagnum mosses  T y r t i k o v , A.P.  (1959), op_. c i t . , p. 5.  109 r e s t i n g on a substratum of organic m a t e r i a l which extended down almost to the base of the active layer.  The remaining two s i t e s were located i n a  large mud b o i l and adjacent depression.  The mud b o i l surface, 1.4-1.5  metres (4.5-5.0 feet) i n diameter, was l a r g e l y devoid of vegetation and, at the centre, rose approximately  20-25 cms. (8-10 ins.) above the  surrounding m o s s - f i l l e d depressions. At each of the s i t e s , ground temperatures were recorded  daily  10 by cables of bead thermistors.  The cables, each of which consisted of  f i v e thermistors, were encased i n lengths of rubber tubing which were sealed to prevent the entry of s o i l moisture.  One of the cables was  i n s t a l l e d i n the earth hummock and two i n the adjacent inter-hummock depressions.  The uppermost thermistor on each of these cables was placed  at a depth of 10 cms. (4 ins.) below the ground surface.  Beneath the  r a i s e d centre of the earth hummock the other four thermistors were spaced at i n t e r v a l s of 25 cms. (10 ins.) to a depth of 110 cms. (43.5 ins.) w h i l s t beneath each of the depressions the remaining thermistors were spaced at i n t e r v a l s of 15 cms. (6 ins.) to a depth of 75 cms. (29.5  ins.).  In the mud b o i l , the uppermost thermistor was i n s t a l l e d at a depth of 23 cms. (9 ins.) below the ground surface and a d d i t i o n a l beads were spaced at i n t e r v a l s of 30 cms. (12 ins.) to a depth of 113 cms. (44.5  ins.).  Only two thermistors were i n s t a l l e d i n the depression adjacent to the mud b o i l at depths of 14 cms. (5.5 ins.) and 24 cms. (9.5 ins.) beneath the A l l the thermistors used were manufactured by the Yellowstone Springs Instrument Company, Series 401 beads, w i t h a tolerance at 0°C of + 0.2°C. The thermistors were c a l i b r a t e d by the B.C. Research Council and by Dr. J . Ross Mackay of the Department of Geography, U.B.C. F i e l d readings were taken w i t h a small bridge, a l s o constructed by Dr. Mackay, and c a l i b r a t e d to read w i t h an operational range of "t 0.1°C.  110  ground surface. Figure 14 shows the mean ground temperature p r o f i l e and the amplitude of the ground temperature fluctuations for four of these s i t e s for the period July 1 to September 12, 1965.^  Table VIII also shows the  mean, maximum and minimum ground temperatures, together with the date of occurrence of the maximum and minimum temperatures recorded by each of the thermistors. Each of the s i t e s exhibits a similar pattern i n which the highest mean and maximum ground temperatures, and the greatest amplitude of ground temperature f l u c t u a t i o n s , were recorded by the thermistors located at the shallowest depth beneath the ground surface.  Strict  comparisons of the thermal regimes at each of the s i t e s are limited by the absence of ground surface temperature data.  With this consideration  in mind, Figure 14 shows that the highest mean temperature and greatest fluctuations were recorded at a depth of 10 cms. (4 ins.) beneath the surface of the earth hummock.  Such a simple comparison  of the p r o f i l e s  i s misleading, however, since the uppermost thermistor i n the cable i n s t a l l e d i n the mud b o i l was located at a depth more than twice that of the uppermost thermistor i n s t a l l e d i n the earth hummock.  I t i s probable,  therefore, that the mean summer ground temperature, and the amplitude of the temperature f l u c t u a t i o n s , at a depth of 10 cms. (4 ins.) beneath the surface of the mud b o i l , were of even greater magnitude than those  T h e means and amplitudes shown for the mud b o i l are actually for the s l i g h t l y longer period June 26 to September 12, 1965. In the depression adjacent to the mud b o l l , continuous readings were only recorded at a single depth, due to a faulty thermistor at a depth of 14 cms. (5.5 Ins.). As a r e s u l t , the p r o f i l e at the f i f t h s i t e could not be plotted. ii  Ill Figure 14  MEAN  GROUND  GROUND  TEMPERATURES  TEMPERATURE  AND  FLUCTUATIONS  -i  25  25  50  £ O  SO  75  -  75  a.  1  — T  /  :  t:  t  M i  MUD  i  _1_  Degrees  •  "  -  i  15  10  100  125 20  125  10  Levels  of  Mean  Ground  Amplitude  EARTH  J  Degrees  Centigrade  5  •"  100  BOIL  16  Thermistors.  of  Temperature  Ground  Profile  Temperature  Fluctuations  HUMMOCK  I  10  Centigrade  L  15  112  TABLE GROUND TEMPERATURES IN  MUD  BOIL,  EARTH  VIII  RECORDED AT DIFFERENT DEPTHS  HUMMOCK AND INTER-HUMMOCK  DEPRESSIONS.  ( i n Degrees Centigrade) Depth below surface ( cms.)  Mean  Max.  4.3 2.4 -0.3 -1.4  7.6 2.8 -0.3 -1.0 -1.9  Date of Max.  Min.  Date of Min.  8.2 5.0 0.9 -0.5  Aug. Aug. Aug. Sep.  10 24* 25* . 1*  ^0.5 -1.4 -2.7 -3.7  June June June June  26 26 26 26  8.7 6.4 3.6 3.2  15.9 5.8 1.8 -0.4 -1.1  July 8 Aug. 24 Aug. 24 Aug. 29* Sep. 3*  -0.4 0.0 -1.4 -2.4 -3.4  Sep. July July July July  3 1* 1 1 1  16.3 5.8 3.2 2.0 2.3  10.5 2.0 0.1 -0.4 -0.8  Aug. Aug. Aug. Aug. Aug.  23 23 21 31 31  -0.2 -0.6 -1.6 -2.4 -2.9  Sep. July July July July  3 1 1 1 1  10.7 2.6 1.7 2.0 2.1  10.3 2.7 -0.2 -0.4 -0.8  Aug. Aug. Aug. Sep. Sep.  23 23 23 12 1  -0.6 -0.7 -1.7 -2.4 -2.9  Sep. July July July July  3 1 1 1 1  10.9 3.4 1.9 2.0 2.1  Ampliti  MUD BOIL: 23 53 83 113  EARTH HUMMOCK: 10 35 60 85 110  INTER-HUMMOCK DEPRESSION: 10 25 40 55 70  4.9 0.4 -0.5 -1.0 -1.4  INTER-HUMMOCK DEPRESSION: 10 25 40 55 70  4.1 0.7 -0.4 -1.1 -1.5  E a r l i e s t date at which temperature was attained.  113 a c t u a l l y recorded at the hummock s i t e .  The most v a l i d comparison of near  surface temperatures, which can be made r e l i a b l y , i s between the hummock and adjoining inter-hummock depressions.  The mean ground temperature  recorded at a depth of 10 cms. (4 ins.) beneath the hummock was 2.7°C and 3.5°C higher than that recorded at an equivalent depth beneath the surfaces of the two depressions. The maximum ground temperature and the amplitude of the temperature f l u c t u a t i o n s also exceeded those i n the depressions by more than 5°C. Each of the s i t e s also e x h i b i t s a s i m i l a r pattern i n which the mean ground temperature and the amplitude of the temperature f l u c t u a t i o n s decreases w i t h increasing depth beneath the ground surface.  As Figure 14  shows, however, the rate of decrease i s not the same at each of the s i t e s . The most gradual decrease occurred beneath the centre of the mud b o i l where the mean ground temperature did not reach 0°C u n t i l depths of 75-80 cms. (29.5-31.5 ins.) below the surface, and the amplitude of the f l u c t u a tions was s t i l l i n excess of 3°C at a depth of 113 cms. (44.5 i n s . ) . These figures contrast w i t h those beneath the surface of the earth hummock where the mean ground temperature reached 0°C at a depth of 60-65 cms. (23.5-25.5 i n s . ) , and amplitudes i n excess of 3°C were not experienced below these depths.  The most r a p i d decrease of ground  temperatures, and diminishing of temperature f l u c t u a t i o n s , occurred beneath the surfaces of the inter-hummock depressions.  The mean ground  temperature dropped to 0°C at the shallow depths of 30-35 cms. (12-14 ins.) and amplitudes i n excess of 3°C were not recorded below 25-30 cms. (10-12 ins.) from the ground surface. The graphs i n Figure 14 and the values i n Table V I I I summarize the absolute magnitude of the ground temperature f l u c t u a t i o n s at each of  114  the s i t e s over the whole of the o b s e r v a t i o n p e r i o d .  The  c o n c e a l s the number and depth o f p e n e t r a t i o n of minor t i o n s which bear a d i s t i n c t mean d a i l y  a i r temperature.  p i c t u r e of these minor  general picture  temperature  fluctua-  temporal r e l a t i o n s h i p t o the changes i n the F i g u r e s 15 and 16 p r e s e n t a more d e t a i l e d  fluctuations  i n the ground  the p a t t e r n of isotherms over the same time  temperatures, by  showing  period.  The near s u r f a c e l a y e r s a t each of the s i t e s underwent a number of d e f i n i t e c y c l e s of warming and c o o l i n g over time p e r i o d s r a n g i n g from t h r e e to n i n e days.  The  l a r g e s t f l u c t u a t i o n s were r e c o r d e d  beneath the s u r f a c e o f the e a r t h hummock ( F i g u r e 15A), where  temperature  changes of as much as 7-8°C i n one day were observed at a depth of 10 (4 i n s . ) .  Maximum temperatures  almost immediate  a c h i e v e d d u r i n g these c y c l e s r e f l e c t e d  response to a warming of the ambient  w i t h l a g f a c t o r s i n v o l v e d b e i n g l e s s than one day. minor  surface.  l a r g e s t f l u c t u a t i o n s , over s i m i l a r  an  a i r temperatures  The p a t t e r n of these  f l u c t u a t i o n s a l s o shows a decrease i n amplitude w i t h  depth beneath the ground  cms.  At a depth of 35 cms.  increasing  (14 i n s . ) , the  time p e r i o d s , were, o n l y of the o r d e r  of 2-3°C or a p p r o x i m a t e l y 25 per cent of those r e c o r d e d at a depth of 10 cms. minor  (4 i n s . ) .  fluctuations  Below depths of 50 cms.  (19.5  i n s . ) most of these  are damped out c o m p l e t e l y , and the thermal regime  a g e n e r a l l y p r o g r e s s i v e warming t r e n d , w i t h the extremes  of the  shows  tempera-  t u r e r e c o r d o c c u r r i n g at the b e g i n n i n g ( c o l d e s t ) and end (warmest) of the observation period. The the mud  p a t t e r n of isotherms i n the ground beneath the s u r f a c e of  b o i l ( F i g u r e 16A)  hummock, due  is difficult  to compare w i t h those of the e a r t h  t o the p r e v i o u s l y - m e n t i o n e d d i f f e r e n c e  of the temperature  sensors.  Broad  comparisons  i n the depth s p a c i n g  w i t h the thermal regime i n  Figure 15  GROUND  TEMPERATURE AND  PATTERNS  ADJACENT  IN  AN  DEPRESSION  EARTH (°C)  HUMMOCK  Depth  911  in  Cms.  117 the earth hummock, however, show that the pattern of d a i l y f l u c t u a t i o n s i s s i m i l a r and extends to greater depths.  Figure 16A also shows the deeper  penetration of the 0°C isotherm beneath the surface of the mud b o i l , almost to a depth of one metre, compared w i t h a maximum depth of 70-75 cms. (27.5-29.5 ins.) beneath the centre of the earth hummock. The decrease of the minor temperature f l u c t u a t i o n s beneath one of the inter-hummock depressions surface layer experienced  i s shown i n Figure 15B. Although the near  as many cycles of alternate warming and cooling  as the earth hummock, comparisons of the temperature maxima, during corresponding  time periods, show that the near surface ground temperatures  beneath the depressions were 5-7°C cooler than at s i m i l a r depths beneath the centre of the earth hummock. As was noted i n the case of the o v e r a l l seasonal amplitudes, the minor temperature f l u c t u a t i o n s penetrated t o much shallower depths beneath the depressions than at any of the other s i t e s . Very few of the warm c y c l e s , f o r example, were f e l t below a depth of 25 cms. (10 ins.), and the maximum penetration of the 0°C isotherm was to a depth of 40 cms. (15.5 ins.) during the l a s t week of August.  Below  25 cms., the ground temperatures i n d i c a t e d a gradual, progressive warming with the extreme temperatures, shown i n Table V I I I , being recorded at the beginning  and end of the observation period. The data obtained i n the ground temperature studies are i n  accordance w i t h the r e s u l t s of the depth of thaw measurements.  Just as  vegetation, i n c l u d i n g the m i c r o r e l i e f f a c t o r , exerts a marked influence on the t o t a l depth of thaw to the f r o s t t a b l e , so i t also influences the ground temperature patterns i n the a c t i v e layer and uppermost parts of the underlying permafrost.  Thus the t o t a l depth of thaw was g r e a t e s t ,  and ground temperatures were highest, beneath unvegetated surfaces and  118 earth hummocks where the substrate was composed predominantly of mineral soil.  Conversely, the depth of thaw was lowest and the ground tempera-  tures were s e v e r a l degrees cooler beneath areas covered by mosses, and i n which the substrate was composed almost e n t i r e l y of organic m a t e r i a l . I n such l o c a l i t i e s , these lower values are probably r e l a t e d to the greater i n s u l a t i n g q u a l i t i e s of organic m a t e r i a l compared to mineral s o i l , the shade produced by m i c r o r e l i e f f a c t o r s , and the afore-mentioned  e f f e c t s of  the evaporation process. Freeze-Back i n the A c t i v e Layer, 1964. The graphs of the temperature penetrations and isotherms at each of the s i t e s show a temporary r e - f r e e z i n g of the surface layers i n response to below-freezing a i r temperatures at the end of August and during e a r l y September, 1965. Ground temperatures beneath the hummock centre were at or just below 0°C to depths of 20-25 cms. (8-10 ins.) f o r three days.  The cooling was not as pronounced i n the inter-hummock  depressions where the ground was frozen for one to two days to depths of 10-15  cms. (4-6 ins.) below the ground surface.  This c o o l i n g of the  ground from the surface downwards was replaced by a period of above-zero temperatures as the mean a i r temperature rose above the f r e e z i n g point again. Unfortunately, i t was not possible to remain i n the f i e l d and record the pattern of the freeze-back at each of the s i t e s .  A partial  record-of the freeze-back was obtained, however, for the mud b o i l s i t e for the three-month period September to December 1, 1964, using temperature values recorded by an a r c t i c thermograph.  The f u l l s i g n i f i c a n c e of  the f o l l o w i n g d i s c u s s i o n of the pattern of isotherms shown i n Figure 16B  . 119 i s l i m i t e d by the absence of any data p e r t a i n i n g to ambient a i r temperatures on the i s l a n d .  To p a r t i a l l y o f f s e t t h i s problem, the temperature  data f o r Tuktoyaktuk have been used as a guide. The mean d a i l y a i r temperature at Tuktoyaktuk f e l l below f r e e z i n g during the second week i n September.  The s t a r t of the freeze-  back on Garry I s l a n d probably began at t h i s time and, as F i g u r e 16B shows, the  0°C isotherm had penetrated to a depth of 23 cms. (9 i n s . ) by Sept-  ember 17.  F i g u r e 16B a l s o i n d i c a t e s that a f u r t h e r lowering of the ground  temperature d i d not take place u n t i l the beginning of the second week of October.  This slowdown i n the r a t e of downward penetration of the cold  may be a t t r i b u t e d to a s l i g h t warming i n the a i r temperatures, which f l u c t u a t e d around 0°C f o r most of the second half of September, but i t may a l s o be r e l a t e d to the moisture conditions of the s o i l .  Once the s o i l  temperatures reach the f r e e z i n g p o i n t , a further loss of heat may tempora r i l y be compensated by the release of the l a t e n t heat of f u s i o n as any moisture i n the s o i l i s converted to i c e . This c o n d i t i o n has been termed 12 the  'zero c u r t a i n ' .  The duration of the zero c u r t a i n condition i s de-  pendent p r i m a r i l y upon the quantity of moisture i n the s o i l .  Cook has  a l s o suggested that i t may be aided by the development of h y d r o s t a t i c pressure i n the unfrozen m a t e r i a l , between the downward penetrating f r o s t l i n e and the underlying permafrost t a b l e , r e s u l t i n g i n a lowering of the 13  f r e e z i n g point of the s o i l .  Recent i n v e s t i g a t i o n s by Mackay, u s i n g s o i l  pressure c e l l s , i n d i c a t e , however, that the r o l e of the h y d r o s t a t i c M u l l e r , S.W.  (1947) op_. c i t . , p. 17.  13 Cook, F.W. (1955) "Near surface s o i l temperature measurements at Resolute Bay, Northwest T e r r i t o r i e s " , A r c t i c , V o l . 8, p. 245.  120  pressure f a c t o r i s l i m i t e d by the low s o i l strength, and hence any de14  pression of the f r e e z i n g point i s quite small. Any depression of the f r e e z i n g point, either by h y d r o s t a t i c pressure or by the presence of minerals i n the s o i l water, complicates the i d e n t i f i c a t i o n of the zero c u r t a i n condition i n the temperature record. Since the tolerance of the thermistors was a l s o T. 0.2°C at 0°C, and the ground temperature records showed a number of days which f e l l i n the range -0.2°C  ure  to + 0 . 2 ° C , the i d e n t i f i c a t i o n of the zero c u r t a i n c o n d i t i o n i n F i g -  16B i s only an approximation. With these considerations i n mind, the duration of the zero  c u r t a i n at a depth of 2 3 cms. ( 9 i n s . ) beneath the surface of the mud  boil  was interpreted as being i n the order of 18 days (September 18 - October 6).  Meteorological records f o r Tuktoyaktuk i n d i c a t e that the mean d a i l y  a i r temperature dropped permanently below f r e e z i n g on October 9, and i n response to the lower a i r temperatures the downward penetration of the cold was resumed.  The 0°C isotherm reached a depth of 5 3 cms. ( 2 1 i n s . )  beneath the surface of the mud b o i l on October 2 6 , and the p o s i t i o n of the permafrost t a b l e , at a depth of approximately 85 cms. ( 3 3 . 5 i n s . ) , , was reached on November 6.  These dates correspond to indices of -245 and - 5 3 6  degree-days of f r e e z i n g r e s p e c t i v e l y f o l l o w i n g the drop i n a i r temperatures permanently below 0°C. Approximate c a l c u l a t i o n s of the duration of the zero c u r t a i n e f f e c t show that i t lasted f o r about 3 6 days  (September  20 - October 2 6 ) at a depth of 5 3 cms. ( 2 1 i n s . ) , and achieved i t s maximum duration, of as much as 48 days, at the permafrost t a b l e .  This general  pattern of an increasing length of the zero c u r t a i n time period w i t h depth Mackay, J . Ross.  Personal communication, October, 1 9 6 8 .  121 can be r e l a t e d to a slowdown i n the r a t e of f r e e z i n g , which i s p r o p o r t i o n a l to the square root of time, and a l s o probably to the presence of greater q u a n t i t i e s of s o i l moisture i n the lower parts of the a c t i v e l a y e r .  The  slow penetration of the f r o s t l i n e provides abundant time f o r the formation of segregated  i c e lenses encountered i n excavations made during the summer  months. The ground was frozen s o l i d l y by the end of the f i r s t week i n November and, as Figure 16B shows, the penetration of the c o l d continued w i t h only minor f l u c t u a t i o n s through to December 1.  Once temperatures of  -2 to -3°C were, a t t a i n e d , the l a g f a c t o r at depth was gradually diminished to the order of seven days throughout the complete p r o f i l e .  The temperat-  ure record was terminated on December 1st, and no f u r t h e r data were a v a i l a b l e concerning the continuation of the c o o l i n g process. The record of ground temperatures from the m o s s - f i l l e d depression surrounding the mud b o i l was f a r l e s s complete due to a malf u n c t i o n i n g of the recorder.  From the extremely  l i m i t e d ground  temperature data a v a i l a b l e , i t appears that the f r o s t l i n e i n t h i s ion had penetrated to a depth of 24 cms. of October.  depress-  (9.5 ins.) by about the beginning  A comparison w i t h the ground temperatures recorded at a  s i m i l a r depth beneath the unvegetated surface of the mud b o i l , i n d i c a t e s that the f r o s t l i n e had penetrated to t h i s l e v e l almost two weeks p r i o r to t h i s date.  The evidence suggests, therefore, that a surface layer of  vegetation, w h i l s t reducing the amount of thawing which takes place during the summer months, also retards the i n i t i a l penetration of the c o l d temperatures during the winter.  122 SUMMARY The  thickness  of the a c t i v e layer on Garry Island i s greatest,  i n excess of one metre (3 f e e t ) , i n areas having l i t t l e or no vegetation cover and where the substrate  i s composed p r i m a r i l y of mineral s o i l .  In  the vegetated areas of the i s l a n d , the maximum depths of thaw,v.60-70 cms. (24-28 i n s . ) , occurred beneath the r a i s e d centres of the 'Dry as-Hummocks'  1  and the t u s s o c k - l i k e forms of the Sheathed Cotton-grass (Eriophorum vaginatum) . In such l o c a l i t i e s , the thickness considerably  by the m i c r o r e l i e f f a c t o r and,  hummocks or tussocks the greater was  of the a c t i v e layer i s influenced i n general, the larger  the  the depth to the permafrost t a b l e .  Uniformly lower depths of thaw were recorded beneath vegetation associations with a s u b s t a n t i a l component of moss i n t h e i r f l o r a l composition, as i n the 'Sedge-Moss F l a t s ' and the inter-hummock or depressions, where the permafrost table was from 18-30  cms.  (7-12  inter-tussock  encountered at depths ranging  ins.) below the ground surface.  The  lower depths of  thaw are believed to be due to a combination of an organic substrate  be-  neath the moss, a higher moisture content and greater shade produced by the m i c r o r e l i e f . These observations were supported by evidence from studies  of  the changing p o s i t i o n of the f r o s t table beneath a small vegetation p l o t approximately 0.9  by 6.1 metres (3 by 20 feet) i n dimension.  Comparisons  of contour maps of t h i s p l o t r e v e a l an inverse r e l a t i o n s h i p between the configurations  of the ground surface and the permafrost table r e f l e c t i n g ,  at l e a s t i n p a r t , the s i g n i f i c a n c e of the m i c r o r e l i e f f a c t o r .  Elevated  parts of the ground surface allow heat to penetrate l a t e r a l l y from the sides as w e l l as v e r t i c a l l y from the top.  Excavations of the p l o t also  123 r e v e a l an inverse r e l a t i o n s h i p between the depth of thaw and the r e l a t i v e abundance of organic m a t e r i a l i n the substrate.  The greatest depths of  thaw, i n excess of 75 cms. (29,5 i n s . ) , occurred beneath the r a i s e d , unvegetated surface of a mud b o i l where the substrate was composed e n t i r e l y of mineral s o i l .  As the r a t i o of organic m a t e r i a l to mineral s o i l i n the  substrate increased, the depth of thaw decreased accordingly, and the e l e vated parts of the permafrost table were located beneath accumulations of organic m a t e r i a l f l o o r i n g depressions  i n the ground surface.  The complete removal of the vegetation cover from two earth hummocks r e s u l t e d i n an increase i n the depth of thaw of 135 per cent over'. that recorded i n c o n t r o l hummocks during a six-week period.  Where the  vegetation cover was only p a r t i a l l y removed, i n an attempt to d i s t i n g u i s h between the l i v i n g and dead components of the organic l a y e r , the corresponding increase i n the depth of thaw was 95 per cent.  Difficulties in  determining accurately the boundary between the l i v i n g and dead organic m a t e r i a l l i m i t the conclusiveness of the data, but the f i g u r e s i n d i c a t e that a layer of peat, 4-5 cms. (1.5-2.C/ ins.) t h i c k , was s u f f i c i e n t to produce a depth of thaw which was 17 per cent l e s s than that recorded i n the hummocks from which the organic layer was removed completely. The type of vegetation cover, m i c r o r e l i e f and composition of the substrate exert a s i m i l a r influence on the thermal regime of the a c t i v e layer and uppermost parts of the underlying.permafrost.  Ground temper-  ature, data obtained f o r four s i t e s on the i s l a n d - a mud b o i l , an earth hummock and two inter-hummock depressions  - e x h i b i t a s i m i l a r pattern i n  which the mean summer ground temperatures, and the amplitudes of the temperature f l u c t u a t i o n s , decreased w i t h i n c r e a s i n g depth beneath the ground surface.  The r a t e at which these decreases take place, however, i s  124 f a r from uniform.  The most gradual r a t e occurred i n mineral s o i l beneath  the. unvegetated surface of the mud b o i l , where the mean ground temperature f o r the summer d i d not reach 0°C u n t i l a depth of 75-80 cms. (29.5-31.5 i n s . ) , and the amplitude of the temperature f l u c t u a t i o n s was s t i l l i n excess of 3°C at a depth of 113 cms. (44.5 i n s . ) .  I n comparison, a s i m i l a r  mean temperature and magnitude of amplitude occurred a t a depth of 60-65 cms. (23.5-25.5 ins.) beneath the vegetated surface of the earth hummock. The most r a p i d decrease of ground temperatures and diminishing of the temperature f l u c t u a t i o n s took place i n the organic substrate beneath the moss-covered  surfaces of the inter-hummock depressions, where a mean  summer ground temperature of 0°C occurred at the shallow depth of 30-35 cms. (12-14 i n s . ) , and amplitudes i n excess of 3°C were not recorded below 25-30 cms. (10-12 ins.) from the ground surface. Ground temperature data f o r the freeze-back i n the mud b o i l f o r the winter of 1964 i n d i c a t e that the zero c u r t a i n c o n d i t i o n l a s t e d approximately 18 days at a depth of 23 cms. (9 i n s . ) below the ground surf a c e , 36 days a t a depth of 53 cms. (21 i n s . ) , and achieved a. maximum duration of as much as 48 days a t the permafrost t a b l e .  This general  pattern of an i n c r e a s i n g length of the zero c u r t a i n time period w i t h depth can be r e l a t e d to a r e t a r d a t i o n of the r a t e of f r e e z i n g and a l s o probably to the presence of greater q u a n t i t i e s of s o i l moisture i n the lower parts of the a c t i v e l a y e r .  The slow penetration of the f r o s t l i n e a l s o provides  abundant time f o r the formation of the segregated i c e lenses encountered i n excavations made during the summer months.  CHAPTER V GEOMORPHOLOGICAL PROCESSES  The purpose of t h i s chapter, and one of the major aims of t h i s t h e s i s , i s to assess some of the contemporary geomorphic processes opera t i n g on Garry I s l a n d .  The s p e c i f i c processes considered involve problems  associated w i t h c o a s t a l r e c e s s i o n , mudslumps, mudflows, and the genesis of c e r t a i n types of patterned ground.  I n each case, wherever a p p l i c a b l e , an  emphasis i s placed on q u a n t i t a t i v e measurements of the r a t e s i o f operation of these processes, and an evaluation of the various f a c t o r s , e s p e c i a l l y the r o l e of permafrost, i n f l u e n c i n g these r a t e s .  COASTAL RECESSION Rapid recession of many sections of the c o a s t l i n e between Point Barrow, Alaska and Langton Bay, N.W.T. , i n p o s t - g l a c i a l and h i s t o r i c times, has been described by several authors c i t i n g both geomorphological and h i s t o r i c evidence.  L e f f i n g w e l l , using maps of the region drawn by  F r a n k l i n i n 1826, reported erosion r a t e s of as high as 30.5 metres (100 feet) a year at Cape Simpson, northern A l a s k a , but concluded that the average r e t r e a t was less than 1.2 metres (4 f e e t ) per annum.''" MacCarthy measured rates of r e t r e a t at Point Barrow ranging from 0.0-4.5 metres  L e f f i n g w e l l , E de K. (1919) "The Canning R i v e r r e g i o n , northern Alaska", U.S.G.S. P r o f e s s i o n a l Paper, No. 109, pp. 169-171.  126 (0.0-14.7 feet) a year.  Mackay has described both geomorphological and  h i s t o r i c a l evidence i n d i c a t i n g s i m i l a r l y r a p i d rates of recession along 3  sections of the c o a s t l i n e i n the Yukon and Northwest T e r r i t o r i e s . Despite the abundant evidence of c o a s t a l r e t r e a t , many of the rates quoted are at best approximations only.  In the h i s t o r i c evidence there are prob-  lems r e l a t i n g to the accuracy of the early maps.  Unfortunately, many of  the distances from the c o a s t l i n e to i d e n t i f i a b l e c o n t r o l points were estimated, thus precluding the c a l c u l a t i o n of accurate rates of c o a s t a l recession.  S i m i l a r l y , the lack of a d e t a i l e d c h r o n o l o g i c a l scale f o r the  area l i m i t s the v a l i d i t y of rates using geomorphic evidence based on the t o t a l recession which has taken place i n a p o s t - g l a c i a l period of, as y e t , unknown duration. Accordingly, a programme of f i e l d studies was Garry I s l a n d f o r the dual purposes of:  conducted on  (1) providing exact data on the  annual rates of recession along c o a s t l i n e s of varying l i t h o l o g y ; and  (2)  i n v e s t i g a t i n g the nature and r e l a t i v e importance of the s p e c i f i c processes which contribute to the observed r e t r e a t values. Evidence of Coastal  Recession.  A c t i v e recession of the Garry I s l a n d c o a s t l i n e , apart from a few l o c a l mudslump f e a t u r e s , c u r r e n t l y i s r e s t r i c t e d p r i m a r i l y to the exposed west and northwest coasts, and to segments of the prominent sand  2 MacCarthy, G.R. (1953) "Recent changes i n the shoreline near Point Barrow, Alaska", A r c t i c , V o l . 6, pp. 44-51. 3 Mackay, J . Ross (1958) "The Anderson River Map Area, N.W.T.", Geographical Branch Memoir, No. 5, pp. 39-40. Mackay, J . Ross (1963) "Notes on the shoreline recession along the coast of the Yukon T e r r i t o r y " , A r c t i c , V o l . 16, pp. 195-197.  127 headlands on the north side of the i s l a n d .  In these l o c a l i t i e s , the  b l u f f s are c h a r a c t e r i z e d by numerous f r e s h exposures w i t h debris p i l e s on, and at the base of, the c l i f f face, and by an absence of vegetation on the faces. H i s t o r i c a l evidence of c o a s t a l r e c e s s i o n on Garry I s l a n d i s a v a i l a b l e but does not y i e l d s a t i s f a c t o r y q u a n t i t a t i v e data.  In a recent  survey, Captain Ages, of the C.S.S. 'Richardson , r e f e r s to a number of 1  hydrographic c o n t r o l p o i n t s , located i n 1930, i n the outer Mackenzie A  Delta.  Of twelve c o n t r o l points shown on P e l l y , K e n d a l l and Whale  (Grassy ?) Islands i n the o r i g i n a l survey, Captain Ages concluded that f o u r , a l l located on P e l l y I s l a n d , had disappeared possibly due to erosion; i n s i x cases, only remnants of the markers remained w i t h the c o l l a p s e frequently a t t r i b u t a b l e to caving i n of the ground; and only two of the markers were s t i l l i n t a c t .  The p o s s i b i l i t y e x i s t s that one of the markers  on K e n d a l l I s l a n d had been moved by n a t i v e s . The 1930 survey a l s o shows the locations of three hydrographic c o n t r o l points on Garry I s l a n d .  Ground  checks made i n 1965 revealed no trace of one of these markers; a second (possibly dismantled), was found on the f l o o r of an i n a c t i v e mudslump, but the t h i r d marker, located on the southeast t i p of the i s l a n d , was collapsed on the c l i f f face (Plate VI-A);.  