UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Relation between secondary structures in Athabasca Glacier and laboratory deformed ice Stanley, Alan David 1965

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
UBC_1966_A1 S7.pdf [ 13.5MB ]
Metadata
JSON: 1.0053046.json
JSON-LD: 1.0053046+ld.json
RDF/XML (Pretty): 1.0053046.xml
RDF/JSON: 1.0053046+rdf.json
Turtle: 1.0053046+rdf-turtle.txt
N-Triples: 1.0053046+rdf-ntriples.txt
Original Record: 1.0053046 +original-record.json
Full Text
1.0053046.txt
Citation
1.0053046.ris

Full Text

R E L A T I O N B E T W E E N S E C O N D A R Y S T R U C T U R E S I N A T H A B A S C A G L A C I E R A N D L A B O R A T O R Y D E F O R M E D I C E B y A L A N D A V I D S T A N L E Y B . S c , A . R . C . S . I m p e r i a l C o l l e g e , L o n d o n U n i v e r s i t y , 1 956 M . S c , T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I960 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F D O C T O R O F P H I L O S O P H Y t i n t h e D e p a r t m e n t o f G E O L O G Y W e a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A J u l y , 1965 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t he r e q u i r e m e n t s f o r an advanced deg ree a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g ree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f 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 be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n Depar tment The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, Canada The U n i v e r s i t y of B r i t i s h Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY of ALAN DAVID STANLEY B.Sc. 9 A.R.C.S.., The Univ e r s i t y of London, 1956 M.Sc,3 The Univ e r s i t y of B r i t i s h Columbia, 1960 WEDNESDAY, FEBRUARY 23, 1966 AT 3:30 P.M. IN ROOM 102 s FORESTRY & GEOLOGY BUILDING COMMITTEE IN CHARGE Chairman; R.F. Scagel W.R. Danner W.H. Mathews J.A. Jacobs J.V. Ross J„R. McKay W.H. White External Examiners M.F. Meier United States Geological Survey Tacoma, Washington, U.S.A. R E L A T I O N B E T W E E N S E C O N D A R Y S T R U C T U R E S I N A T H A B A S C A G L A C I E R A N D L A B O R A T O R Y D E F O R M E D I C E . ABSTRACT Gla c i e r movement produces numerous secondary- structures that include layering formed by d i f f e r e n t types:of ice and the preferred crystallographic. o r i e n t a t i o n of the constituent grains. This thesis describes structure on Athabasca Glacier and shows how they are r e l a t e d to the systems of stress that produced g l a c i e r flow. C v measurements of ice grains at 25 locations on the ablation surface give f a b r i c diagrams that represent r e a l stress f a b r i c s that have two or more areas of concentration containing up to 7% of the data. The diagrams may be separated into two d i s t i n c t groups according to t h e i r l o c a t i o n on the i c e surface. Fabric diagrams from coarse layers near the margins have two or more maxima clustered near the pole to the l a y e r i n g . Diagrams from contorted f i n e layers near the middle of the g l a c i e r have most data concentrated in the same quadrant, but maxima f a l l on the locus of a small circle, of constant radius. The observed radius l i e s between 30 and 50°, and the centre, located i n approximately the same po s i t i o n in a l l diagrams, represents a line, subparallel with the d i r e c t i o n of g l a c i e r flow. The two types of ice and t h e i r d i s t i n c t f a b r i c indicate that two d i f f e r e n t stress systems ex i s t in a g l a c i e r . Ice near the margin i s under shear while that near the centre i s under compression. In laboratory experiments, any increase i n the rate of creep may be a t t r i b u t e d to some, process of r e c r y s t a l l i z a t i o n , Test specimens that have r e c r y s t a l l i z e d under compression are composed of small grains with C v axes that tend to-be oriented i n a small c i r c l e about the unique stress a x i s . Fabrics of compressed ice are i d e n t i c a l to those obtained from ice near the centre of many g l a c i e r s and show that i f ice deforms most r e a d i l y by g l i d e within the basal plane, the f i n a l o r i e n t a t i o n f a b r i c depends upon the l o c a l plane of movement and not the place of maximum resolved shear s t r e s s . GRADUATE STUDIES F i e l d of Study: Geology Structural Analysis Problems i n Sedimentology Advanced Geochemistry J.V. Ross W.H. Mathews R.E. Delavault Other Studies Advanced Geophysics J»A. Jacobs PUBLICATIONS STANLEY,. A.D., 1964 Relation of Copper to rock types i n an. area of known economic mi n e r a l i z a t i o n . . Econ. Geol., V o l. 59, No. 8, 1492. i i hi;.) I qui, i G l a c i e r movement produces numerous secondary struc tures including layers formed by d i f f e r e n t types of ice and the preferred crystallographic orientation of constituent grains. This thesis describes structures on Athabasca Gl a c i e r and shows how they are related to systems of stress that produce g l a c i e r flow. The surface of Athabasca G l a c i e r can be divided into an area? of prominent layers of coarse ice near the g l a c i e r margin and another formed by l e s s d i s t i n c t thick layers of f i n e ice i n the central quarter of the ice tongue to within #00 m of the terminus. The coarse layers trend s u b p a r a l l e l with the g l a c i e r walls arid dip steeply towards the centre. In contrast, layers of f i n e ice near the g l a c i e r centre are near v e r t i c a l and trend p a r a l l e l with the d i r e c t i o n of flow. The layers are deformed about a transverse v e r t i c a l plane into a series of " s i m i l a r " f o l d s with limbs commonly separated by narrow cracks subparallel with the a x i a l plane. Because the.coarse layers near the margins, and the f i n e layers near the centre do not change in shape, sise or attitude down the length of the g l a c i e r they must be formed at or near t h e i r present p o s i t i o n . C v measurements of i c e grains at 25 locations on the ablation surface g i v e - f a b r i c diagrams that represent'real i i i stress f a b r i c s that have two or more areas of concentration containing up to 7$ of the data. The diagrams may be separated into two d i s t i n c t groups according to t h e i r l o c a t i o n on the ice surface. Fabric diagrams from coarse layers near the margins have two or more maxima clustered near the pole to the' la y e r i n g . Diagrams from contorted f i n e layers near the middle of the g l a c i e r have most data concentrated i n the north east quadrant, but maxima are independent of the attitude of any i c e layers. In most diagrams, maxima f a l l on the locus of a small c i r c l e of constant radius. The observed radius l i e s between 3 0 ° and 5 0 ° , and the. centre, located i n .. approximately the same position in a l l diagrams, represents ..a line, subparallel with the d i r e c t i o n of g l a c i e r flow. . The two types of i c e and t h e i r d i s t i n c t f a b r i c i n - • dicate that two d i f f e r e n t stress systems exist i n a g l a c i e r . Ice near the margin i s under shear while that near the centre , i s under compression. • In laboratory experiments, increase i n the rate of creep may be attr i b u t e d to some process of r e c r y s t a l l i z a t i o n . Test specimens that have r e c r y s t a l l i z e d under compression are composed of small grains with C v axes that tend to be oriented i n a small c i r c l e about the unique stress axis. Fabrics of compressed i c e are i d e n t i c a l to those obtained from ice near the centre of many g l a c i e r s and • show that i f i c e deforms most r e a d i l y by glide within the i v basal plane, trie f i n a l o rientation f a b r i c depends upon the l o c a l plane of movement and not the plane of maximum resolved shear stress. V TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS v LIST OF FIGURES v i i ACKNOWLEDGEMENTS x CHAPTER I. INTRODUCTION 1 GENERAL STATEMENT 1 ATHABASCA GLACIER 16 CHAPTER I I . MESOSCOPIC STRUCTURES 23 GENERAL STATEMENT 23 PREVIOUS WORK 35 METHODS OF FIELD STUDY 44 RESULTS OF FIELD STUDY 45 DISCUSSION OF ICE LAYERS 59 SUMMARY 74 CHAPTER I I I . MICROSCOPIC STRUCTURES . 76 GENERAL STATEMENT 76 PREVIOUS WORK 34 METHODS OF FIELD STUDY 93 RESULTS OF FIELD STUDY 96 DISCUSSION OF ICE FABRICS 105 SUMMARY 127 CHAPTER IV. EXPERIMENTAL STUDIES 130 GENERAL STATEMENT 130 PREVIOUS WORK 135 METHODS OF LABORATORY STUDY 140 RESULTS OF LABORATORY STUDY 145 DISCUSSION OF ICE FABRICS 155 SUMMARY 159 CHAPTER V. RELATION BETWEEN ICE STRUCTURES AND STRESS SYSTEMS 160 GENERAL STATEMENT 160 MECHANICS OF ICE MOVEMENT 161 v i Page RELATION BETWEEN FABRIC AND STRESS ORIENTATION SUMMARY I 6 4 1 6 7 CHAPTER VI. CONTRIBUTIONS AND RECOMMENDATIONS 1 6 9 SUMMARY OF CONTRIBUTIONS RECOMMENDATIONS FOR FURTHER WORK 1 6 9 1 7 0 BIBLIOGRAPHY 1 7 2 APPENDIX I. ICE FABRIC DATA AND CONTOURED DIAGRAMS FOR ATHABASCA GLACIER 1 8 4 APPENDIX I I . ICE FABRIC DATA AND CONTOURED DIAGRAMS OF COMPRESSED ICE CYLINDERS 1 9 4 APPENDIX I I I . CREEP CURVES FOR COMPRESSION TESTS 2 0 1 APPENDIX IV. INTERPRETATION OF CREEP CURVES 2 0 8 v i i LIST OF FIGURES Page 1 . PHOTOGRAPH OF ATHABASCA GLACIER. 17 2 . LOCATION MAP OF ATHABASCA GLACIER. 19 3 . MAP OF EASTERN PART OF COLUMBIA ICEFIELD. 21 • 4 . DISTRIBUTION OF CREVASSES IN THE CASTLEGUARD SECTOR OF THE SASKATCHEWAN GLACIER. 3 0 5 . ICE VEIN NEAR THE CENTRE OF THE ATHABASCA GLACIER. 3 4 6 . ICE VEIN WITH COARSE CRYSTALS. 3 4 7 . VIEW UP THE CENTRE OF THE ATHABASCA GLACIER. 4 6 8 . LAYERING FORMED BY PLANES OF DIRT-FILLED BUBBLES. 4 8 9 . DIRT-FILLED BUBBLES OPEN TO THE SURFACE. 4 8 1 0 . OUTLINE MAP OF ATHABASCA GLACIER INDICATING ZONES OF DIFFERENT TYPES OF ICE LAYERS. 50 1 1 . LAYERS OF COARSE ICE. 52 1 2 . DEFORMED LAYERS OF COARSE ICE. 52 1 3 . MAP OF THE OBSERVED LAYERING ON THE SURFACE OF ATHABASCA GLACIER. 53 1 4 . AERIAL PHOTOGRAPH OF ATHABASCA GLACIER. 55 1 5 . DEFORMED LAYERS OF FINE ICE. 57 1 6 . LAYERS OF FINE ICE. 5 8 1 7 . LAYERS OF FINE ICE. 5 8 1 8 . PLAN OF ICE SURFACE NEAR CENTRE OF GLACIER BELOW ICEFALLS. 65 1 9 . PLAN OF ICE SURFACE NEAR CENTRE OF GLACIER. 6 6 2 0 . DIAGRAM TO SHOW MECHANISMS OF FOLDING.: " . . 6 8 2 1 . LONGITUDINAL SECTION OF ATHABASCA GLACIER SHOWING THEORETICAL DISTORTION OF A TRANSVERSE VERTICAL PLANE. 7 0 viii Page 2 2 . OUTLINE MAP OF ATHABASCA, GLACIER SHOWING THEORETICAL SURFACE CONFIGURATION OF A TRANSVERSE VERTICAL PLANE. 71 2 3 . OUTLINE MAP OF ATHABASCA GLACIER SHOWING LOCATIONS OF ICE FABRIC MEASUREMENTS. 94 24. MAP OF FINE LAYERS AND FABRIC DIAGRAMS FROM LOCATIONS 62-11, 6 2 - 1 2 . . . 101 25. MAP OF FINE LAYERS AND FABRIC DIAGRAMS FROM LOCATIONS 62-14, 62-15. 102 2 6 . SYNOPTIC DIAGRAM OF ROTATED FABRICS OF FINE ICE FROM LOCATIONS 6 2 - 3 to 62-3, 62-10 to 62-12, .-AND 62-14 to 62-16. 104 27. FABRIC DIAGRAM AND SUBFABRIC DIAGRAMS FROM LOCATION 62-5. 116 23. FABRIC DIAGRAM AND SUBFABRIC DIAGRAMS FROM LOCATION 62-5. 117 2 9 . FABRIC DIAGRAMS OF FINE ICE WITH SIMPLIFIED 119 to DIAGRAM SHOWING LOCUS AND CENTRE OF POSTULATED to 34. SMALL. CIRCLE. 124 35. SYNOPTIC DIAGRAM OF FINE ICE FABRICS. 126 36. ICE FABRIC DIAGRAMS FROM MOLTKE GLACIER. 123 37. SCHEMATIC DIAGRAM SHOWING APPARATUS TO COMPRESS ICE. 142 3 3 . DIAGRAM SHOWING RELATION BETWEEN FABRIC DIAGRAM AND SECTIONS OF ICE CYLINDER. 144 39. STRAIN-TIME GRAPHS FOR'COMPRESSION TESTS. 146 40. STRAIN-TIME GRAPHS FOR COMPRESSION TESTS. 147 4 1 . FABRIC DIAGRAMS OF COMPRESSED ICE. 150 4 2 . HISTOGRAMS SHOWING INCLINATION OF C v AXES OF 152 to COMPRESSED ICE CYLINDERS. to 44. 154 45. SCHEMATIC DIAGRAM OF PART OF A GLACIER TO SHOW THE DISTRIBUTION OF LAYERS AND ORIENTATION OF ICE GRAINS. 163 ix Page 46. ICE FABRIC DATA AND CONTOURED DIAGRAMS 185 to FOR ATHABASCA GLACIER. to 54. ~ 1 9 3 55. ICE FABRIC DATA AND CONTOURED DIAGRAMS 195 to OF COMPRESSED ICE CYLINDERS. to 60. 200 61. CREEP CURVES FOR ICE CYLINDERS IN COMPRESSION (T -5 .5°C) 202 62. STRAIN-TIME CURVE FOR AXIAL STRESS 136 LBS. 203 63. CREEP CURVES FOR ICE CYLINDERS IN COMPRESSION AXIAL STRESS 31.8 LBS. 204 64. CREEP CURVES FOR ICE CYLINDERS IN COMPRESSION AXIAL STRESS 47.7 LBS. 205 65. CREEP CURVES FOR ICE CYLINDERS IN COMPRESSION AXIAL STRESS 63.6 LBS. 206 66. CREEP CURVES FOR ICE CYLINDERS IN COMPRESSION AXIAL STRESS 79.5 LBS. 207 67. GRAPH OF SHEAR STRAIN RATE vs . SHEAR STRESS 213 68. GRAPH OF n vs. TIME 214 OUTLINE MAP SHOWING SAMPLE LOCATIONS & FABRIC DIAGRAMS. . ,  . . In pocket at back of thes i s . ACKNOWLEDGMENTS Dr. J. V. Ross, of the Department of Geology, o r i g i n a l l y suggested the topic for research and l a t e r supervised the work reported i n t h i s t h e s i s . During the investigation, Drs. J. R. McKay and W. S. Paterson made several constructive comments. Drs. W. H. Mathews and R. V. Best offered valuable advice on many problems and suggested numerous improvements to the general text. The assistance of a l l these people i s g r a t e f u l l y acknowledged. The project could not have been undertaken without the enthusiastic co-operation of numerous members i n the f a c u l t y and s t a f f of the Faculty of Engineering. Assistance and advice was obtained from Mr. P. Demco and other members of his technical s t a f f , who spent considerable time helping me with the experimental work. Mr. W. G. Heslop granted the use of the Faculty's Baldwin tensometer, and Dr. A. Hrennikoff offered advice regarding int e r p r e t a t i o n of creep curves. Funds were not available f o r f i e l d work, but labora tory equipment, including a universal stage used to determine ice c r y s t a l orientations, was purchased with funds from the Department of Geology and Grant #65/6024/270 from the Geolo g i c a l Survey of the Department of Mines and Technical Survey, Ottawa. Typing of o r i g i n a l drafts was done by my wife, E. Stanley, and the f i n a l manuscript was completed by Mrs. A. Abraham. - 1 - CHAPTER I INTRODUCTION GENERAL STATEMENT A . g l a c i e r i s not a s o l i d mass o f u n i f o r m i c e . I t s s u r f a c e i s b r o k e n by numerous f r a c t u r e s o r open c r a c k s and i s composed o f d i f f e r e n t t y p e s o f i c e w i t h a number o f d i s t i n c t y s t r u c t u r e s . The t e r m s t r u c t u r e i s used here t o d e s i g n a t e a l l the r e c o g n i z a b l e elements i n a g l a c i e r and i n c l u d e s mesoscopic f e a t u r e s such as l a y e r s of i c e o b s e r v e d i n hand specimens, and m i c r o s c o p i c f e a t u r e s such as t h e c r y s t a l l o g r a p h i c o r i e n  t a t i o n o f i c e g r a i n s . I c e l a y e r s and o t h e r f e a t u r e s c h a r a c  t e r i s t i c o f t h e a b l a t i o n zone are a l l secondary s t r u c t u r e s t h a t r e s u l t f r o m g l a c i e r f l o w . Measurements o f g l a c i e r flow, and t h e creep o f i c e i n l a b o r a t o r y e x p e r i m e n t s , have been s y n t h e s i z e d i n t o a g e n e r a l i z e d f l o w law, but t h i s law does not i n d i c a t e a r e l a t i o n s h i p between ' s t r e s s axes and secondary s t r u c t u r e s . , D e s p i t e many e x c e l l e n t s t u d i e s , t h e r e l a t i o n s h i p i s not c l e a r l y u n d e r s t o o d and the o r i g i n o f many, s t r u c t u r e s r emains i n doubt. The purpose o f t h i s t h e s i s i s t o : 1) D e t e r m i n e . t h e o r i g i n o f l a y e r e d i c e . 