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An investigation of talus slope development in the Similkameen Valley near Keremeos, B.C. Worobey , George A. 1972

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AN INVESTIGATION OF TALUS SLOPE DEVELOPMENT IN THE SIMILKAMEEN VALLEY NEAR KEREMEOS, B. C.  by  GEORGE A. WOROBEY B. Ed., University of B. C , 1966  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS  In the Department of Geography  We accept this thesis as conforming to the required standard  The University of B r i t i s h Columbia July, 197 2  In p r e s e n t i n g t h i s an  thesis  in p a r t i a l f u l f i l m e n t o f  advanced degree at the U n i v e r s i t y  the  Library  f o r s c h o l a r l y purposes may  be g r a n t e d by  of  t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not  Date  It i s understood that  permission.  Geography  The U n i v e r s i t y o f B r i t i s h Vancouver 8, Canada  J u l  y  l  >  1 9 7 2  -  r e f e r e n c e and  the Head o f my  his  Department of  for  f o r e x t e n s i v e copying o f  by  written  representatives.  requirements  of B r i t i s h Columbia, I agree  s h a l l make i t f r e e l y a v a i l a b l e  I f u r t h e r agree t h a t p e r m i s s i o n  the  Columbia  be  that  study.  this  thesis  Department  copying or  for  or  publication  allowed without  my  -i-  ABSTRACT T a l u s form and development i n t h e Similkameen V a l l e y near Keremeos,  B r i t i s h Columbia was i n v e s t i g a t e d .  Initial  observations  suggested t h a t t a l u s  f o r m a t i o n i n t h e r e g i o n was e n t e r i n g a p a s s i v e  s t a g e and subsequent  a n a l y s i s has c o n f i r m e d t h a t t h e t a l u s s l o p e s  t e n d i n g towards s t a b i l i t y .  V o l c a n i c ash exposed on one t a l u s  a l l o w e d the c a l c u l a t i o n o f r e l a t i v e r a t e s of p a s t and r e c e n t  are  slope talus  a c c u m u l a t i o n which s u p p o r t e d a ' d i m i n i s h i n g sediment y i e l d ' concept  .  A n a l y s i s of c l i m a t e d a t a r e c o r d e d a t Keremeos s i n c e 1930 r e v e a l e d a h i g h f r e q u e n c y of f r o s t c y c l e s .  T h i s suggests  the  i m p o r t a n c e of f r o s t a c t i o n as a mechanism of w e a t h e r i n g a l o n g t h e exposed h e a d w a l l s and i t i s thought t h a t the o c c u r r e n c e of and m a s s i v e t a l u s  abundant  forms i n the r e g i o n i s b a s i c a l l y the r e s u l t of  frost weathering i n association w i t h l i t h o l o g i c c o n t r o l s .  A fence  s t r u c t u r e designed t o capture r o c k f a l l d e b r i s y i e l d e d f a i r  results  and s u b s t a n t i a t e d the v a l i d i t y o f u s i n g v e g e t a t i o n as an i n d e x of s t a b i l i t y on t a l u s  slopes.  A weak b u t not monotonic i n c r e a s e i n sediment s i z e downslope was d e t e c t e d on a number of slopes, c o n t r a d i c t i n g an i n i t i a l v i s u a l impression.  D e b r i s sampled a l o n g l a t e r a l p r o f i l e s on one t a l u s  cone  i s s i g n i f i c a n t l y l a r g e r a t t h e 1% l e v e l t h a n d e b r i s sampled a l o n g the central p r o f i l e .  Some c o r r e l a t i o n between s i z e and a n g l e i s  s i n c e the l a t e r a l p r o f i l e s are a l s o s t e e p e r ;  implied,  i t i s hypothesized that  t r a n s p o r t mechanisms down the s i d e s a r e d i f f e r e n t from t h o s e a l o n g t h e c e n t e r of the c o n e .  Readily observable cross-slope  sorting,  -ii-  r e s u l t i n g i n the development of longitudinal s t r i p s of f i n e and coarse debris, i s explained  i n terms of d i f f e r e n t i a l mass movement mechanisms.  It i s concluded that the talus slopes studied are complex and influenced by a v a r i e t y of processes i n addition to primary deposition. The mapping of one talus cone at a f i v e foot contour i n t e r v a l provided the basis for a d e t a i l e d analysis of talus form.  A sample  of the debris s i z e taken simultaneously with the mapping of the surface allowed f o r the c a l c u l a t i o n and establishment of a fourth degree trend surface, an examination of which i s made i n conjunction with the map and photos of the cone.  P r a c t i c a l implications of the  development of t a l u s as applied to this region are discussed.  -iii-  TABLE OF CONTENTS  Page  ABSTRACT  i  LIST OF TABLES  vii  LIST OF FIGURES LIST OF PHOTOS LIST OF MAPS ACKNOWLEDGMENTS  viii x xiii xiv  CHAPTER I - INTRODUCTION  1  A.  Regional Geology.  1  B.  Mechanisms Involved i n the Formation of Talus.  9  1.  Mechanisms of weathering. - physical - chemical  10 10 12  2.  Rockfall and.primary deposition. - rockfall - downslope movement and accumulation - f a l l sorting - angle of rest  12 12 13 15 16  3.  Modification of the talus slope by mass movement mechanisms. - spontaneous mass movement - talus creep - external disturbance  17 17 18 18  Morphology of talus development. - the headwall - chute formation - talus forms - depth of talus - slope p r o f i l e s  18 19 19 21 21 21  4.  C.  Problems Associated with the Study of Talus Dominated Landscapes. ' 1.  Problems associated with mass movement mechanisms. - accumulation versus mass movement - observations of movement - stability -  24 24 24 25 26  -ivTABLE OF CONTENTS (cont'd)  2.  Problems associated with the morphology and morphometry of talus. - protalus ridges - p r a c t i c a l morphometric "problems - sampling problems  Page  26 26 27 27  CHAPTER II - HYPOTHESES AND METHODS OF INVESTIGATION  30  A.  Lithologic and Topographic Controls.  30  B.  Weathering Mechanisms. - apparent effects - frost action - frost cycles - chemical processes - secondary physical processes  32 32 33 33 35 35  C.  Rockfall Mechanisms.  35  D.  Mass Movement Mechanisms. - cross-slope sorting; formation of fine and coarse s t r i p s - sampling fine and coarse s t r i p s - painted lines  36  E.  Morphometry and Morphology of Talus i n the Similkameen Valley Near Keremeos .  36 43 44  45  1.  Morphometry. - s t a b i l i t y hypothesis - diminishing sediment y i e l d concept - fences designed to capture r o c k f a l l debris - Mazama ash deposit at CC44 - l a t e r a l and central p r o f i l e s compared - downslope sorting - mapping TC26 - sampling TC26  45 45 49 50 56 56 58 59 62  2.  Morphology. - protalus ridges on TC67 - boulder aprons - d i s t r i b u t i o n of vegetation  62 64 64 69  - types of vegetation  71  CHAPTER I I I - OBSERVATIONS  73  A.  73  Geologic Control.  -vTABLE OF CONTENTS (cont'd)  Page  B.  Weathering Mechanisms. - f r o s t action - chemical action - degrees of weathering - root wedging  75 76 84 85 87  C.  Rockfall and Primary Deposition. - observations of r o c k f a l l - fence samples  88 88 89  D.  Mass Movement Mechanisms. - evidence on painted lines - water - wind - creep - snow avalanche - flowing water - disturbance - basal sapping  96 96 101 102 102 103 103 103 104  E.  Morphometry and Morphology of Talus Development Near Keremeos, B.C.  104  1.  Morphometry. - stability - diminishing sediment y i e l d concept - slope p r o f i l e s  104 104 105 110  2.  Morphology. - c l a s s i f i c a t i o n of talus slopes i n the region - map and description of TC26 - miniature talus cone at CC44. - basal sapping as the result of excavation - chutes and funnels  113 113 117 122 123 124  CHAPTER IV - ANALYSIS AND INTERPRETATION  127  A.  P r o f i l e Analysis. - l a t e r a l and central p r o f i l e s compared  127 127  B.  Analysis and Interpretation of Downslope Sorting. - running means along p r o f i l e s - traverse samples  131 131 137  C.  Mass Movement as a Cross-Slope Sorting Mechanism. - f i n e and coarse debris s t r i p s compared - implications of uniform shape parameters  144 144 144  -vi-  TABLE OF CONTENTS (cont'd)  D.  Morphometric Analysis and Interpretation. - trend surface analysis on TC26  Page  150 150  CHAPTER V - CONCLUSIONS  155  A.  Summary.  155  B.  P r a c t i c a l Recommendations for the Region.  158  BIBLIOGRAPHY  162  APPENDIX  170  A.  Maps and Photographs Used.  170  B.  Additional Notes for Map 2.  171  -vii-  TABLES  I. II.  Page  Size-Angle Relationship (Behre, 1933). Temperature Reading on Rock Headwall Below Fence #1 on TC25.  III. IV. V. VI. VII. VIII,  IX. X.  24  November 24 - December 1, 1967.  77  Frost Cycles at Keremeos.  80  Degrees of Weathering.  85  Displacement of Rocks on Line Painted on TC22.  97  C l a s s i f i c a t i o n of Talus Forms Near Keremeos, B.C.  114  Cobble Analysis on Long P r o f i l e s TC21.  127  A. B.  128 128  Comparable Slope Sections TC25. Comparable Slope Sections TC21.  Difference of. Means Test.  129  Trend Surface Analysis TC26; Analysis of Variance and Error Measures.  153  -viii-  FIGURES  1-1.  1-2.  Page  A Typical Cross-Section of the Similkameen Valley Near Keremeos, B.C.  7  Mean Monthly Temperature and P r e c i p i t a t i o n for Keremeos, B.C.  8  1-3.  Evolution of a Chute or Funnel.  20  1-4.  Compound Talus Slope.  22  II-1.  Talus Development at Keremeos.  48  II-2.  Fence No. 1 Across Chute at TC25.  52  II-3.  D e t a i l of Fence.  52  II-4.  Detail of Boulder Apron Development.  68  Temperature Correlation Between Station at TC25 and A.E.S. Station at Keremeos.  79  III-l. III-2.  Mean Monthly Frequency of Frost Cycles at Keremeos.  83  III-3.  Sediment Sample from Fence No. 1.  95  III-4.  Painted Line Along Coarse Strip on TC22.  98  III-5.  Painted Line on TC22.  98  III-6.  Mazama Ash Deposit i n Talus Cone at CC44.  III-7 .  Ash Deposit as Exposed Along Road Cut  106  at CC44.  107  III-8.  Model of Talus Cone at CC44.  107  III-9.  Slope P r o f i l e s on TC21 and TC25.  112  Mean Proportional and Cumulative Proportional Frequency Plots of b A:-xis Along P r o f i l e s on TC21.  130  IV-1.  -ix-  FIGURES (cont'd)  IV-2.  IV-3.  IV-4. IV-5.  Page  Running Mean Plot of b Axes Along Center P r o f i l e on TC25.  132  Running Mean Plot of b Axes Along Right P r o f i l e on TC21.  133  Running Mean Plot of b Axes Along Center P r o f i l e on TC21.  134  Running Mean Plot of b Axes Along L e f t P r o f i l e on TC21.  135  IV-6.  Mean b Axis Plot of Traverse Samples on TC3.  138:  IV-7.  Mean b Axis Plot of Traverse Samples on TC26.  139  IV-8.  Mean b Axis Plot of Traverse Samples on TC48.  140  IV-9.  Mean b Axis Plot of Traverse Samples on TC67 .  141  IV-10.  Proportional Frequency Plots and Cumulative Proportional Frequency Curves of. b Axes on TC3 . Within Cone Proportional and Cumulative Proportional Frequency Plots of b Axis .  IV-11.  IV-12.  IV-13.  Plot of Mean b Axes Along Coarse and Strips on CC52.  142 143  Fine 145  Frequency Plots and Cumulative Proportional Frequency Curves of b Axes Along Fine Strip on CC52.  146  IV-14.  Zingg Shape D i s t r i b u t i o n CC52.  147  IV-15.  Flatness Parameter Along Fine and Strips on CC52.  IV-16.  V-l.  Coarse 148  Sphericity Parameter Along Fine and Coarse Strips on CC52.  149  Rockfall Trajectories.  160  -xPHOTOS  1-1.  Page  The Similkameen Valley at Keremeos Looking East.  5  II-l.  Headwall Near Old Tom Creek.  31  II-2.  Headwall Near Keremeos.  31  II-3 .  Maximum-Minimum Thermometer I n s t a l l e d i n Rock Crevice at TC25.  34  II-4.  CC52.  36  II-5.  Detail of Surface on CC52.  37  II-6.  TC67.  41  II-7.  CC7.  41  II-8.  Looking Up on TC67.  43  II-9.  TC2.  47  11-10  Site of Fence #1 on TC25.  51  11-11.  S i t e of Fence #2 on TC49.  51  11-12.  Fence #1 on TC25.  53  11-13.  Fence #2 on TC49.  53  11-14.  Detail of Chute Above TC49 .  54  11-15.  Headwall, Associated Talus, and Similkameen River at TC49 .  55  11-16.  Mazama Ash Deposit at CC44.  57  11-17.  Talus Resting on River Deposit at CC44.  57  11-18.  TC48.  63  11-19.  TC67.  65  11-20.  TC67.  65  11-21.  D e t a i l of Boulder Apron at the Base of TC25.  66  -xi^ PHOTOS (cont'd)  Page  11-22.  Boulder Apron on TG42.  66  11-23.  TC27 and TC28.  71  11-24.  Closeup of Boulder Apron on TC28.  72  III-l.  Weathered Rock Headwall at TC21.  75  III-2.  Observed Solution on Headwall at TC25.  85  III-3.  Weathering Degree No. 1 ( O i l i e r , 1965).  86  III-4.  Weathering Degree No. 2 ( O i l i e r , 1965).  86  (a & b)  Weathering Degree No. 4 ( O i l i e r , 1965).  86  III-6.  Possible Root Wedging Mechanism.  87  III-7.  Broken Douglas F i r at Apex of TG67 .  III-5  (Sept. 21/67).  89  III-8.  Fence #1 on TC25.  91  III-9.  Fence #1 on TG25.  91  111-10.  Fence #1 on TC25.  91  III-ll.  Fence #2 on TC49.  92  111-12.  Painted Line Above Fence #1 at TC25.  100  111-13.  Painted Line Above Fence #1 at TG25.  100  111-14.  A l l u v i a l Gone Near TC43.  104  111-15.  TC21.  Ill  111-16.  TG48.  117  111-17.  TC26.  119  III-18.  Along Headwall i n Chute of TC26.  121  111-19.  Miniature Talus at CC44.  123  -xii-  PHOTOS (cont'd)  Page  111-20.  Apex of Chute Above TC25.  125  111-21.  Looking up at Funnel Above TC48.  126  Gathered Talus Rubble.  159  V-l.  -xiii-  MAPS  Page  1.  Southwestern B.C.  2  2.  The Similkameen Valley at Keremeos, B.C.  3  3.  Geology of the Keremeos Region.  4  4A.  TC26 With Overlay.  118  4B.  TC26 With Trend Surface.  151  -xiv-  ACKNOWLEDGMENTS Under the advice and guidance of Dr. M. A. Melton, formerly of the University of B r i t i s h Columbia, the investigation was the spring of 1967 . Observations  were made during May  initiated in  through September  of that year and again i n January and the spring and early summer of 1968.  Subsequent observations were made at irregular intervals i n 1969  through 1971.  Sincere appreciation i s extended to Dr. Melton for his  support. Particular thanks are expressed  to the University of B r i t i s h  Columbia and the Geography Department of the u n i v e r s i t y for making available funds, i n the form of research and travel grants, the fieldwork.  to carry out  The use of equipment supplied by the Departments of  Geography, Geology, and C i v i l Engineering was  appreciated.  Credit i s given to Brian Mennell and Lyle Finch who  gave  assistance i n the f i e l d , more i n the s p i r i t of research than for remuneration.  The meteorological record for Keremeos (A.E.S.) was made  available by Mrs. J . A. Russel whose observations of talus a c t i v i t y i n the region were useful.  Appreciation i s extended to my s i s t e r and  her  husband for accomodation during the i n v e s t i g a t i o n . Many gave invaluable assistance with the compilation of the thesis.  Dr. A. L. Farley of the University of B r i t i s h Columbia i s thanked  for his u n f a i l i n g cooperation as advisor and suggestions  for improvements .  Sincere appreciation i s extended to Dr. 0. Slaymaker of the University of B r i t i s h Columbia whose careful readings and c r i t i c i s m s lent coherence to the text.  Peter Lewis of the Geological Survey of Canada gave much  appreciated assistance i n the c a l c u l a t i o n of pre- and post- Mazama rates  -XV-  of talus accumulation.  No expression of gratitude could equal the e f f o r t s  put f o r t h by Dr. Mike Church of the University of B r i t i s h Columbia. His time, expertise, f a c i l i t i e s and encouragement made possible the analyses i n Chapter IV. Suggestions he has made f o r the improvement to the whole work have been invaluable and i t i s hoped that the thesis now has the desired "taughtness".  L a s t l y , to my wife Berne Jean I extend  my most h e a r t f e l t thanks f o r a job well done on the typing of the many drafts.  Without her moral support the thesis would never have been written.  1  CHAPTER I - INTRODUCTION  Near Keremeos i n B r i t i s h Columbia the phenomenon of talus development i s r e a d i l y observable.  I n i t i a l interest for the  investigation was prompted by the abundance and great size of the talus forms found i n the region (see Map 2).  Since preliminary  observations suggested that talus development was entering a passive stage and that the rate of formation i n the past must have been more rapid, the research was launched under the hypothesis that the talus slopes i n the Keremeos area were tending towards s t a b i l i t y . A.  Regional Geology. The area studied (see Map 1) i s properly a part of two  major physiographic divisions of B r i t i s h Columbia that extend along the Similkameen River (see Holland, 1964).  The area on the north  side of the r i v e r i s on the southern flank of the Thompson Plateau, part of the Interior System of B r i t i s h Columbia.  The area on the  south side of the r i v e r i s part of the Okanagan Range of the Cascade Mountains contained i n the Western System.  Geology and structure  (see Map 3) transcend the region, however, and being part of two major physiographic divisions seems to exert no geologic influence on the development of talus. It i s assumed that a l l of the slopes must have formed since the l a s t retreat of the C o r d i l l e r a n Ice Sheet from the area, giving them a geologic age of 10000 (^) years (see Fulton, 1971, p.v and p. 17.)  The v a l l e y i s very steep-walled and deep and represents  the i n c i s i o n of the Similkameen River into a plateau surface.  The  MAP 1.  SOUTHWESTERN  B. C .  3  MAP 2.  SIMILKAMEEN  VALLEY  SCALE  AT KEREMEOS, B. C.  1170000 REFERENCE  3000  COMPILED  FROM  B. C.  AERIAL  HIGHWAY  6000  PHOTOGRAPHS  TAKEN  IN  1966  OR  PERMANENT  S  ROAD  STREAM  INTERMITTENT  TALUS  STREAM  CONES  BOUNDARY  OF  FIELD  AREA  \ j  PIN  CUSHION MOUNTAIN  MAX.-MIN. TEMP.g INSTALLATION  KEREMEOS  \ S  4  K MOUNTAIN  5 mean elevation at river  level i s 1500 feet a . s . l . r i s i n g steeply to  an elevation of approximately 6000 feet on the north side of the r i v e r and approximately 7000 feet on the south side; is of the order of 5000 feet.  thus average r e l i e f  The U-shaped cross-section of the  v a l l e y (see Photo 1-1) suggests that i t must have been shaped by the movement of i c e through i t and the steepness of the v a l l e y walls i s probably attributable to scouring by g l a c i e r s .  The general  Photo 1-1. The Similkameen Valley at Keremeos Looking East. d i r e c t i o n of movement of the Cordilleran Ice Sheet i n the area was from north to south but observed g l a c i a l s t r i a e along the valley walls indicate that the i c e followed the course of the v a l l e y i n this confinement, moving i n a west to east d i r e c t i o n .  I t seems that the  major i c e sheet s p l i t around the north end of the Okanagan Range near Princeton into two lobes, one of which turned to flow to the southeast  6 p a r a l l e l with the Lower Similkameen V a l l e y .  After the retreat of the  continental i c e sheet a period of valley g l a c i a t i o n ensued, r e s u l t i n g in a steepening of the v a l l e y sides, r e d i s t r i b u t i o n of d e t r i t a l material, and formation of cirques on some of the higher peaks.  The steep rock  faces thus produced along both sides of the v a l l e y i n t h i s stretch offer a situation geometrically ideal f o r the development of talus. The Similkameen River has a f a i r l y steep gradient, dropping 150 feet i n the twelve mile stretch of valley studied.  Some flood  p l a i n development has occurred on the p o s t g l a c i a l valley f i l l but i s not wide enough to accommodate extensive meander development.  South  of Keremeos the valley widens and an extensive flood p l a i n with well developed meander loops can be observed.  Figure 1-1 represents  a t y p i c a l section of the v a l l e y . The climate of the v a l l e y bottom i s classed as BSk according to Koppen's c l a s s i f i c a t i o n ranging to Dfb on the uplands.  A low  annual t o t a l of p r e c i p i t a t i o n and a high annual range of temperature prevails within the confines of the valley (see Figure 1-2).  Keremeos  averages ten inches of p r e c i p i t a t i o n annually including about twenty-six inches of snow. 100°F not uncommon.  Summers are hot with temperatures  exceeding  Typical vegetation i s of the parkland variety  in the v a l l e y bottom, i . e . , short grass with a scattering of Douglas f i r and ponderosa pine, ranging to sub-alpine coniferous forest on the higher cooler and wetter slopes . The dryness of the area i s d e f i n i t e l y r e f l e c t e d i n the vegetation and,where overgrazing has occurred, sagebrush has replaced the natural grassland.  The dryness i s b a s i c a l l y  the r e s u l t of a rainshadow effect produced by the Coast and Cascade  FIGURE I - l .  A  TYPICAL  CROSS - SECTION  OF  6500 6000 5500  5000  5000 4500  -•4000  3500 3000  2500  -2000 1500  1000 500  8  JAN  FEB  MAR  APR  FIGURE 1-2.  MAY JUN  JUL  AUG  SEP  OCT  NOV  DEC  MEAN MONTHLY TEMPERATURE AND PRECIPITATION FOR KEREMEOS, B.C.  The average was obtained from data for an eleven year period recorded on the Upper Bench Road, Keremeos, B.C. The f a i r l y high temperature range (45°F.) i l l u s t r a t e s the c o n t i n e n t a l i t y . P r e c i p i t a t i o n i s low, however, having a mean annual total of 10 inches: i t i s concentrated i n June i n the form of convectional storms.  9 Mountains to the west and i s accentuated i n the summer by the extension of hot, dry continental a i r from the south.  The coastal mountains  are also e f f e c t i v e i n producing a continental influence by cutting off  the moderating effects any maritime a i r would have.  A definite  moisture d e f i c i t exists at lower elevations and most crops require irrigation. The rocks of the area studied are arranged i n a c l o s e l y folded band formation normal to the general east-west v a l l e y (see Map 3).  trend of the  They have been i d e n t i f i e d and mapped by  Bostock (1939) as a succession of cherts, lavas, limestones, and other sedimentary forms of Permian age and younger.  Colours are very  drab and from a distance as well as close up give the rocks a dull appearance.  As evidenced by the abundance and great size of talus  forms observed the rocks along this stretch seem very susceptible to disintegration under the effects of weathering. B.  Mechanisms Involved i n the Formation of Talus. Talus i s by d e f i n i t i o n an accumulation of rock debris at the  base of an exposed rock face or c l i f f .  This accumulation i s the net  r e s u l t of gradual decomposition and d i s i n t e g r a t i o n of the rock face by the processes of weathering and mass wasting.  In time, the  c h a r a c t e r i s t i c a l l y angular fragments produced become dislodged i n d i v i d u a l l y or en masse under the influence of g r a v i t y f a l l i n g free of the rock face to eventually assume a position of rest at the base of the c l i f f .  With sustained weathering and rock f a l l  activity  the accumulation grows, assuming a slope referred to as the angle of  repose.  Rapp subdivides the advent of talus formation into  three stages :  10 "1.  Supply - f a l l of debris from the wall down to the surface of the talus. I t i s terminated by the primary deposition of the p a r t i c l e s .  2.  Shifting - the movement of the material down the talus slope a f t e r the primary deposition.  3.  Removal or s t a b i l i t y - movement of material away from the talus slope or s t a b i l i t y of the slope by vegetation and eventual flattening of the p r o f i l e and s o i l formation." (Rapp, 1960a, p. 6.)  1.  Mechanisms of weathering. The weathering of rocks can be defined as the process whereby  s o l i d bedrock at or near the earth's surface i s reduced by physical and chemical means into sediment. i n i t i a l product  Talus formation represents an  along the continuum of the weathering process and  both physical and chemical forces are involved at this stage. Although chemical weathering i s ultimately the more important of the two processes, mechanical breakdown during the i n i t i a l stages of weathering, eg. talus formation, can play a major or even dominant role. A number of weathering processes are recognized (see Reiche, 1962).  Those of p a r t i c u l a r note f o r the present purposes are  the physical processes of f r o s t shatter, f r o s t bursting and root wedging and the chemical processes of hydration, oxidation and solution. The importance of freeze-thaw cycles i n association with water i n rock weathering has been questioned and the d e f i n i t i o n of the e f f e c t i v e limits f o r the same varies g r e a t l y . defined as any fluctuation of temperature  A f r o s t cycle i s  above and below 32°F.  A freeze-thaw cycle implies a f l u c t u a t i o n of temperature below 32°F. of s u f f i c i e n t range occur.  above and  for a d e f i n i t e freeze and thaw to  To exert a wedging action, the frequency of the cycle i s  obviously c r u c i a l but the duration and range of the cycle i s important as w e l l .  Cook and Raiche (1962) noted that freeze-thaw cycles i n the  A r c t i c are much less frequent  than thought to be and found that the  frequency i s much greater i n Southern Canada.  Boyd (1959) found  that i n order for a freeze-thaw cycle to be e f f e c t i v e i t must occur through a range of 25° to 35°F.  Fraser (1959) and others, however,  set the e f f e c t i v e range at 28° to 34°F. e f f e c t i v e range i s that there  The implication of an  must be a s u f f i c i e n t temperature f l u c -  tuation for a d e f i n i t e freeze and thaw to occur. on the duration of the cycle.  But, much depends  A frost cycle of a shorter duration  w i l l require a greater range i n order to be e f f e c t i v e . Wiman (1963) noted that most e f f e c t i v e weathering occurred under so-called "Icelandic" conditions represented  by one cycle every day rather  than under "Siberian" conditions represented but a c y c l e only every four days.  by colder temperatures  I t becomes apparent that the  e f f e c t i v e range probably varies a great deal.  In reference to  duration, Rapp (1957) c l a s s i f i e d f r o s t cycles as follows: 1. 2.  Short frost cycle (several per day). Daily frost c y c l e .  3.  Frost cycle  4.  Annual frost cycle.  of  s e v e r a l days  duration.  5.  Frost cycle of several years.  Stock (1968) noted that the effectiveness of " f r o s t - r i v i n g " i s l a r g e l y determined by the thickness and seasonal  d i s t r i b u t i o n of snow cover  and the amount of water incorporated i n the rock at time of freeze-up. Andrews (1961) concluded that the importance of frost as a weathering agent  has been v a s t l y overstated.  The tremendous force exerted by  the freezing of water confined within the i n t e r s t i c e s of rock, however, cannot be denied and within the recognized  l i m i t s outlined above  12 cannot be discounted as a major mechanism of weathering. Some controversy over the effectiveness of root wedging exists.  