found  Unfortunately, no f i g u r e s are  a v a i l a b l e i n d i c a t i n g the distance of these c o n t r o l points from the o r i g i n a l c l i f f edge, thereby preventing any r e l i a b l e estimate of the r a t e of c o a s t a l r e c e s s i o n i n recent h i s t o r i c time. A d d i t i o n a l evidence of c o a s t a l recession i n h i s t o r i c times can Ages, Captain A.B. Personal communication to Dr. J . Ross Mackay, J u l y 4, 1965. The exact date of the hydrographic survey i n 1930 i s not mentioned.  Plate VI COASTAL  RECESSION  A. C o l l a p s e d hydrographic marker on the c l i f f f a c e along the south coast of Garry I s l a n d .  B. C o a s t a l r e c e s s i o n a l o n g the northwest coast of Garry I s l a n d showing a t r u n c a t e d lagoon.  C. Measurement of c o a s t a l recession rates. Stakes a l o n g the northwest coast of Garry I s l a n d .  129 possibly be i n f e r r e d from the 'disappearance' of i s l a n d s i n the outer d e l t a area.  S i r Alexander Mackenzie's account of the panoramic v i s t a from  Whale (Garry) I s l a n d includes a reference to two small i s l a n d s i n the i c e l y i n g to the northwest by compass d i r e c t i o n . ^  Even a l l o w i n g f o r discrep-  ancies i n Mackenzie's d i r e c t i o n a l observations, there are no i s l a n d s i n that p o s i t i o n today and i t i s possible that they have been removed subsequently by wave a c t i o n .  A l t e r n a t i v e l y , as Mackay has suggested, Mack-  enzie may have observed two patches of d i r t y i c e covered w i t h debris derived from the Mackenzie River break-up.  7  A l b e r t O l i v e r , a native of  the area and our guide during the f i e l d seasons, also t e l l s of the former existence of a small i s l a n d , to the south of Hooper I s l a n d , which has been destroyed by wave a c t i o n during h i s l i f e t i m e . Topographic and s t r a t i g r a p h i c evidence of c o a s t a l recession over even longer periods of time y i e l d s s i m i l a r l y inconclusive r e s u l t s w i t h respect to a c t u a l rates of c l i f f r e t r e a t .  Features developed along  the northwest coast of the i s l a n d include an example of a truncated lagoon, w i t h a s t r a i g h t c o a s t a l shore b a r r i e r and a c t i v e l y receding c l i f f s on e i t h e r side (Figure 17 and P l a t e VI-B) .  Raised, shoreline, features can a l s o  be traced to the coast i n many places, but no evidence of them can be found  Mackenzie, A. (1801) Voyages from Montreal on the River S t . Laurence through the continent of North America to the Frozen and P a c i f i c Oceans j n the years 1789 and 1793, T. C a d e l l , Jun. and W. Davies, Strand; Cobbett and Morgan, P a l l M a l l ; and W. Creech at Edinburgh. Reprinted e d i t i o n (1966) i n March of America F a c s i m i l e S e r i e s , Number 52, U n i v e r s i t y M i c r o f i l m s Inc., Ann Arbor, Michigan, p. 63. Stager, J.K. (1965) "Alexander Mackenzie's e x p l o r a t i o n of the Grand R i v e r " , Geographical B u l l e t i n , V o l . 7, p..,231. Mackay, J . Ross (1963) "The Mackenzie Delta area, N.W.T.", Geographical Branch Memoir, No. 8, p. 6. 7  Figure 17  C O A S T A L  RECESSION  NORTHWEST  COAST  OF GARRY  Truncated  Tundra  p o l y g o n s on c l i f f  Stake  High  centred  top  #95  #31  p o l y g o n s on c l i f f  top  Stake x*"^  Mudslumps Polygonal Scale  Ground  1:17,000  lag  polygons  Stake  Tundra  FEATURES  (Approximate!  #1  ISLAND  131 i n s t r a t i g r a p h i c sections exposed i n the c l i f f s .  The l o n g i t u d i n a l p r o f i l e s  of stream courses d r a i n i n g towards the south coast of the i s l a n d e x h i b i t a c h a r a c t e r i s t i c steepening of the gradient i n the lower parts, which may also r e f l e c t the e f f e c t s of downcutting i n response to c o a s t a l r e c e s s i o n combined w i t h mudslump development.  Exposures along the northwest coast  of the i s l a n d r e v e a l a sequence of l a c u s t r i n e and peat deposits (see F i g u r e 6), and the tops of the high b l u f f s i n places along t h i s same c o a s t l i n e are capped by a truncated s e r i e s of tundra polygons (Figure 17).  The l a c -  u s t r i n e and peat deposits, exposed i n these s e c t i o n s , are i n d i c a t i v e of freshwater conditions which could only have been produced as a r e s u l t of ponding behind a b a r r i e r , since removed, on the seaward margins of the topographic depressions i n which they occur. Thus there i s abundant evidence that the c o a s t l i n e of Garry I s l a n d has undergone considerable r e c e s s i o n i n recent g e o l o g i c a l and h i s t o r i c a l time.  Just how much recession has taken place, and at what r a t e ,  i s impossible to determine, but there may be some s i g n i f i c a n c e i n the f a c t that the depth of water f o r 16-24 kilometres (10-15 miles) o f f the shore of Garry I s l a n d averages only 4-5 fathoms.  Such uniformly shallow depths  may represent an extensive platform of marine p l a n a t i o n , though the possi b i l i t y that i t i s p a r t i a l l y a product of d e l t a i c sedimentation cannot be excluded. Coastal Stake Measurements. Approximately 2.5 kilometres (1.5 miles) of c o a s t l i n e were staked during the summer of 1964 to provide q u a n t i t a t i v e data on the current r a t e s of c o a s t a l r e c e s s i o n ( P l a t e VI-C). . A t o t a l of 95 stakes was i n s t a l l e d along the exposed northwest coast where the b l u f f s l o c a l l y  132 exceed 30.5 metres (100 feet) i n height (Figure 17).  The p o s i t i o n s of  these stakes were checked p e r i o d i c a l l y throughout each of the summers, and the amount of recession was recorded i n metres at the beginning and end of each summer.  Since the exposures i n these b l u f f s covered a wide range of  m a t e r i a l s , ranging from f i n e - g r a i n e d s i l t s and c l a y s , which i n places contained large bodies of segregated ground i c e , to coarse sands and boulders, the data permitted a ready evaluation of the e f f e c t of l i t h o l o g y on the r a t e of r e c e s s i o n . Comparisons of the amount of r e t r e a t recorded at the beginning of the summer w i t h that recorded at the end of the previous summer a l s o gave i n d i c e s of v a r i a t i o n s i n the r a t e of r e c e s s i o n through the year. Average r e t r e a t f i g u r e s tabulated i n August, 1966 showed that the average r a t e of r e c e s s i o n f o r the 95 stakes was 6.4 metres (20.8 f e e t ) , or 2.1 metres (6.9 feet) per annum. As expected, however, t h i s average covered a wide range of i n d i v i d u a l values which ranged from a maximum of 30.6 metres (100.4 feet) to a minimum of 0.1 metres (0.3 f e e t ) . Thirty-one of the stakes were located along a s e r i e s of high b l u f f s ranging from 9.0-30.5 metres (30-100 feet) i n e l e v a t i o n .  Sediments  exposed i n t h i s s e c t i o n of the c o a s t l i n e were f i n e sands, s i l t s or c l a y s , and bodies of segregated ground i c e were v i s i b l e where the c l i f f s cut across the d i s t i n c t i v e scars of o l d mudslumps.  In a d d i t i o n , the tops of  the c l i f f s a l s o cut across a series of well-developed, high-centred tundra polygons and associated network of ice-wedges.  The highest r e t r e a t values  were recorded where the c l i f f s i n t e r s e c t e d and r e a c t i v a t e d a number of o l d mudslumps, and i n these l o c a l i t i e s the average r e c e s s i o n amounted to 20.9 metres (68.6 f e e t ) , or 7 metres (23 f e e t ) a year. (Plate VT.I.-A-) . ...The e f f e c t s of segregated ground i c e were shown by the v a r i a b l e rates of r e c e s s i o n  133  Plate VII COASTAL  A.  Coastal  recession i s  most r a p i d where action  RECESSION  wave  has exposed  of  segregated  in  the c l i f f s .  bodies  ground i c e  B.  The detachment  centred the  cliff  melting the  C. left  Mineral  soil  pinnacle  by t h e c o l l a p s e o f a  tundra  polygon.  tundra  of a  polygon  highfrom  top as a r e s u l t  along  the lines of  ice-wedges.  of  134 recorded by f i v e stakes (#21-25), located, across one of these slumps. During the summer of 1964, no ground i c e was exposed at these points and the average r e t r e a t during the summer was only 3.5 metres (11.5 f e e t ) . Towards the end of that summer, however, a large block was detached from the c l i f f face, and ground i c e was v i s i b l e throughout the summers of 1965 and 1966, when the average r a t e of r e t r e a t increased to 10.5 metres (34.4 feet) per summer.  High rates of recession were a l s o observed i n the areas  of tundra polygons, where melting along the l i n e s of the ice-wedges r e s u l t ed i n an average recession of the c l i f f face of 15.3 metres (50 f e e t ) , or s l i g h t l y more than 5 metres (16.4 feet) a year.  The intervening  polygonal  peat u n i t s showed a much more v a r i a b l e r a t e of r e c e s s i o n , averaging 2.5 metres (8.2 feet) a year.  only  Since the peat i n these polygons forms a  coherent u n i t , which i s undermined by thawing of the i c e - r i c h basal l a y e r s , the rates of recession show a wide range from summer to summer.  I n any  one summer, large overhangs, i n the order of several metres, may be produced w i t h l i t t l e or no m a t e r i a l a c t u a l l y being detached from the c l i f f edge.  By way of contrast, the f o l l o w i n g summer may be characterized by  continued undermining and eventual c o l l a p s e of the complete polygon, and a sudden r e t r e a t of the c l i f f edge by 7-10 metres (23-33 feet) (Plates VII.-B and VllfeC). Sediment types exposed i n the remaining s e c t i o n of the coastl i n e were much more uniform, and consisted of coarse sands and gravels w i t h minor v a r i a t i o n s caused by the development of polygonal ground.  The  average t o t a l r a t e of r e t r e a t along t h i s part of the coast amounted to only 2.6 metres (8.6 feet) or less than one metre (3 feet) per annum.  The  f i g u r e i s even l e s s , .0.6 metres (2 feet) a year, i f a small slump (average 2.7 metres or 8.9 f e e t ) , ice-wedges (average 1.2 metres or 4 f e e t ) , and  135 peat sections (average 0.7 metres or 2.3 feet) are excluded from the c a l culations. In a d d i t i o n to q u a n t i t a t i v e values of a c t u a l rates of recession,  the data also i n d i c a t e that most of the r e t r e a t occurs during the  short summer period.  For most of the year, sea i c e i s packed close to the  shore, and the b l u f f s are buried by large snow d r i f t s which p e r s i s t through l a t e June and e a r l y J u l y .  The measurements show that f u l l y 60-70 per cent  of the observed r e t r e a t occurred during the summer months.  Unfortunately,  i t was not p o s s i b l e to remain i n the f i e l d u n t i l freeze-up occurred, when t h i s percentage would be even higher.  Much of the r e t r e a t recorded between  the l a s t observation of one summer and the f i r s t ing  observation of the f o l l o w -  summer probably represents f u r t h e r detachment of m a t e r i a l from the  c l i f f edge during the month of September. Sand Headland P r o f i l e Studies. Two prominent sand headlands on the north side of the i s l a n d were selected as s u i t a b l e s i t e s f o r d e t a i l e d studies of c l i f f changes throughout the summer months.  profile  These headlands terminate i n abrupt  c l i f f faces, 7-12 metres (23-39 feet) high, many sections of which are c u r r e n t l y undergoing a c t i v e recession as i s i n d i c a t e d by the numerous f r e s h exposures and lack of vegetation on the c l i f f face.  Stable sections  of the c o a s t l i n e , mantled to some degree w i t h a vegetation cover, can be a t t r i b u t e d l a r g e l y to the development of a p r o t e c t i v e sandspit formation at the base of the c l i f f s  ( P l a t e VIIL-A).  The c l i f f s have a f a i r l y s t r a i g h t , uniform appearance, and are generally devoid of g u l l y i n g except f o r the presence of deep 'V'-shaped notches created by the melting out of ice-wedges.  The m a t e r i a l i n these  136 Plate VIII S A N D  H E A D L A N D  A. S t a b i l i z e d c l i f f s o f the sand headland a r e a s p r o t e c t e d by s a n d s p i t s .  C. C r e v i c e s on t h e sand headland surface p r i o r to the detachment of hummock b l o c k s from the edge of the c l i f f .  PROFILE  STUDIES  B. P r o f i l e IV, J u l y 1965, showing the l o c a t i o n s of the stakes.  D.  P r o f i l e I , August  after  1965,  slumping of the thawed  sand had t a k e n p l a c e .  137 headlands i s composed predominantly of medium to coarse sands, w i t h i n t e r calated bands of pebbles, g r a v e l , wood and s h e l l fragments.  Boulders are  generally l a c k i n g , but l o c a l l y they may occur i n s u f f i c i e n t q u a n t i t i e s to dominate the whole exposure. Four l o c a t i o n s , c u r r e n t l y undergoing a c t i v e r e c e s s i o n , were chosen f o r the p r o f i l e studies.  Each of these p r o f i l e s was surveyed at  the beginning and end of the 1965 f i e l d season, and P r o f i l e IV was surveyed again during the summer of 1966. shown i n Figures 18 and 19.  The r e s u l t s of these surveys are  To o b t a i n data on c l i f f p r o f i l e changes over  1-2 weeks, a procedure was adopted s i m i l a r to that used by Twidale i n h i s Q  study of r i v e r bank erosion i n South A u s t r a l i a .  At each s i t e , wooden  dowelling, approximately 45 cms. (18 ins.) i n length and 2.5 cms.  (one  inch) i n diameter, was driven i n t o the c l i f f f a c e , normal to the surface, and the stakes were spaced at approximately equal i n t e r v a l s w i t h only a small portion of each l e f t exposed (Plate VIII'-B). The p o s i t i o n s of these stakes on the four p r o f i l e s are also shown i n Figures 18 and 19.  In each  p r o f i l e , stake 1 was i n s t a l l e d on the headland surface to act as a c o n t r o l p o i n t , and the distance to the edge of the c l i f f was recorded.  The remain-  ing stakes on each p r o f i l e were numbered consecutively from top to bottom of the c l i f f .  Reference to i n d i v i d u a l stakes i n the text a l s o follows the  system used by Twidale:  e.g. stake (1,4) r e f e r s to P r o f i l e I , stake 4.  The v i s i b l e length of the stake was measured and recorded, and at subsequent observations the procedure was repeated so that an increase, or decrease, i n the length of the stake exposed i n d i c a t e d whether e r o s i o n , °Twidale, C.R. (1964) "Erosion of an a l l u v i a l bank at Birdwood, South A u s t r a l i a " , Z e i t s c h r i f t f u r Geomorphologie, Band 8, pp. 189-211.  138 Figure 18  SAND  Profiles  on  HEADLAND  August  1 Positions  of  stakes  31,1965  PROFILES  (I)  139  Figure 19  SAND  HEADLAND  Profiles  on  July  5, 1965  Profiles  on  August 31,1965  1 !  — S.L.—  Positions  Sea  of  stakes  Level  SCALE 0  5 METRES  PROFILES  (2)  140 or d e p o s i t i o n , was taking place.  These changes, measured over two-weekly  periods, were too small to i l l u s t r a t e diagrammatically, and are summarized in Table IX.  At the same time as these readings were being made, a metal  probe was used to determine the approximate thickness of the thawed layer on the c l i f f face. When the p r o f i l e s were f i r s t surveyed i n e a r l y J u l y ,  1965,  l a t e - l y i n g snow d r i f t s s t i l l remained at the foot of the c l i f f s and, i n '9 P r o f i l e I , extended as high as stake (1,8).  The absence of any marked  concentrations of debris on the snow surface i n d i c a t e d that l i t t l e or no m a t e r i a l had been dislodged from the c l i f f face p r i o r to the i n s t a l l a t i o n of the stakes.  Probing revealed that the thawed zone on the c l i f f face  extended to depths of 15-20  cms.  (6-8 i n s . ) , producing an unstable layer  of loosely-packed sand at the surface. The general forms of the p r o f i l e s are shown i n Figures 18 and 19.  The uppermost morphological f a c e t i n each p r o f i l e c o n s i s t s of a small  v e r t i c a l element, u s u a l l y 0.5^1.0 metres (1.5-3.5 feet) high, and accompanied by a short overhang r e f l e c t i n g the binding e f f e c t of the vegetation on the headland surface.  Small earth hummocks dominate t h i s vegetation  a s s o c i a t i o n , and i n many places lunate tension cracks p a r a l l e l the c l i f f edge on the landward sides of these hummocks ( P l a t e V H I - C ) . f a c e t , the p r o f i l e c o n s i s t s e s s e n t i a l l y  Below t h i s  of a f a i r l y uniformly s l o p i n g  element, of 40-50° i n c l i n a t i o n , which i n many cases extends to the base of the p r o f i l e where i t terminates at the beach l e v e l . however, the j u n c t i o n w i t h the beach may  Ih other places,  be more or less obscured by f a l l e n  The other, lower stakes on t h i s p r o f i l e were i n s t a l l e d prog r e s s i v e l y as the snowbank melted.  141  TABLE I X  SAND HEADLAND P R O F I L E CHANGES  Stake #  Profile  I  Profile I I  Profile  III  Profile  IV  .  1  0  0  0  0  (  P )  2  -1  -4  -11  0  (  o )  3  -8.5  -2  -11  - 1.5  (-29.5)  4  -9  -3  -10  - 7  (-16.0)  5  -7  -0.5  - 1  -11  (-22.0)  6  -4.5  -0.5  -10  - 4.  (- 9.0)  7  -5  +1.5  - 9  - .0.5  (- 3.5)  8  -2.5  +1.5  + 2.5  - 2  (+ 3.0)  9  0  +0.5  + 3  + 6  (+23,0^  10  +1  +9  + 6  + 7  (+20.5)  11  +2.5  +7  + 6  + 6  (+17.0)  12  +5  + 2  + 3  (+12. 0}  13  +6.5  0  + 3  (+10.0)  14  +4.5  0  + 6  (+14.0)  15  +6  16  +4  17  0  The f i g u r e s a r e i n c e n t i m e t r e s a n d r e f e r t o t h e p e r i o d J u l y 5 A u g u s t 22, 1965, w h e n t h e l a s t m e a s u r e m e n t s w e r e r e c o r d e d . The f i g u r e s i n b r a c k e t s f o r P r o f i l e I V i n d i c a t e t h e l e n g t h o f s t a k e e x p o s e d o n A u g u s t 22, 1966. Negative values r e f e r t o erosion of t h e c l i f f f a c e , w h i l e p o s i t i v e f i g u r e s r e p r e s e n t t h e a c c u m u l a t i o n o f d e b r i s d e r i v e d from upper s e c t i o n s of t h e p r o f i l e s .  142 debris composed of sand, detached hummocks which show d i s t i n c t signs of washing by wave a c t i o n , and driftwood.  Occasionally, some of the hummocks  come to r e s t on the c l i f f face before reaching the beach l e v e l , and these ;  are responsible for. most of the minor i r r e g u l a r i t i e s shown on the profiles. Comparisons of Figures 18 and 19 and Table IX show that the changes, recorded by the stake measurements account f o r only a minor portion of the t o t a l p r o f i l e changes through the e n t i r e summer. For the period J u l y 5 - August 22, 1965, of the 56 stakes i n s t a l l e d on the four p r o f i l e s , a t o t a l of 23 experienced  an increase i n the length of stake  exposed, i n d i c a t i n g , erosion of the upper sections of the p r o f i l e s . average r a t e of erosion recorded by these stakes amounted to 5.4 (2.2 i n s , ) , with maxima of 11.0. cms.  (4.3 i n s . ) .  The cms.  A f u r t h e r 24 stakes i n -  dicated that deposition had taken place on the lower sections of the . p r o f i l e s , averaging 4.2 cms. (2.4^2.8 i n s . ) .  By way  (1.7 ins.) and reaching maxima of 6-7  cms.  of c o n t r a s t , measurements.taken from the surveyed  diagrams of P r o f i l e s I - I I I show that the upper portions of the c l i f f faces:experienced  a r e t r e a t of 75-100 cms.  (29.5-39.5 ins.) over the  s l i g h t l y longer period ending, August 31, 1965.  The l o s s e s , or erosion,  recorded by the stake.measurements therefore account f o r only 5-6 per cent of the t o t a l p r o f i l e changes, despite the f a c t that they cover approximately 85 per cent of the observation period.  S i m i l a r percentages are  a l s o a p p l i c a b l e to the rates of deposition recorded on the lower parts of the p r o f i l e s . Coincident with these.changes i n d i c a t e d by the.stake measurements, the depth of the thawed zone on the c l i f f face increased to 50-65 cms.  (19.5-25,5 ins.) by August 1, and to 90-100 cms.  (35.5-39.5 ins.) by  143 August 2 2 . Beginning i n l a t e J u l y and early August, prominent cracks, extending f o r several metres across the face of the c l i f f and to depths of 10-20 cms. (4-8 i n s . ) , appeared i n many places i n the upper sections of the p r o f i l e s .  L o c a l l y , as i n P r o f i l e I , the appearance of these cracks  was followed by minor slumping a c t i o n . New cracks also opened up along the boundaries of the hummocks on the headland surface, and p r e - e x i s t i n g cracks were widened and deepened as the hummocks t i l t e d b o d i l y towards the c l i f f edge. In d i r e c t contrast to t h i s long period of r e l a t i v e  stability,  during which the p r o f i l e s underwent slow changes, the events observed i n P r o f i l e s I - I I I w i t h i n the l a s t week of August can only be described as catastrophic.  By August 31, only the three stakes located on the headland  surface as c o n t r o l points remained i n t a c t , and the remainder had been comp l e t e l y o b l i t e r a t e d by mass slumping of the thawed sand from the upper parts of the c l i f f faces ( P l a t e V I I I - D ) .  I n P r o f i l e s I and I I I , the earth  hummock at the top of the p r o f i l e was also detached from the c l i f f edge. As Figure 19 and Table IX show however, slumping d i d not take place on P r o f i l e IV during that summer, nor the f o l l o w i n g summer of 1966, and most of the changes observed i n t h i s p r o f i l e are i n d i c a t e d by the a d d i t i o n a l f i g u r e s i n Table IX.  Towards the end of August, 1966, however, the  hummock was also detached from the top of t h i s p r o f i l e , and a number of stakes was e i t h e r broken or t i l t e d during i t s f a l l .  No attempt was made  to record f u r t h e r changes i n P r o f i l e s I - I I I f o l l o w i n g the slumping, but two stakes were r e l o c a t e d i n the upper part of P r o f i l e I to see whether slumping occurred again during the summer. place at the end of August, 1966.  These stakes were s t i l l i n  144 Relevance of the P r o f i l e Studies to other Coastal Areas.  The  sand headlands were chosen f o r the p r o f i l e studies because the slow r a t e of  change permitted ample time to study the processes involved.  I t was  evident, however, that s i m i l a r changes and processes to those observed on the sand headlands a l s o apply to the t r a c t s of staked c o a s t l i n e on the northwest shore of the i s l a n d .  As noted p r e v i o u s l y , many of the  cliffs  along t h i s section of the coast are a l s o composed of sands and gravels which l o c a l l y are capped by v a r v e - l i k e l a c u s t r i n e sediments and i n t e r sected by a network of ground ice-wedges.  The r e t r e a t f i g u r e s recorded i n  these l o c a l i t i e s correspond w e l l w i t h those made on the sand headlands, and the general appearance of the c l i f f p r o f i l e s i n d i c a t e s that the method of c l i f f r e t r e a t i s the same. In the f i n e r - g r a i n e d sediments the processes are probably the same but d i f f e r i n degree.  This d i f f e r e n c e can r e a d i l y be a t t r i b u t e d to  the higher i c e content of these sediments.  The larger q u a n t i t i e s of water  released on thawing of t h i s m a t e r i a l , together w i t h the f a c t that the c l i f f faces are u s u a l l y much steeper, and frequently v e r t i c a l , preclude the accumulation of any appreciable thickness of thawed m a t e r i a l at the surface.  Frequent probing of the c l i f f s  showed that the thickness of t h i s  thawed layer seldom exceeded 10-15 cms. (4-6 i n s . ) .  The i c e i n these sed-  iments i s also predominantly pore i c e , l o c a l l y augmented by v e i n i c e along bedding and shear planes, but moisture contents are commonly i n the order of  100 per cent by weight, and thawing produces a r e l a t i v e l y mobile mud  which soon s l i d e s to the base of the c l i f f and provides a f r e s h exposure. Whereas slumping i n the sands may have a maximum frequency of only once during an e n t i r e summer, i t may occur d a i l y , or more o f t e n , i n these f i n e r - g r a i n e d sediments.  The r a t e i s even higher i n the c l i f f s w i t h  145 exposures of segregated ground i c e which have moisture contents i n the order of several thousand per cent by weight.  Thawing of the c l i f f s i n  these l o c a l i t i e s produces large q u a n t i t i e s of excess water, and the i n t e r v a l between thawing and slumping of the m a t e r i a l to the foot of the c l i f f reaches a minimum. Coastal recession i n areas where the c l i f f s  intersect well-  developed networks of tundra polygons produces a > d i s t i n c t i v e topography. In such l o c a l i t i e s , as was the case i n the sand headlands, recession takes place most r a p i d l y along the l i n e s of the ice-wedges. are  Where the polygons  of the high-centred type and are located on the tops of the b l u f f s ,  r a p i d melting a l s o occurs i n the basal sections of the polygonal u n i t s which a l s o contain large q u a n t i t i e s of segregated ice,.-. M e l t i n g out of the ice-wedges, w i t h an o r i e n t a t i o n normal to the c l i f f edge, exposes a d d i t i o n a l wedges which l i e p a r a l l e l to the c l i f f , and the subsequent melting of these leads to an i s o l a t i o n of the polygonal u n i t from the main face of the bluff.  In t h i s way a peat block i s formed which r e s t s precariously on a  pedestal of mineral s o i l .  Further melting of the high ice-content basal  sections of the polygon r e s u l t s i n f u r t h e r undermining of the peat block which f i n a l l y tumbles, u s u a l l y i n t a c t , to the foot of the c l i f f , behind d i s t i n c t i v e pinnacles of mineral s o i l ( P l a t e VII-C).  leaving  Under favour-  able c o n d i t i o n s , a complete tundra polygon, up to 10 metres (33 feet) i n diameter, may be removed i n t h i s manner during the course of a s i n g l e summer. Processes at work i n Coastal Recession. From the preceding paragraphs, i t i s quite evident that the c o a s t l i n e of Garry i s l a n d i s r e t r e a t i n g p r i m a r i l y as a r e s u l t of 'thermal  146 erosion', or thawing of the frozen ground, accompanied by slumping of the thawed m a t e r i a l .  Coastal sections composed of sediments w i t h a. high ..  moisture content, p a r t i c u l a r l y i n the. form of i c e segregations, are natura l l y the most susceptible to the sun's rays, and t h i s i s r e a d i l y  substan-  t i a t e d by the observed r e t r e a t f i g u r e s . The m a t e r i a l i n the sand headlands has a frozen moisture content of only 15-20 per cent by weight, and i t was i n b l u f f s composed of these and coarser sediments that the lowest r e t r e a t values were recorded. In t h e i r frozen s t a t e , the water i s present i n the form of pore i c e which acts as a strong cementing agent, but melting of t h i s i c e r e s u l t s i n a considerable l o s s of strength and transforms the sand i n t o a l o o s e l y packed mass.  As the summer progresses, the f r o s t t a b l e r e t r e a t s f u r t h e r  i n t o the c l i f f face and, as the thickness of the thawed zone increases, the surface layer becomes i n c r e a s i n g l y unstable due to the f a c t that the i n c l i n a t i o n of the c l i f f face, 40-50 degrees, i s considerably steeper than the angle of repose of the sand g r a i n s .  F r i c t i o n a l r e s i s t a n c e between the  sand grains may keep most of the thawed layer i n t a c t , but the opening of surface cracks and the changing a t t i t u d e of the stakes i n s t a l l e d on the surface r e f l e c t l o c a l i z e d movements w i t h i n t h i s layer and temporary s t r e s s relief.  This process continues u n t i l the weight of the unfrozen sand  reaches a c r i t i c a l l e v e l capable of overcoming the i n t e r n a l f r i c t i o n a l cohesion, and f a i l u r e occurs.  Generally t h i s f a i l u r e takes place towards  the end of each summer, when the thawed zone i s approximately  one metre  (3 feet) t h i c k , although i t may occur l o c a l l y before t h i s thickness i s reached.  The slumping u s u a l l y takes place along f a i r l y w e l l - d e f i n e d ...  planes a t , or close t o , the p o s i t i o n of the f r o s t t a b l e . Minor slumps are p r i m a r i l y of the r o t a t i o n a l type, but the chaotic mixture of debris at  147  the  foot of the larger slumps i n d i c a t e s considerable overturning and d i s -  i n t e g r a t i o n of the sand masses during t h e i r descent. The above comments are mainly a p p l i c a b l e to coarse-grained sediments w i t h low i c e contents, the thawing of which releases n e g l i g i b l e q u a n t i t i e s of water.  As the i c e content increases however, the volume of  water released upon melting becomes much more s i g n i f i c a n t .  This i s par-  t i c u l a r l y noticeable i n supersaturated sediments where thawing produces large q u a n t i t i e s of excess water.  In such sediments, the water released  imparts an added m o b i l i t y to the thawed layer and g r e a t l y f a c i l i t a t e s i t s removal from the c l i f f face. the  Consequently, the frequency of removal of  unfrozen m a t e r i a l increases from a maximum of once or twice during the  whole summer, as i n the case of the sand headlands, to an almost d a i l y or even hourly occurrence. At the same time, as the volume of water increases,  the mass movement, removal process gradually acquires the character-  i s t i c s of a mudflow rather than a simple slump. On a short term b a s i s , the major r o l e of wave a c t i o n appears to be i n the removal of slumped m a t e r i a l from the base of the c l i f f s . Such removal i s necessary to prevent the accumulation of debris and b u r i a l of  the lower sections of the p r o f i l e , and thus permit the maintenance of  f r e s h exposures f o r the 'thermal erosion' process.  In places where the  beach and foreshore are narrow, as along the b l u f f s on the northwest coast of  the i s l a n d , or where mudflows carry m a t e r i a l from c o a s t a l exposures of  ground i c e d i r e c t l y to the sea, removal by wave a c t i o n may occur almost instantaneously despite the l i m i t e d t i d a l range.  