2) E x p l a i n the p r e f e r r e d c r y s t a l l o g r a p h i c • o r i e n t a t i o n o f g l a c i e r i c e g r a i n s . 3 ) E s t a b l i s h a r e l a t i o n s h i p between secondary s t r u c t u r e s and systems o f s t r e s s . Although g l a c i e r s are considered to be monomineralic tectonites, they are not d i r e c t l y analogous to more durable rocks, f o r the ice i s near i t s melting point and has the unusual property of contracting when i t melts. Despite these differences, some g l a c i e r structures have been compared with folded layers and complex f a u l t systems observed i n deformed rocks, and M e r r i l l (1962) points out that a g l a c i e r forms a natural laboratory f o r the study of s t r u c t u r a l geology. Structural geology i s concerned with the recogni t i o n , representation and genetic i n t e r p r e t a t i o n of a l l the structures observed i n deformed rocks. Most studies are p r i n c i p a l l y concerned with t h e i r . d e s c r i p t i o n , o r i g i n , angular r e l a t i o n s h i p , and the progressive change in geometry during deformation. Possible r e l a t i o n s h i p between these structures, and the orientation of the system of stress has been inferred from detailed investigations of the rocks themselves, and deduced from theories of thermodynamics and mechanics. It i s d i f f i c u l t to determine the o r i e n t a t i o n of a stress system with respect to large scale ; structures observed i n the f i e l d , for the stresses have long since disappeared and can no longer be measured. However, i r r e s p e c t i v e of the manner in which the s t r u c t u r a l elements are formed or d i s  torted, they can be related to each other by a pattern of symmetry which i s a r e s u l t of the o r i g i n a l attitude of layered rocks and the stress o r i e n t a t i o n . Symmetry i s shown by the geometric arrangement of mesoscopic structures, such as f o l d s and l i n e a t i o n s observed i n the f i e l d , and by microscopic - 3 - structures including the s p a t i a l arrangement and c r y s t a l l o  graphic orientation of in d i v i d u a l minerals. Theories r e l a t i n g to the orientation of some minerals under stress have been advanced by numerous workers, including Brace (I960) and Kamb (1959a). Brace uses a modified version of McDonalds f (1957) fracture hypothesis to explain c r y s t a l orientation, and Kamb uses p r i n c i p l e s ' o f thermodynamics as outlined by Gibbs (1906). Mineral orientations predicted by these theories are not the same as those determined f o r tectonites by f i e l d studies, and by microscopic analyses. To substantiate any of the present hypotheses, i t i s neces sary to determine the orientation of minerals by detailed f i e l d observations and to reproduce these orientations under known conditions i n the laboratory. In laboratory experiments, small scale rock speci mens are stressed under known conditions to determine the ultimate strength, the rate of deformation, and the reorienta t i o n of constituent minerals under stress. In most mechanical tests, a load i s applied f o r a short time, but as the specimens are unable to r e c r y s t a l l i z e , they f a i l by shear along p a r t i  cular planes. In most t e s t s , the actual plane of f a i l u r e i s less than 45°'to the unique stress d i r e c t i o n and i s not p a r a l l e l with the plane of maximum resolved shear stress, predicted by theory. The difference between the actual and th e o r e t i c a l planes of f a i l u r e i s partly a function of con f i n i n g pressure (Brace, 1963) and re s u l t s from i n t e r n a l f r i c t i o n . - 4 - Laboratory experiments using rock specimens cannot represent true models of large structures i n durable rocks under similar stress conditions. For any test to be repre sentative, a test material having di f f e r e n t physical parameters, such as highly viscous wax, must be used (Hubbert, 1937). A model of t h i s kind, however, i s not e n t i r e l y s a t i s  factory; for i t reproduces only the gross geometry of large scale features (Ramberg, 1964). In a discussion of the laws of mechanics, Carey; (1954) shows the duration of laboratory t e s t s to be i n s i g n i  f i c a n t i n comparison with geologic time and that data obtained from mechanical t e s t s cannot be used to analyse the s t r a i n of durable rocks. He suggests that the t o t a l ' s t r a i n of a body can be considered as the sum of four components:- a purely e l a s t i c s t r a i n , a p l a s t i c strain., a transient creep that diminishes with time, and a viscous component that. v fis time dependent. I f stress i s applied f o r a considerable time, the viscous component of s t r a i n increases at a slow, steady . rate, and becomes progressively larger than the others. xCarey considers that when the viscous component becomes at least three orders of magnitude greater than the e l a s t i c deforma t i o n , the material behaves essentially.as a f l u i d . Carey describes any material that behaves as a f l u i d , and y e t remains below i t s melting point as a ! r h e i d body'. From the data he quotes, most common rocks necessarily become rheid bodies i f they are stressed for 10*seconds (1,000 years). Obviously, in:laboratory tests i t i s impossible to stress durable rocks u n t i l they become rheid bodies, even i f s u i t  able temperate-pressure conditions could be maintained. Ideal laboratory test specimens should have rheid-values of only a few hours. Ice has physical properties that place i t somewhere between the two extremes of i d e a l and r e a l and since i t has a postulated rheid value of only two weeks, i t i s a suitable material f o r model experiments. Ice specimens have been deformed i n the laboratory, under conditions that duplicate the stress system near the centre of a g l a c i e r , i n order to determine a r e l a t i o n between stress systems and secondary structures. In t h i s t h e s i s , an attempt i s made to use these r e s u l t s to determine a r e l a t i o n  ship between some of the structures observed on Athabasca Glacier, Alberta. Athabasca Glacier was p a r t i c u l a r l y suitable,fore study. :It has a simple geometric shape, and i t i s conveniently located with roads leading d i r e c t l y to i t . Furthermore, excellent a i r photographs and detailed maps of the area are r e a d i l y a v a i l a b l e , and information about the rates of g l a c i e r flow and the bedrock topography are given i n reports by Paterson (1962) and Kanasewich (1964). The main topics of discussion are ice layers and the c r y s t a l s they contain. The presentation of material i n t h i s t h e s i s i s designed to: 1) Introduce the reader to the general topic and discuss important features of previous work. - 6 - 2) Outline methods and results of the present ) study. 3) Discuss the significance of the r e s u l t s with respect to previous studies. 4) Summarize main features of the discussion. Chapters II and III deal respectively with mesoscopic and microscopic structures developed by g l a c i e r flow, and Chapter IV deals with the r e s u l t s of laboratory experiments. Glacier structures are compared with those of experimental t e s t s i n Chapter V. Chapter VI contains an outline of the main contributions of the present study and includes recommen dations f o r future work. Sections given i n the Appendix con t a i n a l l c r y s t a l o r i e n t a t i o n determinations from f i e l d and laboratory measurements, and a l l the r e s u l t s of creep te s t s , together with a short discussion of the flow law of i c e . Glacier structures are not a f a m i l i a r topic. In order to make the subject matter clear, i t i s necessary to show the development of ideas i n a b r i e f review of the early l i t e r a t u r e concerning g l a c i e r flow. Most of the early papers were printed i n journals or books that are now d i f f i c u l t to obtain, and although ideas of some authors have been quoted, the o r i g i n a l work was not consulted. Information about some authors was obtained from the works by Dobrowolski (1923) and Seligman (1949a), and short summaries :given i n a Bibliography published by SIPRE. - 7 - General Theories Glaciers have been studied since the mid 1700's but the early g l a c i o l o g i s t s were unable to explain many perplexing problems concerning the rate and manner in which g l a c i e r s flow. In recent years, several detailed quantitative studies have established a flow law to describe the rate of g l a c i e r movement. This law, however, does not explain the movement and even now, the actual mechanics of ice deformation are s t i l l not c l e a r l y understood. Quantitative Theories The f i r s t systematic measurements of g l a c i e r flow were made i n the middle of the nineteenth century. From these and other measurements obtained during the following twenty years, i t was deduced that g l a c i e r flow resembles that of a highly viscous l i q u i d . Theoretical interpretations were advanced by Finsterwalder (1897), Somigliana (1921), and l a t e r , by Lagally (1934), who extended the interpretations and was able to predict the approximate depth of the Pasterze Glaci e r . These early theories, however, did not accord with l a t e r observations and precise measurements show that flow of a g l a c i e r i s more sensitive to small changes i n thickness than would be expected i f ice behaved as a Newtonian l i q u i d . Streiff-Becker (1938) measured the annual accumulation of snow in the Clarinden-firn snowfield in Switzerland and c a l  culated the t h e o r e t i c a l v e l o c i t y of a g l a c i e r fed by t h i s snow. - g - Because the calculated v e l o c i t y was greater than the maximum v e l o c i t y of the g l a c i e r surface, he was forced to postulate that the g l a c i e r flowed more rapidly at depth. A similar idea was independently suggested by Demorest (1939, 1943) after he had studied the d i s t r i b u t i o n of g l a c i a l s t r i a t i o n s within t h i n bedded a r g i l l i t e s beneath the Clements Glacier i n Glacier National Park. He noted the d e f l e c t i o n of s t r i a t i o n s about obstacles and trenches, and several c i r c u l a r structures produced by eddies i n the g l a c i e r , and.concluded that ice at the g l a c i e r base behaved as a f l u i d . Although he never published a formal mathematical presentation of his ideas, he did state that the maximum rate of movement at the border of an ice sheet probably would be less than a few inches or perhaps f r a c t i o n s of an inch per day..; (Demorest, 1943, p.373). The hypothesis of Demorest and Streiff-Becker became known as 'Extrusion flow'. According to t h i s , movement occurs by shearing along very t h i n planes sub-parallel with the g l a c i e r surface and at high hydrostatic pressures smaller stresses are capable of producing a given deformation. This theory implies that ice at depth i n a g l a c i e r must be squeezed out by the pressure of the overlying material. 'Extrusion flow' remained a possible mechanism for several years because the c o l l e c t i o n of additional information was unavoidably postponed. In the 1950's, v e r t i c a l bore hole measurements were made i n many g l a c i e r s and the deformation calculated. The deformation measurements of every bore hole indicate that ice just below the surface moves f a s t e r than layers • - 9 - deep w i t h i n the g l a c i e r . (Gerard and others, 1952; Sharp, 1953; Mathews, 1959; Meier, I960; Paterson, 1962). The upper 70 m. of a g l a c i e r i s r e l a t i v e l y b r i t t l e and appears to be dragged along by the unde r l y i n g i c e . (Savage and Paterson, 1963). R e s u l t s of most g l a c i o l o g i c a l measurements and of l a b o r a t o r y studies by Rigsby (1958) and Higashi (1959) i n d i c a t e t h a t high h y d r o s t a t i c pressures have l i t t l e e f f e c t on the creep r a t e of i c e . Measured r a t e s of d r i l l hole deformation, movements of survey stakes on g l a c i e r surfaces and the closure of a d i t s have a l l been synthesized i n t o a fl o w law tha t approximates: where £ •»»•• r a t e of shear s t r a i n l v«=» e f f e c t i v e shear, s t r e s s K. ??