As yet, i t has not been conclusively demonstrated  that the  growth of plant roots can exert a force s u f f i c i e n t to fragment rocks. Of paramount importance i n the processes of hydration, oxidation and solution i s the action of water on rock i n association with oxygen and carbon dioxide i n the a i r .  Fragmentation of rock by  physical processes greatly accelerates the rate of chemical decay but, so long as the rock can be penetrated by water, chemical weathering  can occur. The rate and type of weathering i s determined to a large  degree by the c h a r a c t e r i s t i c s of the rock in question. of  the rock to fracture i s an important control.  beds  The s u s c e p t i b i l i t y  The aspect of the  and the degree of j o i n t i n g as well as the resistance of the rock  and i t s basic structure w i l l greatly a f f e c t the r a t e .  How  effective  weathering mechanisms are on a given rock face i n turn determines the r a t e of r o c k f a l l a c t i v i t y and associated talus development. 2 . Rockfall and primary deposition. Rockfalls, and to a lesser degree rockslides and avalanches, are the major sources of debris r e s u l t i n g i n the buildup of talus. Rapp (1960b) l i s t s a number of r o c k f a l l - i n i t i a t i n g mechanisms:  frost  bursting, thermal changes, heavy rains, snow block f a l l s , i c e block f a l l s , chemical weathering, wind, creep, and earthquakes.  Frost action  is probably the most important of these mechanisms e s p e c i a l l y i n climates characterized by frequent frost cycles.  Rocks shattered  and burst by frost action subsequently release fragments when the ice melts.  Short term i.e.,  d a i l y f r o s t cycles, are important  13 e s p e c i a l l y i n their effect on the shallower cracks . r o c k f a l l by " f r o s t - r i v i n g " (Rapp, 1960b) occurs.  In this case  Some examples of  r o c k f a l l i n i t i a t i n g thermal changes are expansion and contraction caused by d a i l y temperature variations or d i f f e r e n t i a l expansion caused by solar heating where different rock types are interbedded or beside patches of snow.  The l o c a l i z e d movement associated with  d i f f e r e n t i a l expansion and contraction of the rock as heating and cooling occur may be an e f f e c t i v e dislodgement mechanism.  Rainfall  can be an e f f e c t i v e i n i t i a t i n g mechanism by: 1. 2. 3.  diminishing the i n t e r n a l f r i c t i o n along j o i n t s or other s l i p planes i n the rock. creation of high hydrostatic pressure i n joints dammed by water transported debris . thawing i c e after previous frost bursting.  (Rapp, 1960b)  Debris incorporated i n snow or i c e masses attached to the rock face ma be carried along when these masses are released.  Debris avalanches  associated with the buildup of hydrostatic pressure i n joints under heavy or prolonged r a i n f a l l are rare but are important  since such a  great volume of debris i s released almost instantaneously.  Wind can  dislodge very loose fragments but i s recognized as only of minor importance.  Roots growing i n cracks along the rock face may be an  e f f e c t i v e prying mechanism; to heavy winds.  especially when the trees are subjected  Creep of any material over the rock face eg. r e g o l i t h  snow, may disengage loose rocks.  F i n a l l y , rocks already dislodged can  knock others loose i f they bounce along the c l i f f face on their way down.  Once dislodged, however, the individual rock fragments come  under the exclusive control of gravity. Individual rocks move down slope by s l i d i n g , r o l l i n g , skipping and free f a l l .  In general, larger rocks w i l l generate greater k i n e t i c  14 energy because of their greater mass and thus w i l l t r a v e l farther down slope.  Where the i n d i v i d u a l fragment eventually comes to rest on the  talus slope depends on a number of f a c t o r s . A rock which has great mass and momentum may r o l l beyond the t a l u s .  Such large rocks  t y p i c a l l y form an apron at the base of the talus. rock f a l l s from the headwall before encountering  The distance the the talus slope can  also a f f e c t the distance i t w i l l travel on the talus slope:  rocks  f a l l i n g further w i l l acquire greater momentum and w i l l tend to travel farther down the slope.  The slope of the headwall and the talus  slope below, however, can a f f e c t distance travelled by individual fragments.  Rocks f a l l i n g from an e s s e n t i a l l y v e r t i c a l c l i f f lose  considerable momentum upon impact with the talus slope, especially i f the slope angle of the talus near the apex i s r e l a t i v e l y f l a t .  If  the headwall i s sloping, however, fragments can gain a considerable horizontal momentum which i s much less dissipated upon contact with the talus slope and, with a bounding action, travel farther downslope.  comparatively  Momentum buildup on f l a t t e r sloping headwalls i s  also limited, however;  e s p e c i a l l y i f the headwall surface i s rough.  As the talus deposit grows i n response to r o c k f a l l a c t i v i t y the surface c h a r a c t e r i s t i c s developed further affect the mode and distance of t r a v e l of r o c k f a l l fragments.  Growth may take place i n layers p a r a l l e l  to the angle at which the materials come to rest.  Distance travelled  by each p a r t i c l e can range from a maximum equal to the total length of the slope down to a minimum of zero.  Since the deposit rests  against i t s source of debris, the headwall, some pieces obviously do not move downslope at a l l before they are covered under subsequent rockfalls.  Rocks r o l l i n g down the surface w i l l be affected by the  slope and degree of roughness of the surface i t s e l f . travel farther on a steep slope than a f l a t t e r slope.  A given rock w i l l A rock f a l l i n g  at high speed along the inclined surface w i l l touch that surface only at the high points with i t s high points i f the rocks comprising the surfac are smaller than the rock r o l l i n g over them. the size  According to Ritchie (1963)  or shape of the rock has l i t t l e bearing on i t s r o l l i n g  c h a r a c t e r i s t i c s except i f i t i s long l i k e a pencil which tends to retard r o l l through eccentric action.  Angular momentum of a rock r o l l i n g  over a surface of smaller rocks tends to increase u n t i l two things tend to slow i t down: r o l l over.  1.  a f l a t t e r slope and 2.  larger materials to  Energy i s l o s t by impact as i t comes i n contact with pieces  of i t s own s i z e .  Progressive slowing down causes the r o l l i n g rock to  sink lower into the i r r e g u l a r i t i e s  of the surface losing more energy  by virtue of more contact with the surface. Momentum i s eventually t o t a l l y dissipated and the rock becomes trapped i n a void between rocks of i t s own s i z e or l a r g e r . F a l l sorting seems i m p l i c i t l y obvious, i . e . , larger rocks have greater k i n e t i c energy so should therefore r o l l further before coming to r e s t .  Tinkler (1966) observed that the proportion of larger sediment  sizes increases downslope on talus sampled i n North Wales. this sorting to the effects of g r a v i t y .  He attributed  Gardner (1971a) noted a  logarithmic decrease i n the mean size of debris upslope on talus observed i n the Lake Louise d i s t r i c t .  Behre (1933), however, noted the exact  opposite on talus slopes observed i n the Rocky Mountains and Caine (1967) found a tendency for rock size to decrease s l i g h t l y downslope on talus observed i n Tasmania but noted that the differences are not s t a t i s t i c a l l y significant.  In view of the discrepancies, therefore, the general law  16 of f a l l sorting should be seen as the statement of only one process on talus slopes.  I t i s clear that primary deposition must be dominated  by this process, but subsequent modification of the surface of the talus slope i s controlled by other processes. The accumulation of rock debris i n this way assumes an angle of rest referred to as the repose slope.  The repose slope or angle of  repose of unconsolidated material has been widely studied (Behre 1933, Meiner 1934, Van Burkalow 1945, Ward 1945, Andrews 1961, Melton 1965, Tinkler 1966, Rahn 1966).  In the case of talus materials, large, angular,  rough surfaced and densely packed rocks tend to support a higher angle of repose.  The maximum angle of repose which can be attained by a given  deposit of rock debris depends on the i n e r t i a required to overcome the internal f r i c t i o n .  When the maximum repose slope i s exceeded, the  p a r t i c l e s s l i d e to readjust to a slope less than the maximum repose angle.  The c o e f f i c i e n t s of s l i d i n g and s t a t i c f r i c t i o n for rock debris  have been placed at 28° and 34° respectively (Melton, 1965) and i t i s interesting to note that a consolidation of slope measure data on talus (Rapp 1960, Melton 1965, Caine 1967,  Stock 1968, Gardner 1968, et al.)  displays a range of 10.5° - 41.5° with modes at 28° and 33° respectively. Whether or not a given deposit w i l l assume the maximum angle of repose depends on the mode of deposition and the time elapsed after deposition.  Deposits which are b u i l t up gradually with a minimum of  disturbance w i l l a t t a i n slopes closer to the maximum.  A deposit  comprised of a certain shape of p a r t i c l e s arranged i n an interlocking matrix or imbricated fashion could support i t s e l f to achieve an angle of rest which would exceed the theoretical maximum repose slope. In natural debris deposits, the process of weathering can r e s u l t i n a  17 cementing of the i n d i v i d u a l p a r t i c l e s which w i l l allow the deposit to exceed the t h e o r e t i c a l maximum repose slope.  Further, debris deposits  held together by the root structure of a s u f f i c i e n t l y dense vegetation cover could maintain slopes i n excess of the t h e o r e t i c a l maximum.  Also,  thin mantles of debris on a well bossed steep bedrock surface could be supported at angles exceeding the t h e o r e t i c a l repose slope.  As can be  seen, however, some agent i n addition to the i n t e r n a l f r i c t i o n of the p a r t i c l e s must be operative before a debris deposit can exceed i t s theoretical maximum. The i n i t i a l establishment tumbling from the headwall may movement may 3.  of a p o s i t i o n of rest by rocks  be only temporary;  subsequent downslope  occur through mechanisms of mass movement.  Modification of the talus slope by mass movement mechanisms. Readjustment of a talus surface can occur i n a number of ways.  The mechanisms involved come under the general heading of mass movement. Spontaneous mass movement or movement exclusive of the effects of a carrying medium occurs when the shearing l i m i t of the material comprising  the slope i s reached.  F a i l u r e i s produced i n a number of  ways . The addition of water through melt or p r e c i p i t a t i o n increases the pore water pressure r e s u l t i n g i n f a i l u r e r e f e r r e d to as "mudflow". S o l i f l u c t i o n i s an important mechanism i n permafrost environments. Water can also act as a l u b r i c a n t .  Behre (1933) noted that talus i n  the Rocky Mountains tended to remain stable i n dry weather but became more mobile i n wet weather. same e f f e c t .  Icing along the points of contact has  the  If the slope becomes steepened by the addition of material,  f a i l u r e i s eventually reached.  Also, removal of material away from  the base of the deposit i . e . , basal sapping, produces f a i l u r e .  18 Talus creep i s another form of mass movement.  The disturbance  created by freeze-thaw action i n water saturated talus r e s u l t s i n a net downslope movement.  Experiments and theoretical calculations by  Scheidegger (1961) suggest that the expansion and contraction created by alternate daily heating and cooling are s u f f i c i e n t to cause net downslope movement r e f e r r e d to as "dry rock creep". External disturbance  of the deposit can produce mass movement.  The impact of f a l l i n g rock and raindrop impact have e f f e c t . of any medium such as water, snow, or i c e over the surface material downslope.  The movement transports  Earth tremors and animal a c t i v i t y are additional  sources of disturbance.  Wind transport has been c i t e d as a possible  mechanism (Rapp, 1960b) but this i s doubtful since most talus material i s too large to be affected by wind. F i n a l l y , through "...the s h i f t i n g and removal of the material the talus formation i s l e v e l l e d out, takes on a more concave p r o f i l e and may be transformed, for example, into an a l l u v i a l cone." (Rapp, 1960,p.6) The c h a r a c t e r i s t i c forms associated with talus development, however, require some explanation. 4.  Morphology of t a l u s development. Talus proper develops e s s e n t i a l l y from r o c k f a l l a c t i v i t y under  the influence of g r a v i t y .  The slope produced represents  the aggregate  deposition of fragments r o l l i n g , s l i d i n g , or bouncing to an eventual position of r e s t .  As the importance of water or avalanching  snow as  a transporting medium increases, talus forms grade into a l l u v i a l cones or avalanche boulder tongues and rockslide tongues (see Rapp 1959) having a d i s t i n c t concave-up longitudinal p r o f i l e . per se, are recognized.  A variety of talus forms  19 To i n i t i a t e the formation of a talus slope a rock face of steep slope must be exposed. or g l a c i a l erosion.  Such a feature could be a c l i f f produced by f l u v i a l  Tectonic a c t i v i t y r e s u l t i n g i n escarpments and  f a u l t blocks are further examples.  The steep rock slope produced, from  which the weathered fragments move by free or bounding f a l l to b u i l d the talus below, i s variously referred as the mountain wall, rock wall, headwall or rock headwall, free wall, free-face or c l i f f face.  The  headwall, to i n i t i a t e talus formation, must have a slope steep enough to  allow for movement of fragments by s l i d i n g , r o l l i n g , bounding or  free f a l l .  Slopes much less than 40° w i l l result i n l i t t l e or no talus  formation since gravity i s unable to overcome s t a t i c f r i c t i o n at low angles.  In general, the headwall has an i n c l i n a t i o n ranging from  40° to 90°. Obviously a headwall of greater height w i l l r e s u l t i n accelerated talus development since more area i s exposed to weathering. of  the headwall controls the rate and mode of destruction by  If  zones of weakness e x i s t a dissection of the headwall  producing g u l l i e s or chutes (see Figure 1-3).  The structure weathering.  ensuesj.  Because weathering i s  concentrated along these zones of weakness r o c k f a l l a c t i v i t y i s greatest here and becomes channelled along the g u l l i e s or chutes.  Rapp (1960a)  noted that the frequency of r o c k f a l l i s d i r e c t l y related to the degree of  dissection of the headwall.  In comparison to a r e l a t i v e l y undissected  headwall the area of rock d i r e c t l y exposed to weathering processes on a dissected one i s much greater.  In addition, water from melt  p r e c i p i t a t i o n i s channelled along the g u l l i e s or chutes. of  and  The force  this flowing water and that which becomes frozen i n the j o i n t s  w i l l i n i t i a t e further r o c k f a l l a c t i v i t y .  A dissected headwall, therefore,  FIGURE 1-3.  EVOLUTION  STAGE I. in  Chute develops i n i t i a l l y as a c l e f t the h e a d w a l l above t h e t a l u s d e p o s i t .  OF A  CHUTE OR  STAGE  2. T a l u s grows as a r e s u l t o f the r o c k f a l l c o n c e n t r a t e d by c l e f t above. As the headwall d i s i n t e g r a t e s t h e c l e f t i s widened and deepened to form a chute or f u n n e l .  CHUTE  CLEFT  TALUS  FUNNEL  TALUS  Y  STAGE 3.  Up b u i l d i n g o f t a l u s and downcutting i n chute e v e n t u a l l y r e s u l t s i n the merging of the two forms.  STAGE 4. With c o n t i nued t a l u s growth, chute becomes l a y e r e d w i t h mantle o f d e b r i s p r o d u c i n g a continuous d e b r i s covered s l o p e from the apex of the chute to the base  o  21 should have greater r o c k f a l l a c t i v i t y . whether a headwall retreats more or less uniformly over the whole of the free face or unequally by dissection with formation of g u l l i e s or chutes w i l l a f f e c t greatly the shape of talus developed below.  In general, talus cones with a convex horizontal p r o f i l e are  associated with a concentrated r o c k f a l l source;  sheet talus develops  when a l l parts of the headwall supply material uniformly.  A headwall  undergoing d i s s e c t i o n retreat might display a v a r i e t y of forms. talus alternating with talus cones can occur.  Sheet  Individual cones may  coalesce to form a compound talus slope (see Figure 1-4). Where a t h i n mantle of debris c o l l e c t s on a steep surface the feature i s called a debris slope.  The debris remains much controlled by the underlying  rock structure. The depth of talus deposits can vary greatly ranging from very shallow c o l l e c t i o n s on debris slopes to substantial depths i n larger formations.  Rapp (1960a) reported a range i n depth from 1 to 35  meters but noted that maximum depths never amount to more than about 1/10 of the height of the talus slope. Debris deposits which are composed of e s s e n t i a l l y homogeneous p a r t i c l e s throughout should develop e s s e n t i a l l y straight slope p r o f i l e s . The slope surface of such deposits approximates an i n c l i n e d plane. Talus deposits, however, are never homogeneous throughout.  Often,  more than one rock type i s present and the individual fragments are never exactly the same size or shape.  Moreover, as a r e s u l t of natural sorting  which may occur along the transportation surface of a talus slope, different parts of the deposit may have d i s t i n c t l y d i f f e r e n t size and slope c h a r a c t e r i s t i c s than others.  The net effect of this heterogeneous  FIGURE I*" 4.  COMPOUND  TALUS  SLOPE-  individual cones coalesce to form a  continuous talus deposit. GULLY - c l e f t i n a steep headwall through which debris i s channelled by free or bounding f a l l to form a talus cone below. The g u l l y usually remains detached from the actual talus accumulation. With sustained a c t i v i t y a gully becomes a chute. CHUTE - a c l e f t which concentrates debris to form a talus cone. Notice that the transportational surface of the talus extends well up into the chute. FUNNEL - a half funnel-shaped c l e f t i n a headwall which i s wide at i t s top and narrower below through which debris i s concentrated to form a talus slope. As with the chute the talus accumulation extends well up into the funnel.  composition  23 i s to produce not only a wide v a r i a t i o n i n the repose angle  among talus slopes but, more importantly, a v a r i a b l e p r o f i l e on each individual slope.  The p r o f i l e of a talus slope represents the complex  and d e l i c a t e adjustment of the debris to the many factors which a f f e c t slope development i n varying degrees along the p r o f i l e some of which are l i s t e d below: 1.  The mode of and the duration since deposition.  2.  Internal f r i c t i o n as controlled by the type, size and shape of debris.  3.  The degree of sorting i n the debris.  4.  The amount, type and d i s t r i b u t i o n of vegetation.  5.  Thickness of the mantle and underlying surface c h a r a c t e r i s t i c s .  6.  S e t t l i n g and r e d i s t r i b u t i o n of debris mechanisms, wash, compaction, weathering.  eg. creep,  Attempts to explain the c h a r a c t e r i s t i c concave longitudinal p r o f i l e of talus slopes i n terms of the size sorting and repose slope concepts have not been successful. Many inconsistencies are apparent. Machatschek (1952) attributed the concavity of the p r o f i l e to the sorting of material on talus slopes, i . e . , from smaller to larger sizes of material down the slope.  The basic assumption he used was that  fines are capable of supporting steeper angles than coarse material. Behre (1933) explained the concave p r o f i l e i n terms of talus he observed i n the Rocky Mountains.  In this case the observed sorting was from  larger to smaller material downslope attributed to the effects of weathering.  He assumed that larger fragments can achieve higher  angles  of rest therefore producing a slope which i s steep at the top and f l a t t e r at the bottom r e s u l t i n g i n a concave p r o f i l e . i s demonstrated i n Table I below:  This r e l a t i o n s h i p  24 Table I  Size-Angle Relationship (Behre, 1933).  Average Diameter i n Inches  Average Slope i n Degrees  12 6 4 2 1  35° 35° 32° - 34° 31° - 32° 26° - 31°  His i s only one set of data, as universal.  Scheidegger  however, and the results cannot be taken  (1970) suggested that i f the formation of  a talus slope i s due to talus creep then angles near the top, where s l i d i n g i s i n i t i a t e d , should be steeper than those near the base, where the materials come to r e s t , r e s u l t i n g i n a concave p r o f i l e .  The  difference i n slope might also be attributed to the difference i n packing of the materials. Materials near the top of the slope may become more packed as a r e s u l t of more concentrated r o c k f a l l a c t i v i t y .  The materials  with greater cohesion near the top would be capable of supporting steeper angles than the lesser packed materials downslope producing a concave profile.  There seems to be no simple explanation f o r this phenomenon  and observations of p r o f i l e s which are e s s e n t i a l l y straight, concave - convex, and even convex (Rapp 1957)  composite  tend to complicate i t  further . G.  Problems Associated with the Study of Talus Dominated Landscapes. 1.  Problems associated with mass movement mechanisms. The central problem i n an explanation of the features exhibited  on a talus slope i s the determination of the following:  i s the talus  surface b a s i c a l l y the r e s u l t of primary accumulation processes or does i t represent the modification of a surface by mass movement mechanisms after accumulation under r o c k f a l l a c t i v i t y ?  Whichever process  25 predominates greatly affects the type of surface produced.  In youth ,  or times of accelerated r o c k f a l l a c t i v i t y , accumulation mechanisms would predominate;  l a t e r , mass movement mechanisms w i l l exert an effect  and a composite form may r e s u l t .  In the f i n a l stages of development, or  when r o c k f a l l a c t i v i t y abates, mass movement processes may come to predominate.  Whatever the stage, the net effect of mass movement i s  to lower the slope.  Perhaps slope can be taken as some indication of  the process predominating,i.e., movement on gentler slopes.  accumulation  on steeper slopes;  mass  However, no l i m i t s have been established  and a great deal more study w i l l be required to define them -- i f i n fact they e x i s t . Actual observations of movement on talus slopes are few. Most of the movement i n i t i a t i n g mechanisms described i n section B of this chapter are t h e o r e t i c a l .  Some insight into net and d i f f e r e n t i a l movement  has been gained by d r i v i n g steel stakes (Rapp 1960) into talus slopes at fixed locations and noting downslope movement over long intervals of time.  Results indicate that the surface layers tend to move most  quickly.  Lines painted c r o s s - a x i a l l y on talus debris observed over long  periods of time indicate d i f f e r e n t i a l movement along the surface e s p e c i a l l y on slopes where the debris i s sorted into s t r i p s of fines and coarse material (eg. Stock, 1968). sorting into s t r i p s and the reasons not understood.  Scheidegger  However, the cause of the  for d i f f e r e n t i a l movement noted are  (1970) hypothesized  that movement may take  place as miniature landslips which occur when talus assumes a c r i t i c a l thickness and slope creating a c r i t i c a l toe c i r c l e along which the l a n d s l i p w i l l occur.  An observation by Rapp (1960a, p. 61) seems to  confirm this theory.  However, observations of f a i l u r e on sand slopes  26 (Van Burkalow, 1945)  indicated that s l i d i n g does not occur along a  c i r c u l a r surface but i s , rather, laminar, being e s s e n t i a l l y p a r a l l e l to the slope.  Van Burkalow suggested that s l i d i n g on talus slopes must  approximate this type of f a i l u r e . A related problem i s the recognition of the degree of a c t i v i t y on a talus slope.  Stakes and painted lines as described above afford  a rough measure of a c t i v i t y .  If remaining unaltered over long periods of  time the slope i s considered to be stable.  Vegetation i s also used  as an indicator: "A rough measure of the permanence of s t a b i l i t y of a talus slope i s also afforded by the growth of grasses or other small shrubs on i t . The unsatisfactoriness of this c r i t e r i o n comes largely from the fact that the time required for grass to advance up the slope results i n a lag; on account of the need for s o i l accumulation the slope may be e s s e n t i a l l y 'at r e s t ' several years before i t i s even scantily occupied by the grass and may well stand for a decade before moderately carpeted."- (Behre, 1933, p. 624) Indirectly, r o c k f a l l a c t i v i t y i s an indicator of the degree of a c t i v i t y or  s t a b i l i t y on a talus slope.  produce a very a c t i v e surface. able to s t a b i l i z e i t s e l f .  Substantial r o c k f a l l a c t i v i t y w i l l As r o c k f a l l abates the surface i s better  Tarpaulin traps have been used as measures  of r o c k f a l l a c t i v i t y (eg. Barnett 1966, Stock 1968);  otherwise,  little  quantitative data regarding s t a b i l i t y i s a v a i l a b l e . 2.  Problems associated with the morphology and morphometry of talus . Descriptions  of the form and shape of weathered c l i f f faces  and associated talus accumulations are r e a d i l y available; Rapp are p a r t i c u l a r l y comprehensive. from similar debris accumulations rock glaciers and a l l u v i a l cones.  those by  Talus forms are e a s i l y distinguished  such as avalanche boulder  tongues,  On some talus slopes a mound of rock  fragments i n the form of a ridge separated by a s l i g h t depression from  27 the base of the talus proper has been observed (Behre 1933, Bryan 1934, Andrews 1961, Stock 1968).  