Where the c l i f f s are  more d i s t a n t from the s h o r e l i n e , the major part of the removal process i s accomplished during storm surges, e s p e c i a l l y i n the l a t e summer and early  fall.  148 Although the chief r o l e of wave a c t i o n on a short term basis i s i n the removal of slumped debris from the base of the c l i f f s , undercutting by waves may storm surges.  direct  l o c a l l y be of major importance during these same  The two lowermost stakes of P r o f i l e I I were removed by waves  during a storm i n early August of 1965.  Wave-cut notches are a common  feature along the high b l u f f s along the northwest coast, and the most spect a c u l a r example of undercutting was observed i n t h i s area i n the summer.of 1964.  In l a t e J u l y of that year, a deep c l e f t , 50 metres (165 feet) long  and up to 7 metres (23 feet) deep, opened up i n the s i t e of an o l d mudslump at a distance of 5-7 metres (16-23 feet) from the edge of the c l i f f .  The  b l u f f s at t h i s point were 15-20 metres (50-65 feet) high, and had been undercut, at beach l e v e l f o r distances of 4-5 metres (13-16 f e e t ) .  As the  summer progressed, the c l e f t gradually became wider and deeper as the whole block t i l t e d b o d i l y seaward u n t i l i t f i n a l l y collapsed i n t o the sea.  Al-  though the formation of t h i s c l e f t exposed a large body of ground i c e , which undoubtedly f a c i l i t a t e d the c o l l a p s e , i t was apparent that d i r e c t undercutting by the waves was p r i m a r i l y responsible f o r the removal or erosion of approximately l i n e i n one s i n g l e block.  5,250 cubic metres (185,000 cubic feet) of coastOn a long term basis t h e r e f o r e , i n some areas,  undercutting by wave a c t i o n may  be the most important process involved i n  c l i f f r e t r e a t , p a r t i c u l a r l y during b i g storms when as much recession may take place as i n several years of "normal" erosion. Erosion due to wind a c t i o n , through d e f l a t i o n of the f i n e r mate r i a l and mechanical dislodgement of i n d i v i d u a l p a r t i c l e s , i s of minor importance, but probably accounts f o r most of the changes recorded by the stakes on the sand headlands before slumping occurred. a c t i o n may  I n d i r e c t l y , wind  c o n t r i b u t e to c o a s t a l r e c e s s i o n i n another way.  Large t r a c t s of  149 vegetation along the northwest coast have been k i l l e d off by s a l t spray, and the reduced binding e f f e c t would a s s i s t i n the detachment of earth hummocks from the c l i f f edge i n these areas. Erosion by running water i s of l i t t l e or no consequence i n the c o a s t a l r e t r e a t process.  The only minor exception was  i n the v i c i n i t y of  the notches i n the sand headlands, where f u r t h e r melting of the ice-wedges and snow accumulations for  temporarily provides s u f f i c i e n t q u a n t i t i e s of water  the t r a n s p o r t a t i o n of m a t e r i a l , and the c o n s t r u c t i o n of miniature  a l l u v i a l fans on the beach.  MUDSLUMPS Many sections of the Garry I s l a n d c o a s t l i n e e x h i b i t a d i s t i n c t ive,  scalloped appearance on a e r i a l photographs, r e f l e c t i n g the  of numerous, l a r g e , crescent-shaped  depressions.  occurrence  Their presence i s a  r e l i a b l e i n d i c a t o r of the existence of massive bodies of segregated ice,  ground  and they are i n f a c t large thermokarst features r e s u l t i n g from the  exposure and melting of t h i s i c e . S i m i l a r features have been described i n other parts of the Canadian A r c t i c , where emphasis has been placed on the r o l e of mudflows found i n the f l o o r s of the depressions and, i n some cases, the term mudflow (coulee de boue) was the only name a p p l i e d to these  150 landforms.^  Mudflows are also found i n a s s o c i a t i o n w i t h the amphitheatres  on Garry I s l a n d , and t h e i r s i g n i f i c a n c e i n the c y c l i c development of the landforms w i l l be discussed below.  Mackay, i n h i s studies i n the Mackenzie  Delta area, has c l a s s i f i e d these features as slumps or ground i c e slumps.^  l  Since the overwhelming c h a r a c t e r i s t i c of a c t i v e features of t h i s type i s the  ubiquitous presence of a s u r f i c i a l layer of mud debris derived from  the  melting i c e ,  the term mudslump i s adopted here.  A map showing the d i s t r i b u t i o n of mudslumps on Garry I s l a n d (Figure 20) suggests the most probable mode of o r i g i n of these features. The mudslumps are almost e x c l u s i v e l y confined to c o a s t a l l o c a t i o n s where the  bodies of ground i c e have been exposed i n the b l u f f s .  The i c e may be  uncovered d i r e c t l y by wave a c t i o n or i n d i r e c t l y as the r e s u l t of oversteepening of the c l i f f p r o f i l e , and subsequent mass movement of the vegetation layer from the c l i f f top. A t one l o c a t i o n on the south coast of the  i s l a n d , such oversteepening had l e d to the downslope motion of a mass  of vegetation extending as much as 25-30 metres (80-100 feet) along, and back from, the edge of the c l i f f ( P l a t e IX-A).  The layer remained f a i r l y  •*-^Washburn, A.L. (1947) "Reconnaissance Geology of portions of V i c t o r i a I s l a n d and adjacent regions i n A r c t i c Canada", Geol. Soc. America, Memoir 22, p. 142. Lamothe, C. and St-Onge, D. (1961) "A note on a p e r i g l a c i a l e r o s i o n a l process i n the Isachsen area, N.W.T.", Geographical B u l l e t i n , No. 16, pp. 104-113. St-Onge, D. (1965) "La geomorphologie de L ' l l e E l l e f Ringnes, T e r r i t o i r e s du Nord-Ouest, Canada", Geographical Branch-Paper, No, 38, p. 46. Mackay J . Ross (1963) "The Mackenzie D e l t a area, N.W.T.", Geographical Branch Memoir, No. 8, pp. 60-65. 1:l  ?  Mackay, J . Ross (1966) "Segregated Epigenetic Ice and Slumps in Permafrost, Mackenzie Delta area, N.W.T,", Geographical B u l l e t i n , No. 8, pp. 59-80.  Figure 20  P l a t e IX M U D S L U M P S  A. S l i d i n g of t h e v e g e t a t i o n l a y e r produced by over steepeni n g of t h e c o a s t a l b l u f f s .  C. Overburden of a f i r s t g e n e r a t i o n mudslump showing the h i g h i c e c o n t e n t .  B. G e n e r a l view of Slump A w i t h a prominent mudflow extending i n t o the sea.  D. Overburden, composed p r e dominantly of m i n e r a l s o i l , of a second- o r l a t e r - g e n e r a t i o n mudslump.  153 i n t a c t during i t s descent, and bold s t r i a t i o n s marked i t s path down the c l i f f face.  The r e s u l t a n t depression was approximately  1.0-1.5 metres  (3-5 feet) deep, so that f a i l u r e probably occurred along a plane more or l e s s p a r a l l e l to the ground surface and a t , or close t o , the base of the active layer.  The bare f l o o r of the depression i s being accentuated  by  deeper thawing and surface flowage r e l a t i v e to the adjacent vegetated  sur-  face, and f a l l e n hummocks around the margin of the hollow i n d i c a t e that i t i s expanding a r e a l l y .  A f u r t h e r continuation of these processes  could  f e a s i b l y lead to the eventual exposure of ground i c e at depth, and the i n i t i a t i o n of slump development.  A few smaller slumps are located around  the edges of some of the l a r g e r lakes, where s i m i l a r undercutting of the banks by wave a c t i o n has exposed the i c e . Figure 20 a l s o shows a c l a s s i f i c a t i o n of the mudslumps i n t o a c t i v e and i n a c t i v e forms.  Since the ground i c e exposures frequently have  i c e contents of several hundred per cent by weight, melting of the permaf r o s t leaves deep depressions which p e r s i s t f o r long periods of time a f t e r e i t h e r complete thawing, i f t h i s ever takes place, or p a r t i a l thawing and r e b u r i a l of the i c e body.  Apart from t h e i r persistence as negative r e l i e f  f e a t u r e s , the i d e n t i f i c a t i o n of these scars on a e r i a l photographs i s a comparatively easy task.  Due to the disturbed nature of the substratum  f o l l o w i n g periods of slump a c t i v i t y , the i n a c t i v e mudslumps support a h i g h l y diagnostic vegetation a s s o c i a t i o n , dominated by grasses, as desc r i b e d i n Chapter I I I . The s t a b i l i z e d headwall scarp of an o l d mudslump, averaging 2-3 metres (6-10 f e e t ) i n height, i s generally smaller than that of an a c t i v e slump, and i t p r o g r e s s i v e l y loses some of i t s i d e n t i t y as i t i s colonized by vegetation.  In l o n g i t u d i n a l p r o f i l e , the f l o o r s of many of  both a c t i v e and i n a c t i v e depressions e x h i b i t a d i s t i n c t i v e ribbed  154 appearance. mud  The r i b s may  be annual f e a t u r e s , representing the deposits of  derived from the melting of the i c e face i n a summer, or they may mark  the terminal p o s i t i o n s of previous cycles of mudslump a c t i v i t y f o l l o w i n g renewed undercutting at the toe of an immediately  preceding c y c l e .  Many of the c u r r e n t l y a c t i v e slumps are second- or l a t e r generation features located wholly, or p a r t i a l l y , w i t h i n the confines of the older mudslumps.  Others are f i r s t - g e n e r a t i o n forms c u t t i n g back i n t o  t e r r a i n which has not been a f f e c t e d previously by slumping processes.  The  headwalls of a c t i v e slumps, ranging i n height up to 10 metres (33 f e e t ) , contain v a r i a b l e q u a n t i t i e s of segregated ground i c e , and r e t r e a t r a p i d l y during the summer months.  The f l o o r s of the depressions are covered, to  varying degrees, w i t h a l i q u i d mud  debris derived from the melting of the  i c e face and the o v e r l y i n g a c t i v e layer or overburden.  Depending upon the  r a t i o of i c e to mineral s o i l i n the headwall exposure, t h i s mud may accumu l a t e as a r e l a t i v e l y s t a t i c or slowly advancing mud  lobe at the base of  the i c e face, or, i n l e s s viscous cases, i t may be concentrated  into  strong, w e l l - d e f i n e d mudflows extending across the f l o o r of the depression ( P l a t e IX-B). Rates of Retreat. Lamothe and St-Onge considered t h i s slumping process to be  one  of the most r a p i d e r o s i o n a l agents operating i n c e r t a i n parts of the arctic.  Their observations during the summer of 1960 showed that the  thermo-scarp r e t r e a t e d an average of 7 metres (23 f e e t ) , w i t h a maximum recorded r e c e s s i o n of 10 metres (33 f e e t ) .  Erosion rates on the l a t e r a l  w a l l s of the depression, w i t h less southerly aspect, were considerably lower, averaging 0.5 metres (1.5 f e e t ) on a northeast-facing slope and  155 2 metres (6.5 feet) on a west-facing slope.  Mackay, using f i e l d obser-  vations i n the Mackenzie Delta area, concluded that the average r e t r e a t of a c t i v e scarp faces i s v a r i a b l e but probably l i e s i n the range of 1.5-4.5 13  metres (5-15 feet) per annum. Three very a c t i v e mudslumps, the l o c a t i o n s of which are a l s o shown i n Figure 20, were i n v e s t i g a t e d on Garry I s l a n d , and data on the annual rates of r e t r e a t were obtained by i n s t a l l i n g a s e r i e s of numbered stakes around the headwalls of each slump.  These stakes were v i s i t e d per-  i o d i c a l l y throughout the 1964 and 1965 f i e l d seasons, and one of them, Slump B> was r e v i s i t e d during the summer of 1966.  The amount of recession  was recorded i n metres and a summary of these observations i s presented i n Table X.  Figure 21 a l s o shows the surface c o n f i g u r a t i o n of Slump B i n  d e t a i l , w i t h the l o c a t i o n s of the various stakes and the l i n e s of r e t r e a t at selected i n t e r v a l s (the beginning and end of the i n d i v i d u a l f i e l d seasons) during the observation period. The f i g u r e s i n Table X confirm Mackay s conclusions that the 1  rates of r e t r e a t are h i g h l y v a r i a b l e and the average values, i n each of the mudslumps, approach or even exceed the upper l i m i t of h i s estimate. The highest average annual r e t r e a t , 6.4 metres (20.8 f e e t ) , was  recorded  i n Slump A on the south coast of the i s l a n d , and t h i s value contrasts w i t h annual averages of 4.6 metres (15.2 feet) and 3.9 metres (12.8 feet) f o r Slump B, located on the north coast, and Slump C, located on the west coast, r e s p e c t i v e l y . In each of the mudslumps, more than 80 per cent of the observed recession occurred during the months of J u l y and August. 'Lamothe, C. and St-Onge, D. (1961) op_. c i t . , p.  Wckay, J . Ross  (1966) op. c i t . , p. 72.  104.  156 TABLE X MUDSLUMPS  - RATES OF RETREAT (Metres)  SLUMP A.  Average  Maximum  Minimum  Summer 1964  5.51  10.40  0.0  Fall  0.84  3.70  0.0  Summer 1965  5.15  9.55  0.0  Summer 1964  3.75  6.50  0.0  Fall  0.88  1.70  0.0  Summer 1965  3.68  6.20  0.0  (July 4/64 - Aug. 22/66)  11.66  21.10  0.0  1964/65  SLUMP B.  1964/65  *(Aug. 22/66 - Aug. 21/67)  4.26(5.96)  6.87  0.0  *(Aug. 21/67 - J u l y 10/68)  1.54  2.90  0.0  Summer 1964  3.14  5.20  0.0  Fall  0.75  1.90  0.0  4.81  6.90  0.0  SLUMP C.  1964/65  Summer 1965  Representative annual r e t r e a t values can be obtained f o r each mudslump by adding together the average f i g u r e s f o r Summer 1964' and F a l l 1964/65. * Information supplied by Dr. J . Ross Mackay. Personal communications August 1967 and October 1968. The r a t e s c i t e d a c t u a l l y represent minimum values since they include measurements based on the l a s t recorded p o s i t i o n s of stakes which had been o b l i t e r a t e d by headwall r e t r e a t . The f i g u r e i n brackets represents the average r a t e of r e t r e a t based s o l e l y on 21 stakes which were s t i l l i n p o s i t i o n on August 21, 1967. By J u l y 10, 1968, only 14 of the o r i g i n a l 27 markers were s t i l l i n t a c t , and of these only 4 were located along a c t i v e l y r e t r e a t i n g sections of the headwall.  A e r i a l reconnaissance of the i s l a n d i n mid-June of 1965 revealed that the mudslumps were s t i l l l a r g e l y f i l l e d w i t h snow, and the paucity of f r e s h debris a t the base of the i c e f a c e , or on the surface of the snow, at the beginning of J u l y , i n d i c a t e s that most of the r e t r e a t recorded during the f a l l represents continued recession during the preceding September before the onset of continuously f r e e z i n g ;air  temperatures.  Since the maximum recession recorded by any of the i n d i v i d u a l stakes .also occurred i n Slump A, i t may seem easy to conclude that slope aspect i s a dominant f a c t o r i n f l u e n c i n g scarp r e t r e a t .  Comparisons made  between stakes located around the same mudslump, however, revealed that the maximum r e t r e a t d i d not always occur on the slopes w i t h the most southerly aspect. The f i e l d studies i n d i c a t e d that the r a t e of recession of a mudslump headwall r e f l e c t s the complex i n t e r p l a y of a number of f a c t o r s i n c l u d i n g c l i m a t e , the height and composition of the scarp f a c e , and the r a t e of removal of the thawed d e b r i s .  Of these, the c l i m a t i c f a c t o r  appeared l o g i c a l l y t o be the most s i g n i f i c a n t , and an attempt was made to e s t a b l i s h the r e l a t i o n s h i p between the r a t e of r e t r e a t , as measured between successive observation periods, and the number of thawing degreedays occurring during the same periods.  Only a c t i v e l y - r e t r e a t i n g sections  of the scarp face i n each of the three mudslumps were used f o r t h i s study, and the recession values thus represent the average readings taken from approximately  18-20 stakes at each of the slumps.  These values were  p l o t t e d against the thawing i n d i c e s and are shown g r a p h i c a l l y i n Figure 22.  The regression l i n e f i t t e d to these points y i e l d e d the f o l l o w i n g  equation:  Figure 22  RELATIONSHIP NUMBER  BETWEEN  OF  THAWING  GARRY  RATE  OF  RETREAT  DEGREE-DAYS  ISLAND  FOR  AND  THREE  MUDSLUMPS  2.5 X  X  *>  2.0  V  « c  *  1.5  •  -*— < *  •  ^_  0 1> •I  OC  «  1.0  CO D  X  •  <>  ^^^^  X  0.5  n v  )  (  •  Slump A  Y = 0.91 + 0.0022 X  r = +0.95  •  Slump B  Y = 0.53 • 0.0034 X  r = +0.87  X  Slump C  Y = 0.39 + 0.0046X  r = +0.87  100  c  c  c  200  Thawing  D e g r e e - Days  300  400  160 Y  c  = 0.50  + 0.004 X  where Y^ i s the estimate of average r e t r e a t of the headwall i n metres for a given value of X, and X i s the number of thawing degree-days.  Computation  of the c o e f f i c i e n t of c o r r e l a t i o n y i e l d e d a value of +0.92 i n d i c a t i n g a strong p o s i t i v e c o r r e l a t i o n between the two v a r i a b l e s .  The equations of  the regression l i n e s and the c o e f f i c i e n t s of c o r r e l a t i o n for measurements taken from the i n d i v i d u a l mudslumps are also given i n Figure  22. 2  By computing the c o e f f i c i e n t of determination  ( r ) i t can be  seen that approximately 85 per cent of the v a r i a b i l i t y i n the observed rates of r e t r e a t can be  'explained' by v a r i a t i o n s i n the a i r temperature  patterns. Each of the mudslumps investigated was  s i m i l a r insomuch as they  were a l l p a r t i a l l y l o c a t e d , a l b e i t to varying degrees, w i t h i n the l i m i t s of an older slump.  For example, Slump A, when f i r s t v i s i t e d , was  located w i t h i n an older slump.  At the end of the observation  wholly period,  recession of the ice face had completely eliminated the evidence of the previous cycle along a l l but a small portion of the rim. evidence of an e a r l i e r cycle was  In Slump B,  found between stakes 170-175 (see  Figure 21), and i n Slump C approximately one-third of the rim was located.  similarly  The s i g n i f i c a n c e of t h i s type of l o c a t i o n i s p r i m a r i l y i n i t s  influence on the s t r u c t u r a l composition of the headwall.  In t e r r a i n which  has not previously been affected by mudslumps, the overburden i s v i r t u a l l y r e s t r i c t e d to the a c t i v e l a y e r , and r a r e l y exceeds 1.0-1.5 metres (3-5 feet) i n thickness although l o c a l l y t h i s f i g u r e may  be augmented by  solifluction.  have a moderately  Moreover, t h i s type of surface mantle may  high ice content ( P l a t e IX-C).  In contrast to t h i s , the composition of the  headwall i n a second- or later-generation slump i s i n t i m a t e l y r e l a t e d to  161 the sequence of events during the previous c y c l e .  The amount of i c e  exposed i s p a r t i a l l y c o n t r o l l e d by the l e v e l at which i t was planed o f f during the previous c y c l e , and i t may be mantled by an overburden of slumped m a t e r i a l only a portion of which corresponds to the current a c t i v e layer.  This type of overburden, which has the appearance of a chaotic  mixture of mud, stones, t u r f and w i l l o w s , also frequently has a very low ice content (Plate IX-D). The amount and type of ground i c e exposed i n the headwall, and the r a t i o of t h i s i c e to the overburden above, i s a c r i t i c a l factor i n f l u e n c i n g the rates of recession.  I t i s the i c e face segment which  undergoes the most r a p i d r e c e s s i o n , and the maintenance of f r e s h exposures of the i c e i s imperative f o r continuous r e t r e a t .  In Table X, i t  was shown that the maximum and minimum rates recorded i n each of the mudslumps covered wide ranges.  Minima, i n actual fact points at which no  recession was observed, i n a l l cases coincide w i t h headwall sections i n which no ground i c e was exposed.  At a l l other points i c e was exposed f o r  some time during the observation period and, i n general, the greatest recession occurred where the r a t i o of ground i c e to overburden was highest, and the former was thus c o n t i n u a l l y exposed throughout-most of the summer months.  Another i n d i r e c t influence of t h i s r a t i o on the rates  of recession i s r e l a t e d to i t s e f f e c t on the v i s c o s i t y of the thawed debris.  High proportions of segregated i c e i n the headwall represent a  greater p o t e n t i a l moisture supply a f f e c t i n g the m o b i l i t y of the d e b r i s , and thereby f a c i l i t a t i n g i t s removal from the base of the i c e face.  In  t h i s respect, i t i s also s i g n i f i c a n t to point out that there was a considerable v a r i a t i o n i n the i c e content of the ground i c e exposures themselves i n each of the mudslumps, and therefore important differences i n  162 the volumes of debris derived from the melting of these sections of the scarp face. A c t i v e removal of t h i s d e b r i s , allowing the maintenance of fresh exposures, i s another important contributor to continued r e t r e a t . In a d d i t i o n , where the headwall i s h i g h , the momentum gained by the debris during i t s descent aids i n i t s displacement from the immediate v i c i n i t y of the foot of the slope. I t i s now possible to re-evaluate the s t a t i s t i c s given i n Table X i n terms of the preceding statements.  The highest average r e t r e a t  values recorded i n Slump A r e f l e c t the combination of the influence of a southerly aspect; the widespread occurrence of segregated ground i c e w i t h ice contents of s e v e r a l hundred per cent, including many bands of almost c l e a r i c e ; an overburden which, although t h i c k , i n many places also contained large q u a n t i t i e s of segregated i c e ; a high headwall ranging up to 10.0 metres (33 feet) i n height; and an extremely active rate of removal of the thawed debris i n the form of strong mudflows.  The l a t t e r f a c t o r was  extremely s i g n i f i c a n t i n sections of the mudslump where the headwall was dominated by t h i c k deposits of slump debris from an e a r l i e r c y c l e .  A brief  v i s i t to the same slump at the end of the 1966 f i e l d season showed that a weakening of the mudflow a c t i v i t y had l e d to an almost complete b u r i a l of the ground i c e exposures i n these sections.  Higher r e t r e a t values recorded  i n both the other mudslumps generally r e f l e c t e d a s i m i l a r combination of these conditions.  The lower average f i g u r e f o r Slump B i s probably most  r e l a t e d to i t s n o r t h e r l y aspect and the prevalence of a weak rate of removal of d e b r i s .  Several f a c t o r s account for the lowest r e c e s s i o n rates  recorded i n Slump C i n c l u d i n g a low headwall averaging only 2.0-3.0 metres (6-10 feet) i n height; ground i c e exposures i n t h i s headwall which were more akin to a frozen mud, w i t h ice contents averaging less than one  163 hundred per cent; and the presence of numerous g u l l i e s on the f l o o r of the depression.  Whilst these g u l l i e s a s s i s t the concentration of the debris  into w e l l - d e f i n e d mudflows, some of which would break through w i t h considerable force to the sea, they provided numerous c o n s t r i c t i o n p o i n t s , at which many of the flows became blocked, r e s u l t i n g i n a h i g h l y i n t e r m i t t e n t , and sometimes complete lack o f , removal of the debris. A b l a t i o n Studies.  The r e t r e a t values c i t e d i n the preceding  paragraphs were r e l a t e d to the rate at which m a t e r i a l , composed predominantly of mineral s o i l , was detached from the rim of the headwall.  I t was  also e s t a b l i s h e d that one of the key f a c t o r s i n f l u e n c i n g t h i s detachment process was face.  the melting back of the segregated  i c e exposures i n the scarp  To obtain a d d i t i o n a l data on t h i s l a t t e r aspect of the r e t r e a t  process a s e r i e s of a b l a t i o n studies was made during the 1965  field  season. The technique employed for these a b l a t i o n studies was  similar  to that used to record changes i n the c l i f f p r o f i l e s of the sand headlands.  A number of stakes was  i n s t a l l e d i n the ice f a c e , normal to the  surface, and the amount of a b l a t i o n was determined by measuring changes i n the exposed lengths of the stakes ( P l a t e X-A). encountered i n using t h i s technique.  Several problems were  F i r s t l y , the d r i l l i n g of the holes  to accommodate the wooden dowelling was  an arduous task due to the  presence of numerous small pebbles i n the segregated  ice body.  These  pebbles were of s u f f i c i e n t s i z e to h a l t the penetration of the d r i l l before the required depth of 45 cms.  (18 ins.) was achieved.  Thus, on one  occasion, a t o t a l of 27 holes was s t a r t e d before seven could be completed to i n s t a l l the stakes on one of the a b l a t i o n p r o f i l e s . though the dowelling used f o r the stakes was  2.5 cms.  Secondly, even (one inch) i n  164  Plate X M U D S L U M P S  A. Ablation studies i n Slump B showing t h e l o c a t i o n s of the s t a k e s in P r o f i l e I.  B. G u l l i e s produced by the d i f f e r e n t i a l m e l t i n g of bands of ground i c e w i t h c o n t r a s t i n g mineral s o i l contents.  C. M e l t w a t e r g u l l y system on the h e a d w a l l i n Slump B.  D. R e j u v e n a t i o n of Slump A caused by u n d e r c u t t i n g a t t h e t o e of the slump l e a d i n g to renewed exposure of the ground i c e .  165  diameter, there were a number of instances where i t was e i t h e r broken o f f or dislodged by hummocks and debris detached from the overhanging r i m above.  T h i r d l y , problems were also introduced i n the a c t u a l measurements  of the amount of a b l a t i o n due to the formation of small p i t s produced by accelerated melting at the base of the exposed p o r t i o n of each stake.  To  a l l e v i a t e t h i s problem and obtain representative a b l a t i o n measurements therefore, a r u l e r was placed across these p i t s , f l u s h w i t h the adjacent ice surface, and the a b l a t i o n l e v e l was i n t e r p r e t e d as being the point of i n t e r s e c t i o n of the r u l e r and the stake. For these a b l a t i o n s t u d i e s , two p r o f i l e s were e s t a b l i s h e d i n Slump B.  Observations, covering periods of 3-4 days, were made at 14  i n t e r v a l s ranging from 2-3 weeks.  P r o f i l e I was located midway between  stakes 180 and 181 (see Figure 21), at a point where the headwall  just  exceeded 8.0 metres (26 feet) i n height and the i c e face was r e l a t i v e l y smooth w i t h only i n c i p i e n t g u l l i e s at the base.  P r o f i l e I I was s i t u a t e d  midway between stakes 187 and 188 where the headwall was just under 6.0 metres (19.5 f e e t ) , high and the lower parts of the i c e face were ribbed by a number of d i s t i n c t g u l l i e s .  The forms of these p r o f i l e s , the  l o c a t i o n s of the a b l a t i o n stakes on each, and the changes i n the p o s i t i o n s of the i c e face are i l l u s t r a t e d i n Figures 23 and 24. Each p r o f i l e was surveyed by s t r e t c h i n g a tape between two rods, one anchored i n the ground surface above the r i m and the other i n the ground i c e f l o o r of the slump, and taking plumb readings to the i c e surface at approximately 0.5 metre (1.6 foot) i n t e r v a l s .  This procedure  On the majority of these days two sets of observations were made, but the changes were too s l i g h t to be recorded on Figures 23 and 24.  Figure 23  Location  of  Ablation  8 9  Stakes  A B C D  July Jul/ July July  E F G H  J u l y 27 July 28 J u l y 30 J u l y 31  1 J K  A u g . 15 A u g . 17 A u g . 19  10 4 5 P m. 10 3 0 P m. 10 3 0 P m.  L  Sep.  12 3 0 P- m.  11  12  5  5 30 P- m. 4 3 0 P- m. 1 3 0 P m. 1 3 0 P m. 4 4 4 4  40 30 00 00  P P P P  m. m. m. m.  Figure 24  ABLATION STUDIES IN SLUMP PROFILE H  S c a l e in M e t r e s  Location Ablation  of Stakes  A B C  July 2 8 July 30 J u l y 31  D E F  A u g . 14 Aug. 1 5 A u g . 17  11 0 0 a m. 10 5 5 a m. 10 4 0 a m.  G  Sep.  1 2 . 4 5 p.m.  5  4 4 0 P- m. 4 0 0 P- m. 2 30 P- m.  G  168 was repeated s e v e r a l times, u s u a l l y at the beginning and end of each observation p e r i o d , and the surveyed p r o f i l e s are indicated by the s o l i d l i n e s i n Figures 23 and 24.  The intermediate p o s i t i o n s of the i c e f a c e ,  as determined by the a b l a t i o n stake measurements, are represented by broken l i n e s i n the same diagrams. A comparison of the i n d i v i d u a l a b l a t i o n stake measurements for each observation period showed that i n P r o f i l e I there was very l i t t l e v a r i a t i o n over the length of the p r o f i l e , and that the i c e face underwent e s s e n t i a l l y p a r a l l e l r e t r e a t (Figure 23).  By way of c o n t r a s t , a s i m i l a r  comparison of the values obtained i n P r o f i l e I I showed a progressive increase i n the amount of a b l a t i o n from the top to the bottom of the profile.  This d i f f e r e n t i a l was most pronounced at the beginning of the  observation period i n l a t e J u l y , when i t was i n the order of 200 per cent, but i t s magnitude gradually diminished u n t i l , by l a t e August, i t was than 100 per cent.  less  This miniature a b l a t i o n - a l t i t u d e gradient can probably  be a t t r i b u t e d to the presence of the g u l l y system, extending over the lower part of the scarp f a c e , which e f f e c t i v e l y concentrated  meltwater,  derived from the Upper part of the i c e f a c e , into w e l l defined-channels. The two lower stakes i n P r o f i l e I I were d e l i b e r a t e l y positioned i n the f l o o r of one of these channels.  The greater r a t e of melting of the i c e  at these l o c a t i o n s may therefore represent the e f f e c t s of a d d i t i o n a l 15 mechanical erosion by the meltwater.  Furthermore, the observed  decrease  i n the d i f f e r e n t i a l rates of a b l a t i o n may p o s s i b l y be a t t r i b u t e d to the ^~*Part of t h i s d i f f e r e n t i a l may a l s o be a t t r i b u t e d to the f a c t that the lower stakes i n P r o f i l e I I were i n s t a l l e d v e r t i c a l l y rather than at r i g h t angles to the i c e surface.  169 gradual c o n t r a c t i o n of the g u l l y system towards the end of the summer. This sequence of events i s apparent i n Figure 24 by the progressive 'straightening' of the i c e p r o f i l e and a diminution i n the v e r t i c a l extent of the lower concave f a c e t . An a n a l y s i s of the rates of r e t r e a t for the rim of the showed a strong p o s i t i v e c o r r e l a t i o n w i t h a i r temperatures.  headwall  Due to the  short time periods (ranging from 7-48 hours) used i n the a b l a t i o n studies i t was  i m p r a c t i c a l to employ the number of thawing degree-days as an index  of a i r temperatures and, i n s t e a d , the number, of thawing degree-hours was used.  