- constant dependent on temperature n a f a c t o r 'dependent on s t r e s s ' S t r a i n of p o l y c r y s t a l l i n e i c e i s a f u n c t i o n of the mechanical behaviour of i n d i v i d u a l c r y s t a l s under s t r e s s and the mutual r e l a t i o n s h i p between c o n s t i t u e n t g r a i n s . The process of p o l y c r y s t a l l i n e i c e movement has been discussed i n the l i t e r a t u r e and some of the main t h e o r i e s are summarized below. Q u a l i t a t i v e Theories Over the l a s t 200 years, d e s c r i p t i o n s of the mechanics of g l a c i e r f l o w have been given i n j o u r n a l s of l i m i t e d c i r c u  l a t i o n , w i t h the r e s u l t that s e v e r a l authors have r e i t e r a t e d the same ideas with only minor changes. Most of the ideas, 10 - however, may be generalised into two main groups - one in which movement occurs as mass displacement over the bedrock or along r e s t r i c t e d planes within the g l a c i e r , and the other i n which movement i s the sum t o t a l of movements by an i n f i n i t e number of in d i v i d u a l ice grains. In the early days of glaciology, De Saussure thought that g l a c i e r s moved wholly by s l i d i n g on t h e i r beds. Agassiz noted that a l i n e of stones placed i n p i l e s across the g l a c i e r progressively deformed 'into a parabola, i n d i c a t i n g that sur face v e l o c i t y i s greatest near the centre and decreases progressively near the margins. Glacier flow i s a combination of both bodily movement over the bed or along r e s t r i c t e d planes within the i c e , as well as continuous deformation of in d i v i d u a l grains within the g l a c i e r . The mass movement of ice over the confining bedrock can be measured d i r e c t l y at the g l a c i e r margins, or obtained by extrapolating the r e s u l t s of surface measurements and bore hole deformation. Marginal s l i p ranges from l+% to 30% of the maximum surface v e l o c i t i e s and values for.basal s l i p have been recorded as '44% (Mathews, 1959); 50% (Perutz and Seligman, 1939); 10%-75% (Savage and Paterson, 1963), and even up to 90$ (McCall, I960). The large value given by McCall was obtained from a cirque g l a c i e r on a steep slope. The amount of basal s l i p f o r most g l a c i e r s probably depends on the configu r a t i o n of the bedrock surface, and possibly also on the presence of a f i l m of water at the contact. Seasonal or periodic increases i n the water on the g l a c i e r bed may cause an increase i n the basal s l i p and account - 11 - f o r s h o r t term j e r k y o r i r r e g u l a r m o t i o n s o f s u r f a c e v e l o c i t y s t a k e s . Both P a t e r s o n ( 1 9 6 4 ) and Weertman ( 1 9 6 4 ) i n v o k e i n c r e a s e d b a s a l s l i p t o e x p l a i n s u r g e s i n the f l o w t h a t have apparent v e l o c i t i e s many t i m e s t h a t o f n o r m a l . g l a c i e r movement. These surges may o c c u r as p r e s s u r e waves or t h i c k n e s s b u l g e s . W i t h i n a g l a c i e r , movement may r e s u l t f r o m d i s p l a c e  ment of l a r g e b l o c k s o f i c e a l o n g p l a n e s or narrow zones. Movement a l o n g zones w i t h i n t h e i c e have been measured by P e r u t z and S e l i g m a n ( 1 9 3 9 ) . S h u m s k i i ( 1 9 5 8 ) has suggested t h a t t h r u s t p l a n e s may d e v e l o p p a r t i c u l a r l y n e a r t h e base of a g l a c i e r , and account f o r anomalous movement and s h e a r i n g o f s e c t i o n s o f d r i l l stems deep w i t h i n the" i c e . T h r u s t movements a l o n g g e n t l y d i p p i n g f a u l t s may e x p l a i n d i r t p l a n e s t h a t c r o p out on t h e s u r f a c e near t h e snout o f some p o l a r g l a c i e r s , a l t h o u g h s i m i l a r s u r f a c e f e a  t u r e s r e s e m b l i n g t h r u s t - l i k e s t r u c t u r e s can r e s u l t f r om d i f f e r  e n t i a l a b l a t i o n ( M c C a l l , I 9 6 0 ) . When i t was demonstrated t h a t m a r g i n a l and b a s a l s l i p o v e r bedrock s u r f a c e s a c c o u n t e d f o r o n l y a s m a l l p o r t i o n o f t h e t o t a l , s e v e r a l g l a c i o l o g i s t s s u g g e s t e d t h a t t h e main movement was due t o i n t e r n a l d i s p l a c e m e n t a l o n g s e l e c t e d p l a n e s w i t h i n t h e i c e mass i t s e l f . These movement p l a n e s were i d e n t i f i e d as ' f o l i a t i o n ' by F o r b e s ( 1 3 4 2 ) ; Moseley ( 1 3 6 9 ) ; and by Dee l e y and F l e t c h e r ( 1 8 9 5 ) . P h i l l i p p ( 1 9 0 5 ) m a i n t a i n e d t h a t movement o c c u r r e d a l o n g c r a c k s p a r a l l e l w i t h t h e bed r o c k s u r f a c e , but most g l a c i o l o g i s t s c o n s i d e r e d t h a t t h i s p r o c e s s was m o d i f i e d by g r a i n l o o s e n i n g a l o n g t h e f r a c t u r e s (Crammer, 1 9 0 4 ) , or by r o t a t i o n o f g r a i n s and i n c r e a s e d p l a s t i c i t y o f - 12 - ice near the base. No clear explanation was ever given f o r the motive force behind g l a c i e r movement, but Charpentier (1341) believed i t to be caused by expansion of freezing water that had seeped down into the i c e , either along obvious cracks or between i n d i v i d u a l grains. 1 Hugi (1342) was the f i r s t to describe g l a c i e r ice as a granular mass, and l a t e r authors suggested that g l a c i e r flow r e s u l t s from numerous small-scale movements of these grains These movements can be considered as: intergranular or r i g i d body displacements i n which entire grains are displaced or rotated, and intragranular movements r e s u l t i n g from i n t e r n a l deformation of i n d i v i d u a l - g r a i n s . In general, these two types of movement are not e a s i l y distinguished because the actual process i s complicated by regelation - a vaguely defined mechanism involving changes of state and transfer of material along c a p i l l a r y fractures to areas of 'low-pressure'. However, i f g l a c i e r flow r e s u l t s e n t i r e l y from a process of l o c a l pressure-melting and vapour t r a n s f e r controlled by c a p i l l a r i t y , there i s no obvious reason why the dominant movement must be downstream. Thomson (1357) was the f i r s t to suggest regelation as a movement mechanism. He postulated that the melting point of ice was lowered at high pressures (-.0075°C. per atmosphere) and i n f e r r e d that ice under stress would become softened but not ' p l a s t i c ' . The same idea was l a t e r restated by Drygalski (1397, 1393) and Mttgge (1900) who considered that i - 13 - must flow i f the thickness exceeds 56 feet. In 1 8 9 7 , Drygalski proposed that ice movement resulted from successive stages of p a r t i a l melting and freez ing that caused grains to 'soften'. He further argued that glacier'movement was an exclusive regelation process i n which material was transferred from 'high pressure' to 'low pressure' areas. Because h i s arguments implied that deep within a g l a c i e r , increased hydrostatic pressure produced f a s t e r move ments, Drygalski must be numbered as one of the e a r l i e s t proponents of ' extrusion flow'-. A regelation process c a l l e d 'idiomolecular transfer' was suggested by T. C. Chamberlin ( 1 9 0 4 ) ' ' • " " • • • ) to explain the process of r e d i s t r i b u t i o n of material from points of lesser to points of greater molecular s t a b i l i t y . R. T. Chamberlin ( 1 9 2 6 , p. 2 9 ) carried the idea s t i l l further by postulating that the process of'ideomolecular exchange was aided by the mutual displacement of grains by rotation or f l a t t e n i n g . Grain rotation has been suggested by several workers, and calculations have been presented to show that each grain need move only 1 / 1 0 , 0 0 0 of i t s diameter every day with res pect to neighbouring grains to produce a v e l o c i t y of 3 ft/day i n a g l a c i e r six miles long. Hamberg ( 1 9 3 2 ) used a sim i l a r idea to show that i f each c r y s t a l rotated 0 . 6 ° per day, a surface v e l o c i t y of 3 0 m/year could be produced i n an ice mass 1 0 0 m. thick. Hamberg ( 1 8 9 5 ) , and Tarr and von Engeln ( 1 9 1 5 ) , a l l thought that regelation did occur and that a displacement - 14 - surface between the ice grains was lubricated by a l i q u i d f i l m that occurs about a l l grains. According to Quincke (1905) t h i s thin f i l m would not become frozen because of i t s s a l t .: content. A saline f i l m has been i d e n t i f i e d by Renaud (1949) who showed that i n i t i a l meltwater from g l a c i e r ice contains a higher proportion of s a l t s than l a t e r meltwater. Nakaya and Matsumoto (1953) have shown that a l i q u i d f i l m can s t i l l exist at temperatures of -05° C. The concept of grain r o t a t i o n was c r i t i c i z e d by Emden (1390), Hagenback-Bischoff (1399), and l a t e r , by Hawkes (1930) who argued that i f rotation did occur, a f t e r any mutual accommodation, further movement could only be accomplished by f l a t t e n i n g and elongation of the grains u n t i l the longest dimension was perpendicular to the d i r e c t i o n of 'pressure'. Since most ice grains have highly i r r e g u l a r shapes, i t i s u n l i k e l y that they can rotate with respect to each other. Tyndall (1353) was one of the f i r s t to r e a l i z e that regelation could also include a process in which grains under stress were fragmented and then displaced before they froze together again. The same general idea was expressed by ' - Helmholtz (1365), and l a t e r by Emden (1390) who suggested that grains were able to adjust themselves to s t r a i n before minute f i s s u r e s appeared. Towards the end of the 19th century, several i n v e s t i  gators demonstrated that ice c r y s t a l s were not b r i t t l e , but yielded under stress. Early experiments by McConnel (1390, 1391) and Mllgge (1395) showed that single ice c r y s t a l s - 1 5 -• deformed by movement on planes perpendicular to the c r y s t a l  lographic C-axis. Subsequently, processes of melting and regelation were no longer considered important, and most g l a c i o - l o g i s t s reasoned that g l a c i e r flow resulted from movements within i n d i v i d u a l ice grains. A discussion of the main ideas current i n the early 1 9 2 0 ' s has been given by Dobowalski ( 1 9 2 3 , p. 1 3 6 - 1 4 6 ) and some of his comments were given in the preceding paragraphs. To show how ice movement resulted from a f r a c t u r i n g process, Tamman pointed out the s i m i l a r i t y between ice defor mation and the creep observed i n metals. He demonstrated that unconfined blocks of p o l y c r y s t a l l i n e metals stressed above t h e i r e l a s t i c l i m i t develop small fractures that become more numerous as the s t r a i n increases. Early fractures are cut by l a t e r fracture planes that form a more acute angle to the unique stress d i r e c t i o n . Hawkes ( 1 9 3 0 ) summarized the mechanisms contributing to g l a c i e r flow as small s c a l e - s l i p displacements along grain contacts and within the grains by t r a n s l a t i o n g l i d i n g along the 0 0 0 1 plane, or perhaps along some other planes produced by fr a c t u r i n g or polygonization. Because early experiments had indicated that s t r a i n i n single c r y s t a l s occurred by t r a n s l a t i o n along the basal plane, i t was inferr e d that flow of ice would occur most r e a d i l y i f t h i s plane was p a r a l l e l with the plane of the greatest resolved shear stress. In g l a c i e r ice the movement plane would na t u r a l l y appear to be p a r a l l e l with the ice layers or - 16 - ' f o l i a t i o n ' . Techniques to determine the orientation of i n d i v i d u a l grains i n g l a c i e r s had been suggested by Klocke (1879) and by Deeley and Fletcher (1895) but the preferred orientation of deformed ice was not determined u n t i l the work of Bader et a l . (1939), and Perutz and Seligman (1939). Most workers presently interested i n the mechanics of ice movement rej e c t grain r o t a  t i o n as a possible ori e n t a t i o n mechanism and emphasize the importance of deformation within i n d i v i d u a l ice grains. One purpose of t h i s thesis i s to determine how ice deformation produces c r y s t a l orientations and other secondary structures in the Athabasca G l a c i e r . ATHABASCA GLACIER Athabasca Glacier (Figure 1) and Saskatchewan Glacier, 7 Km. to the south, are two major outlets of Columbia I c e f i e l d i n the Canadian Rockies. The I c e f i e l d i s roughly centred on the B r i t i s h Columbia-Alberta P r o v i n c i a l border just within the southern boundary of Jasper National Park i n the geographical area of 5 2 ° 08'N, 117° 28'W. (Figure 2). Saskatchewan Glacier has already been examined by Meier (I960) who considers i t a valley g l a c i e r of the alpine type as defined by Ahlmann (1948, p. 62, type I I ) . Columbia I c e f i e l d i s at an average elevation of 2 2 3,000 m. and covers an area of some 285 Km. About 7 Km. of t h i s forms the accumulation zone of Athabasca G l a c i e r . The Athabasca i s a r e l a t i v e l y straight g l a c i e r that flows north-- 17 - FIGURE 1. PHOTOGRAPH OF ATHABASCA GIAOIE1R - 18 - e a s t e r l y f o r a b o u t 6 . 4 K m . t o a w e l l d e f i n e d t e r m i n u s w i t h i n 0 . 2 K m . o f t h e p a v e d B a n f f - J a s p e r h i g h w a y ( F i g u r e ; 3 ) p l 0 0 ; . K m . s o u t h o f t h e s m a l l t o w n o f J a s p e r , A l b e r t a . A s m a l l t e r m i n a l l a k e - S u n w a p t a L a k e - i s t h e s o u r c e o f t h e S u n w a p t a R i v e r t h a t f l o w s n o r t h e r l y t o j o i n t h e A t h a b a s c a R i v e r . I c e i s s u i n g f r o m t h e r i m o f t h e I c e f i e l d a t a n e l e  v a t i o n o f 2 , 7 4 0 m . p a s s e s o v e r t h r e e i c e f a l l s i n a d i s t a n c e o f 2 K m . ' F r o m t h e b a s e o f t h e l o w e s t i c e f a l l a t 2 , 3 0 0 m . t h e i c e s u r f a c e s l o p e s 3 t o 5 d e g r e e s n o r t h e a s t e r l y f o r a d i s t a n c e o f 3 . 8 K m . t o t h e t e r m i n u s , a t a n e l e v a t i o n o f 1 , 9 2 0 m . T h e f i r n l i n e i s a t 2500 m . a b o u t h a l f w a y d o w n t h e h i g h e s t i c e f a l l . B e l o w t h e i c e f a l l s t h e g l a c i e r i s a b o u t 1.1 K m . w i d e a n d o c c u p i e s a v a l l e y w h i c h i s s t r a i g h t e x c e p t f o r a s m a l l b e n d 1 K m . a b o v e t h e t e r m i n u s . T w o s m a l l i c e t r i  b u t a r i e s i n t h e l o w e r s e c t i o n d o n o t j o i n d i r e c t l y w i t h t h e g l a c i e r . A s e i s m i c s t u d y a n d g r a v i t y s u r v e y b y K a n a s e w i c h (1964) s h o w t h a t t h e g l a c i e r o c c u p i e s a v a l l e y h a v i n g a p a r a  b o l i c c r o s s s e c t i o n . I n t h e a c c u m u l a t i o n a r e a t h e i c e i s 220 m . t h i c k , b u t b e l o w t h e h e a d w a l l i t i s o n l y 92 m ; b e l o w t h e s e c o n d i c e f a l l i t t h i c k e n s a g a i n t * o 195 m . F o r 2 K m . b e l o w t h e l o w e s t i c e f a l l t h e t h i c k n e s s r a n g e s f r o m 250 m . t o 320 m . , a n d o v e r m u c h o f t h i s r e g i o n t h e b e d r o c k s u r f a c e i s w e l l b e l o w t . h e l e v e l o f t h e t e r m i n a l l a k e . I n t h e f i n a l 1 . 