A generally acceptable explanation for this  phenomenon, however, has not been advanced.  Behre explains i t as the  r e s u l t of accumulated snow on the talus, between the c l i f f and the valley, which persists into late spring when most of the winter snow has melted. The snow on the talus i s sheltered from the sun by the c l i f f . wasting of debris from the c l i f f  The  i s active at this time of year because  of the high frequency of freeze-thaw cycles.  Debris accumulated on the  snow pack slides and r o l l s e a s i l y o f f the snow pack and concentrates to form a ridge near the base of the talus c a l l e d a "nivation ridge". Bryan (1934) does not agree with this terminology as i t implies formation i n respect to snow accumulation.  He does not see this as the general  case and offers the term "protalus rampart" as being a more suitable name. A number of p r a c t i c a l problems are encountered i n morphometric analysis of talus slopes.  Of significance i s the depth of the talus  deposit since shallow deposits can be much affected by the surface on which they rest.  Determination of the depth of the deposit by excavation  is d i f f i c u l t and indeed p r a c t i c a l l y impossible on p a r t i c u l a r l y deep deposits.  Talus slopes i n general are very steep and usually quite mobile.  Survey work and especially mapping on such a surface i s a p a r t i c u l a r l y d i f f i c u l t undertaking. The  Sampling the debris also presents problems.  most v a l i d method of sampling i s usually the completely  random method whereby each individual i n the population has a known chance of being selected i n the sample.  This  tends to eliminate bias  from the sampling program due to the temptation on the part of the sampler to choose samples which are "good looking" or " t y p i c a l " .  Often,  however, i n geomorphology the data have a systematic trend which renders  28 the data economically unfeasible for completely random sampling.  In  such cases, some systematic method i s employed which u t i l i z e s random sampling at a point, along a l i n e , or within an area based on some predetermined pattern or system.  In many cases systematic sampling  methods compare favourably with completely random sampling.  However,  as Cochran (1966) notes, the "...disadvantages are that they may give poor precision when unsuspected p e r i o d i c i t y i s present and that no trustworthy method for estimating known." (Cochran, 1966, p. 230) The surface of a talus slope i s a transportation surface along which debris i s moving e s s e n t i a l l y i n one d i r e c t i o n , i . e . , from the top to the bottom.  Sampling on a systematic basis along this axis of  transportation i s p a r t i c u l a r l y expedient on talus slopes especially, f o r example, to determine whether or not a s i g n i f i c a n t downslope progression of debris size (sorting) e x i s t s . on the slope a two dimensional  For size frequency analysis  sampling grid i s useful placing one axis  of the grid p a r a l l e l to the axis of movement on the slope and the other perpendicular to i t .  On a talus cone a more representative sample would  be obtained using a r a d i a l grid since the d i r e c t i o n of transport i s not constant but radiates from the apex of the cone.  In this way,  as many  sample stations could be established near the apex of the cone as there would be near the base with the number of samples at each s t a t i o n varying as a function of the area of each g r a t i c u l e .  Establishing the number of  samples required i n a p a r t i c u l a r program i s another problem.  The number  has to be large enough to give v a l i d r e s u l t s yet small enough to be reasonably accommodated within the limits of the program. problem encountered i n 1  sy)  A practical  sampling debris on a talus slope i s the mobility  i s the error variance.  29 of the surface.  To sample without disturbance of the surface i s  d i f f i c u l t and p r a c t i c a l l y impossible i n c e r t a i n cases.  30 CHAPTER II - HYPOTHESES AND METHODS OF INVESTIGATION  A . Lithologic and Topographic Controls . The investigation was confined to a 12 mile stretch of v a l l e y upstream from Keremeos where talus development was observed to be concentrated.  This occurrence of abundant and massive talus forms i s  a r e s u l t of three factors:  rock type, structure, and g l a c i a l h i s t o r y .  The f i r s t factor i s the s u s c e p t i b i l i t y of the cherts, lavas, limestones and other sedimentary rocks i n the area to weathering. was observed that disintegration of the rocks was complete throughout  the 12 mile stretch.  It  quite general and  To the south, however, the  rock forms grade into more resistant quartzite, schist and granodiorite. Upstream, the same basic succession of rock noted above continues (see Rice, 1966, p. 8).  However, as one proceeds northwestward out of the  region the rocks become increasingly more resistant as the r e s u l t of increased metamorphism: " A l l members of the group are more or less metamorphosed and near the contact with the Coast intrusions the a l t e r a t i o n becomes intense. As the contact i s approached the argillaceous sediments, p a r t i c u l a r l y , become coarser grained; feldspar and b i o t i t e develop; and the schistose texture gives place, with a further coarsening of grain, to a gneissic texture so that the sediments grade into the granitoid rock of the main intrusive body." (Rice, 1966, p.8) It seems then, that the weaker rocks found i n the 12 mile stretch under study are more susceptible to weathering than those found immediately to the northwest and south. The second factor i s related to the general j o i n t pattern exhibited by the rocks.  The rocks dip steeply, usually greater than 60°  (see Photo I I - l ) , i n a generally north to south d i r e c t i o n (Map 3). Since the orientation of the v a l l e y of the Similkameen trends generally east-west along the stretch studied, the planes present v e r t i c a l zones  Photo I I - l . Headwall Near Old Tom Creek. The white bed of limestone i n the rock face near Old Tom Creek i l l u s t r a t e s the steep dip (72°) of the beds and the orientation of their s t r i k e normal to the v a l l e y .  Photo II-2. Headwall Near Keremeos. Detail of rock headwall i n the v i c i n i t y of Keremeos along the north side of the v a l l e y . Note the j o i n t planes which aid the penetration by water and subsequent weathering.  of  weakness along which weathering  32  i n association with water can  e f f e c t i v e l y proceed perpendicular to the s t r i k e of the v a l l e y (see Photo II-2) . of  Northwest and south of the 12 mile stretch, the orientation  the j o i n t planes matches that of the orientation of the valley thus  presenting planes p a r a l l e l to the v a l l e y walls. for  Such a pattern allows  fewer effective routeways along which weathering can proceed to  produce wasting e f f e c t i v e for talus formation. The third factor noted was the configuration of the v a l l e y . Along this stretch the v a l l e y i s somewhat confined, having very steep sides with the bedrock exposed along both sides.  Movement of the  Cordilleran Ice Sheet i n the area was b a s i c a l l y from the north to the south.  This would have produced more pronounced scouring - and hence  broadening - i n the north-south trending sections of the v a l l e y .  The  east-west trending section therefore remains more exposed and vulnerable to  the processes of weathering and subsequent talus formation.  Down-  stream, the v a l l e y broadens appreciably and the walls are less steep with much of the bedrock protected with a mantle of t i l l .  Upstream,  the valley i s also somewhat broader and the rocks here, too, remain more protected by a t i l l mantle. B.  Weathering Mechanisms. The rocks exposed to the effects of weathering exhibit some  f a u l t i n g and light f o l d i n g . to  The net effect of the disturbance has been  produce a slight metamorphosis i n the rocks .  Some g r a n i t i c intrusion  has occurred but i s rare i n the region studied.  Weathering has had a  most deleterious effect on these rocks but i n varying degrees of intensity.  The cherts are most immune to decay and remain as the bolder  b l u f f s exposed along the walls of the valley.  Unequal dissection of  33 the headwall i s most c h a r a c t e r i s t i c , being concentrated i n the zones of weaker sedimentary occurred.  and volcanic rock, especially where f a u l t i n g has  The net e f f e c t has been to produce a variety of talus forms  the most common being successions of coalesced cones. Decomposition  and disintegration of the rocks as the result  of chemical and physical weathering respectively are r e a d i l y observable i n the rocks exposed.  It i s suggested that disintegration due to frost  action and decomposition as the r e s u l t of chemical action are the chief mechanisms of weathering. "Frost bursting" and "frost shatter" as the result of water freezing within the i n t e r s t i c e s of the rocks are considered to be the dominant mechanisms of d i s i n t e g r a t i o n . . The following points support this claim: a)  Water i s available throughout (see Figure 1-2)  the freeze-thaw period,  b)  The j o i n t pattern, as discussed i n section A. of this chapter, and the chemical weathering of the rocks (see Chapter III) provide f o r optimal penetration of the rocks by water .  c)  Frost action could b^ e f f e c t i v e along the headwalls since the l i g h t snow cover during the winter provides a minimum of i n s u l a t i o n .  d)  The shattered appearance of the headwall and the angularity and 'freshness' of much of the talus debris suggest f r o s t action.  The frequency of frost cycles (provided water i s available) to a large extent determines  the effectiveness of the mechanism.  In general, the  2 Mrs. Russ el.,, recorder for the Met. Station at Keremeos notes that snow cover i n the area does not vary greatly from an average of about 12 inches. Also, from personal observations i t was noted that the headwall i s kept e s s e n t i a l l y bare of snow by the wind.  more frequent the cycles the greater the destruction of the rocks affected.  34  To determine the frequency of f r o s t cycles i n the region, an  analysis of climate data obtained of the Ministry of Transport  from the Atmospheric Environment Service  (Canada) was made.  A continuous record  for Keremeos station on the Upper Bench Road of that municipality i s available from the year 1930 to the present.  To correlate with these  records a maximum-minimum thermometer was i n s t a l l e d i n the headwall at TC25 (see Photo II-3) and a f r o s t cycles record for the week November 24 to December 1, 1967 was obtained.  The thermometer was  Photo II-3. Maximum-Minimum Thermometer (arrow) Installed i n Rock Crevice at TC25. The thermometer was placed about 3 feet from the surface. located on the headwall inside a rock crevice 150 feet below fence #1 (see following section) on the r i g h t side (interpret l e f t or r i g h t , facing i n the d i r e c t i o n of transport down the talus slope) of TC25 so as to give a  35 reading representative of the temperature a f f e c t i n g the rock.  Analysis  of both sets of frost cycle data i s made i n Chapter I I I . Decomposition due to chemical weathering i s of primary importance i n the region.  The processes  of oxidation, hydration, and solution  seem most pronounced, as substantiated by observations A number of secondary physical  i n Chapter I I I .  weathering processes  have limited  e f f e c t i n the region, including s p l a t t e r i n g effect of raindrops and the wedging action attributed to the growth of plant roots along of separation i n the rocks (see observations C.  planes  i n Chapter I I I ) .  Rockfall Mechanisms. Upon investigation i t was concluded that  (Chapter I.B.2.) predominate.  four r o c k f a l l mechanisms  Of greatest importance would be release  of fragments from rocks shattered and burst by f r o s t action.  Analysis  of frost cycles i n Chapter III supports this claim as well as the effectiveness of " f r o s t - r i v i n g " as a mechanism.  R a i n f a l l could be an  important release mechanism during June when p r e c i p i t a t i o n , i n the form of thunderstorms, i n concentrated. .could have the same e f f e c t .  Meltwater e a r l i e r i n the spring  Expansion and contraction associated with  alternate heating and cooling i s probably an important dislodgement mechanism i n the summer when temperatures exceeding 100°F. are not uncommon and cooling under clear skies at night i s e f f e c t i v e .  Since  many of the headwalls observed exhibit a r e l a t i v e l y dense growth of stunted Douglas f i r trees (see Photo III-6, p.87) root wedging could be important as w e l l .  Observations of the effectiveness of these mechanisms  are included i n Chapter I I I . Creep i s not an important release mechanism since l i t t l e or no r e g o l i t h develops on the very steep headwalls.  Snow block and i c e block  36 f a l l s would have l i t t l e or no e f f e c t i n this area which has only a l i g h t snowfall most winters . Some observations of release caused by wind are included i n Chapter III indicating that wind might be D.  important.  Mass Movement Mechanisms. It i s suggested that d i f f e r e n t i a l s h i f t i n g of debris due to  mass movement mechanisms produces cross-slope sorting on the talus slopes studied and accounts for the development of s t r i p s of fine and coarse debris noted on most slopes (see Photos II-4 and II-5). Hypothetically, debris of a larger size i s capable of greater mobility over the surface  Photo II-4. CC52• Note the alternating s t r i p s of fine and coarse debris across the talus surface. of a talus slope by v i r t u e of i t s greater mass, allowing the development of greater kinetic energy (Chapter  I.B.2.).  Further, the potential for  mobility for a given rock increases i f the surface over which i t w i l l move i s composed of fragments smaller than i t s e l f .  The mobility of smaller  Photo I I - 5 . D e t a i l of Surface on CC52. Note s t r i p of coarse material i n foreground and successive s t r i p of fines i n the background. The packsack gives the scale.  38 rocks, therefore, i s much r e s t r i c t e d due to their limited capacity to develop k i n e t i c energy.  Also, rocks which are r e l a t i v e l y small w i l l  most l i k e l y encounter rocks of the same s i z e or larger on the slope over which they move.  This further impedes their mobility.  In view  of this relationship between size and mobility and i n l i g h t of observations made on talus slopes i n the region studied, i t i s suggested that movement on these slopes occurs i n two d i s t i n c t ways.  In general,  movement downs lope for the larger rocks occurs on an individual basis. Smaller p a r t i c l e s , however, are usually incapable of individual mobility and therefore must move en masse along s l i p planes i n response to spontaneous mass movement mechanisms .  To explain the process i t must  be hypothetically examined i n d e t a i l . Rockfall a c t i v i t y from the headwall i s the source of supply for the?, debris comprising the talus slope.  Fragments both large and  small are continuously added and i n this way  the deposit grows, maintaining  a slope which, under normal circumstances, i s commensurate with the angle of internal f r i c t i o n of the material. Rockfall debris w i l l encounter  the talus slope at or near i t s summit ( i n the case of a cone  near the apex and indeed, i f a chute or funnel has developed, far above the summit of the talus slope).  To preserve a more or less constant  slope on the talus deposit some of this debris must migrate downslope. Some of the larger rocks would be able to move immediately to the base of the slope.  I t was  noted that an apron of larger boulders occurs at  the base of most slopes observed i n the region (see Morphology this Chapter) . Not a l l of the r o c k f a l l debris can move d i r e c t l y to the base of the talus, however, as do the boulders which accumulate to form the apron.  Some become immobile almost as soon as they encounter  the  39 surface of the talus deposit, e s p e c i a l l y the smaller rocks..., the larger ones may  Some of  move a f a i r distance downslope but a l l eventually  become lodged at some point on the talus surface  However, accumulation  w i l l be greatest at or near the apex or summit of the talus where r o c k f a l l a c t i v i t y i s concentrated.  This disproportionate rate of accumulation  w i l l produce the development of steeper slopes at the top of the talus deposit with a successive decrease i n angle downslope.  This may  in  part account for the concave p r o f i l e observed on talus slopes studied i n the v a l l e y (see observations  Chapter III) . The angle near the top  of the deposit cannot continue to increase i n d e f i n i t e l y , however.  At  some point the shear stress within the material w i l l exceed the internal f r i c t i o n of the fragments and f a i l u r e w i l l occur.  The materials w i l l  s l i d e e_n masse or as individuals thus reducing the slope of the surface to one below that which produces f a i l u r e . the slope near the top of the talus may  With successive r o c k f a l l  again be b u i l t up, only to be  readjusted by f a i l u r e . The readjustment probably never involves the entire talus slope at the time of a p a r t i c u l a r event.  Rather, the readjustment i s  probably l o c a l i z e d and would alternate back and f o r t h across the slope thus preserving the basic symmetry apparent on-any talus deposit.  It  i s suggested that this readjustment due to spontaneous mass movement accounts for the sorting which produces a pattern of alternate s t r i p s of f i n e and coarse material observed on most talus slopes i n the region (see Photos II-4 and II-5) . To explain the mechanism, a consideration of the mass movement process  i n d e t a i l w i l l be made.  Upon release by spontaneous mass movement the size of the i n d i v i d u a l fragment w i l l be c r u c i a l i n determining  how  far i t w i l l move  before again coming to r e s t .  40  The larger fragments, once mobile,  are capable of moving greater distances downslope.  The smaller fragments  tend to move only short distances, i f at a l l , because of their small mass and i n a b i l i t y to move over the surface i r r e g u l a r i t i e s of a slope which i s composed for the large part of fragments greater than or equal to their own s i z e .  In this way  the larger pieces  would tend  to divorce the smaller ones near the summit of the deposit. ones move downslope u n t i l contact with either a decreased  The larger  slope or  fragments of a comparable size reduces their momentum s u f f i c i e n t l y to bring them to r e s t .  Some of the larger ones may  travel to the base  to become incorporated as part of the boulder apron.  In this  way  concentrations of fines would develop near the top of the slope.  As  these concentrations of fines develop, their potential for movement en masse increases.  They may  become released en masse i n the form of  miniature landslides, the whole being capable of greater mobility than any one of the individual fragments comprising  the mass.  The  individual  fragments would r i d e e a s i l y over one another, f i l l i n g i n the surface i r r e g u l a r i t i e s they encounter to create fingers or strips of f i n e debris extending down the talus slope (see Photo II-6).  On September 3,  1967  an observation of this phenomenon was made on CC7  (see Photo II-7).  The mass of small-sized debris C~1.5"d.) shows up i n the photograph as a l i g h t brown patch which has moved downslope separating into four d i s t i n c t fingers or lobes. of weathering;  The contrast i n colour i s due to the effects  the l i g h t e r fresher material had s l i d from above onto  the drab weathered surface of the middle portion of the slope. recent but similar occurrence  i s v i s i b l e as a more weathered but  detectable darker patch further to the r i g h t i n Photo II-7.  A less still  By the  41  Photo II-6. TC67. Note the light coloured projections on the right side of the cone indicating recent downslope migration of f i n e s . The banded appearance due to alternating strips of coarse and f i n e debris on the surface i s c h a r a c t e r i s t i c of talus observed i n the region.  Photo I I - 7 . CC7. Note fresh s l i d e of fine debris (arrow).  42 following year the very fresh patch had become weathered so as to become barely detectable on the surface.  A closeup view of the fines indicated  that the new material was a layer some eight inches i n depth. leading edge where the mass came to rest a d e f i n i t e lobe had  At the developed  giving the deposit a 'snout' shaped f r o n t . Once this pattern of alternating bands of f i n e and coarse debris becomes established, successive readjustment would tend to accentuate i t .  due to mass movement  Any large rocks moving downslope w i l l be  able to travel without much resistance over these deposits of fines and w i l l most probably not come to rest on them.  The larger rocks,  rather, would concentrate along the coarse s t r i p s where rocks of a comparable size would impede their movement downslope.  Otherwise, the  larger rocks would tend to move further downslope because of their increased momentum. Also, the i n i t i a l routeways established by the miniature'.landslides of fines become the most l i k e l y routes for successive en masse movement, these being the lines of least resistance i n terms of a surface impediment.  In this way  the f i n e s t r i p s eventually extend  their development to the very base of the talus deposit (eg. see Photo I I - 8 ) . Another observation tends to confirm the theory of development presented above.  In a l l cases, the coarse s t r i p s of debris are much  more stable than the f i n e .  Walking upslope on talus i n the region was  r e l a t i v e l y easy along a coarse s t r i p b u t . p r a c t i c a l l y impossible along a fine strip.  The mobility of the fines made the exercise analagous to  walking 'up' a 'down' escalator. a difference i n the way  The difference i n mobility suggests  i n which the rocks were deposited.  According  to the theory, rocks along the coarse s t r i p s accumulate on an individual basis allowing for imbrication. This creates a greater degree of  1  43  Photo II-8. Looking Up on TC67. Note where lobe of fine debris has overridden coarse rubble near the base of the cone. F i e l d book i n foreground gives scale. compaction r e s u l t i n g i n greater s t a b i l i t y .  The fines, however,  coming to rest en masse, are not allowed to f i t together and remain very mobile under foot. The theory presented above attributes the observed pattern e n t i r e l y to sorting, produced as the r e s u l t of spontaneous mass movement, on the slope.  To determine whether or not other controls such  as shape of debris should be considered, a f a b r i c analysis was made by sampling debris on CC52.  Samples were taken on one fine and one  coarse s t r i p adjacent to one another on the slope. method was  A systematic  employed on each s t r i p taking 25 samples at each of 10 sites  located at 50 foot intervals along the s t r i p . 250 samples over a distance of 450 feet was  In this way a total of  obtained on each s t r i p .  At each s i t e , the samples were selected as randomly as possible by grabbing each with eyes closed.  The a(long), b(intermediate) and  44 c(short) axes were measured and recorded for each rock.  The analysis  is included i n Chapter IV. To detect net and d i f f e r e n t i a l movement to be used as a measure of the degree of a c t i v i t y on the talus slopes, a series of lines were painted.  In p a r t i c u l a r any s i g n i f i c a n t difference i n behaviour on fine  as compared to coarse s t r i p s of debris was sought.  On December 3, 1966  two lines each 50 feet i n length were painted on TC22, the largest talus cone observed i n the region. used.  Yellow paint i n pressurized tins was  Similar l i n e s 100 feet i n length were painted on May 16, 1967  above and below fence #1 on TC25.  In August, 1967 a l i n e 750 feet i n  length was painted on CC52, the p o s i t i o n of the l i n e being established by telescopic alidade.  The l i n e transected a section of the series  of coalesced cones on CC52 which exhibit a well developed pattern of fine and coarse s t r i p s .  The observed disturbance of these lines and additional  observations made on talus slopes i n the region were used as a measure of the importance of other mass movement mechanisms including: avalanche transport, water transport, and wind transport.  talus creep,  The results  of these observations are included i n Chapter I I I . In order to paint a l i n e on a talus slope one must necessarily disturb the surface.  Any movement which subsequently occurs could be the  direct r e s u l t of the disturbance created. way  There seems to be no e f f e c t i v e  of d i f f e r e n t i a t i n g between movement a t t r i b u t a b l e to natural mass  movement mechanisms and that a t t r i b u t a b l e to the disturbance while painting the l i n e .  created  When walking over a talus surface, i n d i v i d u a l  rocks become displaced downslope. to readjust to a lower angle.  Sometimes whole masses of debris s l i d e  The net effect i s to produce compaction  of the debris immediately below the l i n e being painted.  Any movement  45 which occurs along the l i n e may  simply be an adjustment  above i n response to the disturbance below.  of the slope  Results, therefore, should  be interpreted cautiously. E•  Morphometry and Morphology of Talus i n the Similkameen Valley Near Keremeos. 1.  Morphometry. As a major hypothesis of this thesis i t i s suggested that the  talus slopes i n the Similkameen V a l l e y near Keremeos are entering the f i n a l stages of development and are tending towards s t a b i l i t y .  Initial  observations of the talus forms investigated suggested that the talus slopes were entering a passive stage of development.  I t i s assumed that  a l l the talus forms i n this region have developed since the r e t r e a t of the l a s t C o r d i l l e r a n Ice Sheet from the area since scour would have erased any talus previously developed.  Therefore, the talus developed i n this  region probably has an age of about 10000 years (Fulton, 1971).  