These were c a l c u l a t e d by taking the hourly readings from the c o n t i n -  uous temperature record at the climate s t a t i o n , subtracting 32°F from each, and cumulating the t o t a l s f o r the respective observation periods. Figure 25 i l l u s t r a t e s g r a p h i c a l l y the r e l a t i o n s h i p between the a b l a t i o n rates and a i r temperatures.  The regression l i n e f i t t e d to the  p l o t t e d points was determined by the method of l e a s t squares, and the r e s u l t a n t equation  was: Y„c = 0.14 + 0.019  where Y  c  X  i s the estimate of the amount of a b l a t i o n i n centimetres for a  given value of X, and X i s the number of thawing degree-hours.  The  regression equations for the i n d i v i d u a l p r o f i l e data are also shown i n Figure 25. Computations of the c o e f f i c i e n t s of c o r r e l a t i o n (r) and the o  c o e f f i c i e n t s of determination ( r ) y i e l d e d uniformly high values of +0.99 and 0.98  r e s p e c t i v e l y . Thus, approximately  98 per cent of the v a r i a b i l i t y  i n the a b l a t i o n data can be 'explained' by v a r i a t i o n s i n the a i r temperature patterns.  Figure 25 RELATIONSHIP NUMBER  BETWEEN OF  ABLATION  THAWING IN  SLUMP  RATES  AND  DEGREE-HOURS B  THE  171 The Recession Process and E v o l u t i o n of the Gully System. Headwall recession i n a t y p i c a l mudslump involves the  thermal  and mechanical erosion of the scarp face, accompanied by the slumping of the thawed debris and free f a l l or s l i d i n g of the overlying a c t i v e 16 layer.  The r e l a t i v e importance of each of these processes depends  p r i m a r i l y on the nature and composition of the scarp face, and i n p a r t i c u lar,  the type and quantity of ground ice exposed. The recession values, c i t e d i n the preceding paragraphs, des-  cribe the r a t e s at which blocks of m a t e r i a l were detached from the crown of the mudslump. Many a c t i v e l y - r e t r e a t i n g headwalls include small sections i n which the o r i g i n a l ground i c e exposures have been eliminated e i t h e r by complete melting or by b u r i a l beneath deep mantles of thawed d e b r i s . Although active recession may i s extremely slow.  s t i l l take place i n these s e c t i o n s , the r a t e  Small tension cracks are developed along the crown of  the slump, p a r a l l e l to the r i m , and blocks of t u r f or mud,  bounded by these  cracks, gradually t i l t forward and are u l t i m a t e l y detached from the headwall.  Since the thawing of these sections releases l i t t l e or no  moisture,  the debris merely accumulates on the scarp face and the recession i s eventually terminated.  This process, the detachment and free f a l l i n g of  the a c t i v e l a y e r , i s g r e a t l y f a c i l i t a t e d where underlying bodies of ground ice  are exposed i n the main scarp face.  A more rapid recession of the ice  face segment leads to undermining at the base of the a c t i v e l a y e r , the development of large overhangs, and a sudden, r a p i d collapse of large blocks of debris to the foot of the scarp face. The thermal and mechanical erosion of the main scarp face i s Mackay, J . Ross ( 1966)  op. c i t . , p.  74.  172 thus the dominant process i n f l u e n c i n g the r a t e of headwall r e c e s s i o n , and one of the most apparent manifestations of t h i s process i s the presence of a well-defined g u l l y system covering sections of the ice face.  Two  of g u l l y can be d i s t i n g u i s h e d i n the mudslumps on Garry I s l a n d .  types  The  first  type, observed i n Slump A, i s s t r u c t u r a l and occurs i n heterogeneous bodies of ground ice composed of a l t e r n a t i n g , more or less v e r t i c a l bands of frozen mud  and c l e a r ice ( P l a t e X-B).  The frozen muds, w i t h ice contents  averaging only s l i g h t l y more than 100 hundred per cent by weight, melt q u i c k l y and form negative features i n the ice f a c e , while the c l e a r ice bands, which melt more s l o w l y , stand out as p o s i t i v e r i b features. D i f f e r e n t i a l melting of the bands therefore produces an embryonic g u l l y system which i s accentuated the ice face.  by the channelling of meltwater streaming down  The width of the channel i s c o n t r o l l e d by the width of the  d i r t bands, but mechanical and thermal erosion by the running water r e s u l t s i n a maximum amplitude of the g u l l i e s , i n the order of 15-20 (4-6 i n s . ) , at the base of the ice face.  cms.  The amplitude i s p a r t i a l l y con-  t r o l l e d by the f a c t that excavation along the l i n e s of the frozen  mud  r e s u l t s i n greater exposure and thus more r a p i d melting of the r i b s of c l e a r i c e . Since the g u l l y system i s s t r u c t u r a l l y c o n t r o l l e d , there i s no evidence of c y c l i c development, and the pattern remains r e l a t i v e l y stable throughout the summer months.  Where the ground ice has been strongly  deformed, as i n Slump A, the o r i e n t a t i o n of the g u l l i e s i s not n e c e s s a r i l y i n the d i r e c t i o n of steepest slope down the scarp face. In contrast to the diminutive, s t r u c t u r a l l y - c o n t r o l l e d features described above, the second type of g u l l y system includes the pattern of large ridges and g u l l i e s which produces the d i s t i n c t i v e badland  topography described r e c e n t l y by Mackay.  I t i s best developed i n  massive bodies of r e l a t i v e l y homogeneous ground i c e , devoid of any marked s t r u c t u r a l c o n t r o l s , and w i t h ice contents ranging from 100-300 per cent by weight.  These conditions occurred i n Slump B ( P l a t e X-C), and the f o l l o w -  ing d e s c r i p t i o n of the development of the badland topography  i s r e l a t e d to  a number of i n v e s t i g a t i o n s made i n t h i s mudslump. Unfortunately, the e a r l i e s t date at which i t was p o s s i b l e to v i s i t t h i s mudslump was at the beginning of J u l y , when evidence of the 18 ridge and g u l l y system was found between stakes 178 and 190.  Between  stakes 178 and 181, an i n c i p i e n t ridge and g u l l y system was developed on the lower metre (3 feet) of the i c e face while the upper portions of the headwall were smooth.  The r i d g e s , spaced at i n t e r v a l s of 30-35 cms.  (12-14 ins.) e x h i b i t e d a t y p i c a l buttress form, being approximately 20  cms.  (8 ins.) across i n t h e i r upper portions and increasing to about twice t h i s )  width at the base.  The intervening g u l l i e s averaged 6.0 cms. (2.5 ins.) i n  depth near t h e i r heads, and 6-8 cms. (2.5-3.0 ins.) i n depth at the base of the i c e f a c e , w i t h maximum depths below the r i d g e c r e s t s of 10-12 (4-5 i n s . ) .  cms.  Small t r i c k l e s of water were being channelled down the g u l l i e s ,  which were f l o o r e d by clean i c e exposures, but the adjacent ridges were mantled by a s u r f i c i a l d i r t accumulation up to 3.0 cms. (one inch) t h i c k . Between stakes 182 and 190, the ridges and g u l l i e s became p r o g r e s s i v e l y larger and covered an increasing proportion of the ice face u n t i l , by stake 190, they extended to w i t h i n one metre (3 feet) of the base of the active layer and exemplified the t y p i c a l badland topography par excellence. At Mackay, J . Ross (1966) op_. c i t . , pp. 68-69. 'The stake numbers r e f e r to the positions shown i n Figure 21.  174 t h i s p o i n t , the ridges were approximately 3.0-3.5 metres (10-12 feet) apart, as measured between c r e s t s , and reached widths of 2-3 metres (6-10 feet) across near the base of the i c e face.  The depth of the g u l l i e s  increased from an average of 25-35 cms. (10-14 ins.) near the head to a maximum of 1.0-1.5 metres (3-5 feet) at the foot of the slope.  Between  stakes 190 and 196, any ground i c e exposures were s t i l l mantled by snow patches and d e b r i s , and the headwall was not affected by any form of gullying. In e a r l y August, one month l a t e r , several notable changes had occurred i n the appearance of the headwall. Ground i c e was then exposed i n the scarp face between stakes 172 and 191, and the badland topography was only evid ent between stakes 182 and 191.  A l l previous evidence of a gully*•  ing pattern between stakes 178 and 182 had now been e l i m i n a t e d , and the headwall was now e s s e n t i a l l y a smooth i c e face except f o r a few minor r i p p l e s at the base.  Measurements of the s i z e , amplitude and areal extent  of the ridge and g u l l y system between stakes 182 and 191 showed that they covered an increasing proportion of the i c e face as the l a t t e r marker was approached, and t h i s was accompanied by a corresponding increase i n t h e i r dimensions s i m i l a r to the pattern described above.  No further extension of  the badland topography occurred during the month of August, since no a d d i t i o n a l exposures of ground i c e occurred beyond stake 191, and the badland topography was eliminated as f a r as stake 184. Whereas no evidence of a c y c l i c pattern was found i n the g u l l y system i n Slump A, the recession of the headwall of Slump B e x h i b i t s a d e f i n i t e cycle during which the badland topography i s developed and u l t i mately disappears. During the winter months, the mudslumps are s i t e s of deep snow accumulation driven i n by the p r e v a i l i n g winds.  With the  175 a r r i v a l of warmer temperatures i n spring and e a r l y summer, the snow begins to melt and the uppermost portions of the scarp face are the f i r s t to be exposed.  Rapid melting of the i c e and the base of the active layer r e s u l t s  i n the detachment of hummocks and debris from the r i m of the slump which accumulate on the surface of the snow. Water, derived from the melting of the snow and thawing of the i c e face, soon erodes a s e r i e s of deep g u l l i e s i n the i c e surface.  Once the g u l l y pattern has been established  on the i c e face, i t becomes progressively larger and deeper as i t continues to channel the excess water released upon melting of the i c e face.  The  system reaches i t s maximum development when almost the e n t i r e face i s covered by the badland topography with strong channels, 1.0-2.0 metres (3.0-6.5 feet) deep, separated by prominent r i d g e s , of the buttress type, which may be as much as 2-3 metres (7-10 feet) across at the base.  As  noted previously however, the pattern of ridges and g u l l i e s r a r e l y reaches w i t h i n more than one metre (3 feet) of the top of the i c e face,and t h i s probably r e f l e c t s the minimum surface area required to produce a s u f f i c i e n t l y large quantity of water that can be c o l l e c t e d together and channelled 19 i n t o a surface flow ( c f . Schumm, 1956).  Once the ridges reach the  dimensions c i t e d above,they occupy a large proportion of the i c e f a c e , and t h e i r large surface area, coupled w i t h t h e i r a d d i t i o n a l exposure as p o s i t i v e r e l i e f f e a t u r e s , reaches a s i z e whereby melting releases s u f f i c i e n t water to form another set of g u l l i e s on the buttresses themselves.  Entrenchment  and headward extension of these new g u l l i e s gradually reduces, and f i n a l l y eliminates, the large ridges and produces the more c l o s e l y spaced r i p p l e  _ Schumm, S.A. (1956) "Evolution of drainage systems and slopes i n badlands at P e r t h Amboy, N.J.", Geol. Soc. Amer. B u l l . , V o l . 67, p. 607.  176 remnants a t the base of the scarp face.  This e n t i r e sequence, the develop-  ment of new channels at points formerly occupied by ridges during an e a r l i e r period of g u l l y i n g , i s very s i m i l a r to the process of gully-gravure  described 20  by Kirk-Bryan i n the a r i d south-western parts of the United States. The length of time i n which t h i s cycle i s completed of course i s much less than that c i t e d by K i r k Bryan, and appears to vary according to the l o c a t i o n w i t h i n the mudslump. The smooth nature of the i c e face between stakes 173 and 178, except f o r the minor r i p p l e s at the foot of the slope, i n d i c a t e d that the c y c l e had already been completed on these sections of headwall w i t h a northwest or northern aspect, whereas, on a northeast f a c i n g slope the c y c l e was not completed u n t i l l a t e September.  On slopes  with a more e a s t e r l y aspect, the cycle may not be completed before f r e e z i n g temperatures set i n , and remnants of the ridges and g u l l i e s may be buried beneath the d r i f t i n g snow. During the stage of maximum development of the badland topography, mechanical and thermal erosion of the i c e face by running water i s a d e c i s i v e f a c t o r i n f l u e n c i n g the r a t e of recession of the mudslump headwall.  Besides c o n t r i b u t i n g to a c t i v e erosion, the water i s a l s o an  important agent i n q u i c k l y removing thawed debris from the i c e surface, and thereby maintaining a clean exposure f o r more r a p i d thermal erosion.  Since  both thermal and mechanical erosion occur simultaneously, i t i s impossible to evaluate p r e c i s e l y the r e l a t i v e c o n t r i b u t i o n s of each, but comparisons of headwall recession values, over smaller i n t e r v a l s of time, at the i n d i v i d u a l stake p o s i t i o n s demonstrate the e f f i c i e n c y of the mechanical 20 Bryan, K. (1940) "Gully gravure - A method of slope r e t r e a t " , Journal of Geomorphology, V o l . 3, pp. 87-107.  177 erosion.  These comparisons are shown i n Table X I . TABLE XI  RATES OF RECESSION AT SELECTED STAKE POSITIONS IN SLUMP B (Metres). Stake # 179 182 190  July  7-26  J u l y 26 - Aug. 13  2.05 3.30 1.35  Aug. 13 - Sept. 9 1.20 1.10 2.30  1.70 1.80 1.85  The pattern f o r stakes 179 and 182 i s one i n which the greatest r e t r e a t was recorded during the f i r s t observation period i n J u l y , when the ridge and g u l l y system was strongly developed, and a decreasing rate of recession, through August and into September, as the ridges and g u l l i e s disappeared and mechanical erosion was reduced.  In comparison to t h i s , the pattern of  r e t r e a t shown by stake 190 i s one of i n c r e a s i n g rates through to l a t e August and early September, at which time the badland topography had reached i t s maximum development. With the eventual disappearance of the badland topography the i c e face undergoes more or less p a r a l l e l r e t r e a t .  On the smooth i c e face  losses are due mainly to melting i n response to incoming short and r e f l e c t ed long wave r a d i a t i o n , and the water, released by melting, follows a sinuous passage between p a r t i c l e s of a b l a t i o n debris protruding from the i c e surface.  The recession process becomes even slower as the layer of surface  d i r t accumulates to maximum thicknesses of 2-3 cms. (one i n c h ) .  Once t h i s  thickness i s a t t a i n e d , the surface d i r t becomes unstable and moves as a mud s l i d e to the base of the i c e face.  L o c a l l y , i n s t a b i l i t y may be reached  before these thicknesses are a t t a i n e d , being t r i g g e r e d by the impact of stones and debris detached from the overhanging a c t i v e layer.  An i n d i c a t -  ion of the slow nature of t h i s process was obtained by spreading a green  178 f l u o r e s c e i n dye on a clean s e c t i o n of the upper part of the c l i f f face. Despite the f a c t that the scarp face had an i n c l i n a t i o n of 66 degrees, the coloured water took a minimum of 15 minutes to seep down to the base, whereas a s i m i l a r dye introduced i n t o one of the s l i d i n g mud  slimes reached  the base i n a matter of only a few seconds. The Mudslump Cycle. The maintenance of f r e s h exposures of i c e , p e r m i t t i n g the continued recession of the scarp face, i s a c r i t i c a l f a c t o r i n f l u e n c i n g the longevity of the mudslump c y c l e . of ground i c e i s maintained  The length of time that an exposure  i n turn i s l a r g e l y determined by the d e l i c a t e  balance between the rates at which debris i s supplied t o , and removed from, the base of the scarp face. Figure 26 i s a composite p r o f i l e across a s e c t i o n of Slump B for  the period J u l y 4, 1964 to August 13, 1966,  showing the i n d i v i d u a l  mud  lobes, representing the accumulated debris derived annually from melting of the scarp face, and the approximate p o s i t i o n of the buried surface of the ground i c e as determined by a s e r i e s of d r i l l holes.  Figure 27 i s a  generalized diagram of the same p r o f i l e , showing the p o s i t i o n of the i c e 21 face at selected i n t e r v a l s during the same time period. T o t a l recession of the headwall (r) i n t h i s time amounted to a h o r i z o n t a l distance of 16.5 metres (54 f e e t ) , during which the height of the scarp face (h) decreased from an i n i t i a l value (h-^) of 9.1 metres (30 feet) to only 5.7 metres (19 feet) - (h^?) - at the end of the observation period.  This decrease, i n v o l v i n g a reduction of 37.5 per cent, was  The p r o f i l e shown i n Figures 26 and 27 was 181 (see Figure 21) .  due  located near stake  Figure 26  GARRY  ISLAND  MUDSLUMP SLUMP  |-«  Mud 1964  |  PROFILE  1964-1966  B  Lobes  19 6 5  -*-| |  1966  Vertical  Exaggeration  x2  Figure 27  RECESSION  DIAGRAM  OF  A GARRY  ISLAND  MUDSLUMP r  Depression c r e a t e d 1-6  by t h a w i n g  at base of  scarp  A p p r o x i m a t e f o r m e r positions of the ice f a c e 1 2 3  July 4, 1964 (Surveyed) September 4, 1964 July 7, 1965  4 5 6  August 10, 1965 (Surveyed) September 6, J965 August 13, 1966 (Surveyed)  1964 - 1966 H  181 p r i m a r i l y to a slow r a t e of removal of d e b r i s , as i n d i c a t e d by the gently overlapping nature of the i n d i v i d u a l annual lobes, w i t h the r e s u l t a n t b u r i a l of the basal sections of the i c e face.  The reduction would have  been even greater, 44.0 per cent, but f o r the f a c t that the height of the scarp was augmented by a r i s i n g slope of two degrees on the surface above the r i m of the mudslump. In a recent p u b l i c a t i o n , Mackay has derived an equation f o r computing the approximate thawed volume of a u n i t s e c t i o n of a mudslump, 22 provided that the excess water i s f r e e to escape.  Assuming that the  volume changes incurred during thawing of the a c t i v e layer are n e g l i g i b l e , the thawed volume i s approximately where  equal to:  r a + rV  (h - a + d)  r = the h o r i z o n t a l distance of scarp r e t r e a t a = the average thickness of the a c t i v e layer -1 V = the r a t i o of the i n i t i a l volume of frozen ground to the t o t a l volume of segregated i c e h = the height of the scarp face  and  d = the mean depth of thaw at the scarp f o o t .  The above equation was derived from a t h e o r e t i c a l s i t u a t i o n i n which there was p a r a l l e l r e t r e a t of the i c e face, w i t h no a l t e r a t i o n i n height, across a p e r f e c t l y h o r i z o n t a l surface. The major contrast between t h i s s i t u a t i o n and the one i l l u s t r a t ed i n Figure 27 i s that the height of the scarp face (h) did not remain constant i n the l a t t e r .  Since i t was found that the base points of the  surveyed p r o f i l e s i n Figure 27 were located approximately  along a s t r a i g h t  l i n e , i t was p o s s i b l e to overcome t h i s problem by averaging a s e r i e s of measurements taken d i r e c t l y from t h i s diagram.  The mean height of the  22 Mackay, J . Ross (1966) ££. c i t . , p. 71.  182 scarp face, derived i n t h i s manner, amounted to 7.5 metres (24.6 f e e t ) and t h i s value incorporates the changes brought about by the s l o p i n g of the surface to the crown of the slump and basal mantling of the i c e face by -1 thawed debris. The value of V was estimated using the nomograph included 23 i n Mackay's a r t i c l e . A t o t a l of 40 samples (Table X I I ) , c o l l e c t e d at d i f f e r e n t times from the i c e face, gave an average i c e content of 300 cent (weight of i c e to dry s o i l ) , and combining t h i s w i t h an  per  estimated  porosity of the o r i g i n a l unfrozen ground of about 0.3 y i e l d s a value f o r -1 V  of 0.15.  Representative values of the average thickness of the a c t i v e  layer (a) and the mean depth of thaw ( d ) , a l s o taken from Figure 27, were 0.46  and 0.34  metres (1.5 and 1.1 feet) r e s p e c t i v e l y . S u b s t i t u t i o n of  these values into the equation gives an approximate thawed volume along a u n i t section of 0.3 metres (1 foot) width of 7.82  cubic metres (276 cubic  feet). P l a n i m e t r i c measurement of the volume of debris shown i n Figure 27 gives a corresponding  volume of 7.13  cubic metres (252 cubic f e e t ) .  The  close s i m i l a r i t y of these two f i g u r e s i n d i c a t e s the prevalence of a very weak export of m a t e r i a l , and the degree to which most of the thawed debris derived from the melting of the scarp face merely accumulated at the f o o t of the slope.  Assuming that the present status quo remains e s s e n t i a l l y  unchanged, the longevity of the present c y c l e i n Slump B can be r e l i a b l y estimated.  A continuation of the current r a t e of reduction i n the height  of the i c e exposure, one metre (3 feet) per annum, would r e s u l t i n the termination of the c y c l e by approximately  1972.  23 Mackay, J . Ross (1966) ££. c i t . , p. 72.  183 TABLE X I I ICE CONTENTS (WEIGHT OF ICE TO DRY SOIL) OF SAMPLES TAKEN FROM EXPOSURE OF GROUND ICE IN SLUMP B. Sample  T o t a l Weight (grams)  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40  179.06 154.95 161.98 169.10 217.37 183.37 149.90 142.15 165.13 158.99 153.68 173.18 178,70 124.00 180.50 174.37 166.04 180.57 166.31 144.85 155.21 161.12 167.04 187.45 164.43 167.97 156.55 157.04 181.75 163.23 159.13 168.78 168.04 173.80 179.20 166,80 186.88 167.05 157.17 194.69  Average  167.69  Weight of I c e (grams) 112.09 114.47 94.52 123.99 133.59 111.47 107.97 113.66 110.41 131.98 143.81 86.82 133.68 98.73 103.79 100.63 121.18 132.40 95.20 115.62 123.83 109.18 118.80 114.25 95.91 123.53 93,48 120.29 142.38 121.36 127,98 123.69 128.62 100.89 130.97 140.67 142.24 134.46 119.14 148.31  Weight of Dry S o i l (grams)  Ice Contei (%)  66.97 40.48 67.46 45.11 83.78 71.90 41.93 28.49 54.72 27.01 9.87 86.36 45.02 25.27 76.71 73.74 44.86 48.17 71.11 29.23 31.38 51.94 48.24 73.20 68.52 44.44 63.07 36.75 39.37 41.87 31.15 45.09 39.42 72.91 48.23 26.13 44.64 32.59 38.03 46.38  167.37 282.78 140.11 274.86 159.45 155.03 257.50 398.95 201.77 488.63 1,457.04 100.53 296.93 390.70 135.30 136.47 270.13 274.86 133.88 395.55 394.61 210.20 246.27 156.08 139.97 277.97 148.22 327.32 361.65 289.85 410.85 274.32 326.28 138.38 271.55 538.35 318.64 412.58 313.28 319.77 299.85  184 The sequence of events i n Slump A i n d i c a t e s the manner i n which the period of mudslump a c t i v i t y may be prolonged. In August 1964, a second c y c l e of slumping was i n i t i a t e d even before the e x i s t i n g cycle had been terminated. Undercutting at the toe of the l a t t e r r e s u l t e d i n the exposure of ground ice previously buried beneath the mud debris (Plate X-D). of  By the summer  1966, the new exposure had r e t r e a t e d headward to j o i n up, and l o c a l l y  e l i m i n a t e , a l l evidence of the f i r s t c y c l e .  Unless a s i m i l a r sequence of  events exposes the ground i c e buried beneath the f l o o r of Slump B, a continua t i o n of mudslump a c t i v i t y beyond the estimated six-year period appears u n l i k e l y , and the mud surfaces w i l l gradually be colonized by a vegetation 24 succession s i m i l a r to that described i n Chapter I I I .  MUDFLOWS The s i g n i f i c a n c e of mass-wasting as a major geomorphic process i n the moulding of landforms was slowly recognized as a r e s u l t of numerous, independent studies i n a wide v a r i e t y of c l i m a t i c environments.  The  important r o l e of weathering and mass-wasting i n the s c u l p t u r i n g of A r c t i c landscapes i s generally acknowledged, and some authors regard the cumulative e f f e c t of a l l forms of mass-wasting as being the most important l e v e l l i n g 25 1  process operating i n these high l a t i t u d e s .  While t h i s may be undeniably  t r u e , these studies have been dominated by i n v e s t i g a t i o n s of slow-moving forms of mass-movement under the general heading of s o l i f l u c t i o n f e a t u r e s , whereas scant a t t e n t i o n has been paid to more rapidly-moving forms.  Most  Z4" By the summer of 1968, Slump A was v i r t u a l l y i n a c t i v e . Informa t i o n supplied by Dr. J . Ross Mackay, personal communication, October, 1968. 25 Jenness, J.L. (1952) "Erosive Forces i n the Physiography of Western A r c t i c Canada", Geog. Review, V o l . 42, p. 247.  185 of the geomorphological l i t e r a t u r e p e r t a i n i n g to mudflows f o r example cons i s t s of d e s c r i p t i o n s of these features from temperate l a t i t u d e s , and a r i d 26 or semi-arid environments i n p a r t i c u l a r . Few authors have described mudflows i n A r c t i c lands, and one has even expressed s u r p r i s e that they 27 should be important components of mass-wasting  i n these l a t i t u d e s .  This  c e r t a i n l y i s not the case i n permafrost areas u n d e r l a i n by unconsolidated sediments c o n t a i n i n g v a r i a b l e q u a n t i t i e s of segregated ground i c e . During the warm summer months, such sediments are r e a d i l y transformed from t h e i r frozen state to mobile mud s l u r r i e s , and the mudflow i s a ubiquitous feature i n these l o c a l i t i e s . In h i s c l a s s i c monograph d e a l i n g w i t h a l l forms of mass-movement, Sharpe, f o l l o w i n g e a r l i e r work done by Blackwelder, l i s t e d four major conditions which appear to be most favourable f o r the occurrence of mudflows: 1.  an abundant but i n t e r m i t t e n t water supply  2.  the absence of a s u b s t a n t i a l vegetation cover  3.  unconsolidated or deeply weathered m a t e r i a l c o n t a i n i n g enough clay or s i l t to a i d i n l u b r i c a t i o n of the mass, and 28 moderately steep slopes.  4.  In the case of mudflows on Garry I s l a n d , the moisture supply comes p r i m a r i l y from the thawing of the frozen ground, and of bodies of ground i c e i n 26 Blackwelder, E. (1928) "Mudflow as a geologic agent i n semia r i d Mountains", Geol. Soc. Amer. B u l l . , V o l . 39, pp. 465-480. Sharpe, C.F.S. (1938) Landslides and Related Phenomena, Pageant Books Inc., New Jersey, p. 4. 27 Jenness, J.L. op_. c i t . , p. 28 Sharpe, C.F.S. op_. c i t . , p. 56.  186 particular. fairly  As long as f r e s h exposures of i c e are maintained, there i s a  steady water supply throughout the summer months.  The vegetation  a s s o c i a t i o n s range from a continuous mat of herbs, shrubs and sedges on the upland surfaces, to a v a r i a b l e cover of grasses i n the case of second- or later-generation slumps.  The r e s t r i c t i n g influence of the vegetation cover  i s l i m i t e d however by the f a c t that most of the plants are only shallowrooted i n the a c t i v e l a y e r , and the recession of the i c e face frequently r e s u l t s i n an undermining of the plant cover.  The f l o o r s of the depressions,  over which the mudflows t r a v e l , are often devoid of any vegetation at a l l . Since large bodies of segregated ground i c e are best developed  i n s i l t s or  f i n e sands, the predominant mineral s i z e s accord w i t h those s p e c i f i e d by Sharpe.  The slope f a c t o r does not appear to be too c r i t i c a l i n Garry I s l a n d  flows, since the i c e faces frequently have i c e contents of several hundred per cent (expressed as the weight of i c e to dry s o i l ) , and thawing produces large q u a n t i t i e s of excess water which g r e a t l y f a c i l i t a t e mudflow movement over very gentle slopes. Sharpe's c l a s s i f i c a t i o n of mudflows recognized three w e l l defined types - semi-arid, a l p i n e and v o l c a n i c - which he claimed were 29 created d i f f e r e n t l y and bore d i s s i m i l a r r e l a t i o n s to other processes. The s i g n i f i c a n t r e l a t i o n s h i p of mudflows to other processes i n the mudslump cycle has already been a l l u d e d to i n the preceding s e c t i o n . The  perpetu-  a t i o n of t h i s c y c l e depends i n part upon the d e l i c a t e balance between r a t e s of supply of debris t o , and removal of t h i s debris from, the base of the ice scarp.  Unless the debris i s transported away, the base of the i c e face  i s buried and the height of the i c e f a c e , and consequently 29 Sharpe, C.F.S. op_. c i t . p. 57.  the p o t e n t i a l  187 volume of moisture supply which i s capable of c o n t r i b u t i n g to the m o b i l i t y of the flows, i s thus progressively attenuated. Mudflows are the primary agents r e s p o n s i b l e f o r the t r a n s p o r t a t i o n and removal of t h i s debris.  In  t h i s r e s p e c t , i t should be noted that i n a l l the mudflows studied i n the Mackenzie D e l t a area,the only f u n c t i o n a l r o l e observed was that of transporta t i o n of d e b r i s , and there was nothing to i n d i c a t e that mudflows are responsible f o r the a c t u a l excavation of the depressions as suggested by 30 Lamothe. and St-Onge.  On t h i s b a s i s , using the c l a s s i f i c a t i o n c r i t e r i a  established by Sharpe, i t seems v a l i d to d i s t i n g u i s h yet another type of mudflow - the a r c t i c - the genesis of which, and r e l a t i o n s h i p to other processes, i s uniquely or i n t i m a t e l y r e l a t e d to s p e c i f i c permafrost conditions. A l l the mudflows observed i n the Mackenzie D e l t a area are produced by seasonal thawing of the permafrost.  They occur i n a wide range  of s i z e s depending p r i m a r i l y on the nature o f , and volume of i c e contained i n , the sediments.  Small flows, often less than one metre (3 feet) wide,  and considerably shallower i n depth, descend w e l l - d e f i n e d g u l l i e s i n the c o a s t a l b l u f f s and are generated by the melting out of ice-wedges.  Since  the r a t i o of i c e to mineral s o i l i n these exposures may be quite small, and since almost a l l the debris comes from the sediments themselves, rather than from w i t h i n the ground i c e , the importance of sediment type and slope i s probably much more c r i t i c a l than i n the case of the larger flows. Channel gradients i n these g u l l i e s frequently reach 30-40 degrees.  The  influence of sediment type i s a l s o demonstrated i n these small flows.  _  _  Lamothe, C. and St-Onge, D. (1961) "A note on a p e r i g l a c i a l e r o s i o n a l process i n the Isachsen area, N.W.T.", Geographical B u l l e t i n , No. 16, p. 104.  188 The ice-wedges found i n the s i l t - c l a y b l u f f s are larger than those found i n the sand headlands, but the thawed m a t e r i a l found i n the l a t t e r l o c a l i t i e s i s not a f l u i d , mobile mud. The  l a r g e s t mudflows are found i n a s s o c i a t i o n w i t h the mud-  slumps, where i c e c l i f f s i n the headwalls may extend f o r several tens of metres h o r i z o n t a l l y and from 5-10 metres (16-33 feet) v e r t i c a l l y .  Figure  28 represents a contour map of one of these flows on the south side of Garry I s l a n d .  The mudflow i s located w i t h i n the confines of a second- or  later-generation slump, and flows over deposits, having a minimum thickness of 2.75-3.0 metres (9-10 f e e t ) , l a i d down by former mudflows. W h i l s t the main body of the mudflow occupies a w e l l - d e f i n e d channel, t h i s i s generally a secondary c h a r a c t e r i s t i c rather than the r e s u l t of flowing along a pree x i s t i n g channel.  The p o s i t i o n s of two former mudflows are shown on the  same map, and t h e i r temporal sequence was determined by the overlapping nature of the mud deposits.  The p o s i t i o n s of these successive flows are  determined by the general slope trend of the slump f l o o r , and a l s o by points of weakness i n the margins of the e a r l i e r flows. The mudflow i n Figure 28 o r i g i n a t e s at the headwall of a mudslump i n which segregated ground i c e , 2.75-3.0 metres (9-10 feet) t h i c k , i s o v e r l a i n by an average of 1.5-1.8 metres (5-6 feet) of overburden. The mudflow extends f o r a distance of approximately 80 metres (260 feet) from the base of the i c e face to the s h o r e l i n e , and three d i s t i n c t sections can be i d e n t i f i e d i n t h i s distance.  The uppermost section c o n s i s t s of a mud  r e s e r v o i r w i t h a surface area of 135 square metres (1450 square feet) and an average surface gradient of 1 i n 12 ( P l a t e XI-A).  The main channel of  the mudflow, which c o n s t i t u t e s the second s e c t i o n , extends f o r a distance of approximately 43 metres (143 feet) from the o u t l e t of the mud r e s e r v o i r  189  Old Mud  Levees  Scale  Contour interval  0.5 metres  5  Metres 10  15  190  P l a t e XI A  GARRY  ISLAND  MUDFLOW  B. Main channel of the mudflow immediately below the o u t l e t of the mud r e s e r v o i r showing the l o c a t i o n s of the upper and middle rows of markers.  C. T e r m i n a l s e c t i o n of the mudflow showing i t s descent over a wave-cut b l u f f , two p o s i t i o n s of the lower row of markers, and the s u r f a c e of the mud l o b e .  191 to the apex of the mud lobe ( P l a t e XI-B).  The width of the channel, meas-  ured from the inner margins of the mud levees, ranges from 0.75-3.0 metres (2.5-10.0 f e e t ) , and has an average surface gradient of 1 i n 10. There are two noticeable sections of the channel however, where the surface gradient i s as steep as 1 i n 2. One of these sections i s j u s t at the o u t l e t of the mud r e s e r v o i r , and the other i s at the lower end of the channel where the mudflow descends a wave-truncated b l u f f cut i n e a r l i e r mudflow deposits (Plate XI-C).  The t h i r d , and f i n a l , element of the mudflow comprises an  almost s e m i c i r c u l a r mud lobe which covers an area of j u s t over 170 square metres (1830 square f e e t ) on the foreshore ( P l a t e XI-C).  The i r r e g u l a r  nature of the eastern side of t h i s mud lobe (Figure 28) r e f l e c t s the r e s t r i c t i n g i n f l u e n c e of two large driftwood logs on the beach. lobe, which i s approximately  The mud  2 metres (6.5 feet) t h i c k near the apex, has  an average surface gradient of about 5 degrees i n c r e a s i n g to 75 degrees along the terminal edge of the lobe.  The c e n t r a l portions of the mud lobe  have a f r e s h mud surface i n which a s e r i e s of crudely concentric ridge patterns i s v i s i b l e .  The d r i e r , p e r i p h e r a l regions of the lobe however  are characterized by a well-developed  system of transverse and r a d i a l  crack patterns s i m i l a r to those found at the snouts of many g l a c i e r s .  Rates of Movement. Preliminary observations of the mudflows on Garry I s l a n d showed that they e x h i b i t e d highly i r r e g u l a r rates of movement, and attempts were made to record these rates and determine the nature of the processes i n f l u e n c i n g them.  Three l i n e s of styrofoam b a l l s , 6.5 cms. (2.5 ins.) i n  diameter, and two l i n e s of s t i c k s , approximately  50 cms. (19.5 ins.) i n  length, were i n s t a l l e d across the main channel of the mudflow. The  192 points at which the l i n e s of b a l l s were i n s t a l l e d are shown i n Figure 28. Attempts to use table tennis b a l l s as markers were unsuccessful, as they were too buoyant and were e a s i l y moved by wind and surface streams of water.. The p o s i t i o n s of the various markers were recorded at i n t e r v a l s over a 78-hour period, and the r e s u l t s are shown digrammatically i n Figure 29. In the d e s c r i p t i v e comments p e r t a i n i n g to the mud  lobe, an  analogy was made between the pattern of cracks found on the surface of the mud  lobe and those observed i n the snout regions of many g l a c i e r s .  The  flow patterns i n the mudflow, as i n d i c a t e d by the l i n e s of markers, are also analagous to those found i n some g l a c i e r s .  The greatest v e l o c i t i e s  occurred i n the centre of the channel, and there was a decrease towards the margins r e f l e c t i n g f r i c t i o n a l drag against the bordering mud (Figure 29).  levees  In curved sections of the channel, the maximum average v e l -  o c i t i e s occurred towards the outer side of the curve.  The changing  a t t i t u d e s of the l i n e s of s t i c k s a l s o i n d i c a t e d that the surface layers of the mudflow moved more r a p i d l y than the mud at depth.  As the l i n e s of  s t i c k s moved down the mudflow, the markers were gradually r o t a t e d , becoming i n c r e a s i n g l y i n c l i n e d at angles and p o i n t i n g i n a down stream d i r e c t i o n , u n t i l eventually the s t i c k s were l y i n g h o r i z o n t a l l y on the surface of the  mud. Observations over a 78-hour period showed that the upper and  middle l i n e s of b a l l s moved at average rates of 8.5 and 6.0 cms.  (3.3  and  2.4 ins.) per hour r e s p e c t i v e l y , while the lower line; of b a l l s moved at  Figure 29 MUDFLOW  -  RATES  OF  MOVEMENT  194 an average r a t e of 28 cms. (11 ins.) per hour.  31  These o v e r a l l averages  are not t r u l y representative however, since values c a l c u l a t e d f o r shorter lengths of time show that two d i s t i n c t patterns of movement were d i s c e r n i b l e during t h i s period.  During the f i r s t 24 hours of observation, the  average v e l o c i t i e s f o r the upper, middle and lower l i n e s of b a l l s were 2.5, 7.5 and 28.0 cms. (1.0, 3.0 and 11.0 ins.) r e s p e c t i v e l y , while f o r the l a s t 10 hours i n which these rates were recorded the average v e l o c i t i e s f o r the upper and middle l i n e s were 37.0 and 15.0 cms. (14.6 and 5.9 ins.) respectively, and the lower l i n e of b a l l s experienced ment.  p r a c t i c a l l y no move-  These f i g u r e s i n d i c a t e t h a t , during the 78-hour period, there was a  change from an i n i t i a l state i n which the average v e l o c i t y of the mudflow increased f a i r l y r e g u l a r l y towards the terminal mud lobe, to a l a t e r state i n which the greatest average v e l o c i t i e s were recorded i n the s e c t i o n of the channel immediately below the o u t l e t of the mud r e s e r v o i r . The observation period to which the above values apply  ended  at 6.30 p.m. on August 20, 1966. The mudflow was not v i s i t e d again u n t i l 6.00 p.m. the f o l l o w i n g day when i t was found that several major changes had taken place.  A l l the b a l l s , w i t h the exception of two which had been  l e f t stranded on the mud levees,' had been transported down onto the surface of the mud lobe, i n d i c a t i n g that much greater v e l o c i t i e s had occurred during t h i s time p e r i o d . ( P l a t e XII-A).  Markers located i n the upper l i n e  of b a l l s f o r example, which had previously moved a t o t a l of 6.6 metres (21.7 feet) over a period of 78 hours or an average r a t e of 8.5 cms.  These averages represent the mean values of each of the b a l l s i n each l i n e excluding those which were l e f t stranded on the mud levees. Since the lower l i n e of b a l l s was located near to the terminal s e c t i o n of the channel, the markers were frequently r e l o c a t e d and the r a t e c i t e d i s a c t u a l l y an average of three independent sets of measurements.  195  Plate  MUDFLOW  A.  Appearance  lobe surge  -  XII  SURGE  PHENOMENA  o f t h e mud  f o l l o w i n g a period of flow,  f r e s h mud  showing the  surface  transported  and t h e  markers.  B.  Fresh  scour  margins  w h i c h mud channel  C.  Deformation  of  organic  on t h e b e a c h  produced  by t h e a d v a n c i n g  mud  lobe.  and  on t h e i n n e r  o f a mud  indicating  material  striations  marks  levee,  the l e v e l to rose  during  i n the the  surge.  196 (3.4 ins.) per hour., had since been transported an a d d i t i o n a l 48.8 (160 feet) i n only 24 hours;  metres  an average r a t e of s l i g h t l y more than  2 metres (6.6 feet) per hour.  Studies made on other mudflows on the i s -  land show that the v e l o c i t i e s achieved during these surges are considerably higher than those i n d i c a t e d by t h i s average.  During the summer of  1964', a mudflow of s i m i l a r dimensions, located i n the f l o o r of another mudslump, reached v e l o c i t i e s ranging from 1.5-3.0 metres (5-10 feet) per second during one of these surges. As a r e s u l t of t h i s surge, small blocks, previously bounded by d e s i c c a t i o n cracks, were plucked from the inner margins of the mud  levees.  Fresh s t r i a t i o n s and scour marks on these same levees i n d i c a t e that the l e v e l of the mud rose 45-60 cms. the channel ( P l a t e X I I - B ) .  (17.5-23.5 ins.) w i t h i n the confines of  The edge of the mud  lobe advanced by distances  ranging from 1.75-3.5 metres (5.5-11.5 f e e t ) , pushing ahead of i t r a f t s of washed organic m a t e r i a l on the beach ( P l a t e XII-C). approximately  A large driftwood l o g ,  20.5 metres (67 feet) long and up to 0.6 metres (2 feet) i n  diameter, which was anchored on the beach by a 0.9-1.2 metre (3-4- foot) root spread, was a l s o pushed b o d i l y forward by the advancing edge of the lobe.  During t h i s p a r t i c u l a r surge, the mud  lobe d i d not reach the sea,  but on numerous other occasions i t was observed that mudflows had b u i l t prominent lobes out i n t o the sea. underfoot, the mud  Although these lobes are extremely s o f t  i s highly tenacious, and many lobes may r e s i s t wave  erosion f o r several weeks before they are f i n a l l y o b l i t e r a t e d - u s u a l l y during storm surges. The c h a r a c t e r i s t i c wave-like motion of mudflows has been  197 32 described by numerous authors.  Sharp and Nobles, i n t h e i r d e s c r i p t i o n  of the Wrightwood mudflow i n Southern C a l i f o r n i a , gave the f o l l o w i n g account of the flow: "The debris came down the channel above Wrightwood i n a succession of waves o r , more a p p r o p r i a t e l y , surges which u s u a l l y started about 9:00 or 9:30 i n the morning, reached a peak of frequency i n the early afternoon, and tapered o f f to an end by l a t e afternoon. F l u i d i t y was greatest at midday when the surges succeeded each other at i n t e r v a l s of a few seconds to tens of minutes. At other times, p a r t i c u l a r l y i n late, phases of the a c t i v i t y , hours intervened between surges".^3 In another study of the same mudflow, four p o s s i b l e explanations of the surges were offered:  (1) p e r i o d i c sloughing of debris i n the source area;  (2) temporary choking of the channel;  (3) caving of undercut banks; and 34  (4) f r i c t i o n between the moving debris and the channel.  The f i r s t two  f a c t o r s , considered to be the most s i g n i f i c a n t i n the case of the Wrightwood mudflow, appear to be the most s a t i s f a c t o r y explanations f o r the surge phenomena e x h i b i t e d by the mudflows on Garry I s l a n d .  The  immediate  cause of the Wrightwood flow was the melting of winter snow i n the head regions, and the p e r i o d i c i t y of the surges, w i t h maximum frequency occurring during the daytime and a lack of flowage at n i g h t , was thought 35 to be r e l a t e d to d i u r n a l v a r i a t i o n s i n the amount of melting.  I t was  hoped that i t would be possible to check t h i s r e l a t i o n s h i p on Garry 3  ^ F o r example, Blackwelder, E„ (1928) op_. c i t . , pp.. 465-480.  S h a r p , R P. and Nobles, L„H. (1953) "Mudflow of 1941 at Wrightwood, Southern C a l i f o r n i a " , Geol. Soc. Amer. B u l l . , V o l . 64, p. 551. 33  C  34 I b i d . , p. 551. The a r t i c l e c i t e d i s Gleason, C.H. and Amidon, R.E. (1941) "Landslide and mudflow, Wrightwood, C a l i f o r n i a " , C a l i f o r n i a Forest and Range Experiment S t a t i o n , Unpub. r e p o r t , pp. 1-7. 35  S h a r p , R.P. and Nobles, L.H„  (1953) op_. c i t . , p. 551.  198 I s l a n d , since the occurrence of the mudflows i s i n t i m a t e l y r e l a t e d to the thawing of i c e bodies i n the permafrost.  Accordingly, hourly  observations  of the amount of movement and rates of a b l a t i o n of the i c e face, measured by recording the exposed length of n a i l s driven i n t o the i c e , were made continuously over a 32-hour period to determine whether or not there was any c o r r e l a t i o n . The values obtained during t h i s period showed that there was l i t t l e or no s t a t i s t i c a l c o r r e l a t i o n between the r a t e of movement of the mudflow and the r a t e of a b l a t i o n of the i c e face.  The a b l a t i o n measure-  ments, crude as they were, d i d show evidence of a d i u r n a l c y c l e , but there was no evidence of a s i m i l a r c y c l e i n the mudflow v e l o c i t i e s . upper l i n e of b a l l s experienced  Indeed, the  p r a c t i c a l l y no movement at a l l .  Figures  for the maximum movements encountered i n both the middle and lower l i n e s of b a l l s showed that there was a progressive decrease i n the r a t e of movement throughout the period. Attempts were also made to determine the i n f l u e n c e of the v i s c o s i t y of the mud on the flow using the formula given by Sharp and Nobles:  36  2 n = dg sin© Z  0  where  n = the c o e f f i c i e n t of v i s c o s i t y d = the density of the f l u i d debris g = the g r a v i t a t i o n a l force © = the angle of slope of the ground Z= Q  the thickness of the flow (cms.)  Sharp, R.P. and Nobles, L.H. (1953) o£. c i t . , p. 552.  199 and  V  s  = the v e l o c i t y at the surface (cms./sec.)  The use of t h i s formula involves s i m p l i f y i n g assumptions, among which are Newtonian v i s c o s i t y , no marginal or terminal i n f l u e n c e s , no s l i p on the base and no shear s t r e s s on the upper surface, and laminar flow p a r a l l e l to the base.  Of these assumptions, only the second one i s perhaps completely  v a l i d , since the surface v e l o c i t y value i s a maximum taken from the centre of the mudflow. Since the density of the f l u i d was not measured d i r e c t l y , an approximation was made using the data f o r the weight of mineral s o i l and weight of water i n each of the samples taken, and a value of 2.65  gm  cm  as the average u n i t weight of the s o i l d e b r i s . Using the l a t t e r f i g u r e , an equivalent volume was obtained f o r the s o i l , and the o v e r a l l density of the sample was then c a l c u l a t e d .  The c a l c u l a t i o n s of the c o e f f i c i e n t s of v i s -  c o s i t y of the mud at the three l i n e s of b a l l s are shown i n Table X I I I .  TABLE X I I I COEFFICIENT OF VISCOSITY OF A GARRY ISLAND MUDFLOW d  sin 9  z  Upper B a l l s  1.7  .0698  88,4  .00088  5.17 x  10 poises  Middle B a l l s  1.7  . 1045  82.3  .00124  4.72 x  10 poises  Lower B a l l s  1.7  .1736  39.6  .00353  6.39 x  10 poises  n  o  8  8  7  As these f i g u r e s i n d i c a t e , there i s an expected inverse r e l a t i o n s h i p between v i s c o s i t y and r a t e of flow; v i s c o s i t y , the slower the movement.  i . e . the higher the  Since each of the samples taken had  the same f l u i d d e n s i t y , the most s i g n i f i c a n t f a c t o r s i n f l u e n c i n g the r a t e  200 of movement appear to be the angle of slope and the thickness of the flow. In summary, i t i s apparent that the mudflows on Garry I s l a n d e x h i b i t two types of flow which occur i n an a l t e r n a t i n g sequence, a l b e i t with variable periodicity.  The c o n t r o l l i n g f a c t o r determining the type of  flow i s the temporary b l o c k i n g of the channel, i n t h i s case j u s t below the o u t l e t of the mud r e s e r v o i r .  Once blockage  ;  of the channel occurs, e i t h e r  by stagnation of the mud deposit or by clumps of organic m a t e r i a l , the downstream sections of the mudflow are deprived of a d d i t i o n a l supplies of debris, although continued l u b r i c a t i o n of the flow may be aided by streams of meltwater which percolate through and around the blockage.  During t h i s  period the mudflow e x h i b i t s a form of extending f l o w , as witnessed by a pattern of i n c r e a s i n g v e l o c i t i e s i n a downstream d i r e c t i o n ;  an o v e r a l l  general decrease i n a l l v e l o c i t i e s as the l e v e l of the mud i n the channel i s lowered;  and the accompanying development of lunate tension cracks  across the surface of the mud.  Under these flow c o n d i t i o n s , the i n f l u e n c e  of the gradient of the channel f l o o r appears to be more s i g n i f i c a n t than the thickness of the mudflow, since the lower l i n e of b a l l s moved f a s t e r than e i t h e r of the other two l i n e s despite the f a c t that the thickness of the flow was only one-half as great as at the other l o c a l i t i e s .  The de-  crease i n the v e l o c i t i e s towards the end of t h i s phase of extending flow, besides r e f l e c t i n g the t h i n n i n g of the f l o w , probably r e f l e c t s the f a c t t h a t , as the mud levees were exposed, i n c r e a s i n g q u a n t i t i e s of water were channelled off through d e s i c c a t i o n cracks. The phase of extending flow i s terminated f i r s t i n the upper reaches of the mudflow, as shown by the increased v e l o c i t i e s recorded i n t h i s s e c t i o n towards the end of the observation period.  This t r a n s i t i o n  takes place when the accumulation of mud i n the r e s e r v o i r b u i l d s up  201 s u f f i c i e n t pressure to force the blockage of debris downstream.  The i n -  creased v e l o c i t i e s recorded at the upper l i n e of b a l l s corresponded the removal of debris from the c o n s t r i c t i o n j u s t below t h i s l i n e .  with Once the  m a t e r i a l choking the channel has been c l e a r e d , the contents of the mud r e s e r v o i r are discharged r a p i d l y , and the mudflow a t t a i n s i t s greatest v e l o c i t i e s during these pressure surges.  The frequency w i t h which these  surges occur depends on the s i z e and nature of the blockage, the most favourable l o c a t i o n s f o r which are points of c o n s t r i c t i o n or slackening gradient i n the channel, and the r a t e of debris accumulation, and consequently pressure build-up,, i n the r e s e r v o i r area or upstream sections of the channel.  In a d d i t i o n to the pressure f a c t o r , the augmented v e l o c i t i e s  during these surges may a l s o be r e l a t e d to v i s c o s i t y changes as the t h i c k ness of the mudflow increases. Mud Levees. The edges of many mudflows, i r r e s p e c t i v e of t h e i r s i z e , are 37 marked by sharp, l i n e a r ridges termed mud a c t i v e and i n a c t i v e mud Mud  levees.  Figure 28 shows both  levees bordering a s e r i e s of mudflows.  levees are generally symmetrically arranged on e i t h e r side  of the median channel, but there may be a marked asymmetry, w i t h broader, higher levees on the outer curves, where the course of the mudflow i s sinuous.  The r i d g e s , the c r e s t s of which may be e i t h e r sharp or rounded,  vary i n height from only a few centimetres to almost one metre (3 f e e t ) . These heights normally increase towards the terminal portions of the f l o w , but the pattern i s by no means uniform since high ridges o f t e n occur at Sharp, R.P. No. 5, pp. 222-227.  (1942) "Mudflow Levees", J o u r n a l of Geomorphology,  202 points of c o n s t r i c t i o n i n the channel i r r e s p e c t i v e of t h e i r l o c a t i o n along i t s length.  The i n d i v i d u a l levees are highly asymmetrical w i t h the inner  margins being shorter and steeper than the outer sides. r e f l e c t s the f a c t that the inner margin of a mud  This d i f f e r e n c e  levee i s i n i t i a l l y pro-  duced by shearing, along more or less v e r t i c a l planes, developed between mud which has stagnated along the outer edges of the flow and less viscous mud  s t i l l moving i n the a x i a l part of the flow.  The inner faces of levees  bordering a c t i v e mudflows are often characterized by d i s t i n c t i v e scour marks or s t r i a t i o n s i n d i c a t i n g t h a t , once e s t a b l i s h e d , t h e i r slopes may  be  modified by e i t h e r the erosive or p l a s t e r i n g a c t i o n of subsequent mudflows moving down the same channel.  The outer slopes of the mud  levees on the  other hand are shaped e n t i r e l y by d e p o s i t i o n , and they frequently e x h i b i t a m u l t i - l o b a t e character where small flows have topped the c r e s t s of the ridges and cascaded down the outer sides. Excavations of mud  levees bordering i n a c t i v e flows showed that  they are composed of s i l t and clay w i t h very few stone accumulations. upper parts of the levees often e x h i b i t a weak s t r a t i f i c a t i o n . ridges are composed e s s e n t i a l l y of s o l i d i f i e d mud,  The  Since the  t h e i r surfaces are f r e -  quently covered w i t h networks of d e s i c c a t i o n cracks.  Excavations were  a l s o made across the channels of i n a c t i v e mudflows, and these often contained a l a r g e r number of stones than the adjacent levees. In the only d e f i n i t i v e paper r e l a t i n g to mud  levees, Sharp,  describing features i n the St. E l i a s Range, Yukon T e r r i t o r y , a t t r i b u t e d them to be r e s i d u a l features of bouldery a l l u v i u m pushed aside by advan38 cing streams of mud.  3 8  Ibid.  The mudflows on Garry I s l a n d do not traverse  203 steep, boulder-strewn  slopes s i m i l a r to those described by Sharp i n the  mountainous t e r r a i n of the St. E l i a s Range. of the mud  The s t r u c t u r e and  composition  levees on Garry I s l a n d suggest that they o r i g i n a t e i n an en-  t i r e l y d i f f e r e n t manner, and studies of a c t i v e mudflows i n d i c a t e that the levees are produced by a progressive bleeding of moisture from the mud:flows.  The mud  ..  loses water by d i r e c t surface runoff and by p e r c o l a t i o n  i n t o the underlying ground, a process which i s often aided by f r o s t and d e s i c c a t i o n cracks covering the surface, u n t i l the v i s c o s i t y i s such that motion ceases.  This stagnation process occurs f i r s t along the outer  margins of the f l o w , while the c e n t r a l parts are s t i l l r e l a t i v e l y and continue to move. of the stagnant mud,  mobile  Shear surfaces are developed along the inner margins  and t h i s produces the c e n t r a l channel between the  bordering ridges or levees.  The height of the ridges may be increased  by temporary choking of the channel and l a t e r a l s p i l l i n g of the  mud,  which explains the weak s t r a t i f i c a t i o n observed i n the excavations.  In  extreme cases, and e s p e c i a l l y during the pressure surges, the mud may comp l e t e l y override the levees at low, or weak, points and e s t a b l i s h an e n t i r e l y new  course.  PATTERNED GROUND Patterned ground, which may be c l a s s i f i e d on the basis of geometric shape and presence or absence of s o r t i n g , i s a widely-adopted  term  f o r the more or less symmetrical forms, such as c i r c l e s , polygons, nets, steps and s t r i p e s , that are c h a r a c t e r i s t i c o f , though not n e c e s s a r i l y  204 39 confined t o , a mantle subject to i n t e n s i v e f r o s t a c t i o n .  Patterned  ground i n the Mackenzie Delta area i s r e s t r i c t e d p r i m a r i l y to non-sorted types.  Although other f a c t o r s may be involved, the absence of the sorted  forms can l a r g e l y be a t t r i b u t e d to the f a c t that the mantle frequently lacks a s u f f i c i e n t concentration of stones to e x h i b i t marked f r o s t 40 sorting.  This d i s c u s s i o n of patterned ground features on Garry I s l a n d  i s r e s t r i c t e d to a consideration of some aspects of the development of two of the non-sorted forms:  tundra, or ice-wedge, polygons and earth  hummocks.^ Tundra Polygons. Of the non-sorted forms, tundra or ice-wedge polygons cons t i t u t e one of the most widespread types of patterned ground i n the Mackenzie Delta area.  Readily d i s c e r n i b l e on a e r i a l photographs, the  ground e x h i b i t s a polygonal m i c r o r e l i e f pattern formed by the i n t e r s e c t i o n of shallow furrows underlain by ground ice-wedges.  L e f f i n g w e l l , working  on the c o a s t a l p l a i n of North A l a s k a , was among the f i r s t to postulate that the networks of tundra polygons were generated by c o n t r a c t i o n cracks i n the frozen ground, produced by intense stresses created as a r e s u l t of 39 Washburn, A.L. (1956) " C l a s s i f i c a t i o n of Patterned Ground and review of suggested o r i g i n s " , Geol. Soc. Amer. B u l l . , V o l . 67, p. 284. 40 Mackay, J . Ross (1963) "The Mackenzie Delta area, N.W.T.", Geographical Branch Memoir, No. 8, p. 69. ^ A few crudely-sorted stone c i r c l e s were discovered on the f l o o r s of a number of shallow, a r t i f i c i a l l y drained lakes on the i s l a n d . See Mackay, J . Ross (1967) " Underwater patterned ground i n a r t i f i c i a l l y drained lakes, Garry I s l a n d , N.W.T.", Geographical B u l l e t i n , V o l . 9, pp. 33-44.  205 pronounced seasonal changes i n the ground temperature.  H i s 'thermal  contraction' theory was o u t l i n e d as f o l l o w s : "The permanently frozen ground contracts i n the cold A r c t i c winter and cracks are formed which divide the surface i n t o polygonal blocks. In the spring these f r o s t cracks become f i l l e d w i t h surface water which immediately freezes. I n the expansion of the frozen ground as the temperature r i s e s i n summer, the v e i n of i c e becomes more r i g i d than the country formation, and the readjustment takes place i n the l a t t e r . The r e s u l t i s to bulge up the inclosed block e i t h e r bodily or else l o c a l l y along the sides of the i c e . During the next winter's cold wave a new crack forms at the same locus so that a c o n t i n u a l l y growing wedge of ground i c e i s formed. Thus the tundra becomes underlain by a network of ice-wedges, which i n c l o s e bodies of the o r i g i n a l formation',.'.^-} The general p r i n c i p l e s of L e f f i n g w e l l s c o n t r a c t i o n theory 1  have been accepted by most of the subsequent research workers i n v e s t i g a t i n g tundra polygons.  Despite the voluminous l i t e r a t u r e on t h i s subject,  however, the precise d e t a i l s of t h e i r o r i g i n are s t i l l imperfectly understood.  Black and Lachenbruch a t t r i b u t e some of t h i s ignorance to an  absence of q u a n t i t a t i v e , rather than q u a l i t a t i v e , data but i t may a l s o r e f l e c t the paucity of observations d e s c r i b i n g the i n i t i a l development of 44 the  f r o s t crack patterns.  ^ L e f f i n g w e l l , E. de K. (1915) "Ground Ice-wedges. The Dominant form of Ground Ice on the North Coast of A l a s k a " , Journal of Geology, V o l . 23, pp. 635-654. L e f f i n g w e l l , E. de K. (1919) "The Canning River Region, Northern Alaska",. U.S.G.S. P r o f e s s i o n a l Paper, No. 109, 251 p. 43 L e f f i n g w e l l , E. de K. (1915) op_. c i t . , p. 654. 4 J  ^ B l a c k , R.F. (1952) "Polygonal patterns and ground conditions from a e r i a l photographs", Photogrammetric Engineering, V o l . 18, p. 124. Lachenbruch, A.H. (1962) "Mechanics of Thermal Contraction Cracks and Ice-Wedge Polygons i n Permafrost", Geol. S o c . Amer. S p e c i a l Paper, No. 70, p. 5.  206 I n c i p i e n t F r o s t Crack P a t t e r n s .  An examination of the l i t e r -  ature p e r t a i n i n g to tundra polygons reveals abundant references t o , and d e s c r i p t i o n s o f , the polygonal ground i n r e l a t i v e l y advanced stages of development, but s u r p r i s i n g l y l i t t l e r e l a t i n g to the formation of the i n i t i a l f r o s t crack patterns.  L e f f i n g w e l l shows i l l u s t r a t i o n s of i n c i p i e n t 45  cracks on the c o a s t a l p l a i n of north A l a s k a , 46 reference t o s i m i l a r features.  and Black a l s o makes b r i e f  Lachenbruch has made a t h e o r e t i c a l study  of f r o s t crack patterns i n h i s examination of L e f f i n g w e l l s thermal con1  t r a c t i o n hypothesis from the point of view of mechanics, but he does not 47 c i t e any f i e l d evidence to corroborate h i s conclusions. Washburn et a l . , to the w r i t e r ' s knowledge, have produced the only recent paper d e s c r i b i n g 48 the occurrence of f r o s t cracks, a l b e i t i n a non-arctic environment. Observations i n the Mackenzie D e l t a area during the summers of 1964 and 1965 revealed three l o c a t i o n s where i n c i p i e n t f r o s t cracks had developed on the ground surface.  The l o c a t i o n s , each c h a r a c t e r i z e d by an  absence of any major r e l i e f features and e l e v a t i o n s of less than one metre (3 f e e t ) above mean sea l e v e l , included lake-strewn, a l l u v i a l f l a t s on K e n d a l l and Grassy Islands and the f l a t s bordering the lagpons enclosed behind sandspits on Garry I s l a n d . A l l of these s i t e s are frequently inundated during periods of high water, e s p e c i a l l y during storm surges.  