8 K m . t h e b e d r o c k h a s t w o s m a l l r i s e s . P a t e r s o n (1962) m e a s u r e d t h e s u r f a c e v e l o c i t y o f t h e i c e a t m a n y p l a c e s o n t h e g l a c i e r a n d s h o w e d t h a t ^ i n t h e c e n t r a l FIGURE 2. LOCATION MAP OF ATHABASCA GLACIER. - 20 - section of the glacier, the v e l o c i t y decreases from 80 m/yr. below the ice f a l l to 15 m/yr. just above the snout. Time fo r ice to t r a v e l from the accumulation zone to the snout i s estimated at 150 years. An average of 4 metres of ice i s l o s t each year over the surface of the ablation zone below the i c e f a l l s , mainly during the summer months when there i s a considerable flow of meltwater. The central portion of the g l a c i e r i s free of rock debris but both margins are protected by d i r t and large boulders in zones - 100 m. wide at the southeast side and 200 m. wide on the northwest side. The remains of a l a t e r a l moraine.100 m. above the present ice surface indicates that the g l a c i e r was much larger during Pleistocene time and thick moraines near the highway show that the g l a c i e r i s receding now. The Athabasca .Glacier was f i r s t described by S t u t f i e l d and C o l l i e (1903, p. 103-122) who v i s i t e d the area i n 1897. Fluctuations of the g l a c i e r during the past two hundred years have been estimated by F i e l d and Heusser (1954, p. 135) and Heusser (1956, p.282) from t h e i r study of the moraines and growth rings of trees i n the area. Their data indicate that an advance i n the early 13th century stopped i n 1714 when the snout was about 2 Km. beyond' i t s present position. The g l a c i e r then retreated and again advanced almpst as f a r by the f i r s t half of the 19th century. • During the l a s t reces sion, terminal moraines resulted from temporary halts i n 1900, 1903, and 1935. Since 1373, the g l a c i e r has receded an average - 21 - FIGURE 3 MAP OF EASTERN PART OF COLUMBIA ICEFIELD SHOWING LOCATION OF ; ATHABASCA AND SASKATCHEWAN GLACIERS _ of 1 2 . 5 m/yri Periodic surveys of the g l a c i e r made since 1945 by the Water Resources Branch of the Department of Northern A f f a i r s and National Resources, provide evidence that the recession rate has increased, and photographic surveys by F i e l d indicate that the recession has averaged 21 m/yr. i n the l a s t decade. - 2:3 - CHAPTER II MESOSCOPIC STRUCTURES GENERAL STATEMENT F a l l i n g snow accumulates as a sedimentary deposit on the surface of a g l a c i e r . Some of the snow p e r s i s t s i n the accumulation zone during the summer months, and on b u r i a l i s metamorphosed to f i r n and i c e . Because flowage and move ment of ice produces secondary structures similar to those formed i n more durable rocks by deformation, any attempt to determine the r e l a t i o n s h i p of ice structures to stress systems i n the g l a c i e r may help i n understanding the mechanism -by which s i m i l a r structures are formed i n metamorphic or deformed rocks. Secondary structures i n g l a c i e r ice were described i n the mid 1700's, but were seldom the main concern of early g l a c i o l o g i s t s . It i s only since 1950 that they have been investigated i n more d e t a i l and attempts made to correlate them with geophysical measurements. Reviews of, the l i t e r a t u r e on structures i n g l a c i a l i c e have been given by Dobrowolski (1923), Seligman (1949a),, Sharp (1954), Shumskii (1955), and Taylor (1962). However, descriptions of ice structures are by no means consistent, and i n order to avoid further confusion i n terminology i t i s necessary to define here some of the more common terms used to describe the d i f f e r e n t types of i c e , layering structures and other features. - 2 4 - Types of Ice Grain i n g l a c i e r ice, the grains are single cry s t a l s of i c e , but i n snow and f i r n the grains may be aggregates of snow cr y s t a l s . ' Fine ice ' i s formed by aggregates of granular cr y s t a l s 0.5 to 6 mm. i n siz e . On the weathered surface the ice has the appear ance of f i r n . If few bubbles are present the ice may have a blue colour. Coarse bubbly consists of i r r e g u l a r shaped interlocking ice grains containing numerous bubbles of water and vapour. The grains may range i n size from 1 to 10 cm. and they tend to be coarser near the g l a c i e r snout. Coarse clear i s formed by large i n t e r l o c k i n g grains ice containing very few bubbles. In d u l l weather, p a r t i c u l a r l y on rainy days, i t may appear v i v i d blue. Layered Structures Dirt layer or any layer of ice containing extraneous debris layer material. Fine grained material i s d i r t , coarse grained material i s debris. Blue layer any layer with a blue colour. Fine layer layer of fine grained i c e . Coarse layer layer of coarse grained i c e . ' F o l i a t i o n ' has been used to designate: (a) alternating layers of d i f f e r e n t ice types. (b) bubble layers that may not have the same attitude as the ice layers. (c) sets of ice f i l l e d f r a c t u r e s . The term ' f o l i a t i o n ' i s used i n st r u c t u r a l petrology, but there i s no uniformity of d e f i n i t i o n , and i n most descriptions i t i s not clear whether the term refers to the layers or to the planes that separate them. Some authors regard f o l i a t i o n as synono- mous with s c h i s t o s i t y (Turner and Weiss, 1963, p.447) whilst - 25. - others consider i t to be the more or less pronounced aggre gation of p a r t i c u l a r constituent minerals. (Marker, 1932, p.203). In order to avoid confusion, the term ' f o l i a t i o n ' should be u n i v e r s a l l y r e s t r i c t e d or abandoned i n ice studies. In t h i s t h e s i s , the term i s avoided wherever possible; penet r a t i v e planar structures are referred to as S-surfaces, and layers, of bubbles or tabular bodies of ice which d i f f e r from adjacent material are c a l l e d l a y e r s . Surface Structures D i r t band or . i s the surface outcrop of a d i r t or debris debris band layer or the accumulation of d i r t on the surface of an ice layer which contains no extraneous material. Blue band t h i s i s an outcrop of a blue layer on any surface not i n the plane of the layer. Fine band t h i s i s the expression of a f i n e layer on any surface not in the plane of the layer. Ogives or occur on the surface of the ice as a l t e r - Forbes bands nating l i g h t and dark coloured bands, • best observed from a distance. In plan, these bands are hyperbolic or parabolic with the curve convex downstream. Ruptures or Fractures V i s i b l e on the Ice Surface Joint a closed f r a c t u r e . Fault a fracture showing offset of the walls or drag e f f e c t s on the adjacent ice layers. Crack any open fracture with a noticeable separation between the walls. Crevasse a crack with a separation greater than one metre. Ice Veins formed of coarse ice produced by freezing of meltwater ponded i n crevasses, moulins - 26 - and other openings. Any structures, including i c e layers, observed i n f i r n and ablation zones are secondary i f they res u l t from g l a c i e r movement, and primary i f they are produced by any process other than ice deformation. Primary Structures Primary structures are most e a s i l y recognized i n the accumulation area, where snow, f i r n and ice occur in i r r e g u l a r layers, most of which must have been sub-parallel with the general surface at the time of t h e i r formation. The layers may be sedimentary and formed by: 1) Seasonal blankets of snow that give s t r a t i f i c a t i o n , or discordant snow layers in crevasses or avalanche masses. 2) Crusts developed by meltwater and wind on temporary ablation surfaces. 3) Freezing of water that seeps through the f i r n . When the water freezes i t produces ice lenses, glands, and t h i n blue layers. • Primary layers are usually clean, but i n the case of temporary ablation surfaces, they may become d i r t y by the accumulation of windblown material. Excellent descriptions of these structures and comments upon t h e i r possible o r i g i n s have been given by Sverdrup (1935); Ahlmann (1936); Ahlmann and Thorarinsson (1938, 1939); Perutz and Seligman (1939); Sharp (1951); and Nobles (I960). - 27 - Secondary S t r u c t u r e s In the a b l a t i o n zone of g l a c i e r s , movement o f the i c e produces a number of secondary structures,.some of which are d e s c r i b e d below. Ogives Ogives occur on the s u r f a c e of some g l a c i e r s as a s e r i e s of a l t e r n a t i n g l i g h t and dark c o l o u r e d arcuate bands. These, t o g e t h e r w i t h wave-like r i d g e s , f i r s t appear t r a n s v e r s e to the g l a c i e r j u s t below an i c e f a l l , but are deformed by g l a c i e r movement i n t o p a r a b o l i c or h y p e r b o l i c p a t t e r n s which become i n c r e a s i n g l y arcuate downstream. 'Ogives' or 'Forbes bands', have been c o n s i d e r e d as primary and secondary s t r u c  t u r e s ; some workers (King and Lewis, 1961; and F i s h e r , 1962) suggest t h a t o g i v e s r e s u l t from a mechanism i n v o l v i n g both accumulation and a b l a t i o n i n the i c e f a l l , and o t h e r s (Nye, 1959; and A t h e r t o n , 1963) a s c r i b e them to v a r i a t i o n s i n the v e l o c i t y of i c e above a step i n the u n d e r l y i n g bedrock. D e t a i l e d d e s c r i p t i o n s of o g i v e - l i k e s t r u c t u r e s have been given a l s o by A g a s s i z (1847); Forbes (1852); T y n d a l l (1874); Hess (1904); S t r . e i f f - B e c k e r (1943); F i s h e r (1947); ' and L e i g h t o n (1952). P l a n e s o f Rupture (S-planes) Ice at the g l a c i e r s u r f a c e i s r e l a t i v e l y b r i t t l e and some systems of s t r e s s may cause i t to r u p t u r e so t h a t the s u r f a c e e x h i b i t s numerous f r a c t u r e planes and c r a c k s . Gaping - 28 - cracks, c a l l e d crevasses, are commonly believed to extend to depths of about 30 to 35 metres, but the fractures probably continue to even greater depths. Dr. Hans Carol has descended into the Grindelwald Gletscher, to a depth of 75 m. Most crevasses remain open u n t i l they are 'melted out' but some f i l l with snow, f i r n or even water that may freeze to form ice veins. Systematic crevasse patterns have been discussed by Hopkins (1862); Nye (1951); Schwarzacher and Untersteiner (1953); Meier (I960); and Taylor (1962). Hopkins (1862) was one of the f i r s t workers to recognize'that crevasse patterns are related to ice movement. Nye (1951) using data obtained from laboratory investigations of ice under compression, deduced that ice deforms as a plas t i c body, and calculated the stress and v e l o c i t y d i s t r i b u t i o n for a hypothetical g l a c i e r of i n f i n i t e width flowing down a rough surface of uniform slope. He demonstrated that under such conditions crevasses can form, and proposed two fundamental forms of ice movement. 'Compressive flow' occurs when the long i t u d i n a l normal stress at a given depth i s greater than the v e r t i c a l normal s t r e s s , i n which case thrust planes may develop. 'Extending flow' r e s u l t s when the lo n g i t u d i n a l normal stress at given depth i s l e s s than the v e r t i c a l , when transverse fractures may be produced. I f these types of flow do occur, crevasses should develop at r i g h t angles to the d i r e c t i o n of smallest p r i n c i p a l stress. Ablation enlarges any opening but the i n i t i a l size - 29 - of a crevasse would be influenced by: 1) the slope of the g l a c i e r bed. 2) rate of g l a c i e r flow. 3) thickness of the g l a c i e r . 4) the y i e l d stress of i c e . From a study of the Saskatchewan G l a c i e r , Meier (I960,) concludes that, i n practice, crevasses form at a small angle to the normal of the least p r i n c i p a l stress because of: 1) minor differences i n the stress conditions. 2) inhomogeneities of the i c e . 3) rotation of the i n i t i a l rupture. Meier (I960, p.56, 61-62) divides crevasses on the Saskatchewan Glacier into four main groups: •- 1) Splaying crevasses that are longitudinal in mid- g l a c i e r but splay out down g l a c i e r to intersect the margins at an angle s l i g h t l y greater than 45°. Such a system of crevasses may r e s u l t from transverse expansion as a g l a c i e r emerges from a c o n s t r i c t i o n i n the channel. 2) Transverse crevasses that are oriented normal to the flow d i r e c t i o n , convex up g l a c i e r at the mid-glacier position, and p a r a l l e l with the marginal portions of splaying crevasses close to the margins. Meier considers that trans verse crevasses are produced by flow over a bed with a convex lon g i t u d i n a l p r o f i l e . 3) En-echelon crevasses that are a series of short ones arranged p a r a l l e l with one of the other patterns. Meier considers that they are caused by the superimposition of the - 30 FIGURE k. DISTRIBUTION OF CREVASSES IN THE CASTLEGUARD SECTOR OF THE SASKATCHEWAN GLACIER. (Modified a f t e r Meier, i960. Figure 1+1+) - 31 - 'other two patterns'. 4) Chevron crevasses that occur along the margins of a g l a c i e r , intersect the margin at 45° and extend upstream towards the centre of the' g l a c i e r . Such crevasses result from 'pure shear' caused by movement against stationary valley walls. After examining the Franz Josef Glacier i n New Zealand, Gunn (1964, p. 187) concludes that "the crevasse plane i s normal to the maximum tension and p a r a l l e l with the plane of maximum compression." Although.it i s generally assumed that crevasses are tension features, f i e l d measurements indicate that fractures may not be developed normal to the axis of least stress. St r a i n rate determinations by Taylor (1962, p. 737) on the Burroughs Glacier indicate that crevasses form at 45° to the main stress axis. Kehle (1964, p. 271) examined some crevasses- on the Ross Ice Shelf, Antarctica, and found that the rate of h o r i  zontal shear displacement i s 10 to 50 times the separation rate. He also found that the axis of least stress deduced from measurements of surface s t r a i n , was not at right angles to the crevasses, and that the fractures did not contain the regional intermediate axis. I f his calculations are correct, his result contradicts one of the basic assumptions i n st r u c t u r a l geology - that a plane of fracture w i l l always contain the intermediate stress axis. - 32 - Layering; Much of the surface ice i n the ablation zone of a gl a c i e r has a d i s t i n c t , compact, layered structure, commonly referred to as ' f o l i a t i o n ' , formed by d i f f e r e n t types of ice or layers of bubbles. These layers are neither uniform nor regular and they are not exactly p a r a l l e l . In many parts of an ablation surface more than two sets of layers may i n t e r  sect and i t i s d i f f i c u l t to account for these intersecting structures by reference to a simple stress system acting only at the place of observation. 