Talus  formation was probably rapid following the r e t r e a t of i c e from the area. The headwalls, bared to the very f l o o r of the v a l l e y would have presented a substantial weathering surface and i n the cold humid p o s t - g l a c i a l climate would have resulted i n a rapid rate of r o c k f a l l .  Since the  i n i t i a l rapid growth, however, talus formation has probably undergone an ever decreasing rate of development. The main c r i t e r i o n used to substantiate this s t a b i l i t y hypothesis i s the degree of vegetation cover.  As noted i n Chapter I . C . I . , vegetation  can be a very useful and v a l i d index.  Very active slopes subject to  frequent r o c k f a l l a c t i v i t y and mass movement do not, i n general, have a vegetation cover.  In this sense, the mobility of the surface serves  as an impediment to the establishment and growth of plants.  As r o c k f a l l  46 a c t i v i t y abates and, as the surface of the talus slope becomes more stable, vegetation i s able to establish a foothold. The establishment of a vegetation cover does not, however, imply the cessation of a c t i v i t y . Indeed, the talus slope may  continue to grow i f r o c k f a l l a c t i v i t y continues.  What i s implied, rather, i s that a c t i v i t y i s on the decline indicating an approach towards at least temporary i f not permanent s t a b i l i t y . A l l talus slopes observed had some form of vegetation cover on them.  For most, the cover was not complete being concentrated near the  top and/or near the base of the slope.  Some slopes observed had a complete  cover indicating a high degree of s t a b i l i t y and e s s e n t i a l l y the completion of the talus phase (see Photo II-9).  The establishment of some form of  plant cover on a l l talus slopes observed i s interpreted as an indication that the rate of talus development near Keremeos i s decreasing.  Further-  more, this passive stage of development i s not considered to be a temporary phase with rejuvenation to occur sometime i n the future; rather, i t i s interpreted as the approach of the f i n a l stages of talus development.  To substantiate this claim, i t i s necessary to consider  the probable evolution which has occurred since the talus phase began. After the l a s t retreat of i c e from the area (10000* B.P.)  the  headwalls along the v a l l e y were probably bared to their maximum extent; probably to the floor of the v a l l e y .  It can be assumed for the purposes  of this theory that the p r o f i l e of the v a l l e y was e s s e n t i a l l y U-shaped this being  c h a r a c t e r i s t i c of a glaciated v a l l e y and, with certain  modifications, the basic p r o f i l e observable at the present time. I n i t i a l l y , therefore, the headwall i n cross-section probably as i l l u s t r a t e d i n stage 1 of Figure I I - l .  appeared  Rate of talus development would  be rapid at this stage since a maximum surface along the headwall would be exposed to the effects of weathering and the post g l a c i a l climate  47  Photo I I - 9 . TC2. Note the complete v e g e t a t i o n cover and t h e t r a i l c r o s s i n g the cone i n d i c a t i n g a h i g h degree of stability. L i t t l e of t h e h e a d w a l l remains exposed most h a v i n g been c o v e r e d by t h e t a l u s b u i l d i n g up a g a i n s t i t . Rockfall a c t i v i t y w i l l c o n t i n u e but a t a subdued and ever d e c r e a s i n g r a t e . T h i s t a l u s has e n t e r e d i t s f i n a l s t a g e of development.  48  FIGURE H-l.  TALUS  A.  EXPOSURE  KEREMEOS  OF HEADWALL  HEADWALL  MINIMUM  SURFACE  OF ACCUMULATION  SIMILKAMEEN  B.  ROCK  AT  STAGE  MAXIMUM ROCK  DEVELOPMENT  HEADWALL-*\  STAGE  EXPOSURE  OF  RlVER  2  HEADWALL  SURFACE  s^-TALUS  AREA  OF  DECREASES  TALUS  SIMILKAMEEN  INCREASES  RIVER  49 would favour a rapid rate of weathering due mainly to frost shatter. Also, the area of accumulation on the talus i t s e l f would be small allowing for a rapid growth rate.  As soon as a talus deposit begins  to form, however, the rate of growth would decrease as i l l u s t r a t e d i n stage 2.  It can be seen that the rate of development at this stage  would be much reduced as compared to stage 1. sediment y i e l d ' can be applied.  A concept of  'diminishing  As the talus deposit grows i n size i t  covers more of the headwall from which i t derives i t s supply of debris. The rate of supply, therefore, decreases.  Also, as the talus deposit  increases i n size so does i t s surface area.  At any successive  level  of development the talus requires more debris for a s p e c i f i e d increment of growth than i t did for the previous l e v e l .  But, the rate of supply  decreases at each successive level producing a net d e c e l l e r a t i o n i n the rate of growth. now  At some point the effectiveness of r o c k f a l l a c t i v i t y ,  at a much reduced ratejbecomes much reduced having to cover a talus  surface which has increased greatly i n area.  At this point the talus  would be entering i t s f i n a l stage of development and the establishment  of  vegetation on i t s surface would serve as an i n d i c a t i o n of approaching stability. The degree of s t a b i l i t y noted i n the region varies a great deal, however.  Some of the slopes yet appear to be a c t i v e .  a c t i v i t y continues  along the headwall exposed.  Certainly, r o c k f a l l  However, these talus  slopes have grown to vast proportions and have covered the greater portion of the headwall that was  o r i g i n a l l y exposed.  For example, TC22,  one of the larger cones, extends through approximately 1500  feet of  r e l i e f and measures some 2500 feet along i t s base and 3000 feet along i t s longitudinal p r o f i l e .  Talus slopes of this magnitude can reduce the  50 effects of even substantial r o c k f a l l a c t i v i t y . A measure of the degree of present a c t i v i t y on talus slopes i n the region was obtained from two fences designed to capture r o c k f a l l debris constructed on TG25 and TC49 i n the l a t t e r part of May,  1967.  To test the hypothesis, one fence was constructed on a talus cone which was judged to be r e l a t i v e l y active (see Photo 11-10) and the other on a cone considered to be more stable (see Photo 11-11). c r i t e r i o n used was vegetation cover; i n d i c a t i v e of greater s t a b i l i t y .  The main s t a b i l i t y  a more dense growth considered  TC25, considered to be the more active  cone, was also the larger of the two.  As can be seen i n Photo 11-10, a  well developed chute extending far back into the headwall complements this cone.  Fence #1 was  the apex of the cone.  constructed at the entrance to the chute near  So positioned the fence would capture that debris  f a l l i n g from the headwall i n the v i c i n i t y of the apex of the cone as well as that debris t r a v e l l i n g through the chute en route to the talus slope. Galvanized chicken wire s i x feet wide with a two inch mesh was used to construct this fence which measured 188 feet i n length (see Figures II-2 and II-3).  Rockfall and transportation through the chute  i s most concentrated along i t s outer edges, the center remaining more stable as a r e s u l t of the vegetation (trees, shrubs, grasses) which has become established there.  Part of fence #1 i s i l l u s t r a t e d i n  Photo 11-12. Fence #2, constructed on TC49 i s 185 feet long and of the same design as fence #1 (see Photo 11-13).  TC49, however, was  judged to be  less active than TC25 and i n this respect served as a basis for study.  TG49 proved to be a t r a n s i t i o n a l form of talus, however.  comparative  51  Photo 11-10. Site of Fence #1 on TC25. The fence was constructed just above the largest Douglas f i r tree at the apex of the cone where i t grades i n t o the chute above i t . Note how the configuration of the chute tends to accentuate the major j o i n t pattern i n the rock comprising the headwall.  Photo 11-11. Site of Fence #2 on TG49. The fence was constructed at the apex of the cone at the point where i t coincides with the headwall i n the photograph. Note heavy growth of vegetation indicating greater degree of s t a b i l i t y .  52  FIGURE H-2.  FENCE NO. I  i  ACROSS  CHUTE  V  FIGURE H-3.  DETAIL  OF  FENCE  AT  TC  25  53  Photo 11-12. Fence #1 on TC25. Note the headwall i n the background and more stable central portion of chute.  54 Observations of a channel near the apex of the cone indicated that f l u v i a l action was affecting development on the cone. of a i r photos confirmed this (see Photo 11-15).  An inspection  A substantial catchment  basin has developed above TC49 which would serve to concentrate the flow of water onto the talus.  The chute above TG49 was e s s e n t i a l l y void of  debris i n d i c a t i n g that water must flow through i t (see Photo 11-14 below).  Photo 11-14. Detail of Chute Above TC49 . Note how much of the loose debris has been removed from the chute by f l u v i a l action. Modification and deposition due to f l u v i a l effects, however, are minor on TC49. Both fences were sampled on two separate occasions.  On  September 5 and 6, 1967 fences #1 and #2 respectively were sampled. Since the accumulation period ran from the end of May u n t i l the beginning of September a sample for the f r o s t - f r e e season was obtained.  On  Photo 11-15. Headwall, Associated Talus, and Similkameen River at TC49. Note degree of vegetation cover on TC49 i n d i c a t i n g a stable slope. Note also the well developed catchment basin above the cone r e s u l t i n g i n the development of a f l u v i a l channel at the apex of TC49 (see arrow).  56 June 12 and 13, 1968  they were again sampled.  The accumulation period  from September to June provided a sample for the period of f r o s t a c t i v i t y i n the region.  The r e s u l t s of this sampling program are included i n  Chapter I I I . An ash deposit observed on CC44 near the confluence of the Ashnola and Similkameen Rivers afforded a rough measure of the rate of past talus development i n the area and was  used to test the v a l i d i t y  of the 'diminishing sediment y i e l d concept' advanced i n this t h e s i s . On CC44 at a point where a cut for the Southern Trans-Canada Highway truncates a series of cones of t h i s group a layer of volcanic ash preserved  at depth on the largest cone (see Photo 11-16) has been  i d e n t i f i e d (Ryder, 1970,  p. 196) as that of the Mazanaeruption which  occurred to the south of the region 6600 years B.P. 1964,  Westgate et a l . , 1970,  Fulton, 1971).  (Powers  &  Wilcox,  The ash deposit neatly  divides the talus deposit (of which i t i s a part) into that debris which was  deposited i n the i n t e r v a l 10000 - 6600 B.P.  (3400 years) and that  deposited since deposition of the ash (660CT years).  The contact between  the talus deposit and the r i v e r terrace on which i t has developed i s c l e a r l y defined i n the road cut (see Photo 11-17).  Therefore, a record  of the evolution of at least one of the talus slopes i n the area i s available. question was  Employing a telescopic alidade and stadia rod the cone i n surveyed to obtain a rough measure of the volume of debris  b u i l t up prior to the deposition of the ash as compared to the volume b u i l t up since the ash deposit. included i n the observations It was  hypothesized  The results of this analysis are  of Chapter I I I . that a talus cone, e s p e c i a l l y one with a  chute or funnel extending up from i t s apex,should have d i f f e r e n t slope  Photo 11-16. Mazama Ash Deposit at CC44. Arrow shows contact between talus and terrace of the Similkameen River on which i t rests .  Photo 11-17. Talus Resting on River Deposit at CC44. Zone of contact between talus of CC44 and terrace of the Similkameen River, on which the talus r e s t s , i s c l e a r l y v i s i b l e . Note degree of compaction of talus debris which allows i t to support a near v e r t i c a l slope i n the road cut.  58 and debris d i s t r i b u t i o n c h a r a c t e r i s t i c s along the sides of the cone as compared to the middle.  Any talus slope i s a transportation surface over  which debris i s moving i n a downslope d i r e c t i o n .  On a cone, however,  movement i s most concentrated and consistent along the central axis. To note any s i g n i f i c a n t difference, therefore, a number of p r o f i l e s were established employing the abney level and measuring tape method. (A simple technique  was chosen that would allow for a simultaneous  sampling of the debris size on a systematic basis.  King (1966) notes  that slopes measured by this method are accurate to 1/2°.)  A l l profiles  were obtained s t a r t i n g at or near the apex of each cone and then measuring slope segments at 100 foot i n t e r v a l s downslope (or shorter i f the i r r e g u l a r i t y of the t e r r a i n warranted  it).  The slope angle for each  segment was obtained by s i t i n g from station to station with an abney level while standing erect.  Suitable natural targets above and below  were chosen to keep the p r o f i l e oriented i n as straight a l i n e as possible. On TC21 three p r o f i l e s were established (one medial and two l a t e r a l ) and debris size (a,b, and c axes) was sampled at ten foot intervals along each.  On TC25 two p r o f i l e s were taken;  the other down the r i g h t side of the cone.  one down the center and  Debris size was sampled only  along the central p r o f i l e of this cone. Observations made suggested that no downslope sorting occurs on talus slopes i n the region. Methods to v a l i d a t e this hypothesis were sought.  The samples of debris taken i n association with the establishment  of the p r o f i l e s discussed above served as one method to test for downslope sorting.  Another used was the establishment of a series of traverse  grab samples on a number of cones.  In a l l , four talus cones were  sampled employing a systematic method.  A number of cross-slope walks  59 were made on each cone taking samples at ten step i n t e r v a l s . TG48 and TG67 a t o t a l of four traverses were made;  On each of  on TC3 and TC26 a  t o t a l of six and seven traverses respectively were made.  The  traverses  were evenly spaced on each cone to include one traverse at or near the apex, one at or near the base, and two or more i n between. taken at each ten step i n t e r v a l by reaching behind and f i r s t rock touched.  Samples were  selecting the  The lengths of the a, b, and c axes for each rock  were measured and recorded.  The data c o l l e c t e d are analyzed  i n Chapter IV.  To serve as a basis for detailed slope analysis, debris sampling, and talus morphometry, a talus cone of intermediate a large scale.  A cone (TC26 on Map  size was  mapped at  2) with a south-facing aspect  was  chosen since the south-facing slope of the v a l l e y exhibits a greater degree of talus development. cone suggested that i t was  Also, the amount of vegetation cover on the  intermediate between very stable and active  cones, both of which are found i n the v a l l e y .  TC26 has a r o c k f a l l chute  (see Chapter I.B.4.) leading up from i t s apex which is c h a r a c t e r i s t i c of most cones i n the area. form was  F i n a l l y , a cone rather than some other talus  chosen since the cone form i s most prevalent i n this v a l l e y .  A cone of intermediate  s i z e was  larger cones are present  1000  feet long, 1200  (Much  i n the area but the task of mapping TC26 alone  took the writer and a rod man i s 1800  chosen to f a c i l i t a t e mapping.  two weeks to complete.)  feet wide (at the base) and  The cone mapped  extends through  feet of r e l i e f . Mapping was  July 4,5;  accomplished during the summer of 1967  August 22-25;  (June 27-30;  August 30 - September 3) by plane table survey  employing a telescopic alidade.  A large scale map  (1 inch to 100  feet)  with a 5 foot contour interval (^ 1 foot assumed accuracy level) was obtained  (see Map  4A,  p. 118).  A baseline (see I , I I , I I I , I V on Map  4A)  60 was established along the l e v e l talus apron by measurement with a steel tape (accurately as possible by using a spring balance to give readings under constant tension, and measurement i n a short time i n t e r v a l so that temperature flux effects would be minimal) and l e v e l l i n g with the telescopic alidade and plane table.  The four stations along the baseline were  flagged with permanent wooden markers and were used as reference points to establish subsequent triangulation stations i n order to complete the survey.  Station II was chosen as the datum and assigned an a r b i t r a r y  elevation of 100 feet.  Thirty-one triangulation stations, to serve as  a g r i d reference to establish a network of points of elevation from which contours could be drawn, were chosen.  Elevation was calculated f o r each  from the stadia intercept and angle reading on the rod. The plane table was then set up at each baseline station and triangulation station i n turn.  Correct orientation was maintained by s i t i n g back to at least  three other reference points.  The number and location of triangulation  stations were s t r a t e g i c a l l y chosen so that no one alidade shot determining the elevation and location of a point would be at a distance greater than 150 feet or at an angle exceeding 25°. The positions of the f i r s t eleven triangulation stations were established by reference to at least three other reference points, at least two of which were baseline reference points, giving the lower t h i r d of the map the most accurate readings. As the survey proceeded upslope, i t became increasingly d i f f i c u l t and eventually impossible to refer back to the baseline reference points i n order to f i x triangulation stations.  By careful reference back to at  l e a s t three adjacent triangulation stations subsequent triangulation stations were established with what was thought to be a f a i r degree of accuracy.  In l i g h t of this f a c t , however, accuracy probably decreases  61 upslope on the map.  The confinement of the rock walls i n the chute above  the apex of the cone obscured most of the downslope reference  points  r e s u l t i n g i n probably the lowest degree of accuracy for this section of the map.  Wooden lathe targets flagged with cardboard faced with a  fluorescent orange emulsion served very well as markers for each of the triangulation and baseline stations.  At each of the four baseline  stations and thirty-one t r i a n g u l a t i o n stations, a minimum of four and a maximum of 52 points of elevation were established by rod readings employing the telescopic alidade. established.  Three hundred f i f t y - f o u r such points were  Elevation and position of a total of 389 points, then, were  determined and served as the basis for the map.  The f i e l d sketch was  permanently f i x e d to an 18" x 24" plane table mounted on a removable tripod and was conveniently  drawn on a sheet of frosted acetate.  survey was i n i t i a t e d at baseline point I I .  The  Rays were drawn from II to I,  III, and IV and the proportionate map distance was scaled off thereby f i x i n g the points on the map.  Elevations of points I, III and IV were  then determined by l e v e l l i n g i n reference to s t a t i o n I I a r b i t r a r i l y established as the 100 foot datum. The most f r u s t r a t i n g and time consuming part of the survey was to keep the plane table l e v e l and c o r r e c t l y oriented at each station. This was e s p e c i a l l y d i f f i c u l t on the higher slopes of the cone where the angle exceeded 37° and the debris was very mobile.  At each reference  s t a t i o n a network of points was established at a density required to draw f i v e foot contours with r e l a t i v e ease. distance and elevation of each point readings on the rod.  The correct planimetric  were calculated from the alidade  The correct position  was then established for each  point on the map by s c a l i n g off the proportionate  distance with a pair  of dividers along a ray established by the alidade s i t i n g on the r o d .  62 Each rod station was selected to f a c i l i t a t e maximum expression of the terrain.  The contours were drawn i n the f i e l d as the survey proceeded  and as much of the s u r f i c i a l d e t a i l as possible was noted some of which i s contained i n the overlay to Map  4A i n Chapter I I I . No  obstacles were encountered, but the survey was  not without  insurmountable problems,  including the steep and unstable surface, the presence of trees and the gustiness of the wind. On Map  4A only the contours which express the debris covered  slope of the talus cone and associated chute were established by this survey.  Those contours expressing the d e t a i l of the rock headwall,  except for the rock spur (noted on the overlay), were extrapolated from a i r photos and serve to i l l u s t r a t e the basic form only of the rock headwall i n the immediate v i c i n i t y of the talus cone, and should not be taken as correct. A detailed sample of the debris on TC26 was with the survey.  taken i n conjunction  One rock at each rod station was grabbed with eyes  closed and i t s intermediate (b) axis was measured. of the data collected i s included i n Chapter IV.  An i n t e r p r e t a t i o n In passing, i t can be  noted that very large rocks (> 3 f t . dia.) were observed only r a r e l y on the talus slopes i n the region.  As already noted these larger rocks  generally travel to the bottom of the slope where they accumulate a boulder apron.  to form  The few large ones observed at rest higher up on the  talus slope were usually very f l a t or elongate i n shape (see Photo 11-18) which accounted for their unusual position on the slope. 2.  Morphology. The phenomenon l a b e l l e d " n i v a t i o n ridge" (Behre, 1933) "protalus  rampart"  (Bryan, 1934) and "protalus boulder accumulation" (Stock,  1968)  63  Photo 11-18. TC48. Note very large boulder at rest on talus slope i n association with c h a r a c t e r i s t i c a l l y smaller sized fragments. This boulder has a long axis of 10 feet, i t s very f l a t shape accounting for i t s unusual position on the slope.  64 was  observed on one talus slope i n the region.  On TC67 near the base of  the cone a t r a n s i t i o n a l zone of crescent-shaped  ridges can be observed  leading out onto the boulder apron (see Photos 11-19  and 11-20) .  This  phenomenon does not exist on any of the other talus slopes i n the region and a reasonable  explanation for i t s occurrence cannot be given.  has developed according to the hypothesis advanced by Behre, 1933  If i t (see  Chapter I.C.2.) i t must then be a r e l i c t form because of the following: 1.  At no time during the investigation (1966 - 1972) was a substantial snowpack observed on TC67 (or any other slope) .  2.  Climate data since 1930 l i g h t i n this region.  indicate that snowfall i s c h a r a c t e r i s t i c a l l y  It i s feasible that these ridges could have developed according to Behre's theory but only i n a climate regime characterized by heavier snowfall.  As mentioned, this phenomenon occurs only on TC67.  Because  of i t s northern exposure and the existence of a substantial ridge to the east of the cone, TC67 remains sheltered a great deal of the time from the sun.  On September 21, 1967  e n t i r e l y i n shadow u n t i l 1:00  i t was  p.m.  observed that TC67 remained  that day.  A s i m i l a r s i t u a t i o n would  exist during the spring months which could allow any substantial snow pack accumulated during the winter to p e r s i s t late into the spring. It was  observed that parts of some of the ridges have become buried as  the r e s u l t of more recent talus development which suggests that they might be a r e l i c t  accumulation.  Boulder aprons have developed at the base of almost a l l talus slopes i n the region (see Photo 11-21) .  These aprons are the  accumulation  of those rocks which by v i r t u e of t h e i r large s i z e are able to move uninterrupted a l l the way to the bottom of the deposit.. I n i t i a l l y most of these boulders would probably travel a f a i r distance beyond the talus  65  Photo 11-19. TC67• The arrow shows the location of protalus ridges near base of TC67. Note also the r i v e r terrace near the base of the talus cone and well developed a l l u v i a l fan on the opposite side of the Similkameen River.  Photo 11-20. TC67. Arrow shows the location of one of the protalus ridges on TC67 . Note that the ridge occurs at the base where the characteri s t i c a l l y sharp break i n slope occurs . Note also the large size of debris comprising the ridge.  Photo 11-21. Detail of Boulder Apron at the Base of TC25. Note the sharp break i n slope where apron begins . The excavation i n the foreground i l l u s t r a t e s that the boulders extend at depth beneath the talus proper.  Photo 11-22. Boulder Apron on TC42. Note the very sharp boundary between the boulder apron and the talus proper. Hard hat l e f t of center gives scale.  67 deposit i t s e l f depending on the slope of the substratum.  As the deposit  grows, however, the rocks themselves serve as impediments to other rocks r o l l i n g to the base and a f r i n g e deposit of these boulders would accumulate at the base.  In a l l cases, the boundary between the talus slope proper  (composed of much smaller debris) and the boulder apron i s very sharp (eg. see Photo 11-22);  an abrupt change of slope can be noted as w e l l .  (Usually about 10°, i . e . , at point of contact the talus would have a slope ranging from 30°-35°;  the boulder apron correspondingly 20°-25°).  The sharp break i n slope indicates that the boulder apron must be controlled by mechanisms exclusive of those developing the slope above i t since the difference i n angle cannot be attributed to the difference in size of debris (see Chapter I.B.2).  The materials comprising  the  talus slope by v i r t u e of the greater depth of the deposit are more controlled by their internal f r i c t i o n and have a c h a r a c t e r i s t i c a l l y high angle at or near the angle of repose of the material.  The apron,  however, i s a shallow deposit of boulders tending to be c o n t r o l l e d by the slope of the substratum which i s c h a r a c t e r i s t i c a l l y low i n angle. (Most talus slopes i n the area are b u i l t out onto a r i v e r terrace which bounds the v a l l e y on both sides.  See Map  2.)  There are not enough  boulders available to b u i l d the deposit deep enough to allow i t to develop a slope controlled by the internal f r i c t i o n of the rocks.  