The  f r o s t cracks were found to be equally w e l l developed on bare ground 4 5  4 6  L e f f i n g w e l l , E. de K. (1919) 0 £ . c i t . , B l a c k , R.F. (1953) op_. c i t . , p. 130.  ^Lachenbruch, A.H. (1962) op_. c i t . Washburn, A.L., Smith, D.D. and Goddard, R.H. (1963) "Frost Cracking i n a Middle-Latitude Climate", B i u l e t y n P e r y g l a c j a l n y , Nr. 12, pp. 175-189. 48  207 surfaces ( P l a t e X I I I - A ) , and on f l a t s supporting a dense cover of grasses and sedges 20-40 cms. (8.0-15-5 ins.) t a l l (Plate X I I I - B ) .  I n these  l a t t e r areas, the vegetation was f l a t t e n e d , presumably by a combination of p r e v a i l i n g winds, snowfall and f l o o d surges i n the preceding f a l l .  The  vegetation was cut by sharp, k n i f e - l i k e f r a c t u r e s and was probably f r o z e n to the ground surface at the time of the f r o s t cracking to produce the clean break.  I n many places, the cracks were observed to extend beneath  the surfaces of shallow lakes, though none were traced e n t i r e l y across the lake f l o o r .  This i n d i c a t e s that the water, a t l e a s t i n the shallower  parts of the lakes, was frozen to the bottom although water i n the c e n t r a l sections of the lakes may have remained unfrozen a t depth.  The f a c t that  the f i s s u r e s on K e n d a l l I s l a n d cut through the vegetation i n t o the underl y i n g mineral s o i l , would appear to substantiate the view that the cracks were produced by i n t e n s i v e f r o s t a c t i o n ,  The cracks on the bare ground  surfaces are i n t e r p r e t e d as having o r i g i n a t e d i n a s i m i l a r manner, although the p o s s i b i l i t y that they were produced by d e s i c c a t i o n of the s o i l cannot d e f i n i t e l y be excluded. Excavations i n one of the sandspit-lagoon areas on Garry I s l a n d revealed that the f r o s t cracks were best developed i n o r g a n i c - r i c h s i l t s and s i l t y loams.  Mechanical analyses of the s o i l s showed that they  were composed of 59.2 per cent s i l t , 21.3 per cent sand, and 19.5 per cent clay (Wentworth c l a s s i f i c a t i o n c a t e g o r i e s ) .  The s o i l s were mantled by a  t h i n layer of organic m a t e r i a l , and the organic content of the s o i l samples averaged 5.5 per cent by weight of the d r i e d sample.  The s u r f i c -  i a l organic layer and the organic matter at depth, often i n the form of t h i n i n t e r c a l a t i o n s , probably represent*washed erosion of the adjacent c o a s t a l b l u f f s .  peat derived through  The s o i l s a l s o possessed a high  Plate XIII INCIPIENT  FROST  CRACK  PATTERNS  209 moisture content, w i t h frozen samples having an average i c e content of 91.7 per cent (expressed as weight of i c e to dry s o i l ) .  Mackay has a l -  ready documented the granulometric composition of the s o i l s underlying the sedge-covered  f l a t s on K e n d a l l I s l a n d , where the proportions of clay and  sand were s l i g h t l y lower ( s i l t 79 per cent, sand 13 per cent and clay 8  v 49 per cent). Most of the f r o s t cracks e x h i b i t e d l i t t l e or no topographic expression at the ground surface, but some of the larger f i s s u r e s t r a v e r s i n g the unvegetated areas were marked by the presence of shallow troughs 30-70 cms. (12.0-27.5 ins.) across and 10-20 cms.  (4-8 ins.) deep.  When examined i n early August, 1964, the f r o s t cracks on Garry I s l a n d exh i b i t e d a wedge-like form extending down through the a c t i v e layer and i n t o the frozen ground at depths of 50 cms. face.  (19.5 ins.) below the ground sur-  At the surface, the open f i s s u r e s were up to 4 cms.  across, and they remained open to depths of 15-25 cms.  (1.5 ins.)  (6-10 ins.) but  narrowed to only a few m i l l i m e t r e s i n width at the l e v e l of the f r o s t table.  I n many l o c a l i t i e s , the cracks were i n f i l l e d at depth by sand-size  m a t e r i a l that had probably been blown or washed i n from the ground surface.  These miniature sand-wedges are s i m i l a r i n form to the larger scale  features described by Pewe i n the McMurdo Sound area of A n t a r c t i c a . Below the l e v e l of the f r o s t t a b l e , the cracks were occupied by small veins of i c e , approximately one m i l l i m e t r e across, which could be traced  Mackay, J . Ross (1965) "Gas-domed mounds i n permafrost, Kendall I s l a n d , N.W.T.", Geographical B u l l e t i n , V o l . 7, p. 108. 50  '  '  Pewe, T.L. (1959) "Sand-Wedge Polygons (Tesselations) i n the McMurdo Sound Region, A n t a r c t i c - A Progress Report", Amer. Jour., S c i . , Vol.. 257, pp. 545-552.  210 to a depth of 76 cms.  (30 ins.) below the ground surface.  Rarely did the f r o s t cracks i n the sandspit-lagoon areas of Garry I s l a n d r e v e a l any arrangement i n t o a d e f i n i t e polygonal network. The majority of the f i s s u r e s appeared to be randomly d i s t r i b u t e d over the ground surface, and showed no preferred d i r e c t i o n a l o r i e n t a t i o n except f o r a weak tendency to occur along l i n e s developed at r i g h t angles and p a r a l l e l to the margins of the lagoons.  The only other s a l i e n t feature of the d i s -  t r i b u t i o n was the contrast i n the density of the pattern between the s i l t y loam and coarser sand areas of the sandspit.  Although the f r o s t  cracks were present i n both of these areas, the density was much higher i n the s i l t y loam s e c t i o n s . The d i s t r i b u t i o n of the f r o s t cracks on K e n d a l l and Grassy Islands showed a much greater tendency to be organized i n t o crude polygona l patterns.  Figure 30 i s a map  showing the s p a t i a l arrangement of the  f r o s t cracks on a part of the sedge-covered f l a t on K e n d a l l I s l a n d . t h i s diagram shows, the ground surface was  As  subdivided i n t o a number of  highly i r r e g u l a r polygons of v a r i a b l e size, but averaging 2-3 metres (6.510.0 f e e t ) across.  The majority of these i r r e g u l a r l y - s h a p e d polygons  were f o u r - or f i v e - s i d e d , and hexagonal forms were notably conspicuous by t h e i r absence.  Most of the f i s s u r e s on K e n d a l l I s l a n d a l s o e x h i b i t e d  l i t t l e preferred d i r e c t i o n a l o r i e n t a t i o n except i n the v i c i n i t y of the larger water bodies. The s p a t i a l d i s t r i b u t i o n of the f r o s t cracks on Grassy I s l a n d demonstrated the existence of a much more regular polygonal network, a l though on a considerably l a r g e r s c a l e .  On these bare a l l u v i a l f l a t s the  i n d i v i d u a l polygons averaged 20-30 metres (65-100 f e e t ) across, and ragonal forms were predominant.  The pattern of these f r o s t cracks  tet-  211 Figure 30 INCIPIENT  FROST  KENDALL  CRACK  ISLAND,  PATTERN  N.W.T.  212 moreover revealed much stronger trends i n t h e i r preferred d i r e c t i o n a l orientation.  The  larger f i s s u r e s , up to 5 cms.  (2 ins.) wide and  located  i n the f l o o r s of shallow troughs i n the ground surface, were oriented at r i g h t angles to the bank of a d i s t r i b u t a r y of the Mackenzie R i v e r . smaller cracks, less open and having almost no topographic  expression  The on  the ground surface, on the other hand were aligned more or l e s s p a r a l l e l to the same r i v e r bank.  These preferred o r i e n t a t i o n s were e s p e c i a l l y  noticeable w i t h i n distances of approximately 50-60 metres (165-200 feet) -~ from the edge of the channel, but became less d i s t i n c t w i t h i n c r e a s i n g d i s tance from the bank. I t i s generally agreed that f r o s t cracks o r i g i n a t e as a r e s u l t of large thermal stresses created by a sudden c o o l i n g of the ground. "When the t e n s i l e strength (of the ground) i s exceeded near the surface, a tension crack forms and propogates downward. ... The formation of a crack causes a l o c a l r e l i e f of tension i n the s u r f i c i a l m a t e r i a l s . ... Each crack i s , t h e r e f o r e , surrounded by a band i n which cracking has caused appreciable reduction of h o r i z o n t a l tension - the "zone of s t r e s s r e l i e f " . ... The component of thermal tension at the ground surface i n the d i r e c t i o n p a r a l l e l to the crack i s r e l i e v e d only s l i g h t l y , by the cracking and, thus, large h o r i z o n t a l s t r e s s d i f f e r e n c e s occur w i t h i n the zone of stress r e l i e f . A second crack entering t h i s zone tends to a l i g n i t s e l f perpendicular to the d i r e c t i o n of greatest t e n s i o n , and, hence, tends to i n t e r s e c t the f i r s t crack at r i g h t angles. Conversely, the occurrence of an orthogonal i n t e r s e c t i o n generally implies that one of the cracks predated the other". Lachenbruch's conclusion that the angular i n t e r s e c t i o n s of a polygonal network of f r o s t cracks w i l l e x h i b i t a preferred tendency toward an orthogonal p a t t e r n , contrasts w i t h many d e s c r i p t i o n s of  " l a c h e n b r u c h , A.H.  (1962) op_. c i t . , pp. 57-58.  polygonal  213 ground i n which authors have expressed a tendency f o r hexagonal forms and 52 angular i n t e r s e c t i o n s of 120° to predominate.  The i m p l i c a t i o n s of the  hexagonal p a t t e r n , and angular i n t e r s e c t i o n s of 120°, are that the f r o s t cracks o r i g i n a t e d at a s e r i e s of points and each crack developed more or less simultaneously.  In an attempt to determine the v a l i d i t y of Lachen-  bruch' s conclusion, p a r t i c u l a r a t t e n t i o n was paid to the nature of the angular i n t e r s e c t i o n s of the f r o s t crack patterns on Garry and adjacent islands.  A t o t a l of 101 angular measurements was recorded i n c l u d i n g those  shown i n Figure 30. An a d d i t i o n a l f i f t y i n t e r s e c t i o n patterns are. i l l u s t r a t e d diagrammatically i n Figure 31, where an attempt has a l s o been made to i n d i c a t e the r e l a t i v e order of occurrence and propogational d i r e c t i o n of each of the f i s s u r e s .  Primary f r o s t cracks, u s u a l l y the l a r g e r , are  defined as those which o r i g i n a t e d f i r s t at any l o c a t i o n , and t h e i r propogational d i r e c t i o n s were i n f e r r e d , wherever p o s s i b l e , from t h e i r o r i e n t a t i o n w i t h respect to the water bodies ( i . e . cracks which were oriented a t r i g h t angles t o , and propogated outward from, the body of water).  Secondary f r o s t cracks are defined as those which developed l a t e r  at each l o c a t i o n , and these cracks terminate a t , and propogate towards, p r e - e x i s t i n g primary f i s s u r e s . Of the 101 angular measurements recorded, no fewer than 79, or eighty per cent, were of the orthogonal type. As Figures 30 and 31 i n d i c a t e , most of these orthogonal i n t e r s e c t i o n s were formed by the For example: L e f f i n g w e l l , E. de K. (1915) op_. c i t . , p. 638. Black, R.F. (1953) op_. c i t . , p. 129. Conrad, V. (1946) "Polygon Nets and t h e i r P h y s i c a l Development", Amer. Jour. S c i . , V o l . 244, pp. 277-296.  214 Figure 31 DIAGRAMMATIC FROST  CRACK  SKETCHES  INTERSECTION  OF PATTERNS  T II  ILL.  Primary •  Frost  Secondary •  Frost  Orthogonal  60  Angle  —»-  Inferred  of  Cracks Cracks  Intersections  Intersection Pro p o g a t i o n a l  in  Degrees  Directions  of  Cracks  215 junction of a primary and secondary f r o s t crack, and only r a r e l y were two primary f r o s t cracks observed to i n t e r s e c t one another.  The i n f l u e n c e of  a zone of s t r e s s r e l i e f i s a l s o manifest i n the manner i n which many of the secondary f i s s u r e s curve to i n t e r s e c t the primary cracks at r i g h t angles. Where the primary cracks were sinuous, the most favoured l o c i f o r the i n t e r s e c t i o n points of secondary f r o s t cracks were located on the convex sides of the curves.  This i s i n accordance w i t h the d i s t r i b u t i o n a l pattern  of s t r e s s r e l i e f on a curved s e c t i o n of a f r o s t crack as described by 53 Lachenbruch. Angular i n t e r s e c t i o n : values of 60° were by f a r the most common of the non-orthogonal  i n t e r s e c t i o n patterns.  This angle was most f r e -  quently developed as a r e s u l t of the b i f u r c a t i o n of a primary f r o s t crack, and a t points of i n t e r s e c t i o n where two f r o s t cracks of the same order approached one another o b l i q u e l y . Very few of the angles measured were neither 90° nor 60°; and only two examples were found of t r i - r a d i a l i n t e r s e c t i o n s , forming three obtuse angles of about 120°, suggesting that the f r o s t cracks o r i g i n a t e d a t a point ( P l a t e X I I I - C ) . The f i e l d evidence c o l l e c t e d i n the outer Mackenzie D e l t a area thus appears to substantiate the conclusions of Lachenbruch's t h e o r e t i c a l study.  Primary f r o s t cracks were developed, e s s e n t i a l l y i n a random  p a t t e r n , across the ground surface, and the junctions of secondary  frost  cracks w i t h these primary f i s s u r e s showed a d e f i n i t e preferred tendency toward an orthogonal i n t e r s e c t i o n pattern. According to Lachenbruch s 1  c l a s s i f i c a t i o n scheme, the r e s u l t a n t crude polygonal network would Lachenbruch, A.H. (1962) op_. c i t . , p. 50.  216 therefore be c l a s s i f i e d as a 'random orthogonal system'.  54  Only i n the  v i c i n i t y of large bodies of water d i d preferred d i r e c t i o n a l o r i e n t a t i o n s become s u f f i c i e n t l y pronounced to be c l a s s i f i e d as 'oriented orthogonal systems'. The apparent dichotomy between t h i s evidence and the f a c t that most tundra polygons appear to be of a non-orthogonal type has been explained by Lachenbruch to be the r e s u l t of an obscuring of the i n t e r s e c t i o n angles by the growth of large ice-wedges."^  The i n c i p i e n t f r o s t crack  pattern i s p r a c t i c a l l y the only stage i n the development of a network of polygonal ground therefore i n which the angular i n t e r s e c t i o n patterns can be determined w i t h any r e a l degree of accuracy. Moreover, these determinations can only be made i n the f i e l d through ground i n s p e c t i o n , since the f r o s t cracks are generally too small to be i d e n t i f i e d from a e r i a l photographs. The transformation of an i n i t i a l pattern of f r o s t cracks i n t o a network of tundra or ice-wedge polygons requires that recurrent f r a c t u r i n g takes place at the same l o c i .  The evidence c o l l e c t e d on Garry  I s l a n d suggests that once a f r a c t u r e i s formed, i t tends to p e r s i s t as a permanent l i n e of weakness i n the mantle.  Most of the larger cracks r e -  mained as open f i s s u r e s throughout the summer months, p o s s i b l y i n d i c a t i n g that the ground was s u f f i c i e n t l y e l a s t i c to absorb the s t r a i n produced by i t s expansion under the summer's heat and consequently no deformation took 56 place.  Where the ground surface was covered by a t h i n layer of washed  'Lachenbruch, A.H. (1962) op. c i t . , p. 46. 'Ibid. , Figure 13, p. 49. 'Leffingwell, E. de K. (1915)  op_. c i t . , p. 640.  217 peat, i t i s a l s o p o s s i b l e that the maintenance of the open f i s s u r e  may  have been aided l o c a l l y by a s l i g h t d e s i c c a t i o n and shrinkage of t h i s layer.  Even where the cracks were, closed, t h i s probably d i d not take  place before some m a t e r i a l had i n f i l t r a t e d from the ground surface, and the miniature sand-wedges, produced i n t h i s manner, a l s o a s s i s t i n the preserv a t i o n of the l i n e s of weakness. Low-Centred Polygons.  The f r o s t cracks extend down below the  base of the a c t i v e layer where they are occupied by a t h i n v e i n of i c e . Recurrent f r a c t u r i n g at the same l o c i r e s u l t s i n the a d d i t i o n of successi v e increments of i c e , and the eventual formation of a l a r g e , f o l i a t e d ice-wedge.  Accompanying the growth of these ice-wedges, and bounding them  on e i t h e r s i d e , d i s t i n c t i v e ridges are formed which may p a r t i a l l y represent the upturning of s t r a t a adjacent to the growing w e d g e , T h u s the f i r s t polygons to form c o n s i s t of a c e n t r a l , saucer-shaped  depression enclosed  between bordering r i d g e s , and they are accordingly r e f e r r e d to as lowcentred or raised-edge  polygons.  These polygons are best developed i n f i n e - g r a i n e d sediments underlying poorly-drained f l a t s , but i f the drainage i s too poor they do not n e c e s s a r i l y e x h i b i t the c h a r a c t e r i s t i c saucer-shaped  form.  A number  of polygons has developed around the edges of a lagoon enclosed by the sandspit on the n o r t h - c e n t r a l coast of Garry I s l a n d . This lagoon i s open to the sea, and the areas of polygonal ground are frequently inundated during periods of high water.  Such polygons have very l i t t l e  topographic  "^Pewe, T„L. (1966) "Ice-Wedges i n Alaska - C l a s s i f i c a t i o n , D i s t r i b u t i o n , and C l i m a t i c S i g n i f i c a n c e " , Proc: Permafrost I n t e r n a t i o n a l Conference, L a f a y e t t e , Indiana, November, 1963. Nat., Acad, of Sciences Nat. Research C o u n c i l , Washington P u b l i c a t i o n , No. 1287, p. 77.  218 expression and bordering ridges are non-existent. Figure 32 shows the surface contours and c r o s s - s e c t i o n a l prof i l e s of a c l a s s i c a l low-centred polygon form, located at an e l e v a t i o n of 4.5-6.0 metres (15-20 feet) above sea l e v e l .  The polygon i s surrounded by  shallow troughs, marking the p o s i t i o n s of the ice-wedges, ranging i n width from 3.0 to 4.5 metres (10-15 f e e t ) .  In places, the troughs are occupied  by water 0.5-1.0 metres (1.5-3.0 feet) deep (Plate XIV-A), but elsewhere they have been p a r t i a l l y i n f i l l e d by the accumulation of organic m a t e r i a l which supports a vegetation cover composed predominantly of sedges.  The  polygon, ranges i n width from 10.5 to 14.5 metres (35-48 feet) as measured between the c r e s t s of the bounding ridges which reach maximum elevations of 65 cms. (25.5 i n s . ) above the l e v e l of the water i n the adjacent troughs.  These same ridges enclose a shallow depression i n the c e n t r a l  part of the polygon which, at the time of surveying, was f l o o r e d by a marsh-sedge vegetation, but at other times during the summer was occupied by a shallow pool of standing water 5-10 cms. (2-4 ins.) deep.  Central  areas of other low-centred polygons i n the same general l o c a t i o n were occupied by pools of water throughout the summer. The r e t e n t i o n of t h i s water i s aided by the c o n f i g u r a t i o n of the f r o s t table which c l o s e l y f o l l o w s the surface m i c r o r e l i e f as i l l u s t r a t e d i n the p r o f i l e  i n Figure  32. The polygon shown i n Figure 32 was a c t u a l l y part of an extensive area of low-centred polygons located between the large lake and the truncated lagoon on the northwest coast of the i s l a n d (see Figure 1). larger grouping of these polygons i s shown i n Figure 33.  A  As t h i s map  i l l u s t r a t e s , the most c h a r a c t e r i s t i c form of the u n i t polygons was a fouror f i v e - s i d e d f i g u r e .  The s i z e s of the i n d i v i d u a l polygons ranged from  Figure 32 SURFACE OF  CROSS  CONTOURS A TYPICAL  - SECTIONAL  AND CROSS - SECTION AL LOW-CENTRED  PROFIL  POLYGON  PROFILE  S t a n d i n g water - ice f l o o r  S t a n d i n g water - muck floor  Distance in metres  220  P l a t e XIV LOW-CENTRED  A.  Low-centred  edge t u n d r a  or  polygon  central  depression  by  of standing  pool  POLYGONS  raisedwith occupied water.  B.  Infilling  depression flat-topped has  been  growth wedges .  C.  Oriented,  system  of  polygons a  small  courtesy Mackay).  orthogonal  low-centred developed  lake.  around  (Photograph  o f Dr. J . Ross  of  central  to produce a polygon  subdivided  which by t h e  of a d d i t i o n a l i c e -  Figure 33  222 9 to almost 24 metres (30-80 feet) across, but much of t h i s v a r i a t i o n can be a t t r i b u t e d toi the s u b d i v i s i o n of the o r i g i n a l , larger polygonal u n i t s by the subsequent growth of a d d i t i o n a l ice-wedges (Plate XIV-B). I t i s v i r t u a l l y impossible from Figure 32 to determine the angular i n t e r s e c t i o n s of the polygonal network.  Lines drawn along the  c e n t r a l axes of the ice-wedge troughs could be i n t e r p r e t e d to i n t e r s e c t orthogonally, as i n the case of the i n c i p i e n t f r o s t crack patterns, but d e f i n i t i v e conclusions cannot be made.  I n a few locations deep, open  f i s s u r e s i n the ice-wedges, presumably marking the p o s i t i o n s of f r o s t cracks produced during the preceding w i n t e r , could be observed beneath the water, but, unfortunately, none of these were located a t the ice-wedge i n t e r s e c t i o n points.  S i m i l a r l y , the presence of any preferred o r i e n t a t i o n  i n the alignment of the ice-wedges shown i n Figure 33 i s d i f f i c u l t to detect.  A group of polygons around a small lake i n the same area of  patterned ground showed a d e f i n i t e o r i e n t a t i o n w i t h respect to the lake, w i t h the major f i s s u r e s r a d i a t i n g outward from the lake l i k e the spokes of a wheel (Plate XIV-C).  I t i s s u r p r i s i n g that the polygonal network shows  no pronounced o r i e n t a t i o n w i t h the shore of the lake shown i n Figure 33. I f any pattern i s d i s c e r n i b l e , i t i s perhaps suggestive of a crude r a d i a l and concentric arrangement around the f o c a l points A and B.  I f this i n -  t e r p r e t a t i o n i s c o r r e c t , these f o c a l points may represent the former p o s i t i o n s of two small lakes on the f l a t ground around each of which an oriented orthogonal(?) system was developed. Ice-wedge or tundra polygons are not r e s t r i c t e d i n t h e i r development to areas of moist, f i n e - g r a i n e d sediments. Large networks of subdued polygons were a l s o developed on Garry I s l a n d on the surfaces of the  sand headlands (Figure 34). Although these polygons were a l s o of the  223 Figure 34  LOW-CENTRED ON  SAND  POLYGON  NETWORK  HEADLANDS  224 low-centred type, there was a major contrast i n the surface m i c r o r e l i e f . Thus the bounding ridges of the polygons barely rose more than 15-25 cms. (6-10 ins.) above the l e v e l s of the troughs or the c e n t r a l sections of each polygonal u n i t .  The troughs, marking the p o s i t i o n s of the i c e -  wedges, contained no surface water and the i c e was mantled by a layer of moss and sedge growing i n a peat substrate. Only near the edges of the c l i f f s d i d the troughs become more pronounced, where thawing of the i c e wedges had produced prominent feet) deep, i n the c l i f f top.  'V'-shaped notches, 1-3 metres (3.5-10.0 The polygons on the sand headland surface  also e x h i b i t e d a wide v a r i a t i o n i n s i z e , r e f l e c t i n g a s i m i l a r s u b d i v i s i o n process t o that described i n an e a r l i e r paragraph.  The c o n f i g u r a t i o n of  the more prominent surface expressions of the ice-wedges suggests that the headland surface was i n i t i a l l y divided i n t o a s e r i e s of i r r e g u l a r b l o c k s , 25-35 metres (80-115 f e e t ) across, and that these have subsequently been subdivided by the growth of a d d i t i o n a l ice-wedges i n t o a number of predominantly t e t r a g o n a l forms, 6-10 metres (19.5-33.0 f e e t ) across.  The  greater r e g u l a r i t y and uniform widths of the troughs o u t l i n e d i n F i g u r e 34 make i t easier to i n f e r the nature of t h e i r angles of i n t e r s e c t i o n , which appear to e x h i b i t a d e f i n i t e tendency toward a p r e f e r r e d orthogonal pattern. Thus the main e f f e c t s of a coarse sand substrate on the network of patterned ground appear to be i n a s l i g h t l y coarser spacing of the primary crack p a t t e r n s , and a less pronounced topographic expression. The wider spacing of the primary f r o s t cracks may r e f l e c t the lower c o e f f i c i e n t of expansion of frozen sand compared to f i n e - g r a i n e d sediments, and the subdued m i c r o r e l i e f may be r e l a t e d to a more r e s t r i c t e d moisture supply.  225 High-Centred Polygons.  The major sequential stages i n the i n -  f i l l i n g of a low-centred polygon, and i t s transformation i n t o a highcentred form, were o u t l i n e d i n Chapter I I I .  Standing pools of water i n the  c e n t r a l depressions of low-centred polygons are often f l o o r e d by a t h i c k layer of soft ooze, believed to be the accumulated remains of algae. ooze deposit corresponds  The  to the grey s i l t y m a t e r i a l observed i n the basal  sections of high-centred polygons exposed by wave a c t i o n i n the c o a s t a l bluffs.  The c o n t i n u i t y of t h i s deposit i n the same exposures also i n d i c -  ates that the.accumulation of a l g a l remains i s a major f a c t o r i n the i n f i l l i n g of i n i t i a l lakes p r i o r to the development of a system of i c e wedges.  The deposition of the ooze w i t h i n the c e n t r a l areas of  low-centred  polygons leads to a shallowing of the water depths, and allows the areas to be colonized by vascular species i n the sequence a l s o described i n Chapter I I I .  The accumulation of peat r e s u l t s i n a f u r t h e r e l e v a t i o n of  the.central, areas of the polygons r e l a t i v e to the l e v e l s of the bordering ridges ^and, since the grey s i l t layers often have i c e contents of several hundred per cent (by weight), the formation of syngenetic (penecontemporaneous), segregated i c e lenses i n the ooze may a l s o contribute s i g n i f i c a n t l y to an e l e v a t i o n of the surfaces of the c e n t r a l depressions. The sequential stages i n t h i s shallowing process.were r e a d i l y observable i n the group of low-centred polygons shown i n Figure 33, where, i n general, the surfaces of the polygons located around the edge of the f l a t s were l e v e l w i t h the bounding r i d g e s . Nowhere, however, had t h i s i n f i l l i n g process led to the production of the c h a r a c t e r i s t i c , dome-shaped, convex p r o f i l e of a t y p i c a l high-centred polygon ( P l a t e XVVA).  Figure 35  shows the surface contours and c r o s s - s e c t i o n a l p r o f i l e of one of these high-centred forms, located at an e l e v a t i o n of approximately 21-23  metres  226 P l a t e XV HIGH-CENTRED  POLYGON  AND  THERMOKARST  FEATURES  A. C h a r a c t e r i s t i c , domeshaped, convex p r o f i l e of a t y p i c a l high-centred polygon.  B. Thermokarst f e a t u r e s i n an area of h i g h - c e n t r e d polygons exposed by c o a s t a l recession.  227 Figure 35 SURFACE  CONTOURS  OF  SURFACE ABOVE  AND C R O S S - S E C T I O N A L  A TYPICAL  HIGH-CENTRED  PROFILE  POLYGON  C O N T O U R S DATUM  (Cms.)  A  Contour  interval  15 cms  Willow  Water  C RO S S - S E C T I O N A L  and  Sedge  sedge  PROFILE Dry willow  Water filled wed ge Flat, dry and peaty hummocks with narrow litter f i l l e d depressions  Distance in metres  wedge and sedge  228 (70-75 feet) above sea l e v e l .  Compared to t h e i r low-centred counterparts,  these polygons were generally much more regular i n shape and averaged 6-8 metres (19.5-26.0 feet) i n diameter.  A t t h e i r highest p o i n t s , u s u a l l y  i n the centres of the polygons, the surfaces were about 1.5-2.0 metres (5.0-6.5 feet) above the l e v e l of the surrounding troughs.  The l a t t e r ,  marking the p o s i t i o n s of the ice-wedges, were predominantly f i l l e d w i t h moss and sedge although l o c a l l y they contained pools of water 15-50 cms. (6.0-19.5 i n s . ) deep. Most of the areas of tundra polygons on Garry I s l a n d a t e l e vations exceeding approximately 15 metres (50 feet) above sea l e v e l are of the high-centred type.  The h e i g h t - d i s t r i b u t i o n pattern of these areas  appears to be i n t i m a t e l y r e l a t e d to the elevations of r a i s e d shoreline features.  I t i s postulated that most of the polygonal pattern was i n -  i t i a l l y formed on lagoon-flats developed behind small sandspits, or bars, associated w i t h former p o s i t i o n s of the l e v e l of the sea.  Many of these  areas of tundra polygons are extremely l i m i t e d i n t h e i r extent, and they t y p i c a l l y take the form of small pockets occupying the narrow f l o o r s of some of the v a l l e y s .  I n these r e s t r i c t e d l o c a l i t i e s , however, the con-  f i g u r a t i o n s of the networks of ice-wedges e x h i b i t a very d e f i n i t e tendency toward the development of an oriented orthogonal system.  Thus the most  prominent wedge l i n e s were i n v a r i a b l y aligned along the a x i s of the v a l l e y f l o o r , where undoubtedly much of the reason f o r t h e i r prominence was t h e i r accentuation by i n t e r m i t t e n t surface r u n o f f , and the other ice-wedges were frequently aligned at r i g h t angles to these main axes. Thermokarst Features.  The term thermokarst i s used to describe  surface hollows and depressions that o r i g i n a t e through the melting of ground i c e . Because of the high i c e content of many of the sediments, the  229 conditions on Garry I s l a n d are extremely favourable f o r the development of thermokarst topography, e s p e c i a l l y when these sediments are exposed by the recession of the c o a s t l i n e .  Thus the most dramatic manifestations of t h i s  process occur when the r e t r e a t of the c l i f f s exposes massive sheets of segregated i c e r e s u l t i n g i n the development of the large mudslumps described e a r l i e r i n t h i s chapter.  The shallow water depths, u s u a l l y  1-2  metres (3.0-6.5 f e e t ) , around the margins of the larger lakes on the i s land, and the concentrations of coarse g r a v e l and boulders on t h e i r f l o o r s , may possibly be interpreted as evidence of thermokarst enlargement of the 58 lakes i n a manner s i m i l a r to that described by Wallace i n eastern Alaska. A d i s t i n c t i v e type of thermokarst topography was developed on Garry I s l a n d where networks of tundra polygons, of both the low- and highcentred types, had been exposed i n the b l u f f s as a r e s u l t of c o a s t a l recession (Plates XV-B  and XV-C).  