'Foliated' ice has been described by several authors and reviews of these descriptions are given by Dobrowolski (1923); Winterhalter (1944); Schwarzacher and Untersteiner (1953); and Taylor (1962). Recent investigations of layered ice have been, made by Untersteiner (1955); Allen, Kamb, Meier and Sharp (I960); Meier (I960); Taylor (1962); and Gunn (1964). Despite a l l the work that has been done, the o r i g i n of layered ice i s s t i l l perplexing, and the re l a t i o n s h i p of these layers to stress systems and to the preferred c r y s t a l  lographic orientation of ice grains remains unknown. In many reports, the terminology of these layers has not been c l e a r l y defined, and even current descriptions leave much to be desired both i n c l a r i t y and usage. A terminology f o r 'glacier bands' was discussed at a conference held in 1953, by the B r i t i s h G l a c i o l o g i c a l Society. Although several members of t h i s conference made h e l p f u l suggestions, no agree ment was reached and the entire question has been l e f t to the - 33 - d i s c r e t i o n of subsequent workers. A tentative c l a s s i f i c a t i o n used here to describe- some forms of g l a c i e r ice l a y e r i n g , i s an outcome of a study of the Athabasca Glacier and a review of available l i t e r a t u r e . The c l a s s i f i c a t i o n i s not genetic, but i s based on the appearance of layering which, however, probably does r e f l e c t the method of formation. Two main types of secondary layering may be d i s t i n  guished i n an ablation zone: one formed by i n d i v i d u a l layers that are i n f i l l e d fractures or f a u l t s ; the other by alterna t i o n s of d i f f e r e n t types of i c e . Individual Layers Ice Veins Ice veins, analogous to veins i n more durable rocks, occur as i s o l a t e d layers generally a centimetre or two wide, formed by c r y s t a l s of variable bubble content (Figures 5 and 6 ) . Thick veins that contain elongate grains arranged normal to the walls are formed by freezing of surface waters i n fractures, or moulins. Very narrow layers composed of t h i n p l a t e - l i k e grains of clear ice are sub-parallel with a set of transverse fractures that occur every few metres down the g l a c i e r . These are probably i n f i l l i n g s of fractures, and may be the blue layers i d e n t i f i e d by other workers. In general, these v e r t i c a l layers crosscut but r a r e l y offset the repeated layering described below. \:-:.^. .•" :'. '.• „ - 34 ..'••v.. F I G U R E 5. I C E V E I N N E A R T H E C S U T R E C F T H E ATHABASCA G L A C I E R , Vein i s f i l l e d with c o a r s e i c e . G l a c i e r flow towards the r i g h t FIGURE 6 . ICE VEIN WITH COARSE CRYSTALS. Photograph of g l a c i e r surface looking down on layers of coarse i c e that dip 6 3 ° to wards 2 4 0 ° . The ice vein i s composed of elongate c r y s t a l s normal to the walls. Tectonic Layers Fault zones occupied by aggregates of coarse ice c r y s t a l s (generally with few bubbles) occur as narrow zones at an angle to the repeated layers of i c e . Where the two meet, the regular layers are offset or distorted, giving evidence of shearing and d i s l o c a t i o n . Repeated Layers Marginal Sub-parallel with the margins of most g l a c i e r s , including the toe, a pronounced banding of the surface i s due to 9 to 15 cm. thick layers of coarse bubbly ice alternating with t h i n i r r e g u l a r layers of fine grained i c e . Generally, t h i s layering i s not deformed except where i t i s faulted. Centrale|>:.LQ,ngitudinal) Ice i n the centre of some g l a c i e r s i s characterized by highly contorted, f i n e grained layers 2-15 -cm. thick. Folds may be outlined by accumulations of d i r t on the bubble- free surface. PREVIOUS WORK As the e a r l i e s t g l a c i o l o g i c a l reports were not commonly concerned with secondary structures developed in the ic e tongue, these features were either ignored or only sketchily - 3 6 - . described. Because many of the descriptions were published in journals of lim i t e d c i r c u l a t i o n , there was no great i n t e r  change of ideas, with a r e s u l t that the terminology i s con fusing and i t i s d i f f i c u l t to trace the development of theories i n a consistent chronological sequence. The e a r l i e s t theories on the o r i g i n o f - ' f o l i a t i o n ' f a l l n a t u r a l l y into two main categories. On the one hand i t represents a continuation of the primary s t r a t i f i c a t i o n of the f i r n i n the accumulation area; on the other, i t r e s u l t s from ice movement. Agassiz (1847, 1$96) was one of the f i r s t to suggest that ' f o l i a t i o n ' i n the ablation zone was an o r i g i n a l sedimen tary layering deformed by g l a c i a l movement into a series of overlapping layers that r i s e steeply towards the margins and less steeply towards the tongue. The' type of flow was ex pressed i n mathematical form by Fisher (1879) and a similar idea was advanced by Reid (1896). He described a progressive change from the ' f i r n strata' to 'bands' c h a r a c t e r i s t i c of a g l a c i e r tongue and drew the approximate l i n e s of flow i n a hypothetical plan and long i t u d i n a l section. The l i n e s of flow are now referred to as 'Reid Lines'. The concept of 'Reid Lines' was further developed by Hess (1904) who studied the Hintereisferner Glacier, and l a t e r attempted to determine the geometry of layered structures i n experiments of model g l a c i e r s using alternating layers of red and black wax and layers of ice and sand. Although. Agassiz studied many glaci:er.s::;and" o r i g i n a l l y • - 37 - proposed that f o l i a t i o n was e s s e n t i a l l y sedimentary layering, he did observe that where a g l a c i e r was constricted the ' f o l i a t i o n ' was r e l a t i v e l y more intense and better developed than elsewhere, and he suggested that the layers may res u l t •' from ice flow. Forbes (18*42) observed that layers i n the Lower Aar and Rhone Glaciers were near v e r t i c a l and sub-parallel with the g l a c i e r . He concluded that they represented d i s l o c a t i o n planes normal to " l i n e s of greatest pressure". This concept was l a t e r developed by Tyndall (I860, 1874) who, bel i e v i n g ice layers to be independent of any s t r a t i  f i c a t i o n i n the f i r n area, drew attention to the analogy between ice layers and planes of cleavage observed i n metamorphic rocks." To determine a r e l a t i o n between the 'lamination', and 'pressure' he experimented with wax b a l l s and determined.that cleavage i n stressed b a l l s was at right angles to the main stress axis. He applied t h i s idea to show how a 'marginal veined structure' was developed, and i l l u s t r a t e d the structure i n a diagram (1874, p. 186). He also considered that layers' originate i n a trans verse v e r t i c a l plane at the base of an ice f a l l . Hamberg (1932) had investigated g l a c i e r s i n the Sorek Mountains i n Swedish Lapland and noted that there were commonly two or more intersecting planes of ' f o l i a t i o n ' . He suggested that f o l i a t i o n resulted from cracks, sub-parallel to the g l a c i e r margins. He did not consider that the cracks were continuous, but thought they were concentrated at various places i n "space and time", p r i n c i p a l l y near the surface of the g l a c i e r . Phillipp(1905) noted regularly spaced narrow cracks ' - 38 - 0.5 to 5.0 metres apart on the surface of both a r c t i c and alpine g l a c i e r s . .He believed that water i n these cracks would freeze to give transparent blue bands. With the progressive movement of the g l a c i e r , new cracks would appear and the early 'bands' would be gradually o b l i t e r a t e d . A l l the early theories on ' f o l i a t i o n ' were reviewed by Dobrowolsky (1923) who concluded that g l a c i e r s show several types, a l l similar i n appearance but genetically d i s t i n c t . Some layers may'be a continuation of st r a t a from the f i r n but others are produced by movement. Untersteiner (1955) mapped the 'trends of banding' on ten transverse p r o f i l e s on the Pasterze Glacier i n the eastern Alps. He distinguished between a f o l i a t i o n formed from a system of cracks or crevasses as widely spaced layers of clear ice best designated as 'blue bands', and 'FeinbSnderung•'a series of layers of d i f f e r e n t types of i c e . On the surface of the Pasterze, the 'FeinbSnderung' appears as two arcs convex i n the d i r e c t i o n of g l a c i e r move ment. In the upper part of the g l a c i e r near the ice f a l l the layers are nearly v e r t i c a l or dip steeply upstream, but further down the g l a c i e r the dip progressively decreases to 35° near the toe. Untersteiner concludes, that the structure i s not a f i r n s t r a t i f i c a t i o n , but " forms i n a zone of t r a n s i t i o n between the disturbed flow i n the ice f a l l s and the steady flow i n the f l a t tongue." (Ibid. p.504 ) -. According to him, the layers, once formed, are passive but become distorted by movement i n the ice tongue. - 39 - In the study of banding and the d i s t r i b u t i o n of volcanic ash on an alpine g l a c i e r i n Patagonia, Lliboutry (1957) describes 'fine ogives' and layers found below an ice f a l l . . The layers are closely spaced blue and bubbly f o l i a that seem to be spoon-shaped, dipping up-glacier at an angle of 45° •. He comments on the f a c t that, as these layers are p a r a l l e l with the 'plane of greatest resolved shear stress', they could not have been formed normal to the greatest compressive force, and concludes that they "cannot be f o l i a t i o n " . He proposes to c a l l these features ' p l a s t i c layers' or 'flow layers'. Meier (I960, p. 54) recognizes a primary s t r a t i f i c a  t i o n of ice within the ablation zone of the Saskatchewan Glacier. He also i d e n t i f i e s a d i s t i n c t layering expressed by alternating laminae of bubbly and b l u i s h clear i c e , sub-parallel with the g l a c i e r length. P a r a l l e l with the sides of the g l a c i e r and within 1,000 feet of the terminus, the layering forms a spoon- shaped structure dipping up-glacier. Meier (I960, p. 59) concludes that: 1) " F o l i a t i o n i s r e l a t e d to shear deformation." 2) " F o l i a t i o n does not always form p a r a l l e l to planes of greatest shearing s t r a i n . " 3) " F o l i a t i o n appears to form - or be preserved - only at shallow depths." To explain the o r i g i n of t h i s f o l i a t i o n Meier suggests the following 'speculative mechanism'. Under applied stress, ice begins to y i e l d by p l a s t i c flow. Because of s l i g h t differences i n grain shapes and orientation, some areas s t r a i n - 40 - more r a p i d l y , so that a c r i t i c a l s t r a i n may be a t t a i n e d l o c a l l y , and ice g r a i n s become s o f t e n e d . This produces weak zones that w i l l propagate when any a d d i t i o n a l s t r a i n i s c o n f i n e d to a s p e c i f i c plane. These s o f t zones become i n t e r c a l a t e d with l a y e r s of hard i c e to g i v e a ' f o l i a t e d s t r u c t u r e ' . The s o f t l a y e r s need not be o r i e n t e d p a r a l l e l with the d i r e c t i o n of maximum 'shearing s t r a i n ' and may be c o n t r o l l e d by minor p r e v a i l i n g a n i s o t r o p i s i m of the i c e . The r e l a t i v e amounts of hard i c e w i l l be a f f e c t e d by: 1) The t o t a l p l a s t i c s t r a i n . 2) The s t r a i n r a t e . 3) The rate of r e c r y s t a l l i z a t i o n . Meier, however, was p u z z l e d by l a y e r s of f i n e ice that occur near the m i d - l i n e o f the g l a c i e r , (Ibid. p.60). This m i d - g l a c i e r ' f o l i a t i o n ' i s n e a r l y v e r t i c a l and h i g h l y con t o r t e d but t r e n d s p a r a l l e l with the l e n g t h of the g l a c i e r . He has no s a t i s f a c t o r y e x p l a n a t i o n f o r i t s o r i g i n but s t a t e s t h a t i t was not formed p a r a l l e l with the plane of maximum shear s t r e s s as determined by s u r f a c e measurements of the s t r a i n . Meier concludes t h a t ' f o l i a t i o n ' forms on l y at shallow depthSj i r r e s p e c t i v e of the rate of r e c r y s t a l l i z a t i o n at depth. I f the r a t e of r e c r y s t a l l i z a t i o n i s a f u n c t i o n of depth, or ' h y d r o s t a t i c pressure', r e c r y s t a l l i z a t i o n should be g r e a t enough, at some c r i t i c a l depth, t o prevent the propagation of s o f t zones and the r e s u l t i n g i c e would be homogeneous and u n f o l i a t e d . I f the r a t e of r e c r y s t a l l i z a t i o n decreases with depth, an i n  crease i n the amount of s o f t i c e may be s u f f i c i e n t to e l i m i n a t e - a - a l l the hard ice so that the deeper part of a g l a c i e r would be homogeneous and unfoliated. Alle n , Kamb, Meier and Sharp (I960) studied surface ice within the ablation zone of the Blue Glacier on Mount Olympus i n Washington. Exposed on the ice surface are layers of d i f f e r e n t types of i c e , 1-100 cm.. thick, i n t e r c a l a t e d to form a d i s t i n c t ' f o l i a t i o n ' that i s most obvious near the toe and l a t e r a l margins. The layers crop out as two sets of curved bands, convex down g l a c i e r , and dip steeply towards the axis of the g l a c i e r on the concave side of the curve. At the f i r n edge, the angle of dip i s about 80°, but i t becomes pro gres s i v e l y smaller down, the g l a c i e r , so that 400 metres from the terminus i t i s only 30°. All e n et a l , i n f e r that, i n three dimensions, the 'foliation'resembles a series of nested spoons. They conclude that f o l i a t i o n cannot be produced at or near where i t i s observed on the surface of the Blue Glacier f o r the following reasons: 1) The ' f o l i a t i o n ' p a t t e r n does not conform to the simple v e l o c i t y d i s t r i b u t i o n indicated by surface measurements of rates of flcfw. 2) The nearly stress-free condition of surface i c e i n the centre of a g l a c i e r does not constitute a favorable s i t u a  t i o n f o r the development of'fol i a t i o n ' . 3 ) ' F o l i a t i o n ' , once formed, i s a durable feature because i t may be deformed into f o l d s , or faulted near the g l a c i e r margin. 4) The geometry of the pattern changes progressively down the g l a c i e r , whilst the i n t e n s i t y of the'foliation'decreases. - 4 2 - , To explain the o r i g i n of t h i s f o l i a t i o n ' and account fo r the e x i s t i n g surface geometry, Allen et al.