The apron  would be sustained as a leading edge of the talus extending farther out onto the surface as the talus deposit grows.  It would be buried at i t s point  of contact with the talus proper at the same rate as i t would be i t s e l f out onto the surface. this mode of development. talus cones (TC5, TC21,  extending  Figure II-4 i l l u s t r a t e s i n cross-section  Observations  (see Photo 11-21) of a number of  TC22, TC25) which have been excavated at the  FIGURE IE-4.  DETAIL  OF  BOULDER  APRON  DEVELOPMENT  69 base to obtain riprap tend to confirm this mode of development. layer of boulders comprising  The  the apron extends beneath the talus deposit  uninterrupted as far back as the excavations have been made It was  noted that vegetation tended to be concentrated i n two  places on the talus slopes i n the region:  near the top of the slope and  along the base i n association with the boulder apron. A l l talus slopes have some form of vegetation cover usually from about 3/4 Photo I I - 4 ) .  of the way  extending  up to the top of the slope (see  The cover varies from a f a i r l y dense growth of Douglas  f i r (dominant) and ponderosa pine to a low mat  of grass, weeds and sage.  The following hypotheses are advanced as an explanation for this distribution: a)  There i s more moisture available for plant growth near the summit of the talus slope due to the concentration of runoff from p r e c i p i t a t i o n and melt along the headwall. The e f f e c t would be greatest at the apex of talus cones where concentration through the c l e f t or chute i n the headwall above occurs. Downslope, the effect i s lost as the moisture percolates quickly through the permeable talus deposit. Also, any p r e c i p i t a t i o n that does f a l l on the lower slopes of the talus i n f i l t r a t e s quickly and completely creating a dearth of vegetation.  b)  If the debris size near the top of the talus slope i s smaller (yet to be tested i n this thesis) then i t would be better able to support the growth of vegetation since s o i l formation i s accelerated and plant growth i s more possible i n f i n e r textured deposits.  c)  Movement of debris on an i n d i v i d u a l basis near the top of the deposit as compared to movement en masse on the lower slopes would create less disturbance to vegetation attempting to establish i t s e l f on the slope. Therefore, conditions favour growth near the top of the slope.  d)  Potential damage to vegetation by debris r o l l i n g over the talus surface probably increases downslope as the debris gains momentum on i t s t r i p down. On a number of occasions rocks were purposely set loose i n the v i c i n i t y of the apex of a number of talus cones. In a l l cases, the rocks set loose either came to rest a f t e r a short r o l l or continued r o l l i n g  70 with acceleration u n t i l reaching the boulder apron at the base. As the boulders accelerated downslope their apparent potential for damage to vegetation increased. Obviously, this e f f e c t would pertain to only large debris capable of sustaining mobility to the bottom of the slope and i t should be noted that a l l rocks set loose were the largest ones a v a i l a b l e . Small rocks are incapable of sustained r o l l over the rough surface of the talus. It i s suggested that a l l four hypotheses  exert influence.  The effect  discussed i n hypothesis (a), however, i s considered to be very important and i n the f i n a l analysis probably of greatest influence.  To further  substantiate hypothesis ( c ) , i t was noted at a point about 1/2 way  up  the slope on TC21 where a s o l i t a r y sage bush, which had been able to establish i t s e l f along the upslope edge of a f l a t boulder, had been destroyed when overrun by mass movement of r e l a t i v e l y f i n e debris. Additional evidence was  observed on TC3.  Vegetation s t r i p s consisting  of saskatoon bushes and juniper trees extending quite far downslope on that cone were observed to coincide with the s t r i p s debris on the slope.  The unvegetated  of coarse  surface between the s t r i p s of  vegetation consisted of small sized fragments  3" d.).  It i s suggested  that movement along the s t r i p s of coarse rock would be on more of an individual basis.  The saskatoon bushes and juniper trees are gnarled  and contorted, i n d i c a t i n g some damage, but the plants are able to sustain growth.  The s t r i p s of f i n e debris, however, remain unvegetated  since movement probably occurs en masse i n the form of miniature landslides. On a l l boulder aprons a concentration of Douglas f i r and ponderosa pine trees can be noted (see Photo 11-23).  This dense growth  does not extend out beyond the boulder apron ending rather abruptly at i t s edges.  71  Photo 11-23. TC27 and TC28. Note concentration of Douglas f i r trees i n association with the boulder aprons of these cones . This concentration i s best explained i n terms of the following: a)  Water which has i n f i l t r a t e d the talus deposit may seep out along the base of the talus i n the proximity of i t s boulder apron. This additional supply of water may be the requirement necessary to sustain a dense vegetation cover i n the semi-arid environment.  b)  Rather than having the meagre r a i n f a l l distributed evenly over the surface, the boulders of the apron by channelling the runoff may tend to concentrate i t e f f e c t i v e l y thereby creating a network of favourable sites for tree growth between the rocks. This concept i s i l l u s t r a t e d i n Photo 11-24.  It i s suggested that the e f f e c t s outlined i n (a) and (b) above account for the d i s t r i b u t i o n noted. An analysis of vegetation type on talus slopes i n the area was made.  The vegetation i s of the dry parkland v a r i e t y , i . e . , short grass  with scattered Douglas f i r and ponderosa pine trees.  The occurrence  of Douglas f i r as the dominant tree species i s a r e f l e c t i o n of i t s pioneer property of shade intolerance. On the talus slopes a t o t a l of what appeared  themselves,  to be 41 v a r i e t i e s of vegetation were observed  including: fir  5 grasses,  27 weeds, 6 shrubs and 3 trees. Next to Douglas  (Pseudosuga menziesii), ponderosa pine (Pinus ponderosa) was the  most common tree species. were observed as well.  Some juniper trees (Juniperus  The most common shrubs were:  scopulorum)  saskatoon  (Amelanchier sp.), sage (Artemisia tridentata) and sumac (Rhus glabra). In general, the south side of the v a l l e y exhibits a more dense vegetation cover but the difference i s not too s i g n i f i c a n t .  Talus slopes, however,  on the south side of the v a l l e y exhibit a d i s t i n c t l y denser growth especially i n the form of Douglas f i r trees. attributed to aspect; sparse vegetation  This difference i s  a southern exposure being drier produces a more  cover.  "Photo 11-24. Closeup of Boulder iiApron on TC28. Note ponderosa pine tree growing between large rocks comprising the apron.  73 CHAPTER III - OBSERVATIONS  A.  Geologic  Control.  A number of controls exerted by the basic geology of the rocks on rate of rock weathering and associated talus development are discussed in Chapter I I . Two basic rock formations predominate, i . e . , the Shoemaker Formation and the Old Tom Formation (Bostock, 1939).  Variations between  the two were noted but i t was found that these variations produced no discernible difference i n the basic form or degree of development of the talus observed.  There i s some v a r i a t i o n i n the d i s t r i b u t i o n of  development, however (see Map 2). In general, the south-facing  slopes exhibit a greater degree of  talus development than the north-facing slopes . The difference could be the r e s u l t of a climate difference between north-facing as compared to south-facing slopes.  Also, the headwall along the north-facing  slopes  i s less continuous, being dissected frequently by streams t r i b u t a r y to the Similkameen River.  At many points the bedrock remains covered under  a layer of g l a c i a l t i l l . These factors i n conjunction with a more dense growth of vegetation have tended to i n h i b i t talus development on the north-facing slopes.  Two exceptions  are worth mentioning.  Some of the largest and most active slopes are included i n the series of eleven talus cones which have developed along the north-facing slopes of K Mountain.  The dissection of the headwall has produced the  development of two large talus cones with chutes which have merged to form a d i s t i n c t "K" shape which gives this peak i t s name.  The rocks  of the Old Tom Formation exposed here exhibit a set of well-developed joints having a dip of 85° and a s t r i k e perpendicular  to the exposed face.  Water  74 i s able to penetrate these j o i n t s , r e s u l t i n g i n rapid disintegration  and substantial talus buildup.  Another zone of concentrated talus  development along the north-facing slope occurs just downstream from the mouth of the Ashnola River.  Here, a series of s i x impressive talus  cones (TG65 - 70) has developed along the rocks of the Shoemaker Formation exposed at this point. The south-facing slope of the v a l l e y exhibits a r e l a t i v e l y continuous succession of talus forms.  The only s i g n i f i c a n t break i n  the succession occurs where Shuttle, Keremeos, and Armstrong Creeks converge to broaden the valley immediately townsite.  to the north of the Keremeos  A succession of talus cones on the south-facing slope from  Manuel Creek to Armstrong Creek occurs as an i s o l a t e d group along the rocks of the Old Tom Formation and the a r g i l l i t e of the Barslow  Formation.  Talus development i s again encountered on the slopes of Pincushion Mountain located to the northwest of the Keremeos townsite.  Here, the  most substantial and most impressive development i n the area can be The development on TC21  observed.  (see Photo 111-15) and TC22 i s spectacular.  In  a l l , nine large and several small talus cones form this group which have developed from the weak rocks of the Shoemaker Formation exposed here. Further examples are TC48 (see Photo 111-21) where a huge funnel has developed i n association with this cone and the large coalesced cone groups at CC51  and CC52.  An anomaly can be observed at CC38 near Old Tom Creek.  At this  point, the headwall remains e s s e n t i a l l y i n t a c t exhibiting only a very limited development of talus at i t s base.  An inspection of Map 3 shows  that the joint planes i n the rock exposed here are p a r a l l e l to the trend of the v a l l e y .  So aligned, they present an aspect unfavourable  75 for weathering and the rocks remain l i t t l e affected by weathering No dissection has occurred along the headwall.  processes.  The debris comprising the  small amount of talus which has developed i s generally large i n size, an indication that dislodgement exposed face.  occurs i n large plates p a r a l l e l to the  The observation confirms the hypothesis that the aspect  of the joints i n the bedrock exposed along the v a l l e y exerts a s i g n i f i c a n t influence on the degree of talus development since the remainder  of the  south-facing slope exhibits impressive talus development. B.  Weathering Mechanisms. It was hypothesized that a variety of weathering processes i s  active i n the region, r e s u l t i n g i n the advanced state of disintegration observable on most headwalls  (see Photo I I I - l ) .  As discussed i n  Chapter II i t i s thought that both physical and chemical processes have  Photo I I I - l . at TC21.  Weathered Rock Headwall  produced a rapid destruction of the headwalls forming the bold and abundant talus forms observable.  A number of observations substantiate  the effectiveness of these processes.  76 Frost shatter and f r o s t bursting are considered to be the dominant weathering processes i n the region.  Climate data were examined to determine  the frequency and magnitude of f r o s t cycles. The data recorded on the maximum-minimum thermometer i n s t a l l e d inside the headwall at TC25 are found i n Table I I .  To serve as a check,  a standard thermometer was placed outside the headwall and i t s record i s included i n the table as well.  Some difference between the temperature  recorded at the times of observation between the maximum-minimum thermometer and the standard thermometer was noted.  This was expected since one  was placed inside a crevise on the headwall and the other outside. I n i t i a l l y , however, i t was found that some difference existed between the standard thermometer and the maximum-minimum thermometer readings under i d e n t i c a l conditions. The reading for the standard thermometer was assumed correct and the maximum-minimum records were adjusted as noted i n Table I I . Coincidentally, a most opportune week was chosen to make the observation since f r o s t cycles occurred on s i x of the seven days of record;  two of these (November 26 and 30) exceeded the e f f e c t i v e range  of 28°F and 34°F as defined by Fraser (1959). to i l l u s t r a t e that  The observations serve  f r o s t cycles do i n fact occur along the headwall.  On the day of the November 25th inspection i t was noted that i c e had formed along the rock face the night before;  t h i s i c e was already i n  the process of melting at eleven o'clock that morning i n d i c a t i n g that freezing and thawing were occurring i n association with the f r o s t cycles. The readings obtained from this record correlate very well with the record for the same i n t e r v a l at the meteorological station (A.E.S., Canada) on the Upper Bench Road at Keremeos.  The comparison i s  Table I I . TEMPERATURE READING ON ROCK HEADWALL BELOW FENCE #1 ON TG25 • NOVEMBER 24 - DECEMBER 1, 1967 .  Date  Air Temp. °F. Stan. Thermometer  Max.* °F. i n Previous 24 Hours  Min.** °F. i n Previous 24 Hours  1967  Time  1.  Nov.24  11:30 am  42.5  42.0  41.5  --  --  2.  Nov.25  11:30 am  33.0  34.5  34.5  42.0  31.4  3.  Nov.26  4:00 pm  26.5  28.0  28.5  37.o***  21.5***  4. Nov. 27  4:30 pm  29 .0  31.0  29.5  32.0  25.0  5.  Nov.28  4:30 pm  29.5  29.0  29.5  33.0  28.0  6. Nov.29  4:30 pm  33.5  33.0  33.0  34.0  29.0  7 . Nov. 30  4:20 pm  32.0  33.5  32.5  35.5  26.5  8. Dec. 1  4:10 pm  32.0  32.5  31.5  35.5  28.5  * ** ***  Maximum*  Minimum**  A l l maximum readingsi adjusted -1 ,5°F. obtained as the mean discrepancy with standard thermometer. A l l minimum readings adjusted -.5°F. obtained as mean discrepancy with standard thermometer. Maximum and minimum over a 28.5 hour period.  78 i l l u s t r a t e d i n Figure I I I - l .  In general, the readings at Keremeos tend  to exhibit a greater range.  The difference i s not great, however, being  i n the order of magnitude that could be a t t r i b u t e d to the difference i n temperature that would be expected within the shelter of the rock at TC25 as compared to the open a i r temperature recorded at Keremeos. Although the sample for purposes of comparison i s small i t does indicate that temperatures recorded at Upper Bench Road station i n Keremeos are representative of those experienced v i c i n i t y of Keremeos.  along the headwall i n the immediate  (TC25 i s located approximately four miles upstream  from the Upper Bench Road station) . The frequency of f r o s t cycles (see Chapter I . B . I . ) was to obtain the monthly totals for the years 1930 r e s u l t s appear i n Table I I I .  through 1971  Each monthly t o t a l was  tallied  and  the  subdivided into  categories as follows: 1.  FC = a f r o s t cycle i n the range 29°-33°F. i n c l u s i v e .  2.  FD = a frost cycle i n the range outside the l i m i t s established in (1) above but within the range 26°-34°F. i n c l u s i v e i n accordance with the e f f e c t i v e range of 28°-34°F. as defined by Fraser (1959).  3.  BD = a f r o s t cycle of the magnitude 25°-35°F. i n c l u s i v e or greater as defined by Boyd (see Fraser 1959) as the e f f e c t i v e range.  What i s implied by both Fraser and Boyd i s that the outside a i r temperature w i l l have to drop s i g n i f i c a n t l y below 32°F . before water trapped inside rocks w i l l freeze and, correspondingly, w i l l have to r i s e s i g n i f i c a n t l y above 32°F. i n order to melt any ice which has formed.  In essence, they  define the l i m i t s required to i n i t i a t e i c e wedging r e s u l t i n g i n eventual shatter i n rocks affected. the c y c l e .  However, much depends on the duration of  For short cycles even greater ranges would be required.  FIGURE HE" I.  TEMPERATURE  BETWEEN A.E.S.  STATION  STATION  AT  AT  CORRELATION TC 25  KEREMEOS  AND  Table I I I . Year 19 30-31 31-32 32-33 33-34 34-35 35-36 36-37 37-38 38-39 39-40 40-41 41-42 42-43 43-44 44-45 45-46 46-47 47-48 48-49 49-50 50-51 51-52 52-53 53-54 54-55 55-56 56-57 57-58 58-59  FROST CYCLES AT KEREMEOS.  October FC FD BD  1 4 1 2 7 2 0 1 3 1 3 4 3 0 2 4 1 5 6 4 0 0 0 3 3 0 2 2  0 0 1 0 2 0 0 0 0 0 0 0 2 0 3 6 0 4 0 0 2 0 0 2 1 0 0 0  0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 3 0 0 1 0 0 0 0  November FC FD BD  December FC FD BD  6 7 5 9 6 4 5 2 8 7 4 5 7 4 7 6 10 13 5 6 5 4 4 5 2 6 6 2  6 5 8 5 7 6 5 4 6 3 7 5 5 6 2 3 8 2 7 7 3 4 14 4 1 10 9 7  2 1 2 0 4 6 3 8 0 3 1 6 3 4 5 3 6 0 2 4 4 4 2 1 4 3 9 5  4 1 1 0 7 12 2 4 3 3 3 2 2 4 4 9 2 3 0 7 7 5 2 0 2 6 2 1  7 3 2 7 2 3 2 2 2 2 5 5 3 2 1 3 6 3 8 2 3 5 5 10 0 3 8 5  2 4 4 2 1 7 2 3 1 2 2 2 4 2 2 1 5 4 5 2 1 5 3 4 5 1 1 1  January FC FD BD  9 2 7 7 7 7 0 6 9 5 5 6 1 4 6 7 4 9 0 0 9 5 5 4 5 7 3 8 0  3 10 4 5 1 8 0 3 12 2 3 1 0 4 6 6 2 2 0 0 4 1 3 2 5 3 1 3 5  2 1 4 2 1 4 0 5 3 4 1 0 1 3 2 5 4 9 3 2 4 2 5 1 4 4 1 1 3  Februar y FC FD BD  8 1 3 1 8 0 1 6 5 12 0 9 5 4 8 6 7 5 2 3 3 7 7 5 6 1 2 6 4  4 1 6 10 4 1 1 5 4 1 3 3 7 3 5 1 2 3 0 2 6 8 8 0 6 2 1 1 8  10 7 2 8 7 2 10 3 9 3 10 6 3 13 3 8 4 4 7 5 12 4 4 3 9 10 9 1 7  March FC FD  BD  April FC FD  BD  1 3 2 1 3 8 0 4 7 3 2 6 3 1 3 2 0 6 1 5 2 7 3 3 3 5 4 4 3  3 7 5 0 9 3 2 2 2 1 1 2 12 9 3 1 5 6 4 2 4 4 1 10 11 4 3 4 0  3 0 2 0 3 2 2 1 2 0 0 0 1 0 6 2 1 4 0 2 1 0 1 5 12 1 0 0 2  1 0 0 0 1 1 0 1 0 0 0 0 0 0 1 0 0 2 0 2 1 0 1 3 1 1 0 0 2  0 0 0 0 3 2 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 1 0 0 0 0 0  5 3 6 4 7 6 5 10 7 1 3 9 3 11 9 5 4 7 11 5 3 9 5 4 6 7 6 5 4  Tot. Tot. Tot. FD BD FC 25 19 34 26 41 35 20 33 30 32 19 38 24 34 39 31 29 44 33 28 34 29 26 36 41 22 27 36 21  9 23 16 21 16 26 10 18 33 8 13 16 21 16 21 18 16 25 8 19 19 25 24 15 28 16 12 25 28  15 21 16 15 22 19 31 14 21 13 17 13 20 31 14 20 23 27 21 19 30 21 20 20 29 25 20 9 12  Tot. f o r Season  49 63 76 62 79 80 61 65 84 53 49 67 65 81 74 69 68 96 62 66 83 75 70 71 98 63 59 70 61 (over)  Table I I I . (continued) Year 19  October FC FD BD 1 1 3 1 2 2 2 0 0 0 3 3  0 0 1 0 4 1 0 0 0 0 1 4  Total 82  34  59-60 60-61 61-62 62-63 63-64 64-65 65-66 66-67 67-68 68-69 69-70 70-71  Mean Mean Total  2.05 .65  3.08  November FC FD BD  December FC FD BD  January FC FD BD  March FC FD  BD  April FC FD  4 4 4 0 2 11 3 2 0 5 4 4  1 2 1 1 2 1 2 2 2 0 1 3  7 225 141 151 221 144 118 194 131 119 217 175 231 234 135 163  71  0 0 1 0 0 0 0 0 0 0 0 0  2 10 4 3 4 4 3 5 5 7 4 4  6 5 7 2 5 4 3 5 4 0 3 2  4 5 6 3 2 2 1 1 2 4 1 2  5 5 3 0 5 4 7 5 5 6 9 6  8 3 5 4 8 1 1 5 4 1 2 3  5 3 4 4 2 1 1 4 3 6 0 6  5 3 1 5 4 4 3 5 6 2 5 4  1 4 4 3 6 1 1 4 1 1 1 4  February FC FD BD  0 5 3 2 6 2 4 6 4 1 2 2  7 4 4 7 5 10 11 9 6 4 8 7  5 4 3 5 10 12 6 2 3 8 8 4  4 2 1 5 9 1 3 1 10 7 2 3  4 5 4 9 5 6 7 9 4 7 1 3  3 1 4 2 4 4 1 6 1 2 4 8  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . 0 1 0 0 0 0 0 1 0 19  .18 5.62 3.52 3.78 5.52 3.60 2.95 4.85 3.28 2.98 5.42 4.38 5.78 5.85 3.38 4.08 1.78 .48  12.92  12.07  11.11  15.58  13.31  BD  2.48  Tot. Tot;. Tot. FD BD FC  Tot.for Season  25 30 20 26 27 31 35 35 28 26 31 30  23 17 24 16 37 23 12 22 13 12 19 26  17 19 19 14 21 17 12 14 20 23 9 17  65 66 63 56 85 71 59 71 61 61 59 73  9 1230  791  780  2801  19.50  70.03  .22 30.75 19.78  82 Cycles extending over days or weeks may require a f l u c t u a t i o n of only one or two degrees above and below 32°F. i n order to be e f f e c t i v e . too, depends on the depth of penetration of the water.  Much,  A much greater  range of longer duration would be required to freeze and thaw water locked deep i n s i d e the rock.  Water near the surface would be affected by cycles  of a much smaller range and shorter duration.  Ultimately, a l l f r o s t  cycles are important since " f r o s t - r i v i n g " occurs when water on the surface of an exposed rock surface freezes and thaws producing dislodgement of previously loosened fragments r e s u l t i n g i n r o c k f a l l a c t i v i t y . f l u c t u a t i o n i n temperature  A  one degree above and below 32°F. i s usually  s u f f i c i e n t for this mechanism to operate. During the f o r t y year record at Keremeos, a t o t a l of 2801 cycles has occured for an average of 70.0 cycles per year. t o t a l of 1571  frost  Of these, a  or an average of 39.3 cycles per year were greater than or  equal to the e f f e c t i v e range of 28°-34°F. as defined by Fraser.  A total  of 780 or an average of 19.5 cycles per year equalled or exceeded the e f f e c t i v e range of 25°-35°F . as established by Boyd. the assumption  The r e s u l t s support  that f r o s t shatter i s an important mechanism of disintegra-  t i o n of the rocks exposed i n the region.  Figure I I I - 2 i l l u s t r a t e s that  the cycles occur with high frequency throughout the l a t e f a l l , winter, and early spring seasons.  As previously noted, p r e c i p i t a t i o n i s available  i n a l l months of the f r o s t season.  Disintegration by frost shatter  could be sustained throughout the f r o s t season but concentrated a c t i v i t y may  occur during the late winter and early spring i n t e r v a l s .  February  and March are the months of highest frequency of freeze-thaw cycles. During these months more water from snow melt i s available which would render freeze-thaw cycles at this time p a r t i c u l a r l y e f f e c t i v e .  Concentrated  83  FIGURE 3K-2.  MEAN MONTHLY FREQUENCY OF FROST CYCLES AT KEREMEOS  FROST  SEASON  84 r o c k f a l l a c t i v i t y during the spring season, according to the observations of l o c a l residents of Keremeos, tends to confirm this  assumption.  Frost bursting i s probably an important mechanism as w e l l . Freeze-thaw cycles are not required to i n i t i a t e  this mechanism;  rather,  low freezing temperatures of a long duration (eg. several days or weeks) are required to freeze the water confined i n porous rock. records for Keremeos indicate that temperatures  A study of the  do drop to very low  levels (on occasion below 0°F.) and at times for i n t e r v a l s of a week and longer.  At these times rocks which are saturated with water would  be very susceptible to frost bursting. Observations suggest that chemical action i s an important weathering mechanism i n the region.  At many points along the unevenly dissected  headwall and especially i n the c l e f t s where chutes have formed the rock i s found to be i n an advanced state of decomposition.  The rock appears  to be e s s e n t i a l l y 'rotten' and pieces could be broken off e a s i l y with the hands.  Reddish-brown s t a i n i s r e a d i l y v i s i b l e along the planes of  separation i n d i c a t i n g oxidation.  The crumbly texture i s i n d i c a t i v e of  a volume increase which can be attributed to the process of hydration. This i s most prevalent i n the c l e f t s where water from p r e c i p i t a t i o n and melt would be most concentrated to react chemically with the rock i n association with the oxygen and carbon dioxide of the a i r . The effects of solution are considered important as w e l l . evidence for this i s i l l u s t r a t e d i n Photo III-2.  A zone of mineral  p r e c i p i t a t i o n where a spring emerges on the headwall at TC25 observed.  Some  was  I t was concluded that the mineral here precipitated i s derived  by solution along the j o i n t s i n the headwall above.  Of a l l the rock  types exposed i n the v a l l e y , limestone would probably be most susceptible  85  Photo III-2. Observed Solution on Headwall at TC25. The photo shows the course of a small stream which emerges as an intermittent spring further up along the headwall. The dark coloured band i s a zone of p r e c i p i t a t i o n of mineral probably derived by s o l u t i o n from the headwall above. No water was flowing at the time of photography. Pack sack gives scale.  to this process. Various degrees of chemical weathering (Melton 1965; 1965) have been defined.  O l l i e r ' s progression i s given i n Table IV below.  Table IV. DEGREES OF WEATHERING. Degree No,  Oilier  (after O i l i e r , 1965)  Description  1  Fresh;  2  E a s i l y broken with hammer.  3  Rock can be broken by a kick with the boots but not by hand.  hammer tends to bounce o f f .  Can be broken i n hands but does not disintegrate in water. Soft clay with g r i t ; i n water.  disintegrates i f immersed  Examples of rocks considered to be representative of O l l i e r ' s degrees 1, 2 and 4 are i l l u s t r a t e d i n Photos III-3, III-4 and III-5 (a and b)  87 respectively. talus  No r o c k s  slopes  or  headwalls  Finally, some  the  disintegration  illustrates  having  the  of  through  headwalls a  force  However,  in  the  i n  trees  sway  initiating  in  of  area  Douglas these  Whether  to  disintegrate  is  certainly  in  wind,  mechanism.  were  observed  on  the  be  may  wedging.  Photo  Douglas  had  fir  trees  produce  on  III-6 one  of  the  Root rock  some  fir)  trees  growing  action  trees  headwalls  of  might  on the  produce  weathering. or  not  rocks  great  association must  root  Most  wedging  region.  and, the  the  The  the  Possible  physical  force  disintegrated,  stunted  some  sufficient the  of  of  Mechanism.  (usually roots  along  action  III-6.  Wedging  them.  trees  the  establishment  faces  5  degree  investigated.  growth  Photo  O l l i e r ' s  the as  growth yet  enough  with  the  considered  to  has  an  roots  not  can  been  dislodge  prying as  of  rocks  action  important  exert  demonstrated. already  produced rockfall  as  G.  Rockfall and Primary Deposition. Personal observations and accounts by l o c a l residents substantiate  the occurrence of r o c k f a l l a c t i v i t y i n the region. report a c t i v i t y frequently.  Local residents  The slope at TC14 and TC15 on K Mountain  immediately to the south of the Keremeos townsite i s referred to most often as the s i t e of these observations. almost to r i v e r l e v e l have been observed.  Substantial f a l l s reaching Residents agree that r o c k f a l l  a c t i v i t y i s concentrated during the spring season.  