M e l t i n g along the l i n e s of the i c e -  wedges had transformed the shallow troughs into prominent trenches several metres deep.  In the sand headland areas, the melting of the ice-wedges  imparted a c h a r a c t e r i s t i c notched appearance to the c l i f f s .  In the area  of high-centred polygons, located on the northwest coast of the i s l a n d (see Figure 6), the trenches were as much as 3-4 metres (10-13 f e e t ) deep, and the i n d i v i d u a l polygonal u n i t s had been l e f t standing as i s o l a t e d mounds of peat.  M e l t i n g of the ice-wedges had a l s o l e f t the sides of the  polygons unsupported, and a considerable amount of slumping had taken place thereby accentuating the convexity of t h e i r surface p r o f i l e s .  Since  the majority of the areas of high-centred polygons on the i s l a n d also W a l l a c e , R.E. (1948) "Gave-in lakes i n the Nabesna, Chisana and Tanana r i v e r v a l l e y s , eastern Alaska",. J o u r n a l of Geology, V o l . 56, pp. 171-181. 58  230 appear to have been a f f e c t e d by thermokarst a c t i o n , though u s u a l l y to a lesser degree, i t seems reasonable to i n f e r that the development of the t y p i c a l convex p r o f i l e of these polygons may represent the operation of t h i s same slumping process. I t should be noted that the examples of thermokarst topography c i t e d above were, or could have been, developed e n t i r e l y by the operation of e x i s t i n g n a t u r a l processes without any recourse to an amelioration of climate.  Three further examples, observed during the f i e l d seasons, dem-  onstrated the r a p i d i t y w i t h which thermokarst features can be developed by an interference w i t h the n a t u r a l conditions.  The f i r s t example was  associated w i t h attempts to lower a r t i f i c i a l l y the l e v e l of a lake by digging a d i t c h across the peat b a r r i e r damming, i t s o u t l e t .  The water was  led out through t h i s a r t i f i c i a l channel, at an e l e v a t i o n of approximately 36.5 metres (120 feet) above sea l e v e l , and then allowed to seek i t s course to lower e l e v a t i o n s .  own  Immediately p r i o r to the opening of the  channel, the depth of thaw j u s t beyond i t s o u t l e t was recorded as 30-35 cms. (12-14 i n s . ) , yet a f t e r only three weeks of i n t e r m i t t e n t flow t h i s had increased f i v e f o l d , to over 1.5 metres (5 f e e t ) , and the surface mat of  l i v i n g vegetation was l i t e r a l l y f l o a t i n g on the thawed substrate.  Without f l o o d i n g , the p o s i t i o n of the f r o s t table might have r e t r e a t e d by approximately 10 cms. (4 ins.) at the most during the same three-week period. The second example was much more impressive i n terms of i t s e f f e c t on the surface topography.  As discussed e a r l i e r i n Chapter I I , the  majority of the stream courses on Garry I s l a n d have i l l - d e f i n e d channels, and, consequently, the flow of water i s e a s i l y diverted from i t s normal path.  An example of t h i s occurred when water was diverted from i t s  231 o r i g i n a l course to f o l l o w w e l l - d e f i n e d , s u b - p a r a l l e l paths between the base camp and the coast.  A t the c o a s t l i n e , t h i s path terminated a t a s e r i e s of  tundra polygons, the existence of which was only feebly expressed a t the ground surface.  Surface r u n o f f , derived p r i n c i p a l l y from melting snow, was  observed to be f l o w i n g along these paths at the beginning of the 1965 f i e l d season.  I n the summers of 1967 and 1968 there was s l i g h t seepage down the  paths, but no flow.  The e f f e c t s of t h i s r e - r o u t i n g of the water were  apparent by the summer of 1967, where r a p i d thermokarst  erosion of the i c e -  wedges had occurred over distances extending back to about 30-35 metres (100-115 f e e t ) from the c o a s t a l b l u f f .  This erosion had produced a number  of prominent troughs, approximately 2 metres (6.5 feet) wide and, a t the 59 i n t e r s e c t i o n points of the ice-wedges, 2 metres (6.5 f e e t ) deep.  By  1968, the inter-ice-wedge areas of several polygons had been undermined by thaw to produce subsurface overhangs as much as 5 metres (16.5 f e e t ) square 60 and 0.6-1.0 metres (2-3 feet) high. The t h i r d example of the development of thermokarst features occurred i n an area where a dog had been tethered during the 1965 f i e l d season.  The vegetation cover of a c i r c u l a r area, approximately 3 metres  (10 feet) i n diameter, was k i l l e d as a r e s u l t , and the accelerated thawing had l e d to a s e t t l i n g of the ground surface and the c r e a t i o n of a bowl61 shaped depression, 20 cms. (8 ins.) deep, by the summer of 1968. 59 Information supplied by Dr. J . Ross Mackay, personal communi c a t i o n , August 27, 1968. 60 Information supplied by Dr.. J . Ross Mackay, personal communi c a t i o n , October, 1968. Ibid.  232 Earth Hummocks. The term earth hummock was f i r s t introduced by Sharp to describe low, rounded knobs of f i n e m a t e r i a l c o n s i s t i n g of an earthen  core  62 covered by a t i g h t mat of moss, grass and scrubby p l a n t s .  According to  Washburn's c l a s s i f i c a t i o n scheme, they f a l l i n t o the category of  non-sorted  63 nets.  On Garry I s l a n d , these m i c r o r e l i e f features are generally confined  to well-drained s i t e s where they form a continuous, three-dimensional mesh on the g e n t l y - i n c l i n e d upland surfaces and the steeper v a l l e y - s i d e slopes. Although, as w i l l be discussed below, i t i s p o s s i b l e that s i m i l a r micror e l i e f forms may be produced i n d i f f e r i n g environments by the operation of d i s s i m i l a r processes, t h i s s i t u a t i o n contrasts markedly w i t h that described by Raup i n the Mesters V i g D i s t r i c t of northeast Greenland.  Raup found  that ( t u r f ) hummocks, which from h i s d e s c r i p t i o n s and i l l u s t r a t i o n s appear to be i d e n t i c a l to the earth hummocks on Garry I s l a n d , occurred only on s i t e s abundantly supplied w i t h gently-flowing surface water, derived from the melting of perennial snowdrifts or the thawing of frozen ground, 64 throughout most of the summer season.  P e r e n n i a l snowdrifts are l a c k i n g  on Garry I s l a n d , and no incidence of surface runoff was observed on the hummock s i t e s during three summers' observations.  Moreover, earth hummocks  were almost conspicuous by t h e i r absence on the lower, poorly-drained f l a t s °^Sharp, R.P (1942) " S o i l structures i n the St. E l i a s Range, Yukon T e r r i t o r y " , Journal of Geomorphology, V o l . 5, pp. 282-283. C  Washburn, A.L. (1956) " C l a s s i f i c a t i o n of patterned ground and review of suggested o r i g i n s " , Geol. Soc. Amer. B u l l . , V o l . 67, p. 830. 63  64 Raup, H.M. (1965) "The structure and development of t u r f hummocks i n the Mesters V i g D i s t r i c t , Northeast Greenland", Meddelseer om Grinland, Bd. 166, Nr. 3, p. 5. Raup f u r t h e r states that t u r f hummocks may be common on d r i e r s i t e s , but here they are always i n some stage of disintegration.  233 where they are u s u a l l y replaced by the tussock forms of the Sheathed Cotton-grass (Eriophorum vaginatum) or f e a t u r e l e s s mats of moss and sedge. The apparent dichotomy between these environmental conditions i l l u s t r a t e s one of the most s a l i e n t aspects of patterned ground s t u d i e s . Hummocky ground, f o r example, has been extensively described i n both geomorphological and b o t a n i c a l l i t e r a t u r e , , where numerous names have been applied to s u p e r f i c i a l l y s i m i l a r forms.  Anatomically, however, i t i s  evident that the broad term 'hummocky ground  1  has been used loosely to i n -  corporate i n d i v i d u a l forms w i t h widely d i f f e r i n g s t r u c t u r e s . W h i l s t i t i s possible that these d i s s i m i l a r s t r u c t u r e s may be nothing more than d i f f e r ent expressions of the same, or s i m i l a r , genetic processes, i t i s equally probable that they each represent important m o d i f i c a t i o n s of these i  processes i n response to s i g n i f i c a n t v a r i a t i o n s i n such s p e c i f i c environmental conditions as s o i l s , vegetation, slope and a v a i l a b l e moisture supply. Several authors have recognized that types of hummocky ground can be c l a s s i f i e d e i t h e r on the basis of the plant species of which they are composed, or on t h e i r i n t e r n a l composition. . A c l a s s i f i c a t i o n according to plant species a f f o r d s d i s t i n g u i s h i n g c r i t e r i a f o r those m i c r o r e l i e f features which have a tussock form.  I n d i v i d u a l tussocks are developed  by  the upward growth of a s i n g l e plant on a columnar base of i t s own dead leaves and r o o t s , and the height of these tussocks i s f u r t h e r accentuated by d i f f e r e n t i a l f r o s t a c t i o n and the doming-up of mineral s o i l beneath the plant.  On Garry I s l a n d , the Sheathed Cotton-grass (Eriophorum vaginatum)  i s the. major tussock-forming species, and i t t h r i v e s on f l a t to gentlys l o p i n g , poorly-drained surfaces.  Since the s t r u c t u r e and development of  tussocks have been described i n d e t a i l by Hopkins and Sigafoos, they w i l l  234 not be discussed f u r t h e r h e r e . ^ A c l a s s i f i c a t i o n of hummocks on the basis of t h e i r i n t e r n a l composition i s much more complex, but i t would seem l o g i c a l to make a fundamental s u b d i v i s i o n r e l a t i n g to the degree of homogeneity of the substrate.  I n t h i s way the hummocks which are composed e n t i r e l y of peat could  be d i f f e r e n t i a t e d from those which have a prominent mineral core.  It is  i n t o t h i s l a t t e r category that the hummocks on Garry I s l a n d f a l l and, since the domed mineral core i s the most diagnostic feature of these m i c r o r e l i e f forms, Sharp's nomenclature of earth hummocks has been adopted. The Structure of Earth Hummocks.  Information p e r t a i n i n g to the  structure of earth hummocks was c o l l e c t e d using the f o l l o w i n g methods. Three l o c a t i o n s were selected s u b j e c t i v e l y to i l l u s t r a t e diagnostic hummock features a t s p e c i f i c l o c a t i o n s on a t y p i c a l slope p r o f i l e , and a f o u r t h l o c a t i o n where the hummocks had coalesced i n t o s t r i p e forms.  A t each of  these l o c a t i o n s the surface c o n f i g u r a t i o n was obtained by superimposing a 1.8 metre (6 foot) square- g r i d h o r i z o n t a l l y above the ground surface, and., taking plumb readings to the surface at h o r i z o n t a l i n t e r v a l s of 10. cms.» (4 i n s . ) .  This data was used to prepare contour maps w i t h a 2.5 cm. (one  inch) contour i n t e r v a l , rough copies of which were made a t the time to permit f i e l d checks.  On the slope p r o f i l e , the g r i d s i z e was u s u a l l y  s u f f i c i e n t to show a group of hummocks, but where the s t r i p e features were developed the process was repeated four times t o cover a 3.6 metre (12 foot)  Hopkins, D.M. and Sigafoos, R.S. (1951) "Frost a c t i o n and vegetation patterns on Seward Peninsula, Alaska", U.S_.G.S_. Bulletins, No. 974-C, pp. 51-101. Hopkins, D.M. and Sigafoos, R.S. (1954) "Role of f r o s t t h r u s t i n g i n the formation of tussocks",. Amer. ...Jour. S c i . , V o l . 252, pp. 55-59.  235 square p l o t .  Before the g r i d was removed, the, dominant aspects of the  vegetation cover were a l s o mapped. P r o f i l e l i n e s were selected to give representative l o n g i t u d i n a l - and cross-sections of a t y p i c a l hummock i n each of the l o c a t i o n s , and excavations t o the f r o s t t a b l e i n l a t e August provided the s t r u c t u r a l data. Figure 35 and P l a t e XVI-A show earth hummocks on the gentlyi n c l i n e d upper portions of a slope p r o f i l e .  I n d i v i d u a l hummocks rose  about 12-14 cms. (4.5-5.5 ins.) above the mean l e v e l of the surrounding depressions, and they were approximately c i r c u l a r i n o u t l i n e , averaging about 50-60 cms. (19.5-23.5 ins.) i n basal diameter.  I n p r o f i l e the  hummocks were broadly convex, and generally they d i d not e x h i b i t any marked asymmetry.  The i n t e r v e n i n g depressions commonly took on the form  of shallow, open troughs. There were quite pronounced d i f f e r e n c e s between the. vegetation associations of the hummocks and the depressions as shown i n Figure 37. The higher, d r i e r s i t e s of the hummock centres were dominated by the A r c t i c Avens (Dryas i n t e g r i f o l i a ) , A r c t i c Blueberry (Vaccinium uliginosum var. alpinum), small sedges (Carex sp.), l i c h e n s and dry moss pads ( c h i e f l y Dicranum sp.).  The A r c t i c Blueberry was p a r t i c u l a r l y abundant on the sides  of the hummocks and sometimes extended down i n t o the f l o o r s of the. depressions, but these were dominated by the A r c t i c White Bell-heather (Cassiope tetragona) growing i n a damp substratum of mosses ( c h i e f l y Aulacomnium and Sphagnum sp.).  Small willows ( S a l i x a r c t i c a ) were o c c a s i o n a l l y found on  the surface of the hummocks, but they were most abundant on the lower parts of the s i d e s .  There were a l s o appreciable d i f f e r e n c e s , between  hummocks and depressions, i n the r e l a t i o n s h i p of t h i s vegetation cover to the underlying surface.  The plants on the hummocks formed a t i g h t , i n t e r -  236  Figure 36  EARTH LOCATED  ON UPPER  SURFACE  HUMMOCK PART  CONTOURS  STRUCTURAL  I I I 11  Contour  Living  interval  vegetation  2.5 cms.  OF SLOPE  ABOVE  PROFILE  DATUM  PROFILES  Peat  t'Xvlvl  SCALE 20 40  0 r  Mineral  = =  ^^  K = = B  ^  soil  60 Cms.  H = = 3 I I B B  237 Figure 37 EARTH LOCATED  ON  UPPER  HUMMOCK PART  OF  V E G E T A T I O N  SLOPE  PROFILE  TYPES  i—i—i  Edge  V*"|  Lichen/avens/sedge association  [•:•:';:}  Moss  Ave n s  fS3r3  Willow  Sedge  of  Hummock  and/or  Blueberry  species  Scale  20  in c m s .  40  60  Heather  patch  Plate XVI  E A R T H  H U M M O C K S  all'  •UBI :—,  A. E a r t h hummock l o c a t e d on t h e upper p a r t of a s l o p e p r o f i l e showing t h e almost c i r c u l a r o u t l i n e .  B. E a r t h hummock l o c a t e d on t h e m i d d l e p a r t o f a s l o p e p r o f i l e showing the e l o n g a t i o n i n a downslope direction.  C. E a r t h hummock l o c a t e d on t h e lower p a r t o f a slope p r o f i l e e x h i b i t i n g an almost p e r f e c t c i r c u l a r form.  D. S t r u c t u r e of a t y p i c a l e a r t h hummock showing t h e m i n e r a l c o r e , t h e wedges o f o r g a n i c m a t e r i a l beneath the t r o u g h s , and an i n t e r mittent buried organic layer near t h e t o p o f t h e permafrost .  239 woven mat which was i n t i m a t e l y bound to the ground below by root systems which extended down i n t o the peat and, i n some cases, i n t o the mineral core.  P l a n t s occupying :the depressions on the other hand tended to be very  shallow rooted, and were only loosely anchored i n the moss which i n t u r n rested loosely on the underlying peat. Figure 36 also shows the s t r u c t u r a l features of these hummocks along the i n d i c a t e d p r o f i l e l i n e s .  The l i v i n g t u r f mat, i n c l u d i n g a zone  of brownish, loosely-packed organic m a t e r i a l , averaged 4-8 cms. (1.5-3.0 ins.) i n t h i c k n e s s , but increased l o c a l l y to almost 15 cms. (6 ins.) i n some of the l a r g e r depressions.  Beneath t h i s surface mat was a layer of  t i g h t , black peat averaging 5-8 cms. (2^3 ins.) i n thickness i n the c e n t r a l mound areas, but t h i c k e n i n g to form organic wedges penetrating down to the f r o s t t a b l e beneath the depressions.  I t i s perhaps s i g n i f i c a n t that the  p o s i t i o n s of these organic wedges d i d not always coincide exactly w i t h those of the surface depressions.  Moreover, these organic wedges f r e -  quently d i d not extend down e i t h e r v e r t i c a l l y , or w i t h uniform width, to the f r o s t t a b l e , but were often decidedly convex i n a downslope d i r e c t i o n , tapering to t h i n s t r i p s towards the base of the a c t i v e l a y e r .  Local  thickenings of the same peat layer were a l s o evident beneath some of the c e n t r a l mounds, often i n close a s s o c i a t i o n w i t h minor depressions on the hummock surface.  The c e n t r a l core of the hummocks consisted of a promin-  ent dome of mineral s o i l .  This core reached i t s maximum t h i c k n e s s ,  approximately 35 cms. (14 ins.) under the centres of the hummocks, but .. l a t e r a l l y i t was g r e a t l y attenuated and o c c a s i o n a l l y was absent completely beneath the depression areas.  The b a s a l , s t r u c t u r a l feature of these  hummocks was a buried organic layer which occupied a p o s i t i o n close to the frost table.  This layer always a t t a i n e d i t s greatest prominence towards  240 the l a t e r a l margins of the hummocks where i t was nearly always observed to u n i t e w i t h the organic wedges.  I n l o n g i t u d i n a l , or downslope, sections i t  was best developed on the upslope sides of these same wedges.  The basal  organic layer reached i t s maximum thickness, 2-3 cms. (0.75-1.25 i n s . ) , i n these l a t e r a l p o s i t i o n s , but i t thinned appreciably towards the centres of the hummocks where only t h i n traces were sometimes present.  I n some i n -  stances the organic layer could be traced e n t i r e l y beneath the complete hummock s t r u c t u r e , but i n others i t appeared to be absent i n the c e n t r a l areas.^  The m a t e r i a l beneath the organic layer consisted of mineral s o i l  s i m i l a r i n composition to that forming the hummock cores. Figure 38 and P l a t e XVI-B show a t y p i c a l earth hummock located on the middle slope region of the topographic p r o f i l e . 15-20  The hummock rose  cms. (6-8 ins.) above the surfaces of the depressions, but rather  than being c i r c u l a r i n o u t l i n e , i t e x h i b i t e d a d e f i n i t e elongation i n a downslope d i r e c t i o n .  W h i l s t the hummock was s t i l l broadly convex i n pro-  f i l e , l o n g i t u d i n a l l y there was a d e f i n i t e asymmetry w i t h the downhill face steeper than that on the u p h i l l s i d e .  The intervening depressions were  i  stronger features than those described on the upper slope, and were more continuous, narrower and had steeper sides.  The s t r u c t u r a l diagrams i n  Figure 38 show that t h i s hummock was s i m i l a r i n composition to the one described on the upper slope, and the vegetation a s s o c i a t i o n s of the hummock and depression areas were a l s o s i m i l a r , as i s i n d i c a t e d by the map Since the f r o s t t a b l e continues to recede i n t o September, the p o s i t i o n of the buried organic layer i s perhaps more a p t l y described as a t , or j u s t above, the base of the a c t i v e l a y e r . A d d i t i o n a l excavations of these and other hummocks to depths below the f r o s t t a b l e i n l a t e August demonstrated a greater extent of t h i s l a y e r , but confirmed that i n some i n stances i t i s completely l a c k i n g beneath the centres of some hummocks.  Figure 38  EARTH LOCATED  ON MIDDLE  SURFACE  HUMMOCK PART  CONTOURS  STRUCTURAL  | | | 11 Living  Contour  interval  vegetation  2.5 cms.  OF SLOPE  ABOVE  PROFILE  DATUM  PROFILES  Peat  rlvMv]  20  Mineral  SC A t E 40  soil  60  Cms.  Figure 39 EARTH LOCATED  ON  MIDDLE  HUMMOCK PART  OF  V E G E T A T I O N  i—i—i  Edge  |",|  L i c h e n / a ve n s / s e d g e association  |."Q°,°|  of  PROFILE  TYPES  Hummock  [v.y.'vj  Moss a n d / o r  Heather  Willow  Avens Sedge  SLOPE  Blueberry  spec  S c a l e in cms. 0  20  40  60  patch  243 of vegetation types shown i n Figure 39. Figure 40 and P l a t e XVI-C show a large earth hummock located on the lower slope near the base of the topographic p r o f i l e .  This hummock  rose as much as 30-35 cms. (12-14 ins.) above the adjacent depressions, and i t was approximately c i r c u l a r i n o u t l i n e , averaging 70-75 cms. (27,5-29.5 ins.) i n basal diameter.  The s t r u c t u r a l and vegetation patterns (Figure  40, P l a t e XVI-D and F i g u r e 41) of t h i s hummock and the neighbouring  depress-  ions a l s o followed the same pattern as that described higher up the slope, but a few notable exceptions are worthy of mention.  The proportion of the  hummock occupied by the mineral core was greater, and the buried organic layer reached thicknesses of 5-8 cms. (2^3 ins.) beneath the hummock areas. In the depressions, the.proportion of moss was much higher and they were also much damper than the depressions higher up the slope.  Other small  changes i n the vegetation types included the presence of the Narrow-leafed Labrador-tea (Ledum p a l u s t r e ssp. decumbens) and Mountain Cranberry (Vaccinium v i t i s - i d a e a ) w i t h the lichens/avens/sedge a s s o c i a t i o n ; the i n c l u s i o n of the Common Crowberry (Empetrum nigrum) and Mountain Cranberry w i t h the sedge species; and the appearance of tussocks and the Glandular B i r c h (Betula glandulosa) which are l a r g e l y absent on the higher slopes. F i g u r e 42 shows another hummock p r o f i l e excavated on the lower slope close to the j u n c t i o n w i t h the f l o o r of the depression.  This hummock  was a l s o almost c i r c u l a r i n o u t l i n e , but averaged almost 1.2 metres (4> f e e t ) i n diameter.  The height of the hummock, 20^25 cms. (8-10 ins.) was consid-  erably less than the one shown i n F i g u r e 40, although two large tussocks of the Sheathed Cotton-grass (Eriophorum vaginatum) rose s e v e r a l centimetres above i t s general surface.  The c o n t i n u i t y of the vegetation mat was broken  by the growth of these tussocks, but even i n between i t was extremely  thin.  Figure 40  EARTH LOCATED  ON  LOWER  SURFACE  HUMMOCK PART  CONTOURS  STRUCTURAL  Living  Contour  interval  vegetation  2.5 cms.  Peat  OF  ABOVE  SLOPE  PROFILE  DATUM  PROFILES  ESD  M  ineral  soil  245 Figure 41 EARTH LOCATED  ON  HUMMOCK  LOWER  PART  OF  V E G E T A T I O N  SLOPE  PROFILE  TYPES  •*•»•« V *•' « 1 > *. <•' A  —  i—i—i  Edge  \i2*\  Lichen / ovens / sedge a s s o c i a t i o n with L a b r a d o r tea and Cranberry  EZ3  of  Hummock  or  Tussock tol^  Sedge  [::*.Vvl  Moss a n d / o r  tussock Heather  Willow  Avens  rilSill Sedge  V  species  Cranberry  with  and  S c a l e in cms. 20  birch  Blueberry  Crowberry  0  Ground  40  60  patch  246 Figure 42 STRUCTURAL  PROFILE  LOCATED  AT  OF  THE  AN  FOOT  EARTH OF  A  HUMMOCK SLOPE  Tussocks  0  Scale  20  40  60 c m s .  Figure 43 M U D - B O I L SURFACE  C O N T O U R S  ABOVE  DATUM  247 The underlying peat layer was only a few centimetres t h i c k over the centre of the hummock, but i t thickened l a t e r a l l y and extended down i n t y p i c a l peat wedges beneath the adjacent depressions.  The s i z e of the mineral  core i s a l s o much greater than that shown i n Figure 40, and the mineral s o i l was by f a r the dominant constituent of the hummock. The buried organic layer e x h i b i t e d the same t h i c k e n i n g towards the margins of the troughs, but i t was even thinner and l e s s continuous beneath the centre of the hummock. The appearance of the tussocks r e f l e c t s an obvious change i n the plant composition of the vegetation cover, and i n the. depressions the build-up of a s u b s t a n t i a l layer of moss was more pronounced than at locat i o n s higher up the slope. F i g u r e 43 shows a large mud b o i l located on the f l o o r of the depression c l o s e to the j u n c t i o n w i t h the slope above.  The mud  boil,  t y p i c a l of many developed i n s i m i l a r l o c a t i o n s , was almost c i r c u l a r i n outline,, averaging 1.2-1.4 metres (4-5 f e e t ) i n diameter, and i t s c e n t r a l area rose 25-35 cms.  (10-14' ins.) above the adjacent depressions.  A large  part of the surface of the mud b o i l was completely devoid of, or only s c a n t i l y covered w i t h , vegetation (Figure 44).  The bare mud areas were  often covered w i t h a. network of miniature cracks which gave a blocky appearance to the surface.  In places these cracks had developed  strong r a d i a l furrows 10-15 cms.  (4-6 ins.) deep.  into  Small sedges (Carex  were the dominant species of the sparsely vegetated areas of the mud surface.  sp.)  boil  The Common Crowberry (Empetrum nigrum) and Mountain Cranberry  (Vaccinium v i t i s - i d a e a ) were, prominent i n the larger surface furrows and along the margins of the mud b o i l where they were found i n a s s o c i a t i o n w i t h the Narrow-leafed Labrador-tea (Ledum, palustre ssp. decumbens).  Also  f l a n k i n g the outer slopes of the mud b o i l was a f l o r a c h a r a c t e r i z e d by  248  Figure 44 M U D - B O I L V E G E T A T I O N  i—i—i  E d g e of  H^v^  Sedge  Mud-Boil species  Cranberry p2-;T>j  Sedge  lyXXX]  Moss  E%?%1  Heather  or Tussock  with  and  Crowberry  tussock with  Sedge  TYPES  W i Mow Ground  species  Blueberry Bare  birch patch  ground  249 willows ( S a l i x arctica),, A r c t i c Blueberry (Vaccinium uliginosum) , Glandu l a r B i r c h (Betula glandulosa) and small tussocks of the Sheathed Cottongrass (Eriophorum.vaginatum).  Sedges, A r c t i c White B e l l - h e a t h e r , and the  Sheathed Cotton-grass, along w i t h s e v e r a l moss species, were the.dominant plants of the surrounding depression areas. S t r u c t u r a l l y , the mud b o i l s were made up e n t i r e l y of mineral soil.  The surface mantle of vegetation and peat was very t h i n and discon-  tinuous, but i t thickened towards the margins where s i m i l a r peat wedges occurred beneath the depressions.  The buried organic layer was a l s o ex-  tremely patchy, and i n many places was non-existent.  One other notable  feature of the mud b o i l was the occasional presence of small q u a n t i t i e s of dark, organic m a t e r i a l embedded i n the mineral s o i l at various l e v e l s . I n d i v i d u a l hummocks were generally to be found from top to bottom of most slope p r o f i l e s , and on a l l but the g e n t l e s t slopes the hummocks were a l i g n e d i n a downslope d i r e c t i o n .  L o c a l l y , however, the  hummocks had coalesced to produce d i s t i n c t i v e , continuous vegetated s t r i p e features which were a l s o a l i g n e d i n the same manner.  These s t r i p e features  were often r e a d i l y d i s c e r n i b l e through the c o n t r a s t i n g vegetation patterns of the r a i s e d centres and the i n t e r v e n i n g depressions.  On g e n t l y - s l o p i n g  t e r r a i n , the d i f f e r e n c e i n e l e v a t i o n between the ridges and the furrows was  seldom more than a few centimetres.  On steeper slopes, averaging 10-  15 degrees, e s p e c i a l l y those which were south-facing or the s i t e s of l a t e l y i n g snow patches, the s t r i p e forms achieved much greater prominence. Figure 45 and P l a t e XVII i l l u s t r a t e some of the aspects of these earth hummock s t r i p e s .  The r i d g e s , which were sometimes continuous  over distances of about 10-20 metres (30-65 f e e t ) , were approximately 80 cms.  (27.5-31.5 ins.) i n width and as much as 50-60 cms.  70-  (19.5-23.5 ins.)  250 EARTH  Figure 45 HUMMOCK  STRIPES  ]  Mineral  soil  251  Figure 46 E A R T H  H U M M O C K  V E G E T A T I O N  S T R I P E S  T Y P E S  1 Metre  i—i—i  Edge  [JVT j  L i c h en / a ve n s / sed g e association  K"°'°*l  Avens  of Hummock  Sedge species and Bea r ber ry  Stripes \yy//ss]  Moss Heather Sedge  with species  Willow Blueberry  patch  P l a t e XVII EARTH  HUMMOCK  STRIPES  A. S t r i p e f e a t u r e s produced by the c o a l e s c e n c e of e a r t h hummocks.  B. E x c a v a t i o n a l o n g the l o n g i t u d i n a l a x i s o f an e a r t h hummock s t r i p e , showing the p r o g r e s s i v e b u r i a l of t h e o r g a n i c material. (Tape extended to 1 f o o t f o r s c a l e ) .  C. T r a n s v e r s e o r c r o s s s l o p e e x c a v a t i o n of an e a r t h hummock s t r i p e , showing t h e m i n e r a l core and wedges of o r g a n i c m a t e r i a l beneath the troughs. (Pocket tape case, 2 i n c h e s , shows scale).  253 high.  Seldom, however, were these ridges simple s t r a i g h t f e a t u r e s , and  they frequently e x h i b i t e d a beaded form i n v o l v i n g a d i s t i n c t l a t e r a l d i s placement across the slope.  The i n t e r v e n i n g troughs were very strongly  developed, and often took on the form of narrow, steep-sided c l e f t s . The vegetation cover of the s t r i p e s (Figure 46) was s i m i l a r to that described f o r the. hummocks, except f o r higher percentages  of Cassiope  tetragona and moss occurring i n small depressions on the surfaces.of the r i d g e s , and the absence of Eriophorum vaginaturn and B e t u l a glandulosa from the vegetation types.  The underlying peat layer was continuous but highly  i r r e g u l a r i n thickness, ranging from a few centimetres to 45 cms. ins.).  (17.5  L o c a l thickenings of peat m a t e r i a l occurred i n close a s s o c i a t i o n  w i t h the hollows on the s t r i p e surface and w i t h the narrower widths i n the beaded forms.  The mineral core of the ridges (see Figure 45), v a r i e d i n  thickness from 20-45 cms. f r o n t a l downslope end.  (8.0-17.5 i n s . ) , and was t h i c k e r near the  This mineral core frequently contained t h i n , taper-  ing wedges of organic m a t e r i a l , which extended down below the t h i c k e r portions of the. peat layer above.  These wedges dipped steeply downward i n  an upslope d i r e c t i o n , and detached,elongated  s t r i p s of organic m a t e r i a l ,  wholly incorporated w i t h i n the mineral s o i l , showed the same general orientation.  The f r o n t a l lobe of the s t r i p e showed a wedge of organic  m a t e r i a l i n the process of being buried by the mineral core ( P l a t e XVII-B), and t h i s could be traced upslope i n t o the buried organic l a y e r .  In cross-  s e c t i o n , the p r o f i l e s revealed wedges of organic m a t e r i a l extending down i n places to u n i t e w i t h organic m a t e r i a l at the f r o s t t a b l e ( P l a t e XVII-C). Apart from the.presence  of the_buried organic l a y e r , these features show a  d i s t i n c t s i m i l a r i t y to those described by Sharp, and t h i s would seem to j u s t i f y the adoption of h i s nomenclature f o r the m i c r o r e l i e f . f e a t u r e s .  254 The S i z e and Form of Earth Hummocks.  