(1960, P.618) propose that,at the base of the ice f a l l s , a l l pre-existing structures are brought into a v e r t i c a l transverse attitude. Once formed, the structures are passive and during subsequent movement down the g l a c i e r they are rotated into a spoon shape that crops out on the surface as a curved band convex down g l a c i e r . At the base of the ice f a l l , the structures are made v e r t i c a l due to the increase i n l o n g i t u d i n a l compression that r e s u l t s from the slowing of the forward v e l o c i t y where there i s an abrupt change i n slope below an ice f a l l . The p r i n c i p a l feature of the mechanism proposed by Allen et aL.had been suggested e a r l i e r by Tyndall (I860, p. 384-386), who referred to the zone of intense compression at the base of the ice f a l l s on the Grindelwald and Rhone Glaciers as a 'structure m i l l ' . In a study of the ablation surface of the Burroughs Glacier i n Southern Alaska, Taylor (1962) i d e n t i f i e d three types of layered i c e . One type, formed of fine layers,occurs on most of the g l a c i e r surface above an elevation of 225 m. Coarse grained ice without f i n e grained layers occurs near the g l a c i e r margins and covers a zone .25 to .5 Km;, wide near the eastern terminus of the i c e . The t h i r d type consists of very coarse grained i c e , near the base of the g l a c i e r , now exposed in discontinuous narrow zones at the ice margins, p a r t i c u l a r l y around nunataks. Taylor did not discuss the r e l a t i o n s h i p between ' f o l i a t e d ' ice and stress systems but i n f e r s (Ibid. p. 51) - 43 - that f o l i a t i o n . . . " i s produced by tensional, compres- si o n a l , and shear stresses. The f o l i a t i o n plane develops i n a d i r e c  t i o n of least resistance which i s determined by the configuration of the v a l l e y walls and flow, the stress f i e l d i n the g l a c i e r , and the aniso tr o p i c properties of the i c e . " To explain layers of f i n e grained ice i n the lower Burroughs Glacier, Taylor suggests a process i d e n t i c a l with that proposed by Meier f o r ' f o l i a t i o n ' i n the tongue of the Saskatchewan Glacier. Gunn (1964) examined f o l i a t e d ice' on the ablation surface of the Franz Josef Glacier i n New Zealand. A v e r t i c a l l o n g i t u d i n a l f o l i a t i o n crops out over most of the g l a c i e r but within a few hundred metres t h i s gives way to a transverse f o l i a t i o n which dips up-glacier at angles of 30 to 60°. He correlates these two types of f o l i a t e d ice with the d a i l y s t r a i n rat e. Longitudinal f o l i a t i o n ' i s produced i f the s t r a i n rate i s l e s s than 0.01% compression. Greater str a i n s produce 'transverse tectonic blue bands' that grade into a transverse f o l i a t i o n when the compression s t r a i n rate becomes 0.04%.. From the previous work, summarized above, i t i s obvious that the term ' f o l i a t i o n ' has been loosely used to designate d i f f e r e n t kinds of layered structure. Recent authors have proposed that i t i s either produced near the s i t e where i t i s observed on the surface (Meier, I960, Taylor, 1962) or that i t i s formed as a transverse v e r t i c a l layer within a 'structure m i l l ' at the base of an ice f a l l , and, once formed, behaves passively during l a t e r g l a c i e r movement (Allen et al.. I960,. . - 44 - ' and Untersteiner, 1955). To avoid further confusion i n t e r  minology, the term layering w i l l be used wherever possible i n the following pages. METHODS OF FIELD STUDY To determine the d i s t r i b u t i o n of d i f f e r e n t types of layered i c e , a study was made of a g l a c i e r with a simple geometric shape - the Athabasca G l a c i e r . Layering on the sur face of the ablation zone of the Athabasca Glacier was i n v e s t i  gated i n July of 1962 and 1963, from the terminus to the lowest ice f a l l . As i t was not f e a s i b l e to map the entire ablation zone on a scale small enough to show thi s layering i n d e t a i l , work was r e s t r i c t e d to three narrow transverse s t r i p s ; the f i r s t , 900 m. above the snout, the second, 1,500 m. upstream, halfway between the snout and the lowest ice f a l l , and the t h i r d , just 300 m. below the ice f a l l . A l l the obvious surface features along these s t r i p s , including layering, were mapped i n the conventional manner using a Brunton compass. D e t a i l was plotted on a map at a scale of 10 feet to one inch, by reference to a central g r i d of three p a r a l l e l nylon chains l a i d out across the g l a c i e r , 20 feet apart and anchored at each end with eight inch spikes. Trends of the layering were observed r e a d i l y on the surface of the ice but the dip was d i f f i c u l t to obtain unless there was a second face or a natural v e r t i c a l exposure such as a crevasse wall. The dip of the f o l i a t i o n could, however, be determined from a r t i f i c i a l exposures made by chopping small - U5 - holes about 15 cm;., deep. In many of these holes, layering, indistinguishable on a fresh surface, became r e a d i l y discer n i b l e a f t e r exposure for a few hours. (Figures 16.and,17)• RESULTS OF FIELD STUDY The main purpose of the f i e l d study was to examine ice layers, but several other secondary structures were also noted and are b r i e f l y described here. Although ogives cannot be detected by direct obser vation on the g l a c i e r surface, a e r i a l photographs of the ablation zone show at least two series of alternating dark and white curved bands which appear to become progressively more convex and l e s s d i s t i n c t downstream. Several groups of moulins were observed but no attempt was made to study t h e i r progressive development nor the r e s u l t i n g d i r t cones which are present on the g l a c i e r surface at lower elevations. The ablation zone of the g l a c i e r i s reasonably f l a t , but t r a v e l over the surface i s made d i f f i c u l t by a series of small ridges trending sub-parallel with the length of the g l a c i e r (Figure 7). Over most of the surface the ridges are generally 1 to 1.5 metres apart and just less than a metre high, but they become progressively larger during the summer, p a r t i c u l a r l y along the eastern margin, where they may be 2 to 2 g metres in height. Although the ridges appear to be. r e l a t e d to some process of d i f f e r e n t i a l ablation, perhaps similar to that of penitents, there i s no obvious explanation f o r t h e i r — 4 6 — lac!: of a n y obvious f o l i a t i o n . - 47 - development. To a casual observer, the g l a c i e r surface i s a con fusing array of cracks, crevasses, and numerous layered struc tures that have a simple surface configuration seemingly related to i c e movement. The more obvious structures are composite layers formed by segregation of bubbles (Figures 8 and 9) or by d i f f e r e n t types of ice (Figures 11 and 15). Following the c l a s s i f i c a t i o n of Kamb (1959b, p.1893) the d i f f e r e n t types of ice have been designated: 1) Coarse bubbly ice 2) Coarse clear ice 3) Fine ice Coarse bubbly ice i s composed of large c r y s t a l s that may range up to 20 cm. i n si z e . The grains are complex i n shape and t h e i r mutual contacts are so i r r e g u l a r and intergrown that the ice resembles a three-dimensional jig-saw puzzle. The complex intergrowths prevent the rapid d i s i n t e g r a t i o n of the ice as i t melts along the grain boundaries. Within the grains and at the contacts, numerous spherical bubbles may be clustered into i n d i s t i n c t layers,, that may have attitudes markedly d i f f e r e n t from the general layering formed by d i f f e r e n t types of i c e . The d i s t r i b u t i o n of bubbles appears to be independent of the'ice layers, f o r one large ice grain may extend with no obvious disc o n t i n u i t y across bubble-poor, and bubble-rich layers. Coarse clear ice i s formed of large c r y s t a l s that range from 3 to 12 cm. in diameter. The ice c r y s t a l s are - 4$ - FIGURE 8. LAYERING FORMED BY PLANES OF DIRT-FILLED BUBBLES. View looking down- g l a c i e r showing near v e r t i c a l bubble planes. FIGURE 9. DIRT-FILLED BUBBLES OPEN TO THE SURFACE. V e r t i c a l photograph showing planes of bubbles. - 4 9 - closely i n t e r l o c k i n g , and are only distinguished from those of coarse bubbly ice by the lack of bubbles. Coarse clear ice i s found i n stagnant areas near the snout and margins of the g l a c i e r , i n blue layers within the layers of coarse-bubbly i c e , and also i n sheets and pod-like aggregates formed by freezing of meltwater in some crevasses or moulins. (Figures 5 and 6). 'Fine ice i s formed by aggregates of grains ranging from 0.5 to 6 mm. i n size that i n t h i n sections appear equant with smooth contacts. On weathered surfaces, f i n e i c e looks l i k e f i r n but at depth i t forms a s o l i d compact mass. The bubble content of fine ice i s variable, and where bubbles are concentrated into layers, the weathered surfaces are weakly banded. This banding may be accentuated by accumulations of d i r t on the surface of bubble-poor layers. (Figure 13). Although the coarse clear and coarse bubbly ice occur in narrow i s o l a t e d layers over the entire surface, most of the ablation zone i s composed of either f i n e i c e or coarse bubbly ice i n repeated layers. These fine layers and coarse layers are generally r e s t r i c t e d to certain parts of the ablation zone, and depending upon the predominant type of layer, the sur face of the Athabasca Glacier may be divided into two d i s t i n c t areas. (Figure 10). The marginal portions of the g l a c i e r are charac t e r i z e d by coarse bubbly ice i n pronounced layers that are sub- p a r a l l e l with the margins themselves whilst ice i n the central portion has a less obvious layering formed by contorted layers of f i n e grained ice. - 5 1 - Marginal Zone Ice in the outermost part of the g l a c i e r , adjacent . to the bedrock walls, and in a zone near the snout, has a furrowed surface. The furrows r e s u l t from d i f f e r e n t i a l weath ering of d i s t i n c t layers of coarse ice averaging 9 to 1 5 cm.., thick, intercalated with a few discontinuous, narrow zones of fine grained ice (Figures 1 1 and 1 2 ) . The weathered surface has a honeycomb texture but i s generally clean - d i r t occurring only i n well defined melt- water channels or at the bottom of open bubble holes (Figure 9 ) . Beneath the weathered and honeycombed surface, s o l i d i c e exposed i n excavated p i t s or under d i r t cones consists of large grains, averaging from 5 to 1 0 - cm. i n size that are highly i r r e g u l a r and c l o s e l y i n t e r l o c k i n g . The s o l i d ice i s remar kably clear, but, on exposure to sunlight, disc shaped bubbles ('Tyndall figures') flattened i n the 0 0 0 1 crystallographic plane, develop r a p i d l y and- spread to the grain contacts. The exposed ice then assumes a milky colour and.within a few minutes, the surface i s as spongy as the surrounding surface i c e . With continued exposure the ice melts, mainly on the grain boundaries, and only the complex i n t e r l o c k i n g shapes prevent complete d i s i n t e g r a t i o n of ice at the g l a c i e r surface. Surface trends of layers marked i n an outline map of the Athabasca Glacier (Figure 1 3 ) were determined from i n s  pection of a e r i a l photographs and from ground observations. Trends are generally consistent, but near tectonic planes the layers may be 'drag-faulted' and indicate a r e l a t i v e forward - 5 2 - F I G U R E 1 1 . L A Y E R S OF C O A R S E I C E . V i e w d o w n t h e s o u t h e a s t e r n s i d e o f t h e A t h a  b a s c a G l a c i e r . N o t e t h e o b v i o u s l a y e r s o f c o a r s e i c e t h a t d i p s t e e p l y t o w a r d s t h e c e i . t r e o f t h e g l a c i e r a t t h e l e f t . L e v e l s u r f a c e t o t h e l e f t i s a s n o w m o b i l e r o a d . F I G U R E 12. D E F O R M E D L A Y E R S OF C O A R S E ICE. V i e w d o w n t h e s o u t h e a s t e r n s i d e o f t h e A t h a b a s c a G l a c i e r . N o t e h o w t h e s t e e p l y d i p p i n g c o a r s e l a y e r s h a v e b e e n d e f o r m e d a d j a c e n t t o a f a u l t . Traverse line / C revas se y Coarse ice layers. Fine ice layers. / Dip of layers FIGURE 13. MAP OF THE OBSERVED LAYERING ON THE SURFACE OF ATHABASCA GLAC ' cR - 54 - motion of the central part of the g l a c i e r (Figure 12). Through out the length of the g l a c i e r , the layers have very l i t t l e change in attitude; near the margins they dip steeply towards the centre, but near the toe they dip up-glacier at 15° to 30°. Ae r i a l photographs (Figure 14) show that coarse layers c h a r a c t e r i s t i c of the g l a c i e r margins do not continue across the central part -of the g l a c i e r to unite with layers on the opposite side. . Generally, the coarse layers become f a i n t e r towards the ice centre where they occur only as small lenses intercalated within fine i c e . Central Zone On clear.sunny 'days, the central quarter of Athabasca Glacier has a cobble-like surface of dazzling white with numerous small r e f l e c t i n g planes. When these planes are viewed by an observer standing on the ice they look l i k e cry s t a l 'faces' up to 5 or 7 cm., i n size, but they cannot be detected by closer inspection. Excavations i n these white areas show them to be underlain by a uniform mass of f i n e ice with subordinate layers of coarse ice grains. Within the cobble-like areas of the surface, are small i r r e g u l a r patches of f i n e ice layers 2 to 15 cm. thick with t h i n lenses of coarse-grained i c e . The ice i s formed by equant grains 0.5 to 6 mm. i n size, with smooth contacts and variable bubble content. .Some of the small bubbles may be concentrated into i r r e g u l a r planes that do not conform to the general a t t i  tude of the ice layers. - 55 - FIGURE 14- AERIAL PHOTOGRAPH OF ATHABASCA GLACIER TO SHOW SURFACE TRENDS OF ICE LAYERS. Marginal l a y e r s do not extend across the centre. Fine i c e at the centre i s h i g h l y contorted. (Photo F l i g h t No. A.16703-20) - 56 - Down the e n t i r e l e n g t h of the c e n t r a l zone of the Athabasca, the l a y e r s of f i n e i c e have been deformed i n t o s t e e p l y plunging f o l d s that resemble s t r u c t u r e s described as s i m i l a r f o l d s i n s t u d i e s of deformed rocks (De S i t t e r , 1956, p. 181). Commonly, the f o l d s have amplitudes of l e s s than one metre and the a x i a l planes are n e a r l y v e r t i c a l and most are t r a n s v e r s e to the d i r e c t i o n of g l a c i e r movement (Figures 15, 16, 17). P a r a l l e l w i t h the a x i a l plane i s a system of n e a r - v e r t i c a l cracks that commonly occur on the f o l d limbs so as to separate one f o l d from another. The s u b - v e r t i c a l cracks are spaced at i n t e r v a l s of .5 to 5 metres down the g l a c i e r and they extend away from the c e n t r a l zone to curve u p - g l a c i e r and merge w i t h cracks that i n t e r s e c t the coarse l a y e r s near the g l a c i e r margins. These cracks have steep d i p s , and t h e i r g e n e r a l appearance does not seem to change s i g n i f i c a n t l y over the l e n g t h of the g l a c i e r . I t i s assumed that they are a near-surface f e a t u r e , produced at or near where they are observed. The area occupied by f i n e l a y e r s c o i n c i d e s c l o s e l y w i t h the s e c t i o n of the g l a c i e r t h a t flows as a d i s t i n c t u n i t . According to measurements of the h o r i z o n t a l surface v e l o c i t y given by Paterson (1962, F i g . 