In the spring of 1966  a section of the wooden p i p e l i n e at the base of TC25 was torn out by debris t r a v e l l i n g down this slope. A number of observations of r o c k f a l l events were made: 1.  May 27, 1967. A rock about 5 inches i n diameter f e l l from the l e f t headwall during inspection of fence #1 on TC25.  2.  May 30, 1967. While working on fence #1 at TC25 much debris was seen and heard f a l l i n g from the headwalls. Rain was f a l l i n g at the time.  3.  May 31, 1967. Rain which started the previous day continued f a l l i n g throughout this day of observation. Much debris was observed f a l l i n g from the r i g h t headwall while working on fence #2 at TC49.  4.  June 15, 1967. Rocks could be heard tumbling down headwall while climbing up TC49 to inspect fence #2. Rain was recorded the day before.  5.  Recently damaged Douglas f i r trees attributed to r o c k f a l l a c t i v i t y were observed on TG25 (June 1968) and TC67 (September 1967), eg. see Photo III-7.  6.  July 26, 1971. A large ponderosa pine tree located about 50 feet from the headwall about one-half way up TC26 was observed to have been damaged by recent r o c k f a l l a c t i v i t y . Five large branches had been broken from the tree.  In retrospect i t should be noted that very l i t t l e r o c k f a l l a c t i v i t y observed i n proportion to the time spent i n the f i e l d .  was  The record above,  however, i l l u s t r a t e s the importance of r a i n f a l l as a release mechanism  89  Photo III-7 . Broken Douglas F i r at Apex of TC67 (Sept. 21/67). The damage was attributed to rockf a l l a c t i v i t y . Note loose rocks at base of tree. Hardhat gives scale. in the region.  Rain storms were recorded on only a few occasions during  the investigation;  observed r o c k f a l l a c t i v i t y occurred almost invariably  i n association with these storms. Debris captured i n the two fences constructed provided some measure of the rate of r o c k f a l l a c t i v i t y i n the region and substantiated the hypothesis that vegetation could be used as an e f f e c t i v e index of stability.  At the commencement of each sample, the fences were prepared  by c l e a r i n g out any debris i n or on the chicken wire barricade. To keep the wire mesh f l u s h with the surface, several large rocks were placed along the upslope edge of the fence.  These rocks were sprayed l i b e r a l l y  90 with yellow paint i n order to be able to i d e n t i f y them i f they became incorporated i n the sample.  Any that were, were excluded.  In this  manner both fences were set up for the f i r s t sample beginning May Fence #1 was  subsequently inspected on September 5, 1967.  31,  1967.  Much  evidence of r o c k f a l l a c t i v i t y and/or debris transport through the chute on TC25 was  observed.  near the headwall  The fence was  considerably damaged on both sides  i n d i c a t i n g the effects of r o c k f a l l a c t i v i t y .  The  i n i t i a l assumption that the right side of the chute seemed most active was  confirmed by the fact that most damage occurred on this side where  about 35 feet of fence had been l e v e l l e d .  Two of the steel pipe posts  had been considerably bent downslope and four of the 2" x 2" wooden stakes had been ripped out (see Photo III-8).  It was  t h i s damage had been caused by a substantial avalanche the adjoining headwall on this side. during the i n t e r v a l May  concluded that of debris from  In a l l , 139 rocks were captured  31 through September 5, 1967.  No estimate can  be made of the sample l o s t where the fence had been l e v e l l e d . rocks t r a v e l l i n g at high speeds l e f t (see Photo III-9).  Also, some  only a hole i n the fence as evidence  In these cases the diameter of the hole was  taken as  representative of the s i z e of the rock and this was recorded as the measurement of the intermediate axis .  A number of very large rocks were  captured as i l l u s t r a t e d i n Photo 111-10.  Obviously, these rocks were  not t r a v e l l i n g at very high speeds when coming into contact with the fence. 3  Total volume captured was of  calculated at 213,486 i n . by taking the cube  the intermediate axis as representative of the volume of the rocks  (this provides an overestimate of the volume; approximately  see Gardner, 1970) or  123 cubic feet of debris.  On September 6, 1967  fence #2 was  inspected.  More rocks were  91  Photo III-8. Fence #1 On TC25. Observation Sept. 5/67 showing damage to fence attributed to r o c k f a l l . Note steel pipe post bent downslope.  Photo III-9. Fence #1 on TC25. Note hole about 12" d. i n fence observed Sept. 5/67 indicating rock t r a v e l l i n g at high speed.  Photo 111-10. Fence #1 on TC25. Note large boulder captured by fence,  92 captured but these were generally small i n s i z e .  As expected the larger  portion of the sample and the largest rocks were captured by that section of the fence extending across the f l u v i a l channel near the apex of TC49 (see Photo 11-14, p.54).  I t was concluded that the existence of this  f l u v i a l channel accounted largely for the apparent s t a b i l i t y of the rest of TC49.  Rockfall debris would be e f f e c t i v e l y concentrated by this channel  allowing the remainder of the slope to s t a b i l i z e i t s e l f .  The channel  i s V-shaped i n p r o f i l e , some 20 feet deep and 40 feet wide and extends about one-half way down the cone.  There i s not a substantial buildup  of debris at the terminous of this channel, however, i n d i c a t i n g that r o c k f a l l a c t i v i t y must be limited on this slope.  Photo I I I - l l shows  large debris captured by fence #2 at the bottom of the f l u v i a l channel. The fence broke when an attempt was made to clear these boulders out after they were measured.  In a l l , 275 rocks were captured.  The combined  3 volume of these rocks was calculated at 77,356 i n . or approximately  93 45 cubic feet of debris.  This volume was substantially less than that  captured for the same period at fence #1 and supports the hypothesis that TC49 i s more stable than TG25. After sampling, both fences were cleared of a l l debris and the damage done to them repaired.  Both were again prepared f o r sampling;  this time for the period extending through the frost season. Fence #2 was again inspected on June 12, 1968 after nine months had elapsed.  Unfortunately, the sample obtained i n fence #2 for this  .second interval cannot be taken as representative. A much larger sample was obtained -- 589 as compared to 275 rocks i n the previous i n t e r v a l -but a major portion of the sample was l o s t .  The section of fence  extending across the f l u v i a l channel had become completely l e v e l l e d by debris moving down the channel.  Since a major portion of the previous  sample -- and e s p e c i a l l y a l l the larger boulders -- had been captured by the fence i n the channel, i t i s assumed that the bulk of the volume was l o s t i n the second attempt.  Total volume i n the absence of any large  3 boulders was only 20,771 i n . or approximately 12 cubic feet of debris, considerably less than the f i r s t sample. '. Some estimate of the volume l o s t can be made.  In the f i r s t sample the volume of debris captured by  that section of fence through the channel alone represented approximately 507o  of the t o t a l sample.  If this same relationship i s applied to the  second sample, then an adjusted total volume can be calculated: adjusted volume (approximate) = volume captured 0.5 = 41,000 i n .  3  = 24 cubic feet On June 13, 1968, fence #1 was inspected and sampled. inspection without sampling had been made on November 24, 1967.  A previous At this  94 time, a number of large holes were patched up and an estimate of the size of the intermediate axis of the rocks making the holes was recorded and included i n the June 13, 1968 sample.  On June 13, the fence was  found to be e s s e n t i a l l y intact although about 20 feet of fence  again  on the more active r i g h t side of the chute -- had been torn out by rockfall activity.  It was not f e l t that a major portion of the sample  had been l o s t , however.  Measurement was completed as i n the other three  samples and a t o t a l of 1492 rocks was recorded.  In the interval 3  September 5, 1967 to June 13, 1968 a t o t a l volume, therefore, of 907,283 i n . or approximately 519 cubic feet of debris had been captured.  The r e s u l t s  of this sample tend to confirm the hypothesis that r o c k f a l l a c t i v i t y i s concentrated during the f r o s t season since the volume i s more than three times as great as the previous sample.  Compared to the adjusted volume  calculated for the sample at fence #2, the second sample from fence #1 supports the i n i t i a l assumption  that TC25 i s more active than TC49 .  A frequency plot of the sample obtained from fence #1 (June 13, 1968) i s shown i n Figure III-3 (plots of the other samples exhibit a similar distribution).  The plot i l l u s t r a t e s that the d i s t r i b u t i o n i n size of  intermediate axes would probably have a mode somewhere below 3 inches. Unfortunately, the mesh size of the wire used i n the fences was 2 inches i n diameter.  Rocks having an intermediate axis of 2 inches or less  could e a s i l y escape through the mesh.  In view of this i t i s f e l t that  no r e l i a b l e way of estimating the mode can be employed.  Chicken wire of  a heavier gauge and smaller mesh size i s available but was not used because of  the cost factor.  In retrospect, much better r e s u l t s would probably  have been obtained using the more expensive wire.  More of the smaller-  sized debris would have been captured and the heavier gauge would have  95  FIGURE HT-3.  SEDIMENT (AT TC 25  SAMPLE FROM FENCE SEPT. / 67 - JUNE/68)  NO. I  400-i 380 H 360-j 340320300280260 240-4  >O  220-j  200-| z>  UJ  o  £ u.  180  H  160140120100806040200  T—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i  i I I i—r=i—| I I l—r  I 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 INTERMEDIATE AXIS IN INCHES  96 provided a more sturdy fence. The observations confirm the r e l i a b i l i t y of using vegetation as an indicator of s t a b i l i t y .  This index was  location of the two fences constructed. vegetation cover on TC49 was stable slope.  interpreted as an i n d i c a t i o n of a more  fence #2,  sampling were.identical  the  The more dense and complete  Since the fences were approximately  (fence#l, 188 feet;  185 f e e t ) ;  the same i n length  and since the i n t e r v a l s of  the results substantiate the assumption.  volume captured by fence #1 was intervals.  used i n determining  The  s i g n i f i c a n t l y greater for both sample  Since the results obtained represent only a crude estimate of  the actual r o c k f a l l which occurred and, r e a l i s t i c a l l y , represent only that year for which a sample was  taken, they cannot be taken as conclusive.  However, i n view of the fact that fence #1 has since been a l l but completely  l e v e l l e d by r o c k f a l l a c t i v i t y while fence #2 remains e s s e n t i a l l y  i n t a c t , i t i s f e l t that the index can be used with some confidence. D.  Mass Movement Mechanisms. Movement was  detected on l i n e s painted on TC22, TC25 and CG52  but i t i s f e l t that the results must be interpreted very cautiously (see Chapter II.D.). Two  lines each 50 feet i n length were painted cross-slope on  TC22 on December 3, 1966. May  12, 1967.  These l i n e s were subsequently inspected on  Only the lower l i n e could be found.  Being only 50 feet  in length, the p o s s i b i l i t y of the upper l i n e being wiped out by s l i d i n g debris i s l i k e l y .  TC22 appears to be a r e l a t i v e l y active talus cone  and evidence of slides of the magnitude required to erase the l i n e are v i s i b l e on this cone.  The lower l i n e exhibited only minor disturbance  over the f i v e month i n t e r v a l .  A few rocks had moved on an i n d i v i d u a l  97 basis but the l i n e had remained e s s e n t i a l l y of d i f f e r e n t i a l movement had occurred. on TC22 was again inspected.  intact.  No bending  On June 11, 1968  indicative  the lower l i n e  On this occasion, some thirteen months  after the i n i t i a l inspection, the l i n e exhibited widespread disturbance. The l i n e transects four d i s t i n c t s t r i p s of fine and coarse debris on the slope, i . e . , f i n e , coarse, f i n e , and coarse from r i g h t to l e f t across the slope.  I t was  noted that more disturbance had occurred on the  coarse s t r i p s as compared to the f i n e s t r i p s .  A l l rocks along the coarse  s t r i p s had at least moved out of position as i l l u s t r a t e d i n Figure III-4. A number of individual  rocks had been displaced and had moved downslope  as far as 113 inches from the l i n e . s t r i p s did not exhibit  The l i n e painted across the fine  as much disturbance although a number of  rocks had moved varying distances downslope. of the displacement  of rocks  individual  Table V below i s a summary  observed.  Table V.  Displacement of Rocks on Line Painted on TC22.  T, . Position  Number of Rocks ~. . , Displaced  ^ f ^ f °^ Displacement n  1.  Fine s t r i p #1  12  1" to 29"  2.  Coarse s t r i p #1  15  2" to 14"  3.  Fine s t r i p #2  33  3"  4.  Coarse s t r i p #2  14  2" to 20"  D i f f e r e n t i a l movement had occurred as w e l l .  to  113"  The l i n e on both coarse  s t r i p s had become appreciably bent downslope as i l l u s t r a t e d i n Figure III-5, On May  16, 1967  two lines each 100 feet i n length were painted  above and below fence #1 on the chute leading up from the apex of TC25. Both lines were located on the right side of the chute which appeared to be the most a c t i v e part.  These lines were inspected 3% months l a t e r  98  F I G U R E ILT-4. PAINTED  LINE ON TC 22  ALONG  COARSE  ORIGINAL  :AS  F I G U R E HI-5. PAINTED  FINE STRIP I  COARSE  LINE  STRIP I  ON  FINE  STRIP 2  LINE  OBSERVED  TC 22  STRIP  JUNE  (AS OBSERVED  COARSE  11/68  JUNE/68)  STRIP 2  99 on September 5, 1967.  The lower l i n e had remained e s s e n t i a l l y i n t a c t ,  although part of the l i n e had become bent about one foot downslope. The upper l i n e was e s s e n t i a l l y obliterated during the same i n t e r v a l (see Photos 111-12 and 111-13).  The i n s t a l l a t i o n of fence #1 no doubt  contributed to the difference i n the degree of disturbance between the two lines since debris t r a v e l l i n g through the chute was being captured by fence #1 during this i n t e r v a l . In the l a t t e r part of August 1967, a l i n e 750 feet i n length was painted on CC52 (see Map 2 and Photo II-4).  To maintain an accurate  l e v e l , the position of the l i n e was established using a Keuffel and Esser telescopic alidade and stadia rod.  The l i n e was f i x e d to a suitable  bench mark located at the base of a huge Douglas f i r tree on the l e f t side of the slope of CC52. The l i n e was resurveyed on June .12, 1968. Readings along the l i n e were compared to the bench mark reading of 4.76 feet by sighting onto the rod at approximate nine foot intervals along the l i n e . A total of 89 readings made along the 750 foot l i n e indicated a d e f i n i t e net downslope movement of the l i n e .  The difference i n elevation was  converted from feet to inches and these readings i n turn were converted to net downslope movement according to the following r e l a t i o n s h i p : Net downslope movement i n inches = v e r t i c a l difference i n inches .57358 where:  .57358 = s i n . of 35°, taken as the average slope of talus along the l i n e .  Net downslope movement ranged from a minimum of .9 inches to a maximum of 15.6 inches with a mean displacement of 6.14 inches along the l i n e . One negative reading (-1.3") was obtained.  This anomaly i s interpreted  as an error i n the survey rather than a net upslope movement.  Again, as  with the observations of the l i n e painted on TC22 greatest movement  Photo III-12. Painted Line Above Fence #1 at TC25. As observed May 16, 1967.  Photo 111-13. Painted Line Above Fence #1 at TC25. As observed Sept. 5/67. Note almost complete destruction of l i n e . Note also distance large boulder has moved as indicated by arrows .  101 occurred along the coarse s t r i p s of debris . Assuming this d i f f e r e n t i a l movement i s exclusive of the effects of the disturbance created by walking over the talus surface when painting the l i n e then some difference in the mechanisms of mass movement a f f e c t i n g coarse debris s t r i p s as compared to fine debris s t r i p s i s implied i n the observations. a v a r i a t i o n i n mode of deposition, degree of compaction, c h a r a c t e r i s t i c s exerts some influence; at this time.  Perhaps  or fragment  but, no inference can be made  An analysis of fragment parameters as related to coarse  and f i n e s t r i p s of debris i s included i n Chapter IV. Observations of mass movement mechanisms i n the region are now presented.  Water i n the form of melt or p r e c i p i t a t i o n i s assumed  important as a movement i n i t i a t i n g mechanism.  In this case the water  serves as a lubricant along the points of contact i n the deposit. If the deposit i s resting at or near i t s c r i t i c a l angle and becomes saturated with water, the i n t e r n a l f r i c t i o n of the mass may be s u f f i c i e n t l y reduced to i n i t i a t e spontaneous mass movement i n the deposit.  Such f a i l u r e was  never a c t u a l l y observed during the investigation but i n d i r e c t l y i t was substantiated on two occasions.  On May 30, 1967 TC25 was climbed i n order  to inspect the fence which had been established on that cone.  The normal  route, which follows a s t r i p of coarse debris along the right margin of the cone, was used.  As always, the rocks remained f a i r l y stable under  foot providing for a good access route.  While working on the fence above,  a f a i r l y heavy r a i n storm was experienced.  Following the same route down  i t was noted that the coarse s t r i p of rocks had become extremely mobile. Every rock stepped on, moved, and i n some instances a whole section of the slope gave way when stepped on.  Obviously, the r a i n had been i n -  strumental i n reducing the internal f r i c t i o n of the deposit.  A similar  102  s i t u a t i o n was recorded on the same slope on November 24, 1967 when the rocks which had become wetted by melting snow were observed again to be very unstable underfoot. 3 Mrs. Russel  reports observing some very substantial debris  slides on TG3 above her place of residence on the Upper Bench Road. She notes that debris moves down as a mixture of rock and snow during the winter season when snow covers the talus slope.  Otherwise, releases  have been observed as rocks r o l l i n g and bouncing over the surface at a high v e l o c i t y creating a cloud of dust en route to the base of the talus.  She further notes that the debris avalanches occur usually i n  association with a f a l l of r a i n or wet snow and none have been observed occurring during the summer season. Wind has been considered a possible mass movement-initiating mechanism.  On a number of occasions winds gusting at very substantial  v e l o c i t i e s were experienced while working on the talus slopes i n the region.  Most intense winds occurred late i n the afternoon on p a r t i c u l a r l y  hot days during the summer i n the form of convectional updrafts.  These  updrafts become concentrated into intense gusts near the apex of the cones e s p e c i a l l y where chutes or funnels have developed i n the headwall. No actual disturbance of debris on the talus surface was ever observed, however. Creep may be an important mass movement mechanism and may have been detected by the l i n e s painted on TC22, TC25 and CC52.  Freeze-thaw  cycles might be an important c r e e p - i n i t i a t i n g mechanism i n view of the high frequency of cycles i n t h i s area.  In order to be e f f e c t i v e , however,  the debris must have a high water content. 3  Recorder at A.E.S. Met.  The dry Keremeos climate,  Station at Keremeos.  103  therefore, may  tend to l i m i t the effectiveness of this mechanism.  Dry  rock creep, the r e s u l t of thermal expansion and contraction as postulated by Scheidegger  (1961), may be important.  Diurnal temperature ranges  during the summer can be high providing i d e a l conditions for the operation of this mechanism. As mentioned, debris slides composed of a mixture of snow and rock have been observed on TC3.  Snow avalanche, therefore, may  be  another  important mass movement mechanism but would be l i m i t e d by the characteri s t i c a l l y l i g h t snows recorded i n the v a l l e y . Evidence of flowing water acting as a transporting mechanism of debris was observed on TC49 and a number of the talus slopes along K Mountain.  TC49 has already been i d e n t i f i e d as a t r a n s i t i o n a l talus  form which w i l l probably eventually become an a l l u v i a l cone.  Well  developed catchment basins i n the chutes and funnels above the slopes along K Mountain e f f e c t i v e l y channel the flow of water onto the slopes and evidence of wash i s apparent.  The c h a r a c t e r i s t i c a l l y dry climate,  however, l i m i t s the effectiveness of this mechanism i n the region.  A  number of a l l u v i a l cones were observed i n the area but these forms are considered to be d i s t i n c t from talus (see Photo 111-14). Disturbance of the talus surface by animals and people i n the region must be considered an important movement-initiating mechanism. A sizeable population of goats and deer which inhabit the region were observed frequently on the slopes. t r a i l s on them.  Many of the talus slopes have game  Hunters, prospectors and mountain climbers frequent the  talus slopes as w e l l .  The very mobile s t r i p s of fine debris found on  most slopes provide ideal downslope routes for climbers. Natural basal sapping of talus deposits does not occur i n this  104  Photo 111-14. A l l u v i a l Cone Near TC43. Note the water-scarred gentler-sloped surface which i d e n t i f i e s this feature as an a l l u v i a l cone. The dense vegetation cover indicates a greater a v a i l a b i l i t y of water. Arrow shows recent mudflow scar near center of photo. region  since most of the talus i s perched high above r i v e r l e v e l on a  terrace which bounds the v a l l e y on both sides along this stretch.  Basal  sapping has occurred on TC5, TC21, TC22, and TC25 where excavations to obtain riprap have been made.  On these slopes, the talus  immediately  above the excavations has f a i l e d along s l i p planes extending several hundred feet upslope.  The mass movement of the debris has resulted i n  the formation of slopes much steeper than those on the adjacent undisturbed talus . E.  Morphometry and Morphology of Talus Development Near Keremeos, B.C. 1.  Morphometry. Indications of s t a b i l i t y on the talus slopes investigated were  sought.  A few of the slopes had well established game t r a i l s on them,  eg. one was observed on TC25 just below the weed and grass cover found near the apex of that cone;  a game t r a i l observed on TC2 can be seen  105 in Photo II-9;  about midway on the slope of TC22 another of these t r a i l s  indicates a c e r t a i n degree of s t a b i l i t y since such features could not develop on active slopes. The chutes and funnels which complement more than one-half  of  the talus slopes i n the region provide another i n d i c a t i o n . In themselves, the chutes and funnels are an expression of the v a r i a b l e nature of the headwall e x h i b i t i n g alternate zones of weak and r e s i s t a n t rock.  The  degree to which these features have evolved, however, indicates a late stage of development (see Chapter I.B.4.).  A l l chutes and  funnels  observed i n the region have reached the f i n a l stage of development. This observation i s interpreted as an i n d i c a t i o n of impending s t a b i l i t y and as such supports the s t a b i l i t y hypothesis  advanced i n this thesis.  Calculations of respective rates of accumulation before and after the deposition of Mazama Ash at CC44 support  the 'diminishing sediment  y i e l d concept' advanced i n Chapter II to explain the impending s t a b i l i t y of talus slopes i n the region.  A number of assumptions are made.  It i s assumed that a l l of the talus debris at the s i t e has accumulated since the l a s t r e t r e a t of continental i c e from the region. According years B.P.)  to the hypothesis  advanced, the rate prior to ash deposition (6600  should s i g n i f i c a n t l y exceed the rate a f t e r ash deposition.  Figure III-6 i l l u s t r a t e s i n cross-section the s i t u a t i o n at CC44.  As  exposed i n the roadcut the Mazama ash occurs at an average depth of 10 feet below the surface of the talus although the depth varies greatly as i l l u s t r a t e d i n Figure III-7.  Beneath t h i s , an average of 15 feet  additional talus material rests on the r i v e r terrace. Before rates of deposition can be calculated, some assumption regarding the nature of the subsurface must be made.  The exact p r o f i l e  FIGURE HT-6. MAZAMA ASH DEPOSIT IN TALUS CONE AT  CC  44 -HEADWALL  ROAD  CUT  F  RIVER  TERRACE  (MAXIMUM POSSIBLE 647'  DEPTH  OF T A L U S )  B  H  107  FIGURE HT-7.  ASH  DEPOSIT  AS  EXPOSED  ALONG  ROAD  CUT  522'  FIGURE  EI-8.MODEL  OF  TALUS  CONE  AT  CC  44IW,TH  ASH  DEPOSIT)  108 of the boundary between talus and the surface on which i t rests cannot be defined without  excavation of the entire talus deposit.  can be established, however.  Some l i m i t s  A maximum depth would be defined by an  extension of the r i v e r terrace back to a v e r t i c a l headwall, i . e . , along l i n e AB i n Figure III-6.  This s i t u a t i o n i s u n l i k e l y , however.  depth i s defined by l i n e EF.  A minimum  It i s assumed that the talus deposit must  be at l e a s t this deep as defined by the depth exposed along the road cut i f the observed slope of 34.8° i s taken as representative throughout i t s development.  This s i t u a t i o n , too, i s u n l i k e l y i n view of the expected  p r o f i l e of a glaciated v a l l e y . between these l i m i t s .  The actual p r o f i l e probably l i e s somewhere  A precise d e f i n i t i o n of the p r o f i l e i s not  required for the present purposes, however. maximum and minimum volume of accumulation  To test the hypothesis, a  prior to ash deposition w i l l  be calculated and compared with the volume accumulated after ash deposition occurred. A model of the talus cone at CC44 w i l l be used (see Figure III-8) with the following assumptions: 1.  