The l i t e r a t u r e contains  few references to the s p e c i f i c s i z e , spacing or form of hummocks, and, when these dimensions are given, they are frequently extremely generalized and d e s c r i p t i v e .  For example, Sharp, d e s c r i b i n g earth hummocks i n the S t .  E l i a s Range, wrote: "The Wolf Creek hummocks, are 1 to 2 f e e t high w i t h ground dimensions of 1 to 5 f e e t . On f l a t s or slopes of 5 degrees the hummocks are crudely hemis p h e r i c a l , but on steeper slopes they develop an elongation across the slope. The downhill side i s higher and steeper than the u p h i l l s i d e , and i n a few places the upper surface grades back i n t o the h i l l slope without an i n t e r v e n i n g depression, thus forming a small t e r r a c e " . ^ The diagrammatic i l l u s t r a t i o n of an earth hummock i n Sharp's paper suggests that they are s i m i l a r to the m i c r o r e l i e f features found on Garry I s l a n d , and the two structures may indeed have a s i m i l a r o r i g i n . The change from a roughly hemispherical to an elongated form was a l s o observed on Garry I s l a n d , but the d i r e c t i o n of elongation appeared to be downslope rather than across i t . P r e l i m i n a r y observations i n the f i e l d suggested that there might be a c o r r e l a t i o n between the form of the hummock and the angle of the slope.  Attempts to e s t a b l i s h such a simple c o r r e l a t i o n proved f r u i t l e s s ,  however, since the prevalence of smooth, convex-concave slope p r o f i l e s provided very few slope segments of constant i n c l i n a t i o n where s u f f i c i e n t l y large samples could be obtained to examine t h i s r e l a t i o n s h i p .  However,  these observations suggested a change i n the s i z e and form of the hummocks between the tops and bottoms of these same slope p r o f i l e s .  S h a r p , R.P. (1942) " S o i l structures i n the S t . E l i a s Range, Yukon T e r r i t o r y " , J o u r n a l of Geomorphology, V o l . 5, p. 283. 0/  255 The f i e l d method adopted to i n v e s t i g a t e these changes was based on that used by S t r a h l e r and Koons to measure t e r r a i n  roughness.  68  F i v e slope p r o f i l e s were selected to cover the p o s s i b l e v a r i a t i o n s i n aspect.  The c r o s s - p r o f i l e s of the slopes were then surveyed and, on each of  them, s t a t i o n s were e s t a b l i s h e d f o r sight l i n e s across the slope. The slope p r o f i l e s and the locations of the sampling s t a t i o n s are shown i n Figure 47. The l o c a t i o n s of the s t a t i o n s were determined  subjectively,  rather than o b j e c t i v e l y as i n S t r a h l e r ' s study, at points where the hummock form appeared to be v i s u a l l y d i f f e r e n t from that at the adjacent upslope station.  A t each of these points an alidade was set up, and a h o r i z o n t a l  sight l i n e was made along the contour to a s t a d i a rod.  Since the hummocks  were not a l i g n e d p e r f e c t l y along the contours, i t was necessary to i n t e r pret the sight l i n e as an angular sector. The s t a d i a was moved w i t h i n t h i s sector to the highest or lowest points of hummocks or depressions r e s p e c t i v e l y , parts of which a c t u a l l y crossed the sight l i n e .  A tape was  also stretched along the contour to provide data on the spacing of these m i c r o r e l i e f f e a t u r e s . I n order to provide s u f f i c i e n t l y large samples f o r s t a t i s t i c a l comparisons, the procedure-was repeated a t each s t a t i o n w i t h another sight l i n e along the contour i n the opposite d i r e c t i o n . Data on hummock heights were obtained by s u b t r a c t i o n of successive s t a d i a height readings as representing the v e r t i c a l distance through which the ground p r o f i l e i s d i s p l a c e d between adjacent hummocks and depressions along the angular sight l i n e sector. The data were then  S t r a h l e r , A.N. and Koons, D. (1960) "Objective and. Q u a n t i t a t ive Methods of T e r r a i n A n a l y s i s " , U.S_. Dept. of the Navy, O f f i c e of Naval Research, Geography Branch, P r o j e c t NR 387 - 021, Contract Nonr 266 - 50, 51 p.  256 Figure 47  SLOPE  PROFILES  EARTH  SHOWING LOCATIONS  HUMMOCK  SAMPLING  OF  STATIONS  1  O  2  6  4 Distance  in  e  Metres  10  257 processed by frequency d i s t r i b u t i o n a n a l y s i s to provide i n d i c e s of mean height, variance and standard d e v i a t i o n . Since most of the frequency  dis-  t r i b u t i o n s were not markedly skewed (Figures 48-52), i t was not considered necessary to. transform the data before f u r t h e r s t a t i s t i c a l t e s t s could be performed. The mean values f o r the hummock heights are presented i n Table XIV.  The means were f u r t h e r analysed by running paired ' t ' - t e s t s on each  p r o f i l e to determine whether or not the d i f f e r e n c e s between the means f o r adjacent sampling s t a t i o n s were s i g n i f i c a n t a t the .01 or .05 s i g n i f i c a n c e levels.  The procedure f o r the ' t ' - t e s t followed that o u t l i n e d by Croxton  and Crowden, where i t i s assumed that the samples are independent, and 69 that the sample means f o l l o w a normal d i s t r i b u t i o n . Reference to the range values i n Table XIV shows that at each of the s t a t i o n s there was a considerable v a r i a t i o n i n the heights of the hummocks. This range value, c a l c u l a t e d as the d i f f e r e n c e i n centimetres between the height of the largest and smallest hummocks observed along the i n d i v i d u a l sight l i n e s , increased i n a downslope d i r e c t i o n .  The greater  uniformity of hummock heights i n the upper portions of the slope p r o f i l e s was due to the absence of any extremely large hummocks i n these l o c a t i o n s . Despite these v a r i a t i o n s , each of the f i v e p r o f i l e s shows that there was a gradual increase i n the mean height of the hummocks from the top to the bottom of the slope.  The majority of these changes were found to be s i g -  n i f i c a n t a t the .01 l e v e l (Table XIV).  I t i s a l s o q u i t e noticeable that  most of the n o n - s i g n i f i c a n t values encountered were i n t e s t s i n v o l v i n g Croxton, F.E. and Crowden, D..J. (1955) A p p l i e d General S t a t i s t i c s , P r e n t i c e - H a l l , Inc., Englewood C l i f f s , N.J., Second E d i t i o n , p. 651.  258 Figure 48 HISTOGRAMS  OF  STATION 25  HUMMOCK  HEIGHTS  -  PROFILE  STATION  1  2  r  X = 7 92  20  X = 10.06  20  n = 53  n =51 15  oi  15 -  v  10  0  6  Height  10  12  0  (Cms.)  STATION  6  Height  1?  18  (Cms.)  3 STATION  20  X = 13.11  -  4  20  n = 60 u  1  X = 17. 68  15 -  n = 50  10  0  6  Height  12  18  (Cms.)  6  12  Height  18  24  (Cms.)  STATION  5  STATION  5  24  30  6  X =21.03  X =16.15  n = 54  n = 65  -  0  6  12  18  Height  24  (Cms.)  30  36  0  I  I-  Height  18  (C r  24  30  259 Figure 49 HISTOGRAMS  STATION  OF  HUMMOCK  HEIGHTS  1  -  PROFILE  STATION  II  2  25 X = 7. 3 2  20  n = 55  u  0  6  Height  (Cms.)  STATION  3  5 -  6  (Cms.)  X =15.24 n = 56  6  12 18 24 30  Height  STATION  5 X = 19.81  '5 r  4  15 r  0  12 18 24  STATION  (Cms.)  » 5-  •  Height  6 12 18  STATION  n = 55  0  15 .  Height  X = 12.50  »  n = 68  0  18  12  X = 9.75  n = 51  (Cms.)  6 X =15.54  15  n = 67  " 10  0  6  12 18 24  Height  (Cms.)  30  0  6 12 18 24 30 Height  (Cms.)  260 Figure 50 HISTOGRAMS  OF  STATION  HUMMOCK  HEIGHTS  S TAT  1  20  - PROFILE  ION  20  X » 7.01  III  X =10.97  n = 59  n - 67 15 •  10 •  10  5 •  0  6  Height  12  6  ICms.  Heigh t  •  2  18  (Cms.)  3  S TAT ION 25  X = 12.80  20  *  cr e  STATION  n = 68  is  4 X = 17.37  15 r  o  n - 73  10  10 4)  6  12  Height  18  (Cms.)  5 .  24  6  12  Height  18  24  •b  (Cms.)  STATION  30  6  20 r  STATION  X = 23.47  5 •  0  n » 69  n s 61  io r «  6  12  18  Height  X • 22.25  15 •  5  24  LrftL  30  (Cms.)  10 •  36  42  r  12  18  Height  24  (Cms.)  30  36  42  261 Figure 51 HISTOGRAMS  OF  STATION 30  HUMMOCK  HEIGHTS  - PROFILE  IV  1  r STATION  25  X « 6.71 n . 80  20  20  X = 9.45 15  15  10  10  0  6  Height  12  n *63  0  18  STATION  6  Height  (Cms.)  12  18  (Cms.)  3  25  STATION  20  "  4  X = 12.80 n •56  15  X = 15.54  15  n - 50 Z  10  10 ar  «  0  6  12  Height  18  5  6  24  12  Height  (Cms.)  18  STATION STATION  24  (Cms.) 6  5 X -21.03 n • 52  10  0  6  12  18  Height  24  t f b  (Cms.)  30  36  X -21.64 n - 50  10 •  0  6  12  Height  18  24  (Cms.)  Lb  30  36  262  Figure 52 HISTOGRAMS  STATION  OF  HUMMOCK  HEIGHTS  -  PROFILE  V  1  30  STATION  2  X = 7.32 n - 70  20  X = 7.62 «  15  n s66  15  10  5 -  0  6  Height,  12  0  (Cms.)  STATION  6  Height  12  (Cms.)  18  3 STATION  20  4  X =11.28  X = 13.72  n = 63  n = 58 10 -  10  0  20  6  12  18  Height  (Cms.)  STATION  5  24  0  r  rl  6  12  Height  (Cms.)  STATION  15 -  X = 17. 3 7  18  24  JZ3  6  15  X = 21.03  n = 72 u  10  6  12  Height  18  24  (Cms.)  30  30  n - 63  10  0  6  12  Height  18  24  (Cms.)  30  36  263 TABLE XIV ANALYSIS PROFILE  I  OF GARRY  ISLAND  EARTH HUMMOCK DATA -  Sample Size  Range  X  s  1 (Top)  51  11.28  7.92  3.12  2  53  11.28  10.06  2.74  3  60  21.03  13.11  3.99  4  50  23.16  17.68  5.33  5  54  25.30  .21.03  6.00  6 (Bottom)  65  28.65  16.15  6.33  t  Significance Level .01 .05  3.66  S.  7.35  S.  5.08  S.  2.43  N.S.  4.21  S.  4.35  s.  3.44  s.  2.69  S.  3.94  S.  3.69  S.  6.60  S.  S.  (Azimuth - 285 )  1 (Top)  55  14.63  7.32  2.66  2  68  13.72  9.75  3.37  3  55  21.34  12.50  5.33  4.  56  27.43  15.24  5.35  5  51  26.52  19.81  6.31  6 (Bottom)  67  25.30  15.54  6.07  PROFILE I I I  (Cms.).  (Azimuth •- 360 )  Station  PROFILE I I  HEIGHTS  (Azimuth - 180 )  1 (Top)  59  11.28  7.01  2.59  2  67  17.68  10.97  3.89  3  68  18.90  12.80  4.45  4.  73  27.13  17.37  5.54  5  61  34.75  23.47  8.88  6 (Bottom)  69  28.35  22.25  6.53  N.S.  0.80 5.36  S.  4.81  S.  . 0.89  N.S.  264  TABLE  PROFILE  IV  Station  (Azimuth -  XIV  (Continued)  55 ) X  Sample Size  Range  1 (Top)  80  14.33  6.71  3.00  2  63  13.41  9.45  3.84  3  56  17.68  12.80  2.20  4  50  21.34  15.54  4.66  5  52  24.69  21.03  6.49  6 (Bottom)  50  22.56  21.64  5.47  PROFILE  V  s  t  Significance Level .05 .01  4.76  S.  4.64  S.  3.86  S.  4.83  S.  0.51  N.S.  0.90  N.S.  (Azimuth - 230 )  1 (Top)  70  13.72  7.32  2.57  2  66  15.54  7.62  3.72  3  63  24.08  11.28  4.36  4  58  25.30  13.72  5.21  5  72  24.08  17.37  5.81  6 (Bottom)  63  27.43  21.03  7.03  5.08  S.  2.78  S.  3.70  S.  3.28  S.  265 paired means at the terminal parts of the p r o f i l e s .  This probably  r e f l e c t s the f a c t that an attempt was made to e s t a b l i s h s i x s t a t i o n s , approximately equally spaced, on each of the p r o f i l e s .  Where the  topographic p r o f i l e consisted of a short, steep mid-section and r e l a t i v e l y longer upper c o n v e x i t i e s and lower c o n c a v i t i e s , as i n P r o f i l e I I I , the s t a t i o n s i n these terminal p o s i t i o n s were probably too close together.  Three of the p r o f i l e s show that towards the base there was a  tendency f o r the mean height of the hummocks to decrease again, and two of these cases were s i g n i f i c a n t at the .01 l e v e l .  On the other two  p r o f i l e s , IV and V, the mean height of the hummocks increased r i g h t to the base of the p r o f i l e .  V a r i a t i o n s i n aspect may be p a r t i a l l y r e s -  ponsible f o r t h i s , but i t appears to be more r e l a t e d to the drainage conditions a t the foot of the slope.  Where i t was observed that there  was a decrease i n hummock height at the base of the slope, the p r o f i l e s terminated i n semi-closed depressions w i t h poor drainage.  There was  considerable evidence of a moss-peat accumulation on the f l o o r of the depression, and the trough areas between the i n d i v i d u a l hummocks showed moss accumulations as described i n the preceding s e c t i o n . I t i s t h i s i n f i l l i n g of the depressions that i s mainly responsible f o r the apparent decrease i n height of the hummocks. I n the case of p r o f i l e s IV and V 'active' stream channels drained the foot of the slope, and there was l i t t l e evidence of the b u i l d up of organic m a t e r i a l . Data on the s i z e s of the hummocks were obtained by combining the h o r i z o n t a l distance measurements between each depression, and these data were subjected to the same form of a n a l y s i s . The r e s u l t s of the analyses are presented i n Table XV. As i n the case of the height data, there was a considerable range i n the s i z e s at each s t a t i o n , but the  266 TABLE XV ANALYSIS PROFILE  OF  GARRY  ISLAND  EARTH HUMMOCK DATA  SIZES  (Cms.).  I Sample Size  Range  X  s  1 (Top)  50  107  73.20  22.23  2  52  99  86.06  25.88  3  58  122  87.22  27.76  4  48  130  94.77  26.49  5  47  122  99.16  31.70  6 (Bottom)  64  147  99,92  31.72  1 (Top)  55  99  77.90  24.41  2  66  99  81.66  25.88  3  54  155  95.15  34.82  4  55  145  98.60  . 31.37  5  49  170  112.60  42.80  6 (Bottom)  66  147  111.30  31.12  1 (Top)  57  102  76.43  17.86  2  65  91  77.09  19.66  3  66  76  80.24  22.25  4.  71  84  82.27  20.09  5  59  97  94.84  21.23  67  127  99.67  23.24  Station  t  2.66  Significance Level .01 .05 S.  0.23  N.S.  1.41  N.S.  0.73  N.S.  0.12  N.S.  0.81  N.S.  PROFILE I I  2.41  N.S.  S.  0.54  N.S.  1.89  N.S.  0.17  N.S.  0.26  N.S.  0.85  N.S.  0.56  N.S.  PROFILE I I I  6 (Bottom)  3.44 1.20  S. N.S.  267  TABLE  XV  (Continued)  PROFILE IV Station  Sample Size  Range  X  s  1 (Top)  78  107  69.98  21.77  2  61  102  74.42  19.56  3  54  97  85.88  22.81  4  48  112  89.23  26.44  5  48  107  99.95  23.19  6 (Bottom)  48  114  97.49  26.39  1 (Top)  68  137  71.98  22.81  2  64  94  76.28  20.14  3  61  142  81.56  25.81  4  56  122  82.60  25.98  5  70  119  88.98  20.27  6 (Bottom)  61  140  99.26  22.78  PROFILE  t  Significance Level .01 .05  1.24 2.87  N.S. S.  0.68 2.09  N.S. N.S.  S.  0.48  N.S.  1.13  N.S.  1.27  N.S.  0.22  N.S.  1.53  N.S.  V  2.71  S.  268 increase i n range values i n a downslope d i r e c t i o n was not as marked.  As  Table XV shows, there was an increase i n the s i z e of the hummocks t o wards the base of the slope, but t e s t s of paired means y i e l d e d very few s i g n i f i c a n t values.  Tests on the mean hummock s i z e of samples 1 and 6 of  each of these p r o f i l e s , however, y i e l d e d ' t ' values of 5.00, 6.42, 6.10, 6.30 and 6.73 f o r p r o f i l e s I to VI r e s p e c t i v e l y , a l l of which were s i g n i f i c a n t at the .01 l e v e l , and i n d i c a t e that there i s a s i g n i f i c a n t increase i n the s i z e of hummocks i n a dpwnslope d i r e c t i o n . Although moderate success, demonstrating changes i n the s i z e of hummocks, was achieved using t h i s method, i t was hoped that more success could be obtained using the idea of an 'index of c i r c u l a r i t y . 1  The s i z e measurements were made by taking readings d i r e c t l y from the metal tape.  Insomuch as the tape was f i x e d along the sight l i n e , while  the points e s t a b l i s h i n g hummock and depression p o s i t i o n s were considered w i t h i n an angular s e c t o r , the l i n e a r distances obtained were not a true i n d i c a t o r of the s i z e of the hummocks. Moreover, these readings measured only the v a r i a t i o n s i n the cross-slope dimensions of the hummocks, and gave no i n s i g h t i n t o corresponding changes i n the downslope dimensions. The idea of an index of c i r c u l a r i t y was introduced therefore to i n v e s t i g a t e changes i n the r a t i o of downslope to cross-slope dimensions of hummocks at d i f f e r e n t p o s i t i o n s on the topographic p r o f i l e .  Equi-  dimensional hummocks would have an index of 1.0, w h i l s t hummocks which were elongated down or across the slope would have indices greater or less that 1.0 r e s p e c t i v e l y . P r o f i l e V was selected to i n v e s t i g a t e t h i s index as w e l l as c e r t a i n angular properties of the hummock faces.  Three sample p l o t s were  established near the top, middle, and base of t h i s p r o f i l e .  Each p l o t  269 extended f o r a distance of approximately 8 metres (26 f e e t ) i n a downslope d i r e c t i o n , and f o r v a r i a b l e distances along the contours on e i t h e r side of the p r o f i l e l i n e .  The sampling procedure consisted of t a k i n g the  f i r s t 25 hummocks i n t h i s p l o t on e i t h e r side of the p r o f i l e l i n e , and measuring t h e i r downslope and cross-slope dimensions.  These values were  then used to c a l c u l a t e the index of c i r c u l a r i t y . The mean index of c i r c u l a r i t y f o r 50 hummocks at the upper part of the slope p r o f i l e was 1.05 w i t h a maximum and minimum of 1.47 and 0.82 r e s p e c t i v e l y .  Eighty per cent of the hummocks i n t h i s p l o t had an  index greater than 1.0, and only eight per cent had an index of l e s s than 1.0.  The mean index f o r 50 hummocks i n the middle section of the p r o f i l e  however was 1.95. The maximum and minimum values of 2.58 and 1.42 show that a l l the hummocks, without exception, e x h i b i t e d an elongation i n the downslope d i r e c t i o n .  I n the t h i r d p l o t , located a t the base of the  p r o f i l e , the mean index of c i r c u l a r i t y was 1.09, w i t h a maximum and minimum of 1.31 and 0.82 r e s p e c t i v e l y .  Once again only eight per cent of  the hummocks had an index value of less than 1.0. P a i r e d t e s t s of the mean index values were run using the value f o r the middle p l o t against the values f o r the p l o t s i n the terminal p o s i t i o n s of the p r o f i l e , and y i e l d e d 't  1  values of 21.57 and 24.40.  .01 l e v e l .  Both these values are s i g n i f i c a n t a t the  These f i g u r e s i n d i c a t e t h a t , i n a d d i t i o n to changes i n the  height and s i z e of the hummocks i n a downslope d i r e c t i o n , there i s a l s o a s i g n i f i c a n t change i n the form of the hummocks from an almost c i r c u l a r o u t l i n e a t the upper slope p o s i t i o n , to an elongated form on the steeper portions of the slopes, and a r e t u r n to an almost c i r c u l a r shape at the foot of the slope.  Since only eight of the one hundred and f i f t y hummocks  i n v e s t i g a t e d showed an elongation across the slope, these f i n d i n g s contrast  270 w i t h those observed by Sharp.  70  At the same time as the index of c i r c u l a r i t y measurements were being made, the i n c l i n a t i o n s of the downslope and upslope faces of the i n d i v i d u a l hummocks were a l s o recorded. An a r b i t r a r y decision was made that i f the two i n c l i n a t i o n s d i f f e r e d by less than f i v e degrees the hummock would be classed as symmetrical. For the 50 hummocks i n the upper p l o t , i t was found that 72 per cent were steeper on the downslope face, 18 per cent were symmetrical and only 10 per cent had steeper faces on the upslope side.  The mean angle of the downslope face was 48 degrees  compared to 31 degrees f o r the upslope face.  I n the middle p l o t the  c l a s s i f i c a t i o n gave corresponding values of 72, 18 and 10 per cent and 55 and 42 degrees.  Most of the hummocks thus exhibited a marked  asymmetry s i m i l a r to. that observed by Sharp, but decidedly d i f f e r e n t from the observations of Raup who found that t u r f hummocks have steeper upslope 71 faces.  I t was also noticeable that many of the hummocks were not  aligned p e r f e c t l y i n a simple upslope-downslope d i r e c t i o n , but were sometimes o b l i q u e l y oriented to the general d i r e c t i o n of the slope. Furthermore the d i r e c t i o n of the oblique tendency was found to be highly v a r i a b l e over even small areas.  The studies of the angles of the hummock  faces also revealed the influence of lemming a c t i v i t y , which was e s p e c i a l l y evident i n s i t e s frequently occupied by l a t e - l y i n g snow patches.  At these  s i t e s the downhill faces of the hummocks were frequently ..vertical, or even overhanging, and were punctured by the burrows of these small 70, 'sharp, R.P. (1942) OJJ. c i t . , p. 283. 71,"Sharp, R.P. (1942) op_. c i t . , p. 283. Raup, H.M. (1965) op_. c i t . , p. 105.  271 rodents. I t was mentioned e a r l i e r that the l o c a t i o n s of the f i v e p r o f i l e s were c a r e f u l l y selected ,to t r y to evaluate the varying form of the hummocks on slopes with d i f f e r e n t aspects.  As Table XV shows, the  r e s u l t s were not p a r t i c u l a r l y i l l u m i n a t i n g , although i t may be s i g n i f i c a n t that the l a r g e s t hummocks encountered were on the south-facing slope or conversely on northeast-facing slopes, the most favourable s i t e s f o r l a t e l y i n g snow patches.  I t was i n these same two environments that the  hummocks were v i s u a l l y the most d i s t i n c t , a n d where the tendency to coalesce i n t o a s t r i p e form was best developed.  On a smaller s c a l e , i t  was found that the influence of aspect gave a f u r t h e r q u a l i t y of asymmetry to the i n d i v i d u a l hummocks. One hundred hummocks were studied on a westf a c i n g slope and i t was found t h a t , using s i m i l a r c r i t e r i a to the preceding i n c l i n a t i o n s t u d i e s , 14 per cent of the hummocks could be classed as symmetrical, 10 per cent had steeper faces on the south-facing s i d e , while 76 per cent of the hummocks had a steeper slope on the north-facing side. At the same time i t was noticed that the north-facing sides tended t o be shorter and higher when compared to the g e n t l e r , longer p r o f i l e s f a c i n g i n a southerly d i r e c t i o n . '  I n summary, these studies show that there i s a considerable  change i n the forms of i n d i v i d u a l earth hummocks i n a downslope d i r e c t i o n . Hummocks show s i g n i f i c a n t increases i n height and s i z e from the top to the base of a slope, and appear to go through a c y c l i c a l form change from c i r c u l a r through elongated and back to a c i r c u l a r form. I n d i v i d u a l hummocks e x h i b i t a preferred o r i e n t a t i o n i n a downslope d i r e c t i o n , and where they coalesce to form s t r i p e s they demonstrate the same p r e f e r e n t i a l alignment.  Downslope faces of the hummocks are steeper than  corresponding  272 upslope faces by an average of 15 degrees.  On west-facing slopes the  influence of varying aspect imparts an a d d i t i o n a l f a c t o r of asymmetry w i t h north-facing sides of the hummocks being shorter, higher and an average of 15 degrees steeper than the opposing south-facing sides.  Each of these  f a c t s deserves f u l l consideration i n any discussion concerning the o r i g i n and development of these m i c r o r e l i e f features. The o r i g i n and development of Earth Hummocks.  I n the  voluminous l i t e r a t u r e that has been published d e s c r i b i n g various forms of patterned ground, numerous theories have been proposed concerning t h e i r origin.  Although i t i s now almost u n i v e r s a l l y agreed that they are the  r e s u l t of f r o s t a c t i o n , there i s s t i l l a great deal of controversy cerning the precise mode of o r i g i n of many of these forms.  con-  Washburn, i n  his c l a s s i c a l review of these features, l i s t e d no fewer than nineteen d i f f e r e n t hypotheses, summarized according to the dominant processes,  that  various authors have proposed to e x p l a i n t h e i r genesis, and concluded that the o r i g i n of most forms i s uncertain and, i n the majority of cases, i s • polygenetic.  7 2  The most commonly accepted o r i g i n f o r the doming-up of the mineral s o i l to form the earth cores of hummocks f o l l o w s the theories pro73 posed by Thoroddsen and Beskow.  I n h i s d i s c u s s i o n of the formation of  ' t h u f u r j , Thoroddsen concluded that the mineral s o i l p a r t i c l e s were 72  Washburn, A.L. (1956) op_. c i t .  73 Thoroddsen, Th. (1914) "An account of the p h y s i c a l geography of Iceland w i t h s p e c i a l reference to the plant l i f e " , pp. 187-343, i n Kolderup Rosenvinge, L. and Warming, E. The Botany of Iceland, V o l . 1, 675 p. Beskow, G. (1930) " E r d f l i e s s e n und Strukturboden der Hochgebirge im L i c h t der Frosthebung, Geol. Foren. Stockholm, Forh., Bd. 52, pp. 622-638. Information c i t e d i n Raup, H.M. (1965) op_. c i t . , p. 15.  273 gradually moved upward under the hummocks through the combined a c t i o n of deep f r e e z i n g i n the troughs and the upward movement of c a p i l l a r y water i n 74 the hummock centres.  Beskow claimed that deeper, more-rapid f r e e z i n g of  the damp trough areas took place while the centres of the hummocks remained unfrozen at depth, and the r e s u l t i n g pressures forced m a t e r i a l i n t o the unfrozen c o r e s . ^  The d i s t r i b u t i o n of snowfall was considered to be an  important f a c t o r by Griggs, who suggested that i t s e f f e c t would be to create d i f f e r e n c e s i n the growing season period between hummocks and 76 troughs, i n favour of more l u x u r i a n t growth on the hummock centres.  He  further claimed that the snow would exert l a t e r a l pressures against the sides of the hummocks thereby squeezing them higher. In the chapter on permafrost c o n d i t i o n s , i t was shown that the r a i s e d hummock centres are s i t e s of deeper thaw during the summer than the adjacent troughs.  Excavations of d i f f e r e n t hummocks through the summer  months showed t h a t , i n each case, there was a gradual increase i n the water content down to the p o s i t i o n of the f r o s t t a b l e , and t h i s was accompanied by an increase i n the percentage of f i n e m a t e r i a l w i t h depth.  Where these  excavations: were continued below the p o s i t i o n of the f r o s t t a b l e , i t was evident that the mineral s o i l contained many small i c e lenses of the s i r l o i n type.  The s i z e of these lenses increased w i t h depth and w i t h the  s i z e of the hummock, and i n the mud b o i l s there was a d i s t i n c t layer of clear i c e near the base of the a c t i v e l a y e r . Unfortunately i t was not 74 Thoroddsen, Th. (1914) op_. c i t . 75  Beskow, G. (1930) op_. c i t .  76 Griggs, R.F. (1936) "The vegetation of the Katmai D i s t r i c t " , Ecology, V o l . 17, pp. 380-417.  274 possible to obtain a complete p i c t u r e of the penetration of the f r o s t l i n e during the f a l l and winter months, but, from the l i m i t e d data a v a i l a b l e , i t appears that f r e e z i n g of the ground surface occurs most r a p i d l y i n the trough areas where the moist organic m a t e r i a l acts as a good conductor of heat.  The penetration of the f r o s t l i n e i s slower under the hummocks and  once the troughs are completely f r o z e n , any confined pressures could r e s u l t in f u r t h e r continued slow penetration below the hummocks.  The combinations  of slow f r e e z i n g and f i n e m a t e r i a l i s extremely favourable f o r the formation of i c e lenses and, provided that there i s a source of water, the growth of these lenses may  cause a general doming of the hummock surface;  Assuming that the doming.of the hummocks i s p r i m a r i l y a consequence of d i f f e r e n t i a l f r o s t a c t i o n between the hummock.centres and the adjacent troughs, several authors have expressed concern over the type of topography upon which t h i s process could work during the i n i t i a l stages of hummock development.  Beskow thought that t h i s r e l i e f could develop from  chance v a r i a t i o n s i n the s o i l surface and vegetation cover, but the ubiquitous occurrence of these features would seem to require much more than simple chance v a r i a t i o n s i n the surface f o r m . ^  Raup suggested that  these micro-elevations could be achieved i n a number of ways such as cobbles, boulders, l o c a l sand and s i l t deposits i n stream beds, moss p o l s t e r s i n snow beds, upfrozen stones, p r e - e x i s t i n g g e l i f l u c t i o n features or p r i m a r i l y through the development of a normal i r r e g u l a r surface i n mats 78 of aquatic mosses.  The general paucity of stones and the occurrence  hummocks i n l o c a t i o n s which are not, and never were, occupied by stream C i t e d i n Raup, H.M. 'Raup,, H.M.  (1965) o£. c i t . , pp. 15-16.  (1965) op_. c i t . , pp. 106-107.  of  275 channels would appear to eliminate the p o s s i b i l i t y that the earth hummocks on Garry I s l a n d had a s i m i l a r mode of o r i g i n . . Attempts to lower the l e v e l of a lake on the i s l a n d during the ;summer of 1965 provided a valuable opportunity t o study t h i s problem.  A  lowering; of the water l e v e l exposed a g e n t l y - s l o p i n g , vegetation-free lake bottom which, towards the s h o r e l i n e , was l o c a l l y mantled by a l i t t e r of peat debris 4-5 cms. (1.5-2.0 ins.) t h i c k .  By the end of the summer, t h i s  surface was covered by a network of d e s i c c a t i o n cracks.  Observations  during the summer of 1966 showed that some of these cracks had been accentuated  i n t o a t r o u g h - l i k e form, probably i n part by. f r o s t a c t i o n  during the preceding f a l l , but a l s o by running water derived from spring melting of snow. The l a r g e s t troughs, as much as 20-30 cms. (8-12 ins.) wide and 15-20 cms. (6-8 ins.) deep, ran d i r e c t l y down the slope and extended as f a r as the new. shoreline on the peat-free surface.  I n other  places, c o n s i s t i n g of bare mineral s o i l , a s i m i l a r , though less prominent, network of troughs was a l s o evident.  Although the surface was s t i l l  largely  devoid of any vegetation cover, a few small sedges had taken root on the peat mat. Only time w i l l t e l l whether or not t h i s pattern of cracks w i l l develop i n t o a system of earth hummocks, but these observations suggest that the formation of earth hummocks may be polygenetic from even the most i n c i p i e n t stages.  The i n i t i a l topography may be produced by a combination  of d e s i c c a t i o n and f r o s t a c t i o n l o c a l l y accentuated by r i l l w o r k .  In this  respect the former two processes r e s u l t i n a s u b d i v i s i o n of the ground i n t o a block form, and subsequent development of the major cracks provides the framework f o r subsequent hummock development.  Some of the i n i t i a l r e l i e f  and alignment pattern of the hummocks however may be the r e s u l t of running  276 water during t h i s i n i t i a l stage. may  I t i s also quite probable that an analogy  be drawn at t h i s stage between earth hummock formation and the