8 to 14) i c e i n the c e n t r a l quarter of the Athabasca moves as a u n i t , w h i l s t towards the margins, the v e l o c i t y decreases. . In summary, the a b l a t i o n surface of the Athabasca G l a c i e r can be d i v i d e d i n t o two d i s t i n c t zones on the b a s i s of: - 5 7 - F I G U R E 1 5 . D E F O R M E D L A Y E R S O F FINE I C E P h o t o g r a p h o f t h e i c e s u r f a c e n e a r t h e c e n t r e o f t h e A t h a b a s c a G l a c i e r . D i r e c t i o n o f g l a c i e r f l o v ; i s t o t h e r i g h t . - 5P - FIGURE 16. LAYERS OF F I N E ICE. Photograph of the i c e surface near the centre of the Athabasca G l a c i e r . Ice axe points i n the d i r e c t i o n of flow, and i s p a r a l l e l with the trend of the f i n e layers. Note the series of near v e r t i c a l transverse f r a c t u r e s that are f i l l e d by t h i n plates of coarse i c e - blue bands. FIGURE 17. LAYERS OF F I N E ICE. Photograph of ice surface near centre of Athabasca G l a c i e r ; sane viev; as Figure l6 , showing holes dug to determine the dip of the la y e r s . - 59 - 1) S u r f a c e v e l o c i t y measurements. 2) Type of l a y e r i n g . 3 ) S t y l e o f f o l d s . Because the s t r u c t u r e s w i t h i n the two zones are so d i s t i n c t i t i s c o n c l u d e d t h a t , t h e y r e s u l t from d i f f e r e n t s t r e s s domains. DISCUSSION OF ICE LAYERS G e o p h y s i c a l measurements can be made w i t h r e a s o n a b l e a c c u r a c y t o d e t e r m i n e q u a n t i t a t i v e f l o w laws t o e x p r e s s g l a c i e r movement. These l a w s , however, n e i t h e r e x p l a i n t h e a c t u a l m echanics o f g l a c i e r f l o w n o r account f o r t h e secondary s t r u c  t u r e s produced by t h e movement. Nye (1951) has shown a p o s s i b l e r e l a t i o n s h i p between a h y p o t h e t i c a l s t r e s s system and i n d i v i d u a l p l a n e s such as c r a c k s and c r e v a s s e s . I t i s d i f f i c u l t , however, t o c o r r e l a t e a s i m p l e s t r e s s system w i t h p l a n e s o f b u b b l e s and i n t e r s e c t i n g s e t s o f r e p e a t e d i c e l a y e r s , p a r t i c u l a r l y when they have been deformed i n t o complex g e o m e t r i c shapes. Most t h e o r i e s d e a l i n g w i t h s e c o n d a r y s t r u c t u r e s i n g l a c i e r s a r e concerned m a i n l y w i t h t h e d i s t r i b u t i o n and o r i g i n o f t h e most o b v i o u s l a y e r s t h a t c r o p out on t h e s u r f a c e near t h e g l a c i e r m a r g i n s . A l t h o u g h t h i s i s t h e most pronounced f e a t u r e i n many g l a c i e r s , t h e r e a re o t h e r t y p e s o f l a y e r s , and t h e s i g n i f i c a n c e o f a l l o f them s h o u l d be d i s c u s s e d b e f o r e t h e y a re r e l a t e d t o any h y p o t h e t i c a l s t r e s s system. R e l a t i o n  s h i p s between s t r u c t u r e s and s t r e s s systems w i l l be d i s c u s s e d a t g r e a t e r l e n g t h i n a subsequent c h a p t e r , but d i s t i n c t i o n s - 60 - between the layers are described below. The surface of most g l a c i e r s exhibits both isolated layers and repeated layers of d i f f e r e n t types of i c e . I n d i v i  dual layers of ice commonly re s u l t from freezing of water i n cracks and other open spaces. They are e a s i l y recognized, and because t h e i r o r i g i n i s obvious, they need not be discussed further. Repeated layers of d i f f e r e n t types of ice are less e a s i l y explained, and because these layers are not c l e a r l y distinguished or described i n the l i t e r a t u r e , i t i s necessary to show that some g l a c i e r s have at least two d i s t i n c t types. As described previously, layered ice at the surface of the Athabasca Glacier may be divided into two d i s t i n c t types: prominent layers of coarse ice near the g l a c i e r margin, and layers of f i n e ice i n the central part of the g l a c i e r . In descriptions of other g l a c i e r s , authors do not state that the central zone has a d i f f e r e n t type of layering, but the struc tures of the Athabasca are not unique and the two-fold d i v i s i o n may be recognized on g l a c i e r s elsewhere. Most g l a c i e r s have a prominent layering that p a r a l l e l s the margins and i s transverse -near the snout. This i s the structure noted by Agassiz (1847), and i d e n t i f i e d as ' f o l i a  t i o n ' by Chamberlin and Salisbury (1909) and most other g l a c i o l o g i s t s . However, i n many g l a c i o l o g i c a l studies, a passing reference i s made to a series of contorted layers of f i n e ice found near the centre of the ablation surface. Godwin (1949, p.328) depicts a series of i r r e g u l a r layers near - 61 - the centre of the Great Aletsch Glacier, l a b e l l e d as "buckel i c e " on a diagram by Vaeschi. A similar diagram given by Untersteiner (1955) f o r the Pasterze Glacier shows a series of folded layers i n a central zone that i s i d e n t i f i e d as the 'FIENNAHT'. Allen et al.(1960) mention a series of folded layers of fine-grained i c e present on the surface near the centre of the Blue Glacier. Gunn (1964, p. 173) describes secondary structures on the Fox and Franz Josef Glaciers i n New Zealand. Ice'in the Fox G;lacier has a prominent ' f o l i a t e d ' transverse struc ture that crops out on the surface as a series of arcs concave up the g l a c i e r . Along the l a t e r a l margins, the 'foliation'dips inwards at angles of 70° to 9 0 ° , and along 'the mid-line the dip i s 50° to 70° up-glacier. In contrast, the Franz Josef Glacier has two d e f i n i t e structures: transverse layers near the snout and l a t e r a l margins, and a steeply dipping l o n g i t u  d i n a l ' f o l i a t i o n ' that crops out over most of the ablation surface above the snout. In a detailed study of the Saskatchewan G l a c i e r , Meier (i960, p. 54) notes t h a t i n ' t h e - c e n t r a l : z o n e y : v e r t i c a l layers of f i n e ice have been deformed into a series of t i g h t f o l d s . The a x i a l plane of these fo l d s i s nearly v e r t i c a l , and i s p a r a l l e l with a transverse set of closely spaced v e r t i c a l j o i n t s and fractures. Rutter (1962) describes v e r t i c a l l o n g i  t u d i n a l layers from near the centre of the Gulkana Glacier i n Central Alaska. From the statements of other g l a c i o l o g i s t s and b r i e f - 62 - personal examinations of numerous g l a c i e r s elsewhere i n B r i t i s h Columbia, i t i s evident that the ablation surfaces of many- gl a c i e r s have a number of d i f f e r e n t types of layers. On the basis of d i f f e r e n t types of repeated layering, the ablation surface may be divided into two areas: a marginal zone, and a central zone whose width i s probably a function of g l a c i e r shape, and rate of flow. Before discussing the r e l a t i o n between the d i f f e r e n t types of layers and stress conditions, i t i s necessary to know where the layers are formed and how they are affected by the ice movement. Meier (I960, p. 60) considers that ice ' f o l i a t i o n ' i s formed at shallow depth close to where i t i s now observed. In contrast, Allen et a l . (I960) suggest that i t i s produced as a v e r t i c a l plane f a r up the g l a c i e r and deformed by movement down the ice stream. Any study of the deformation of planar struc ture must surely indicate a path of ice movement. The surface geometry of ' f o l i a t i o n ' on the Blue and other g l a c i e r s i s said to have been produced by r o t a t i o n of a transverse v e r t i c a l plane formed at the base of an i c e f a l l i n a 'structure m i l l ' . The main reasons f o r t h i s assumption are restated below: 1) ' F o l i a t i o n ' i s a durable feature f o r i t can be folded faulted. 2) The geometry changes progressively down- gl a c i e r although the i n t e n s i t y gradually decreases in t h i s d i r e c t i o n . 3) The ' f o l i a t i o n ' does not conform with the simple v e l o c i t y d i s t r i b u t i o n obtained by surface measurements. - 6 3 - 4) ' F o l i a t i o n ' i s well developed at the centre of the g l a c i e r surface, and t h i s area i s "....nearly stress-free". ' F o l i a t i o n ' on the Blue Glacier i s not a simple structure: Kamb (1959b,p. 1899) reports that complex fol d s and f a u l t s do occur and^/fine ice may form up to 20% of the central zone of the g l a c i e r . . For the purpose of the following discussion, however, i t i s necessary to consider only the d i s t r i b u t i o n of the coarse layers that are c h a r a c t e r i s t i c of the marginal zone. F i r s t l y , i f layering can only be produced i n a 'structure m i l l ' , those g l a c i e r s with no ice f a l l s should be without layered i c e . The Saskatchewan Glacier has no apparent ice f a l l , yet Meier (I960, p. 52-54) notes two d i s t i n c t types of layers. His description of them could well be applied to layers observed on the Athabasca Glacier, which has three ice f a l l s . Secondly, not a l l ice f a l l s have a transverse layered structure at t h e i r base. Gunn (1964) states that there i s no transverse structure i n the ice at the base of the ice f a l l on the Franz Josef Glacier i n New Zealand. On the Blue Glacier, s o l i d ice observed through windows in the f i r n just above the base of the f a l l , exhibits crude transverse planar features, probably produced by crevassing i n the ice f a l l . On the Universidas Glacier i n the central Chilean Andes, Ll i b o u t r y (1958, p. 2 6 6 ) notes that transverse blue bands- just . below an ice f a l l dip up-glacier at 45°• He concludes that - 6 4 - these bands' were formed along 'planes of maximum shear' at the base of the ice f a l l . Below the f a l l s on Athabasca Glacier, the ice i s well exposed and the main transverse structures are v e r t i c a l cracks and j o i n t s s i m i l a r i n size and attitude to ruptures observed elsewhere on the ablation surface. The widest cracks are f i l l e by f i r n and represent snow-filled crevasses produced i n the ice f a l l s (Figure 18). In one section near the centre of the g l a c i e r , ice layers are transverse-but generally, they trend down-glacier (Figure 18) and are s i m i l a r to fine layers i n other parts of the g l a c i e r (Figure 19). Thirdly, i f a v e r t i c a l transverse layer of constant volume i s deformed by g l a c i e r flow, i t should become progres s i v e l y thinner with time. Although the actual movement i s very complex, i t can be s i m p l i f i e d by ignoring any v e r t i c a l component and any e f f e c t s of ablation. In the following discus sion i t i s assumed that ice layers are passive and that a l l movements are r e s t r i c t e d to a horizontal plane. During any movement the layer should become progressively deformed into some d i s t i n c t shape similar i n geometry to the f o l d s observed i n deformed rocks and described by s t r u c t u r a l geologists. De S i t t e r (1956, p. 181) considers that rock deforma t i o n r e s u l t s from complex interactions between three basic f o l d mechanisms that can be distinguished by the characteris t i c f o l d shapes they produce. These fold,shapes or s t y l e s are described as: FIGURE 16. PLAN OF ICE 8 U R F A C E NEAR C E N T R E OF GLACIER BELOW ICEFALLS. W WHlte aroo, no obvious layers ^ F l n e layers S Crooks y Dtp of layer FIGURE 19. PLAN OF ICE SURFACE NEAR CENTRE OF OLACIER - 6? - 1) Concentric f o l d s . Concentric folds i n layered rocks are produced when a l l movements are p a r a l l e l with the layer surface. Within a f o l d the thickness of any layer remains constant. 2) 'Similar' f o l d s . In layered rocks deformed by cleavage or shear f o l d i n g , a l l movement takes place along a series of p a r a l l e l shear planes that do not change po s i t i o n during defor mation. The thickness measured p a r a l l e l with the movement plane remains constant at a l l times but i n the r e s u l t i n g geometric shapes, described as 'similar f o l d s ' , the limbs are r e l a t i v e l y thinner than the crest. 