The talus cone represents a segment of a r i g h t c i r c u l a r cone.  2.  The talus cone i s bounded by v e r t i c a l faces of coalescence, i . e . , the talus cone i n question coalesces with adjacent talus cones.  3.  H/L - --a. constant, i . e . , the cone has maintained of 34.8°.  a constant  slope  The total volume i n Figure III-8 i s : H  V = / A(h) ..: dh where, A(h) = the area of any one segment as a function of height and, dh = the increment of height. In Figure III-8 the area of the sector of a c i r c l e of radius r which  109 subtends  on angle of 0< r a d i a n s  is  2  A =Tr".  o<  l/20<r  2TT  b u t , r = L(H-h) H t h e r e f o r e V = 1/2  n 2  o•I  L(H-h) H  dh.  o r , V = 1/60CL H , w h i c h i s the f o r m u l a f o r a segment of a r i g h t circular  cone.  Now,c<= 4 4 . 4 ° = 0.77445 r a d i a n s and, i n F i g u r e III-8 (see F i g u r e III-6 H T - 465 L  T = 647  H  M = 455  hi =  also):  633 440  L  B = 612  Then, t o t a l p o s s i b l e volume accumulated i n 10,000 years  is:  V T = 1/6 0 < : ( L T ) 2 ( H T ) = l/6<*(647')2(465')  2i 25.1 x 1 0  6  ft.3  Maximum p o s s i b l e volume accumulated i n 3400 y e a r s p r i o r t o ash deposition i s : V  max.  =  =  1  /  6  * V  <«M>  l ^ c x ^ S ' ) 23.5 x 1 0 6  2  ^ ' )  ft.3  110 And,  minimum probable volume accumulated prior to ash deposition i s : V . = V - V„ min. max. B  where, V  =  g  1/60^) (H ) 2  B  = 1/6(X^612 ») (440«) 2  ^ 21.3 x 10 f t . 6  3  therefore V . = 23.5 x 1 0 f t . min. 6  =  3  2.3 x 106 f t .  - 21.3 x 1 0 f t . 6  3  3  The volume accumulated i n 6600 years (post-Mazama time) i s : PM  T  max.  25.1 x 1 0 f t . 6  3  1.6 x 1 0 f t . 6  Therefore,  - 23.5 x 1 0 f t . 6  3  3  the maximum possible rate of accumulation prior to ash deposition  3 is V /3400 or 6921 f t . /year. max.  The minimum probable r a t e before ash  3  deposition i s V . /3400 or 664.9 f t . /year. min. }  And, the rate of accumulation  3 since ash deposition i s V^/6600 or 241 f t . /year (this compares reasonably 3  with the amounts captured  on TC25 and TC49 i n 1967-68, i . e . , 642 f t . and  3 69 f t . r e s p e c t i v e l y f o r fence #1 and fence #2).  At best, the rate of  accumulation before ash deposition was approximately 30 times that after ash deposition;  at least, about three times greater.  The r e s u l t s support  the 'diminishing sediment y i e l d concept' and substantiate that the rate of accumulation on at least one talus slope i n the region has decreased during p o s t - g l a c i a l time. Longitudinal slope p r o f i l e s established on TG21 (see Photo 111-15) and reproduced i n Figure III-9 i l l u s t r a t e that l a t e r a l p r o f i l e s , i n general, are steeper than central  p r o f i l e s (see Chapter IV).  the p r o f i l e s appear to be nearly r e c t i l i n e a r .  As i l l u s t r a t e d ,  A l l f i v e p r o f i l e s , however,  Photo 111-15.  TC21 •  FIGURE IE-9.  SLOPE  PROFILES  ON  TC  21  AND  TC  PROFILES RIGHT  (950')  C E N T E R (1180')  PROFILES  ON  TC  21 RIGHT (1570') CENTER (1500') LEFT  (1355')-  ON  25  TC  25  113 are s l i g h t l y concave gradually decreasing from 36°-37° near the apex to 33°-34° near the base.  A sharp break i n slope occurs where the  boulder apron begins, a phenomenon observed  i n association with a l l  boulder aprons investigated i n the region.  The p r o f i l e s were established  on two separate talus slopes but they are very s i m i l a r throughout. Other observations of slope were made on talus slopes i n the region and i n general the slopes are steepest near the apex.  Although additional  p r o f i l e s were not established i t i s concluded that the concave p r o f i l e i s the general case i n the region. 2.  Morphology. The talus slopes observed  to a number of c r i t e r i a . i n the region.  i n the region were c l a s s i f i e d according  B a s i c a l l y , only two forms of talus have developed  The very uneven dissection of the headwalls has resulted  i n the formation of either d i s t i n c t talus cones (coded as TC on Map 2) or groups of cones which have become coalesced (coded as CC on Map 2). Talus slopes observed  i n the region have been c l a s s i f i e d i n Table VI.  The following c r i t e r i a were used to c l a s s i f y the slopes according to s i z e : 1.  Huge (H) = slopes measuring > 2500 feet across the base and extending through > 1500 feet of r e l i e f .  2.  Very Large (VL) = 2000 - 2500 feet across the base and extending through 1200-1500 feet of r e l i e f .  3.  Large (L) = 1500-2000 feet across the base and having 1000-1200 feet of r e l i e f .  4. Medium (M) = 1000-1500 feet across the base and 500-1000 feet .of r e l i e f . 5.  Small (S) = < 1000 feet across the base and < 500 feet of r e l i e f .  S t a b i l i t y was judged according to the apparent degree of a c t i v i t y on the slope and the degree of vegetation cover.  According to vegetation  d i s t r i b u t i o n , many slopes had more than one area of concentration,  114 Table VI. CLASSIFICATION OF TALUS FORMS NEAR KEREMEOS, B.C. Identification  Headwall Configuration  1  2  3  4  5  6  CC1 TC2 TC3 TC4 TC5 TC6 TC7 TC8 TC9 TC10 TC11 TC12 TC13 TC14 TC15 TC16 TC17 TC18 CC73 TC72 CC71 TC70 TC69 TC68 TC67 TC66 TC65 CC64 CC63 TC62 TC61 CC60 CC56 CC57 CC58 CC59 TC55 CC54 CC53 CC52 TC51 TC50 TC49 TC48 TC47  D D C D D C D C C C C C F F F C C  M L VL\ M L M L S S S S M L H VL L M M M VL M S M S VL S VL S M L L M S S L S VL H H H L S L H M  S S S S S S S N N N N N N N N N N N N N N N N N N N N W E E E N N N N N S S S S S S S S S  S TTS A RA A RA A RA RA RA RA A A A A S RA RA TTS TTS TTS A A RA RA RA A TTS A RA RA TTS TTS TTS RA TTS RA RA A A S TTS TTS A TTS  S S T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T W T  c  D  c  D C C C F C C D D D D D D D D D C C D D D D F F C  Size  Aspect  Stability  Veg. Type  Veg. Dist. 7 CC CC T M T,S,B B T T T T T T B ,M S M,T CC T T CC T,B T,B T T T,S . T,M T T T T,B T,B CC T CC CC T,B CC T,B T,B T,B T,B CC CC CC T,B CC  Boulder Apron 8 _  B B B B B B B B B B B B B B B B B B B B B B B B B B B B B  :  -  B  -  B B B B B B  -  B B (over)  115 Table VI. (continued) Identification  Headwall Configuration  Size  Aspect  Stability  Veg. Type  Veg. Dist.  Boulder Apron  1  2  3  4  5  6  7  8  TC46 TC45 CC44 TC43 TC42 TC41 TC40 TG39 CC38 TC37 TC36 TC35 TG34 CC33 TC32 CC31 CC30 CG29 TC28 TC27 TC26 TG25 TG24 TC23 TC22 TG21 TC20 GG19  C C D F C C  M M M VL H M L M S M VL H VL S L S M S S S M L L VL H H VL L  S S S S S  TTS TTS TTS S S S A TTS RA RA RA RA S A S RA RA RA RA TTS TTS A RA A A A A S  T T S T T T T T T T T T T T T T T T T T T S S W W  T T CC T,B M T,B T,B T,B CC T,B T,B T,B T,B T,B T,B CC T,B CC T,B T,B CC T,B T,B T,B T,B T,B T,B CC  B B B B B B B B  c c  D C F C F D C D C D D D C C C F C D D D  s s s s s s s s s s s s s s s s s s s s s s  E  w w  S  -  B B B B  -  B  -  B B B B B B B B B B B  -  Notes: 1.  I d e n t i f i c a t i o n (see Map 2). a) TC indicates a d i s t i n c t talus slope. b) CC indicates a coalesced group of cones.  2.  Headwall configuration. a) C indicates that a chute complements the cone or cones. b) F indicates that a funnel complements the cone. c) D indicates that the headwall i s dissected . but that no chute or funnel has developed.  3.  Size. a) H indicates a huge talus slope. b) VL - very large. c) L - large. d) M - medium. e) S - small. (over)  116 Table VI.  (continued)  4.  Aspect. a) N indicates a north-facing slope. b) S - south-facing. c) E - east-facing. d) W - west-facing.  5.  Stability. a) S indicates a stable slope. b) TTS - tending towards s t a b i l i t y . c) RA - r e l a t i v e l y a c t i v e . d) A - a c t i v e .  6.  Vegetation type. a) T indicates predominantly trees with weeds and grass. b) S - predominantly shrubs with weeds and grass. c) W - predominantly weeds and grass.  7.  Vegetation d i s t r i b u t i o n . a) T indicates a concentration at the top of the slope. b) B - concentration at bottom. c) S - concentration along side or sides. d) M - concentration i n middle. e) CC - a complete cover of vegetation.  8.  Boulder apron. B indicates that a boulder apron has developed at the base of the slope.  117 i.e.,  T,B,S  for this c r i t e r i o n i n Table VI would imply concentration of  vegetation at the top, bottom and along the sides of the slope. A good example Photo 11-10 chute.  of a huge coalesced cone i s shown i n Photo II-4.  shows a very large talus cone complemented by a well developed  Photo 111-15 i l l u s t r a t e s a huge d i s t i n c t cone without a chute  or funnel above it.TC48 with a well developed funnel i s i l l u s t r a t e d i n Photo 111-16.  Photo 111-16. TG48 . Note well developed funnel extending far into the headwall. TC26 was mapped (see Map 4A) as outlined i n Chapter I I , and as shown i n Photo 111-17 i s medium i s size and complemented by a well developed chute.  A boulder apron s k i r t s the base of the cone and as  i l l u s t r a t e d on the overlay to Map 4A i s distinguished by a sharp break i n slope which i s typical f o r boulder aprons observed i n the region. The boulders comprising the apron on the l e f t side are very large (some > 25 f t . d i a . ) .  The talus rests on the surface of a r i v e r terrace which  i s exposed along the l e f t side as i l l u s t r a t e d on the overlay.  TC26 i s  bounded on both sides by adjacent talus cones with which i t has coalesced the l i n e of demarcation indicated by a d e f i n i t e V-bend i n the contours  CONTOUR CONSTRUCTED  FROM  1967  PLANE  T A B L E  SURVEY  INTERVAL -  6  F E E T COMPILED  BY  0.  A.  W OR O B E Y  I0Q8  119  Photo 111-17. upslope. boulders.  TC26.  The trough produced where they j o i n i s f i l l e d with large In essence, therefore, the boulder apron extends from headwall  to headwall on TC26.  As can be seen i n Photo III-17 an uneven growth  of Douglas f i r and ponderosa pine trees has talus surface.  become established on the  The oldest trees were estimated to be about 100 years  of age indicating a certain degree of s t a b i l i t y on the slope.  As can  be seen i n the photo the growth i s concentrated near the apex where a continuous mat of bush, weeds and grass extends from about 2/3 the way up to the entrance to the chute (see overlay).  Many dead trees are s t i l l  standing but, as can be seen i n the photo, many logs are strewn over the surface.  Below the zone of continuous vegetation, the talus surface  i s sorted into d i s t i n c t s t r i p s of fine and coarse debris which i s c h a r a c t e r i s t i c of talus slopes i n the region.  The coarse strips are  120 usually quite narrow with the wider f i n e r s t r i p s of debris between. The t r a n s i t i o n from coarse to f i n e , however, i s abrupt.  Longitudinal p r o f i l e s  of the cone are quite r e c t i l i n e a r but an inspection of Map 4A indicates that they are s l i g h t l y concave, being steepest near the apex. The steep slope i s maintained i n the chute where a maximum of 38° i s recorded. Debris was noted as being l e a s t stable near the apex and i n the chute where slopes are steepest.  Some i n t e r e s t i n g isolated features were noted.  Near the base on the right side two a u x i l i a r y can be observed (see overlay).  cone-like features  The one on the extreme r i g h t i s most  d i s t i n c t and forms the boundary between TC26 and the adjacent talus cone. grass .  Both are covered with a dense growth of bush, shrubs, weeds and The one on the right has a d e f i n i t e convex longitudinal p r o f i l e ,  being steepest at i t s base where i t merges with the boulder apron. o r i g i n of these features presents an i n t e r e s t i n g problem.  The  Both are  covered with talus debris and are distinguishable only by their morphometric c h a r a c t e r i s t i c s and their vegetation cover.  Extending above the one  furthest to the r i g h t to the rock spur on the right side of the chute are two d i s t i n c t g u l l i e s separated by ridges on the talus surface. These g u l l i e s and ridges show up very well on Map 4A and are noted on the overlay.  The features suggest f l u v i a l action.  Water channelled  by the chute above during a p a r t i c u l a r l y intense storm would be most concentrated along the c l e f t separating the rock spur from main headwall on the r i g h t .  So concentrated, i t could have produced  observed either by channel flow or mudflow.  the g u l l i e s  The a u x i l i a r y cone-like  feature at the base could represent the net accumulation of any debris transported downslope by the water. Near the base on the l e f t side a depression was observed on  121 the  talus surface.  This depression can be attributed to either compaction  of the talus debris or, more probably, an i r r e g u l a r i t y on the surface beneath since the depth of the talus would be quite shallow at this point. The unequal dissection has produced a rock spur which protrudes a f a i r distance downslope as shown on the overlay and forms the right margin of the chute for about 1/3 of i t s extent. A c l e f t between the rock spur and the headwall on the right,which i s bare of debris, channels some of the debris transported down the chute.  An interesting phenomenon  was noted on the l e f t side of the chute where i t joins with the headwall at the 900 foot l e v e l . At this point i t appears that the level of the rubble which mantles the surface of the chute has suddenly 18".  dropped about  As Photo 111-18 i l l u s t r a t e s the surface of the headwall i s covered  with a f a i r l y complete growth of lichens which ends abruptly about 18" above the debris i n d i c a t i n g that the headwall has been recently exposed as a r e s u l t of a drop i n level of the debris . An explanation for the  •  Photo 111-18. Along Headwall i n Chute of TC26. Note discontinuity of l i c h e n growth on headwall at about 18" above debris indicating s e t t l i n g of debris i n the chute.  122 occurrence  could be a sudden s l i d i n g away of a considerable portion of  the debris i n t h i s part of the chute or a r e l a t i v e l y compaction of the same.  instanteous  A claim stake marker i s located on a ponderosa  pine stump at this point and a cache of blasting caps and assorted mining tools were found i n the headwall nearby. was  It i s concluded  that a prospector  doing some blasting along the headwall and that the shock of the  explosion could have created the s l i d i n g or s e t t l i n g r e s u l t i n g i n a lowering of the debris surface. at  The debris maintains a very steep slope  this point and i s very mobile underfoot.  It i s feasible that the  sudden shock of an explosion could have produced the s e t t l i n g observed. On June 15, 1967 CC44.  an i n t e r e s t i n g phenomenon was  observed at  The cut of the Southern Trans-Canada Highway through the base of  these cones i s an e s s e n t i a l l y perpendicular wall composed of talus debris. Through compaction and s o i l formation as the result of weathering the talus debris has become most cohesive being able to support a slope near 90°.  At one point along the cut, loose talus debris on the surface of  the talus slope immediately above the cut was being dislodged by a p a r t i c u l a r l y gusty wind noted that day.  The debris being dislodged  was  i n the process of a c t i v e l y forming a miniature talus cone at the base of the cut. at  The debris was  being channelled by a c l e f t which had formed  this point along the cut (see Photo 111-19).  As the debris came  into .contact with the apex of the miniature cone, i t tended to spread i t s e l f out evenly preserving the c h a r a c t e r i s t i c a l l y symmetrical of the cone.  Most of the debris dislodged was  before t r a v e l l i n g more than one-half way  shape  f i n e and most stopped  down the miniature talus slope.  The larger rocks moved d i r e c t l y to the base of the deposit forming apron at the base.  The sorting of the debris downslope was  an  striking.  Photo III-19. Miniature Talus at GC44. Dust t r a i l l e f t by debris dislodged by wind from the talus surface of CG44 i s v i s i b l e at top of photo. Miniature cone formed from talus debris dislodged,which appears at the base of the cut, i s about 6 feet high. Note coarser rubble at the base of the cone. Note also the very cohesive talus deposit through which the highway cut has been made. Sand-sized  p a r t i c l e s remained at the top becoming covered as subsequent  f a l l s of debris occurred.  From time to time masses of debris, already  deposited near the apex,slid to readjust the slope.  The slope of the  deposit was measured by placing a survey rod f l a t on the surface and laying an abney l e v e l on the rod.  I t was found to have a constant  slope  of 34.9°. At the base of a number of talus slopes i n the region  excavations  to obtain a suitable riprap have been made. As a r e s u l t of this basal  124 sapping, the loose surface layers immediately above the excavations have s l i d away exposing a much stabler talus surface beneath.  The  newly exposed surfaces rest at angles exceeding 38° as compared to 33°-34° for the adjacent undisturbed areas of the talus slopes . The material comprising  the newly exposed steeper surfaces was found to be  i n a state of chemical decay.  S o i l formation had already begun and the  debris i n general tended to be more compacted.  This greater degree of  consolidation allows these materials to support much steeper  angles.  The debris covered surfaces of the chutes and funnels which have formed above many of the talus slopes i n the region are d i s t i n c t l y different from the talus surfaces below them.  In general, the slopes  of the chutes and funnels are greater than those on the talus slope below. Angles of rest are usually > 37°.  This may be a r e f l e c t i o n of the shallow  depth of the debris i n the chute or funnel allowing i t to be  supported  at a higher angle determined by the slope of the bedrock surface on which i t r e s t s .  In general, no observable downslope or c r o s s - a x i a l  sorting i s v i s i b l e i n the debris and a high degree of a c t i v i t y i s indicated by the lack of vegetation on the surface of chutes and funnels (eg. see Photo 111-20).  The surface remains very active as this debris  is conveyed down onto the talus surface below.  Since the slope of the  surface i n chutes and funnels i s steep, debris cannot accumulate to very great depths before s l i d i n g and removal from the chute or funnel takes place.  It was noted that the cross-axial p r o f i l e of the funnel  complementing TC48 i s concave-up as compared to the convex-up p r o f i l e of the talus cone i t s e l f  (see Photo 111-21) .  At t h i s point, the aspect of  the bounding headwalls i s such that the r o c k f a l l  t r a j e c t o r i e s onto  either side of the funnel are b a s i c a l l y perpendicular to the axis of  125 transport down  and  funnel  downslope  through  perpendicularly  has  developed,  out  the  funnel.  from  producing  the  the  A  cross-axial  headwalls  concave  on  profile  slope  either  side  observed.  Photo 111-20. Apex of Chute Above TC25. Note the l a c k of v e g e t a t i o n on the s u r f a c e of the c h u t e and the i n t e n s e d i s i n t e g r a t i o n of the adjacent headwall.  leading of  the  Photo 111-21. Looking up at Funnel Above TG48. Note the concavep r o f i l e (arrows) of the funnel i n the background as compared to tt convex-up p r o f i l e of the talus surface i n the foreground.  127 CHAPTER IV - ANALYSIS AND  A.  INTERPRETATION  P r o f i l e Analysis. Profiles established on TC21 and TC25 were used to test for a  suggested difference between l a t e r a l and central p r o f i l e s on talus cones. As plotted i n Figure III-9 some difference i n slope was  detected.  Table VIII i l l u s t r a t e s the comparisons downslope for comparable slope sections on TC25 and TC21.  The l a t e r a l p r o f i l e on TC25 i s an average of  1° steeper than the central p r o f i l e ;  on TC21  the right and l e f t p r o f i l e s  are an average of 0.8° and 0.3° steeper respectively than the central profile.  In a l l three cases, therefore, the l a t e r a l p r o f i l e was  to be steeper than the central p r o f i l e . measurements i s * 0.5°  (King, 1966).  found  The error of individual slope  However, the standard errors of  the means of 10 measurements on TC25 and 15 and 14 measurements on l i s t e d i n Table VIII are - 0.15°, - 0.12°, and - 0.13°  TC21  respectively.  Lateral p r o f i l e s , therefore, are steeper than central p r o f i l e s measured. Cobble a, b, and c axes were measured at 10 foot intervals along each p r o f i l e on TC21.  A d e f i n i t e difference i n mean cobble s i z e  was detected between the l a t e r a l and central p r o f i l e s .  Cobbles, i n  general, are larger on the l a t e r a l p r o f i l e s (see Table V I I ) . Table VII.  Measure a axis b axis c axis  COBBLE ANALYSIS ON LONG PROFILES TC21 Mean along Right P r o f i l e 4.9" 3.1" 1.8"  Mean along Center P r o f i l e  Mean along Left P r o f i l e  2.6" 1.7" 1.0"  4.0" 2.8" 1.7"  A difference of means test (see Blalock 1960, pp. 173-176) was applied, the results of which are tabulated below:  Table VIII.  A.  COMPARABLE SLOPE SECTIONS TG25  Downslope Position 100 feet 1 2 3 4 5 6 7 8 9 10  B. Downslope Position x 100 feet 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15  Difference i n Slope: Right-Center (in degrees) 37.0 37.5 35.5 36.0 35.0 36.0 35.0 35.5 35.0 35.5  36.0 = 35.0 = 35.0 = 34.5 = 35.0 = 34.5 = 34.5 = 34.0 = 34.0 = 34.5 =  +1.0 +1.5 +0.5 +1.5 0.0 +1.5 +0.5 +1.5 +1.0 +1.0  COMPARABLE SLOPE SECTIONS TC21  Difference i n Slope: Right-Center ( i n degrees) 36.0 38.0 37 .0 " 36.5 36.5 36.5 37.0 36.0 35.0 35.0 35.0 35.0 34.5 34.0 33.5 -  -• -• -• -  35.7 = 37 .0 = 35.7 = 35.5 = 35.7 = 35.5 = 35.5 35.0 = 34.8 = 34.5 = 34.4 = 34.2 = 34.0 33.7 = 31.7 =  +0.3 +1.0 +1.3 +1.0 +0.8 +1.0 +1.5 +1.0 +0.2 +0.5 +0.6 +0.8 +0.5 +0.3 +1.8  Difference i n Slope: Left-Center ( i n degrees) 37 .0 36.7 36.2 35.7 36.5 36.0 35.5 35.2 35.0 35.0 34.2 34.0 34.0 34.0  "• -• -• -• -• -• -• -• -• -• -• -• --•  35.7 37 .0 = 35.7 = 35.5 = 35.7 = 35.5 = 35.5 = 35.0 = 34.8 = 34.5 = 34.4 = 34.2 = 34.0 = 33.7 =  +1.3 -0.3 +0.5 +0.2 +0.8 +0.5 0.0 +0.2 +0.2 +0.5 -0.2 -0.2 0.0 +0.3  129 Table IX.  DIFFERENCE OF MEANS TEST  2 Tailed Means  T*t*i  (a axis) r i g h t vs center right v s . l e f t l e f t vs. center (b axis) right vs. center right vs. l e f t l e f t vs. center (c axis) r i g h t vs. center r i g h t vs. l e f t l e f t vs. center  df  t  Test  at 1% L e v e l  4  0.194 0.455 0.345  248 262 258  11.83 1.87 4.20  different not s i g n i f i c a n t l y different  diff,  0.278 0.309. 0.235  236 278 235  5.22 1.14 4.67  different not s i g n i f i c a n t l y different  diff,  0.165 0.182 0.143  245 280 240  4.95 0.77 4.73  different not s i g n i f i c a n t l y different  diff.  Means along l a t e r a l p r o f i l e s are s i g n i f i c a n t l y d i f f e r e n t at the 17  0  significance  level from means along the central  other, even at the 5% l e v e l .  p r o f i l e but not from each  Mean"' proportional and cumulative proportional  frequency plots of the b axes according to Wentworth (Figure IV-1) further i l l u s t r a t e the difference.  divisions  i n inches  The s i m i l a r i t y of the  plots for the l a t e r a l p r o f i l e s i s most apparent whereas the plot for the central  p r o f i l e where the mode l i e s i n a much smaller  strikingly different.  A Rolmogorov-Smirnov  size category i s  test (Miller and Kahn, 1962,  pp. 464-470) for goodness of f i t validates this visual d i f f e r e n c e . the plots for the l a t e r a l p r o f i l e s are s i g n i f i c a n t l y d i f f e r e n t plot for the central  p r o f i l e at the 17 significance 0  p r o f i l e plots are not s i g n i f i c a n t l y different other, however.  The results  the characteristics 4  t.  Q5  level;  Q 1  from the  the l a t e r a l  at the 1% l e v e l from each  indicate that some difference does exist  between l a t e r a l as compared to central  = 1.960 and t  Both  in  p r o f i l e s along  = 2.576 for > 120 df.  5 Running means based upon 15 sample groups with a 5 sample overlap downslope on each p r o f i l e .  130  FIGURE  X2>  I.  MEAN  PROPORTIONAL  PROPORTIONAL AND CUMULATIVE FREQUENCY PLOTS OF b AXIS  ALONG PROFILES  ON TC 21  RIGHT  100 -i  T—i—r  .31 .63L25 2.5 5 10 20 40 80 WENTWORTH DIVS.(ins.)  CENTER  100 -i  80-  z  60-  UJ o 40-  Ul  0_ 20-  T—1 1 I I I 31 .63 1.25 2.5 5 10 20 40 80 WENTWORTH DlVS.(ins)  LEFT  I  I  !  .31.63 1.25 25 5 10 20 4080 WENTWORTH DIVS.(ins.)  131 talus slopes investigated. This substantiates the hypothesis i n Chapter I I . may  Some correlation between s i z e of debris and angle of slope  e x i s t which would suggest  along  formulated  some difference i n the mechanism of transport  central as compared to l a t e r a l p r o f i l e s .  I t was  earlier  suggested  that transport down the center of a cone would probably be more rapid and concentrated than  transport along the sides.  In this event, coarse debris  would tend to accumulate more along the sides of the cone where i t s momentum would be reduced.  Also, a steeper slope may be achieved along the  sides where there i s less disturbance.  The r e s u l t s , however, are based  e s s e n t i a l l y upon the observations on a single talus cone i n the region. B.  Analysis and Interpretation of Downslope Sorting. With the exception of the boulder aprons noted, i t appeared that  no observable downslope sorting occurs on the slopes studied, this being stated as a hypothesis i n Chapter I I . Running mean plots of the b axes as measured along the p r o f i l e s on TC21 and TC25 tend to contradict the hypothesis.  The plots (Figures IV-2,  IV-3, IV-4 and IV-5) indicate that a s l i g h t increase of grain s i z e occurs upslope and downslope from the 200-400 foot position on a l l p r o f i l e s . However, the 957 confidence range i l l u s t r a t e s that only on TC25 i s the 0  difference s t a t i s t i c a l l y s i g n i f i c a n t i n an upslope d i r e c t i o n . from  Downslope  the 200-400 foot position means are s i g n i f i c a n t l y different on a l l  p r o f i l e s at the 57o l e v e l .  The change, however, i s not monotonic and, as  i l l u s t r a t e d , i s only a weak trend.  I t i s i n t e r e s t i n g to note that a mat  of grass and sage covers the upper t h i r d of both slopes and that the smallest mean b axes recorded on both TC21 this band of vegetation.  and TC25 occur midway along  This i s probably best interpreted as an indication  that vegetation i s better able to establish i t s e l f at this point i n  132  FIGURE  EC-2.  RUNNING  ALONG  CENTER  MEAN  PLOT OF  PROFILE  ON  TC  b  AXES  25  14 13 -1  H  12  95%  CONFIDENCE  RANGE (FOR T H E MEANS) BOULDER APRON BEGINS HERE  CO LU  O  81 7  CO X  6  H H  5H  < LU  i  H ~~1  75  1  1  1  175 275 375  1  475  DOWNSLOPE  — 1  575  1  675  1  775  DISTANCE  1  1  1  1  —  875 975 1075 1175  IN  FEET  133  FIGURE  1 2 - 3 . RUNNING RIGHT PROFILE  DOWNSLOPE  MEAN  PLOT OF b AXES ALONG  ON TC 21  DISTANCE  IN  FEET  134  FIGURE 121-4. RUNNING MEAN PLOT OF b AXES ALONG  CENTER  PROFILE  ON  TC 21  135  FIGURE  1 2 - 5. ALONG  RUNNING LEFT  DOWNSLOPE  MEAN  PLOT  PROFILE  ON  DISTANCE  IN  OF b AXES  TC 21  FEET  136 association with the smaller grain size of the debris rather than as a control exerted by vegetation light the observation the concentration  on the d i s t r i b u t i o n of grain s i z e .  In this  tends to confirm an hypothesis made e a r l i e r about  of vegetation  near the apex of talus cones i n the  region. As i l l u s t r a t e d i n Figure III-9, the slope angle decreases s l i g h t l y downslope from the 200-400 foot position with a corresponding increase in grain s i z e .  Some c o r r e l a t i o n between grain size and angle may exist  i n this respect which could explain the downslope trend.  But, the r e s u l t s  tend to contradict the c o r r e l a t i o n between larger-sized debris and steeper angle existing on the l a t e r a l p r o f i l e s already discussed.  The r e s u l t s  suggest that d i f f e r e n t transport mechanisms are operational on d i f f e r e n t parts of the talus  slope.  On TG25 the mean at the 1175 foot position i s s i g n i f i c a n t l y larger (see Figure  IV-2)  than a l l others on that plot with the exception of the  one at the 575 foot p o s i t i o n .  The debris at the 1175 foot position i s  part of the boulder apron and t h i s s i g n i f i c a n t difference would be expected. Included with the plots on TC21 (Figures IV-3, are the population position.  IV-4 and IV-5)  confidence ranges of the material at each downslope  I t i s i n t e r e s t i n g to note that these overlap  on a l l three  p r o f i l e s suggesting that the differences which have been detected are weak.  Distributions of a l l samples are positvely skewed and kurtosis  varies between s l i g h t l y platykurtic and leptokurtic but no downslope trend i s discernable.  Sorting (as indicated by the Trask sorting c o e f f i c i e n t )  i s good for a l l plots and shows no downslope trend; shape and flatness and s p h e r i c i t y parameters.  neither do Zingg  In p a r t i c u l a r , flatness  and s p h e r i c i t y are remarkably uniform downslope.  137 A downslope difference i n mean cobble s i z e was detected through an analysis of the traverse samples on TC3, TC26, TC48, and TC67.  However,  the differences detected were weak and did not occur on a l l cones sampled. Downslope plots of mean b axis according  to cross-slope traverse samples  are shown i n Figures IV-6, IV-7, IV-8 and IV-9.  The 957<> confidence  range for the means indicates that debris sampled along the boulder aprons i s s i g n i f i c a n t l y larger i n a l l cases, as expected.  Other weak  downslope differences are indicated by the plots but no d e f i n i t e general trend e x i s t s . Again, as with the data collected along the p r o f i l e s on TC21 and 25, the 957 confidence 0  ranges for the populations  of debris  at each traverse overlap, i n d i c a t i n g l i t t l e c o r r e l a t i o n between s i z e .and downslope p o s i t i o n . Of the four cones sampled by traverse, TG3 exhibited the most pronounced trend of downslope sorting.  The proportional frequency and  cumulative proportional frequency plot of b axes on TC3 i n Figure IV-10 i l l u s t r a t e s the general increase i n s i z e downslope.  Within cone plots  are shown for TC3, TC26, TC48 and TG67 i n Figure IV-11.  A Kolmogorov-  Smirnov test indicates that the d i s t r i b u t i o n on TC3 i s s i g n i f i c a n t l y different from that on TC26 at the 5% l e v e l ; differences between cones e x i s t s .  no other  significant  The difference detected would be  related to the lesser progressive increase o£ grain s i z e downslope on TC26 (Figure IV-7) as compared to that on TC3 (Figure IV-6). has a significant; proportion of grain sizes recorded  Also, TC26  i n the smallest  categories of the Wentworth divisions (Figure IV-11) which are''lacking on TC3.  The r e s u l t s suggest a difference i n cobble c h a r a c t e r i s t i c s  between TG3 and TC26 which may be r e l a t e d to geology. Skewness, k u r t o s i s , Zingg shape, and flatness- and s p h e r i c i t y  133  FIGURE 32!-6.  MEAN b SAMPLES ON TC  AXIS 3  2 3 DOWNSLOPE  PLOT  4 TRAVERSE  OF TRAVERSE  5 6 POSITION  139  FIGURE IZ-7.  MEAN  SAMPLES  ON  b  AXIS  TC  26  PLOT  OF  TRAVERSE  15  1  2  DOWNSLOPE  1  3  1  4  TRAVERSE  1  5  POSITION  -i 6  r  7  FIGURE  Iff-8.  MEAN  TRAVERSE  b AXIS  SAMPLES  PLOT OF  ON TC  , j 1 1 2 3 DOWNSLOPE TRAVERSE  ,  48  4 POSITION  FIGURE  W-  9.  MEAN  b  AXIS  TRAVERSE  SAMPLES  DOWNSLOPE  TRAVERSE  ON  PLOT  OF  TC 67  POSITION  FIGURE  32-10  PROPORTIONAL  TIONAL  0 0  FREQUENCY  TRAVERSE 1  31 63 1.2525 5 10 20 40  b AXIS TRAVERSE 5  IN  CURVES  TRAVERSE 2  31.631.252.5 5 10 20 40  b AXIS  FREQUENCY  IN . INCHES  TRAVERSE 6  INCHES  ( WENT. DIVS.)  OF  b  PLOTS AXES  AND ON  TRAVERSE 3  CUMULATIVE TC  3  TRAVERSE 4  PROPOR  FIGURE  Jf  EMI. WITHIN CONE PROPORTIONAL FREQUENCY PLOTS OF b AXIS  i  i—i—i—i—l  r—i  1  .31 .63 1.25 25 5 10 20 40  b BETWEEN CONES  b AXIS IN INCHES  i  i  i—i  i  I  .31 .631.25 25 5 10 20 40  AXIS  IN INCHES  AND CUMULATIVE  f—i—i—i—i—i—r—•  .31 .63 1.25 2.5 5 10 20 40  (WENTWORTH  DIVISIONS)  r  I  PROPORTIONAL  i—i—i—i—i—i  .31 .6312525 5 10 20 40  144 parameters calculated for the traverse samples indicate no downslope trend. C.  Again, flatness and s p h e r i c i t y show remarkable uniformity downslope.  Mass Movement as a Cross-slope Sorting Mechanism. Plots of mean b axis along the f i n e and coarse strips on CC52  are i l l u s t r a t e d i n Figure IV-12.  The plots are of adjacent s t r i p s of  debris on the same slope and serve to i l l u s t r a t e that cross-slope sorting of debris e x i s t s .  Also, a s l i g h t increase i n size downslope i s s i g n i f i c a n t  at the 57 l e v e l on the fine s t r i p . 0  As i l l u s t r a t e d i n Figure IV-13  this  can be attributed to a progressive reduction i n the frequency of the smallest sizes down the f i n e s t r i p .  This progression suggests sorting i n conjunction  with mass movement processes whereby smaller fragments come to rest f i r s t where debris moves downslope en masse, and tends to substantiate the hypothesis  that movement occurs en masse along the fine s t r i p s .  Since  the same progression i s lacking along the coarse s t r i p a d i f f e r e n t mechanism of transport, as already postulated, i s suggested. Additional calculations from the data suggest no fragment c h a r a c t e r i s t i c s which would tend to exert influence on the formation of fine and coarse s t r i p s . along both s t r i p s . 1.264  As expected, good sorting exists at a l l points  (Mean Trask sorting = 1.309  for the coarse s t r i p . )  Distributions are p o s i t i v e l y skewed and  markedly p l a t y k u r t i c i n general. displays no marked trends.  for the fine s t r i p ;  D i s t r i b u t i o n of Zingg shape (Figure IV-14)  The uniformity of flatness and sphericity as  noted on a l l other downslope plots occurs on the f i n e and coarse s t r i p s as well as indicated by Figures IV-15  and IV-16.  A l l plots of flatness and s p h e r i c i t y parameters calculated from the data, which were collected using a v a r i e t y of techniques on a number of slopes, indicate d e f i n i t e uniformity downslope.  In addition, plots  145  FIGURE  EE-12. COARSE  PLOT OF MEAN b AXES ALONG AND FINE STRIPS ON CC 52  DOWNSLOPE  DISTANCE  IN  FEET  FIGURE  EZH3. CURVES  FREQUENCY OF  b  AXES  b  PLOTS ALONG  AXIS  IN  AND FINE  CUMULATIVE STRIP  ON  INCHES (WENTWORTH  PROPORTIONAL CC  52  DIVISIONS)  FREQUENCY  (downslope in feet)  147  FIGURE EZr 14.  ZINGG  SHAPE  DISTRIBUTION  FINE STRIP  COARSE STRIP  NUMBER OF COBBLES  NUMBER OF COBBLES 0  5  10  7  o  15 4  CC 52  20  25  0  5  10  15  20  25  50  o o  z  100 150  CO  r-  o -o m  p  2a  o ~ 25( co  z  R  z TI  1  30(  ^1 350^  m m 400 450^  i  20  _ l  PERCENT 40 I  60 . , i , J,  i,  PERCENT  80 100 L.  9 ,  MEAN TOTAL  MEAN  OTAL  /a.  K E Y  BLADE  FLAT ; ELONGATE  ROLLER  ELONGATE  BUT SQUARE  BLOCKY OR ROUND DISC  FLAT BUT SQUARE OR ROUND  FIGURE  EZH5. ON  FLATNESS  C C  PARAMETER  ALONG  FINE  AND  COARSE  STRIPS  52  COARSE STRIP ( mean = .556)  95% —i 0  1 50  1 100  DOWNSLOPE  1 1 1 1 1 1 1— 150 200 250 300 350 400 450  DISTANCE  IN  FEET  \.o-t  CONFIDENCE  gc (limits are o t o i ) a+b IF CLOSE TO 0, THEN VERY FLAT; IF CLOSE TO I, THEN MORE OF A CUBE  FLATNESS =  CO  CO .8 LU  • FINE STRIP (mean= .509)  -i 0  i 50  i 100  DOWNSLOPE  •  i  1 1 1 1 1— 150 200 250 300 350 400 450  DISTANCE  IN  FEET  RANGE  150 of Zingg shape indicate no discernable progression of change downslope, though a l l shapes are present. Ritchie's hypothesis  These observations  tend to confirm  (Chapter I) that mobility of debris i s independent  of shape, i . e . , shape of a rock does not i n h i b i t i t s r o l l i n g a b i l i t y unless i t i s elongate, eg., shaped l i k e a p e n c i l .  I f shape exerted a  control then some progressional change downslope i n the parameters calculated would be expected;  no change was detected, however.  Further,  the flatness and sphericity parameters calculated (see representative values i n Figures IV-15 and IV-16) suggest that no eccentric shapes predominate i n the debris which has accumulated i n the form of talus slopes i n the region.  This suggests that jointing of the headwall exerts  a uniform e f f e c t r e s u l t i n g i n a non-eccentric pattern of fragmentation. This inference i s further augmented by the basic balance i n the d i s t r i b u t i o n of Zingg shape exhibited by  a l l plots.  The r e s u l t s coincide with the  observations made of the j o i n t i n g along the headwalls i n the region.  In  general, the rocks exhibit a very complete joint pattern as a r e s u l t of the i n t e r s e c t i o n of at least three d i s t i n c t planes of j o i n t i n g . D.  Morphometric Analysis and Interpretation. The debris comprising  with the mapping program.  the surface of TC26 was sampled i n conjunction  The b axis of one cobble was measured at each  rod s t a t i o n (a t o t a l of 276 measurements).  In this way, a f a i r l y complete--  i f not random -- sample of the talus surface was obtained.  From the  detailed surface data collected a trend surface analysis was made.  First  through sixth degree regression equations involving x and y (independent position variables) and z (the dependent cobble measure (b axis) variable) were calculated.  The fourth degree equation was chosen to plot a trend  surface (see overlay to Map 4B) since the equation had a c o e f f i c i e n t of  152 determination of .466 and was  s i g n i f i c a n t at the 17 l e v e l on the F test. 0  The 6th degree equation explains 49.77» of the variance.  The increased  explanation, however, i s not worth the increase i n complexity involved with the higher order equations (see Table X). What i s most s t r i k i n g i s the upward slope of the trend surface in the lower l e f t portion of the cone.  This i s obviously the r e s u l t of  a concentration of very large-sized boulders i n association with the boulder apron at this point (see discussion Chapter III.E.2.). In general the surface indicates larger cobbles a l l along the apron with a fringe extending up along the right side where TC26 merges with an adjacent cone. As already discussed, the trough of intersection where the cones coalesce i s f i l l e d with larger cobbles as indicated by the trend surface.  On the  talus proper the trend surface indicates a zone of coarser cobbles down the center of the slope bounded on either side by zones of f i n e s .  It i s  i n t e r e s t i n g to note with an inspection of Photo III-17 that the zones of fines correspond c l o s e l y to areas of concentrated tree growth as one would expect.  As can be seen, the generalized d i s t r i b u t i o n of fines and  coarse material on the talus proper i s oriented p a r a l l e l to the axis of transportation down the cone.  This suggests some control exerted by  variable mass movement mechanisms on the slope. capable of i n d i v i d u a l movement downslope may  Larger cobbles, being  tend to accumulate along  the central axis where transport i s concentrated.  The f i n e s , incapable  of individual movement downslope, could tend to accumulate near the apex initially.  Upon assuming a c r i t i c a l angle, however, readjustment could  occur by release en masse i n the form of miniature s l i d e s which would tend to avoid the coarser accumulations along the central axis moving, rather, to accumulate along the l a t e r a l portions of the cone.  This, of  Table X.  TREND SURFACE ANALYSIS TC26;  Surface  Sum of Squares  1  2  3  4  5 6  * **  DF  Mean Square  ANALYSIS OF VARIANCE AND ERROR MEASURES Coeff. of Determination  Standard  Residual DF  Residual Mean Sauare  F 29.83 29.83*  .177  23.87  increment total  .34 .34  2 2  .17 .17  276  .57  increment total  .28 .61  3 5  .92 .12  273  .48  19.17 25.79*  .321  - 21.69  increment total  .18 .80  4 9  .45 .89  269  .42  10.85 21.22*  .415  + 20.13  increment total  .98 .90  5 14  .20 .64  264  .39  5.05 16.47*  .466  - 19.23  increment total  .38 .94  6 20  .63 .47  258  .38  1.64 12.19**  .485  + 18.87  increment total  .22 .96  7 27  .31 .35  251  .39  0.82 9.20**  .497  18.66  s i g n i f i c a n t at the 17o l e v e l . not s i g n i f i c a n t at the 17 l e v e l . 0  154 course, contradicts the observations i t was  i n section A of this Chapter where  found that debris sampled along l a t e r a l p r o f i l e s on TC21  coarser than that sampled along the central p r o f i l e .  It should  noted, however, that the l a t e r a l p r o f i l e s taken on TC21  was be  were along  the  extremities of the cone where, as already noted i n a discussion of the surface c h a r a c t e r i s t i c s of TC26 (Chapter III.E.2.), a boulder fringe has developed.  As i l l u s t r a t e d by the trend surface on the overlay to Map  however, the finer debris on TC26 i s located between the coarser along the center and the extremities of the cone. established along comparable sections on TC21.  4B,  deposits  No p r o f i l e s were  The r e s u l t s suggest that  accumulation and readjustment mechanisms on the slopes are complex and w i l l require further study before they are completely understood.  155 CHAPTER V - CONCLUSIONS  A.  Summary. The massive and abundant talus forms i n the Similkameen Valley  near Keremeos, B.C.  were investigated.  I t i s assumed that a l l of the  talus has accumulated i n the last 10000 years and i t i s concluded,that talus formation i n the region i s entering a passive stage of development. The slopes observed have grown to near maximum proportions,covering to a great extent the headwalls from which sediment i s derived.  A 'diminishing  sediment y i e l d concept' was applied and calculations of rates of accumulation  afforded by the incorporation of Mazamaash i n one talus  cone support the concept.  The net effect has been a reduction i n the  rate and influence of r o c k f a l l a c t i v i t y r e s u l t i n g i n a tendency towards stability.  This i s substantiated by the establishment of vegetation on  a l l talus slopes observed;  samples obtained from fences designed to  gauge rate of r o c k f a l l i n the area confirmed  the v a l i d i t y of using  vegetation as an index of s t a b i l i t y . L i t h o l o g i c control largely accounts f o r the form and degree of the talus development noted.  The  exposure of r e s i s t a n t cherts i n t e r -  bedded with weaker volcanic and sedimentary rocks has resulted i n an uneven d i s s e c t i o n of the headwalls under the influence of weathering. Talus cones occurring i n i s o l a t i o n or as coalesced groups are the net result of the uneven dissection;  south-facing slopes of the v a l l e y display  greatest development. The frequency  of f r o s t cycles suggests the importance of the  mechanisms of f r o s t shatter and frost bursting, these being considered the dominant weathering mechanisms i n the region.  Observations indicate  156 that the chemical processes of oxidation, hydration and solution are important as w e l l .  A number of secondary physical processes, including  root wedging, may have limited e f f e c t . Observed concentration of r o c k f a l l a c t i v i t y during the spring season suggests the importance of " f r o s t - r i v i n g " as a release mechanism. Lubrication and buildup of hydrostatic pressure by water i s also considered effective.  The expansion  and contraction associated with the character-  i s t i c a l l y high diurnal range of temperature i n summer may be a s u f f i c i e n t force to set rocks loose.  Attempts to measure rates of r o c k f a l l a c t i v i t y  met with f a i r success i n the construction of fences on TC25  and TC49.  The loss of a substantial portion of certain samples, however, l i m i t s the effectiveness of the method. Net and d i f f e r e n t i a l downslope movement of debris was on lines painted on three talus slopes i n the region.  detected  In general, more  disturbance and greater net downslope movement was recorded on coarse as compared to fine s t r i p s of debris.  The r e l i a b i l i t y of this method  of detecting mass movement on the slope i s questioned i n l i g h t of the disturbance to the slope when the l i n e i s painted.  Notwithstanding,  the  observations made suggest that mechanisms of mass movement d i f f e r between f i n e and coarse s t r i p s .  Further study of the phenomenon i s warranted.  Spontaneous mass movement as the r e s u l t of l u b r i c a t i o n by water ( r a i n f a l l and melt) was  i n d i r e c t l y observed.  A number of other  mass movement mechanisms are recognized as important, including talus creep, flowing water, snow avalanche, animal and human disturbance and basal  sapping. I t i s thought that reasonable explanations have been given for  the occurrence of boulder aprons and the d i s t r i b u t i o n of vegetation  157 on talus cones observed i n the region.  A s a t i s f a c t o r y explanation for  the occurrence of "protalus boulder accumulations" on TC67 could not be given but i t i s thought that the ridges may Measurements on TG21  represent a r e l i c t accumulation.  indicate that debris along l a t e r a l p r o f i l e s  i s s i g n i f i c a n t l y larger at the 17 l e v e l than debris sampled along the 0  central p r o f i l e .  Also, some c o r r e l a t i o n between s i z e and angle i s implied  since the l a t e r a l p r o f i l e s are steeper than the central p r o f i l e . r e s u l t s substantiate the hypothesis  The  that transport mechanisms down the  center are d i f f e r e n t from those along the sides of the cone.  Further  study i n this d i r e c t i o n might be worthwhile. According  to i n i t i a l observations made, i t was  hypothesized  that  no downslope sorting of the debris exists on talus slopes i n the region. Analysis of data c o l l e c t e d on longitudinal p r o f i l e s and traverse samples contradict the hypothesis; was  detected.  a s l i g h t increase i n cobble size downslope  The trend i s weak and not monotonic but an associated  downslope decrease i n angle suggests a c o r r e l a t i o n between size and  angle.  This contradicts the c o r r e l a t i o n between size and angle determined by comparison of central and l a t e r a l p r o f i l e s on TC21.  The r e s u l t s indicate  that d i f f e r e n t transport mechanisms operate on different parts of the slope. Fine and coarse s t r i p s of debris found on most talus slopes observed displayed no s i g n i f i c a n t differences i n fragment c h a r a c t e r i s t i c s which might account for the sorting observed.  I t i s concluded that the  cross-slope sorting into f i n e and coarse s t r i p s of debris i s a function of v a r i a b l e mass movement mechanisms.  I t i s suggested that the larger  cobbles accumulate on an i n d i v i d u a l basis along the slope whereas the fine materials accumulate en masse i n the form of miniature slides as s t r i p s  158 adjacent to the coarse material. Calculation of Zingg shape and flatness and s h e r i c i t y parameters from data c o l l e c t e d i n a v a r i e t y of ways indicates no detectable downslope trend.  This observation tends to confirm R i t c h i e ' s hypothesis  mobility of debris i s independent of shape.  that  The lack of a predominant  shape type i s a r e f l e c t i o n of the very complete j o i n t i n g of the headwall. The mapping of TC26 on a large scale for the morphometric analysis was  attempted.  A useful map  purposes of  was  produced which  v e r i f i e d some of the assumptions made regarding talus morphology i n the region.  Trend surface analysis based on sampling of the debris i n  conjunction with the mapping of TC26 provided good r e s u l t s .  The fourth  degree surface plotted explains 46.67 of the variance i n the data 0  portrays the gross s u r f i c i a l d e t a i l of the cone very w e l l .  and  The generalized  d i s t r i b u t i o n of fines and coarse material portrayed by the trend surface on TC26 suggested control exerted by d i f f e r e n t i a l mass movement mechanisms. The d i s t r i b u t i o n has been explained i n terms of i n d i v i d u a l and en masse movement of debris on the slope. The investigation has produced some i n t e r e s t i n g as well as worthwhile r e s u l t s .  The attempt, however, i s r e a l l y only a beginning.  Since the occurrence of abundant and impressive talus forms i s rare i n accessible regions i t i s thought that the Similkameen Valley near Keremeos, B.C.  affords an ideal opportunity for an expanded study of the  d i s t r i b u t i o n , form and mechanics of talus development. B.  P r a c t i c a l Recommendations for the Region. The occurrence of a substantial number of talus slopes near  Keremeos presents advantages and disadvantages to the residents of the area.  Both past and present talus a c t i v i t y have e f f e c t .  159 Perhaps the most welcome advantage i s the ready supply of suitable r i p r a p , located at the base of most slopes, which i s used to protect the banks of the Similkameen River during peak flows.  This  debris would be i d e a l , as well, to use as f i l l i n the construction of railway and highway beds. Construction of highways i n close proximity to talus slopes, however, can prove to be dangerous.  At CC44, the course of the  Similkameen River hugs the north side of the v a l l e y very c l o s e l y . At this point the Southern Trans-Canada Highway has a cut which truncates a series of coalesced talus cones.  This i s p o t e n t i a l l y dangerous f o r  any passerby i n l i n e with debris moving down the talus slope.  A ditch  skirts the edge of the highway between i t and the cut but such a ditch would not be e f f e c t i v e i n containing the debris as such ditches are where cuts are made through shear rock faces (see Figure V - l ) . Ritchie (1963) suggested a series of fencing techniques  Photo V - l .  to accomodate the  Gathered Talus Rubble  FIGURE  Y-l.  ROCKFALL  TRAJECTORIES  161 various t r a j e c t o r i e s of debris encroaching  upon highways.  Rockfall produces additional problems i n the v a l l e y .  The  accumulation of large boulders at the apron or base of talus slopes occurs frequently on l e v e l terrace land which i s p o t e n t i a l l y arable. This land usually remains unproductive since removal of the is costly.  boulders  An exception appears i n Photo V - l which shows talus rubble  gathered into strips near the base of talus cones at CC7. reclaimed i n this way was  planted i n a l f a l f a .  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Geografiska Annaler, v o l . 45, 1963, pp. 113-121. Winkler, Erhard M. "Weathering Rates as Exemplified by Cleopatra's Needle i n New York City." Journal of Geology Education, 1965, pp. 50-52. Young, A. Scree P r o f i l e s i n West Norway. Premier Rapport de l a Commission Pour 1'Etude des Versants, University of Amsterdam, 1958. . "Slope P r o f i l e Analysis." Z e i t s c h r i f t fur Geomorphologie, Supplementband 5, 1964, pp. 17-27.  170 APPENDIX.  A.  Maps and Photographs Used. T e r r e s t r i a l photo coverage was obtained i n the form of black and  white prints and coloured slides using a 35 mm.  camera.  A i r photo  interpretation and the construction of a base map for the area were accomplished employing B.C. Government (Department of Lands, Forests and Water Resources, V i c t o r i a , B.C.) a i r photos l i s t e d below i n Table 1: Table U  LIST OF AIR  PHOTOS  Photo #  Scale at River Level  Date of Exposure  1.  B.C. 5007 - 65-84  1:10900  May  2.  B.C. 5208 - 020-028 041-045  1:35700  Sept.3/66  1:35700  Sept.3/66  3.  31/59  B.C. 5214 - 001-003; 037-039; 097-104; 125-127;  178, 179  Suitable topographic map coverage was available (Surveys and Mapping Branch, Department of Mines and Technical Surveys, Ottawa) and a l i s t of the maps used i s found i n Table 2. Table 2  LIST OF TOPOGRAPHIC MAPS  T i t l e of Map  Number  1.  Map  Keremeos  Scale  Date  1:50,000  1939  341A  (82E/4) 2.  Ashnola  92H/1-E  1:50,000  1960  3.  Penticton (advanced print) Hedley (advanced p r i n t )  82E/S-W  1:50,000  1965  92H/8.-E & W  1:50,000  1966  4.  171 B.  Additional Notes for Map 2. The rocks as i n d e n t i f i e d by Bostock (1929, 1930) are as follows: 1.  Independence Formation:  2.  Shoemaker Formation:  3.  Old Tom Formation:  4.  Springbrook Formation:  5.  Marron Formation:  chert, greenstone.  chert;  some t u f f , greenstone.  greenstone; basalt flows, s i l l s , bosses; some d i o r i t e . mainly conglomerate; shale.  mainly b a s a l t i c l a v a l ;  some breccia, t u f f ,  conglomerate. 6.  Olalla  7.  O l a l l a syenite.  8.  Barslow Formation:  9.  Blind Creek Formation:  10.  pyroxenite.  Kobau Group:  some sandstone,  argillite. limestone.  quartzite, s c h i s t , greenstone.  

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