3) Flow f o l d s . Flow fo l d s are produced when the d i r e c t i o n of movement does not remain constant. Ice layers are too regular to be flow f o l d s and t h e i r outcrop pattern i n the ablation zone does not conform to any geometric f o l d produced by concentric or shear f o l d mechanisms. Assuming that ice i s passive and the t o t a l area of cross section remains constant during g l a c i e r flow, the limbs should become more attenuated but the thickness i n the c r e s t a l area should remain constant. I f ice layers were deformed by some sim i l a r f o l d mechanism the layers near the margins would rep resent the f o l d limbs and the g l a c i e r centre would be equi-- 63 - F I G U R E 2 0 . D IAGRAM TO SHOW M E C H A N I S M S OF p ;OtB ING. I - 69 - v a l e n t t o t h e f o l d c r e s t . D e s c r i p t i o n s o f ' i c e - f o l i a t i o n ' do not mention any- p r o g r e s s i v e change i n t h e r e l a t i v e t h i c k n e s s o f t h e l a y e r s down the g l a c i e r , n or do they r e f e r t o any o b v i o u s d i f f e r e n c e s be tween the t h i c k n e s s o f l a y e r s a t t h e margins and the t h i c k n e s s o f t h o s e near the c e n t r e . These d e s c r i p t i o n s i n d i c a t e t h a t g l a c i e r movement i s not a shear mechanism. Because l a y e r s remain . n e a r l y the same t h i c k n e s s , i t may be argued t h a t g l a c i e r f l o w produces c o n c e n t r i c f o l d s , by sh e a r p a r a l l e l w i t h t h e l a y e r . I n c o n c e n t r i c f o l d i n g t h e con vex s i d e o f the f o l d l i m b moves towards t h e c r e s t r e l a t i v e t o t h e concave s i d e ( F i g u r e 2 0 ) . A c t u a l measurements show t h a t g l a c i e r movement i s i n the o p p o s i t e d i r e c t i o n ; t h e i n n e r p a r t o f t h e l a y e r moves more r a p i d l y t h a n the o u t e r . The o u t c r o p p a t t e r n s of l a y e r i n g on the B l u e and o t h e r g l a c i e r s do not c o i n c i d e w i t h the s u r f a c e v e l o c i t y d i s t  r i b u t i o n d e t e r m i n e d f r o m measurements o f s u r v e y s t a k e s . On t h e A t h a b a s c a G l a c i e r t h e y do not even c o i n c i d e w i t h t h e t h e o r e t i c a l d i s t o r t i o n o f a t r a n s v e r s e p l a n e t h a t was o r i g i n a l l y v e r t i c a l a t the base o f the i c e f a l l s . The p r o b a b l e s u r f a c e d i s t r i b u t i o n f o r t h i s p l a n e , as i t i s p r o g r e s s i v e l y d i s t o r t e d , can be o b t a i n e d f r o m v e l o c i t y measurements g i v e n by P a t e r s o n ( 1 9 6 2 , F i g u r e s 8 t o 1 4 ) . Assuming t h a t t h e b a s a l s l i p i s 5 0 % o f the s u r f a c e v e l o c i t y and t h a t d r a g o f t h e s u r f a c e i c e and th e upward motion can be p a r t l y i g n o r e d , the p r o g r e s s i v e d e f o r  m a t i o n can be shown i n c r o s s s e c t i o n and p l a n . A l o n g i t u d i n a l c r o s s s e c t i o n i s g i v e n i n F i g u r e 2 1 and the s u r f a c e o u t c r o p * Transverse plane — vertical at the ice tall and the progressive * displacement in 5 year intervals. F I G U R E 21. LONGITUDINAL SECTION OF ATHABASCA GLACIER SHOWING THEORETICAL DISTORTION OF A TRANSVERSE VERTICAL PLANE B Y GLACIER FLOW. I. / Transverse plane :-. vertical at the ice tall and the progressive f dispracement in 5 year intervals. X Dip of plane. FIGURE 22. OUTLINE MAP OF ATHABASCA GLACIER SHOWING TH E ORETTC AL SURFACE CONFIGURATION OF A TRANSVERSE VERTICAL PLANE DEFORMED BY FLOW DOWN THE GLACIER. - 72 - i s given i n Figure 22. Each l i n e i n the f i g u r e s represents the plane at i n t e r v a l s of f i v e years. Despite any obvious g e n e r a l i z a t i o n s i n c o n s t r u c t i o n , the f i g u r e s are;:reasonably accurate, f o r the p o s i t i o n of the l a y e r a f t e r the f i r s t f i v e years corresponds c l o s e l y w i t h the observed p o s i t i o n of a s e r i e s of crevasses developed i n the i c e f a l l s . The t h e o r e t i c a l surface d i s t r i b u t i o n of l a y e r s i n P'igure 20 i s markedly d i f f e r e n t from t h e i r a c t u a l surface d i s t r i b u t i o n (Figure 13) sketched from a e r i a l photographs (B.C. F l i g h t Mo. A.167034, Nos. 16 to 22) and f i e l d measurements. A c t u a l l a y e r s d i f f e r from the t h e o r e t i c a l d i s t r i b u t i o n of l a y e r s i n the f o l l o w i n g ways: 1) No transverse l a y e r s of coarse i c e near the g l a c i e r centre. 2) Consistent trends down the length of the g l a c i e r . 3) Steeply d i p p i n g l a y e r s w i t h no p r o g r e s s i v e change i n a t t i t u d e . I t i s assumed that the coarse l a y e r s are produced at or near where they are observed on the g l a c i e r s u r f a c e s . On a e r i a l photographs, the prominent l a y e r s .'seem to become f a i n t e r away from the margin and' do not continue across the c e n t r a l part of the g l a c i e r . This i s s u r p r i s i n g , f o r i n the g l a c i e r centre, p a r t i c u l a r l y at the base of the i c e f a l l s , the a c t i o n of a ' s t r u c t u r e m i l l ' would be most i n t e n s e . Below the i c e f a l l s , some f i n e l a y e r s are t r a n s v e r s e but many trend down the g l a c i e r (Figure 18) and appear to be s i m i l a r t o f i n e l a y e r s observed elsewhere (Figure 19). - 73 - Over most of the central zone the layers of f i n e ice trend p a r a l l e l with the gl a c i e r movement but they have been deformed into similar f o l d s . These fo l d s generally have the same shape and attitude and there i s nothing to indicate that the f o l d s have been rotated by l a t e r g l a c i e r movement. In fa c t , the f o l d s and the f i n e ice must be produced at or near where they are observed 5for the following reasons: 1) The f o l d axes are near v e r t i c a l or steeply dipping i n a l l parts of the g l a c i e r . .. 2) There i s no s i g n i f i c a n t change i n the styl e of f o l d i n g or the general size of the fol d s down the length of the g l a c i e r . 3) Commonly, i n d i v i d u a l f o l d s are confined between ruptures that- are 'formed near the surface. These observations a l l indicate that the f o l d s originate near the surface and that the f i n e i c e i t s e l f i s a near surface feature. In cores obtained by Kamb and Shreve (1963a)from various depths i n the Blue G l a c i e r , the amount of fin e ice decreased with depth. Fine ice occurs in a l l cores from above 114 metres, but ice from below t h i s depth i s nearly bubble free and 'structureless'. SUMMARY Ice exposed on the ablation surface of most g l a c i e r s has numerous d i f f e r e n t layered structures, including planes of bubbles and d i f f e r e n t types of i c e . Irregular patches of coarse ice or f i r n represent pre-existing open spaces that have f i l l e d with snow, f i r n or meltwater that has become frozen. Coarse ice of similar o r i g i n occurs as narrow veins and is o l a t e d layers p a r a l l e l with cracks and crevasses. Repeated layers of di f f e r e n t types of ice are not r e a d i l y explained, and contorted layers and intersecting sets of structures are d i f f i c u l t to correlate with a simple system of stress. On the basis of the type of layers, the ablation surface of the Athabasca Glacier and g l a c i e r s elsewhere may be divided into two d i s t i n c t zones. Marginal Zone Central Zone Crystal size Crystal shape Layering Trend Folds Faults Coarse ice 5 to 10 cm. diameter Sinuous, i n t e r  locking Layers 9 to 15 cm. thick Sub-parallel with g l a c i e r walls Uncommon Faults uncommon .Fine ice 0 . 5 to 6 mm. diameter Polygonal to round 2 to 15 cm. thick P a r a l l e l with g l a c i e r flow Commonly s i m i l a r f o l d s Fractures and ruptures common Down the length of the g l a c i e r there i s no obvious change i n the general appearance or attitude of coarse layers - 7 5 - near the margins, or the geometry of contorted layers of f i n e ice near the centre. It i s assumed that both types of layers are produced at or near where they are observed on the g l a c i e r surface. Their r e s t r i c t e d d i s t r i b u t i o n indicates that two stress domains exist within g l a c i e r s : a central zone under a simple system of compression (or tension) and a marginal zone where the system i s affected by confining wall rock. - 76 - CHAPTER" III MICROSCOPIC STRUCTURES GENERAL STATEMENT In the accumulation zones of glaciers, the surface i s composed of small uniform ice granules that have a-"weak preferred crystallographic orientation with many C v axes nor mal to the g l a c i e r surface (Perutz and Seligman, 1939,* Fuchs, 1 9 5 9 ; Gow, 1 9 6 4 ) . In contrast, ice c r y s t a l s i n the ablation zone are i r r e g u l a r i n size and shape, and have a weak preferred orientation that i s very strong near the g l a c i e r toe (Rigsby, 1 9 5 5 ) . S i m i l a r i t i e s between ice c r y s t a l s i n g l a c i e r s and quartz grains i n dynamically metamorphosed sandstones and other tectonites have been .described by MacGregor ( 1 9 5 1 ) . Perhaps the examination of g l a c i a l i c e , using techniques of st r u c t u r a l petrology may help to determine the mechanics of ice movement and the r e s u l t s used as a simple -model f o r comparison with the more complex structures developed by deformation of durable tectonites._ Microscopic examination of some deformed .rocks shows that many minerals, p a r t i c u l a r l y micas, have a preferred orien t a t i o n . Determination of the re l a t i o n s h i p of c r y s t a l orienta t i o n to an inferred stress system causing rock deformation constitutes part of the larger f i e l d of petrofabrics. The term ' f a b r i c ' was f i r s t used by Knopf as' an - 76 - CHAPTER III MICROSCOPIC STRUCTURES GENERAL STATEMENT In the accumulation zones of glaciers, the surface i s composed of small uniform ice granules that have a.weak preferred crystallographic orientation with many C v axes nor mal to the g l a c i e r surface (Perutz and Seligman, 1939> Fuchs, 1959', Gow, 1964). In contrast, ice c r y s t a l s i n the ablation zone are i r r e g u l a r i n size and shape, and have a weak preferred orientation that i s very strong near the g l a c i e r toe (Rigsby, 1955). S i m i l a r i t i e s between ice c r y s t a l s i n g l a c i e r s and quartz grains i n dynamically metamorphosed sandstones and other tectonites have been described by MacGregor (1951). Perhaps the examination of g l a c i a l i c e , using techniques of str u c t u r a l petrology may help to determine the mechanics.of ice movement and the r e s u l t s used as a simple -model f o r comparison with the more complex structures developed by deformation of durable tectonites._ - Microscopic examination of some deformed rocks shows that many' minerals, p a r t i c u l a r l y micas,, have a preferred orien t a t i o n . Determination of the re l a t i o n s h i p of c r y s t a l orienta t i o n to an inferred stress system causing rock deformation constitutes part of the larger f i e l d of petrofabrics. The term ' f a b r i c ' was f i r s t used by Knopf as'an - 77 - equivalent to 'GEFUGE', and has been described by F a i r b a i r n (1949, p. 2): "In general terms, according to Sander, the f a b r i c of an object i s described by a l l the s p a t i a l data which i t contains, i r r e s  pective of the external shape or boundaries of the object." Included i n the term f a b r i c are a l l the d i r e c t i o n a l properties of an aggregate, the geometric shape of i n d i v i d u a l units and v e c t o r i a l properties such as crystallographic orien t a t i o n . F a i r b a i r n (1949, p. 2-3) c l a s s i f i e s f a b r i c s according to t h e i r o r i g i n , as depositiont-..'., growth, or deformation f a b r i c s , In g l a c i e r s , deposition;! f a b r i c s are formed i n the accumulation zones by regular bedded snow, growth f a b r i c s r e s u l t from the r e c r y s t a l l i z a t i o n of snow or the freezing of water ponded i n cracks, crevasses or moulins, and i n the abla t i o n zone, deformation f a b r i c s are produced by ice movement. Ice movement a l t e r s . the size and shape of i n d i v i d u a l grains and tends to change the orient a t i o n of t h e i r crystallographic axes. In a discussion.of the preferred orientations of a f a b r i c by Paterson.. and Weiss (1961, p. 861), dimensional and. vect o m l properties that constitute a fabric, are regarded as measureable, small scale geometric features which include: 1) The l a t t i c e planes and l i n e s within i n d i v i d u a l c r y s t a l s . 2) The shapes of inequant grains. 3) The arrangement of grains of sim i l a r properties ( s i z e , shape, mineralogy, etc.) into planes, l i n e a r streaks or other inequant patterns. - 78 - They recognize two kinds of f a b r i c elements, which they define as crystallographic and non-crystallographic. 1 ) Non-crystallographic elements include the preferred orientation of grain boun daries or shapes, and t e x t u r a l d i s c o n t i  n u i t i e s such as bedding or layering In heterogenous aggregates. 2 ) Crystallographic elements are l a t t i c e planes or s p e c i f i c l i n e s that exist throughout i n d i v i d u a l grains, (for example ( 0 0 1 ) i n micas, ( 0 0 0 1 ) i n quartz) and they may pervade an entire c r y s t a l l i n e aggregate i f the constituent grains have a preferred crystallographic o r i e n t a t i o n . Both kinds of f a b r i c elements can be recognized i n g l a c i e r i c e : most non-crystallographic elements, including the d i s t r i b u t i o n of grains of d i f f e r e n t size and shape are r e a d i l y apparent but the crystallographic f a b r i c s are l e s s e a s i l y recog nized. The study of the crystallographic orientation of ice grains, i n other words, ice f a b r i c s , i s the main topic of t h i s chapter. The determination and significance of crystallographic f a b r i c s w i l l be discussed at greater length i n a succeeding section, but a b r i e f description of the non-crystallographic f a b r i c elements w i l l be given here. Non-Crystallographic Elements F i r n i n the accumulation zone of a g l a c i e r occurs - 79 - a s s m a l l r o u n d e d g r a i n s o f u n i f o r m s i z e , s i m i l a r t o f i n e i c e i n t h e a b l a t i o n z o n e . G r a i n s o f c o a r s e i c e i n t h e a b l a t i o n z o n e a r e m u c h l a r g e r , t h e y h a v e h i g h l y i r r e g u l a r c o n t a c t s , a n d i t h a s b e e n r e p o r t e d t h a t t h e i r s i z e i n c r e a s e s p r o g r e s s i v e l y t o w a r d s t h e g l a c i e r t o e . A p r o g r e s s i v e c h a n g e i n t h e s i z e o f i c e g r a i n s h a s b e e n o b s e r v e d b y S e l i g m a n (1949b, 1950) f o r g l a c i e r s i n t h e S w i s s A l p s a n d N o r w a y , a n d m a n y o f S e l i g m a n ' s o b s e r v a t i o n s h a v e b e e n c o n f i r m e d a t K e b n e k a j s e , S w e d e n , b y A h l m a n n a n d D r o e s s l e r (1949). H i s m o s t s i g n i f i c a n t c o n c l u s i o n s m a y b e s u m m a r i z e d a s f o l l o w s : - 1) T h e c r y s t a l s i z e i n c r e a s e s f r o m a c c u m u l a t i o n z o n e t o t h e g l a c i e r s n o u t . 2) T h e g r a i n s i z e i s s m a l l e s t i n l i n e s o f f a s t e s t f l o w , s u c h a s a t t h e c e n t r e o f t h e g l a c i e r , a n d t h e l a r g e s t c r y s t a l s o c c u r i n d e a d i c e . T h e l a r g e s t c r y s t a l s f o u n d i n a c t i v e i c e h a v e a m e a n d i a m e t e r l e s s t h a n 2.5 c m . . 3) T h e r e l a t i o n s h i p o f c r y s t a l s i z e t o l e n g t h o f t r a v e l a n d t o r a t e o f g l a c i e r m o v e m e n t i n d i c a t e t h a t t i m e i s o n l y o n e o f s e v e r a l f a c t o r s t h a t i n f l u e n c e t h e c r y s t a l s i z e . 4) L o c a l ' s h e a r s t r e s s e s ' a n d l o c a l p r e s s u r e v a r i a t i o n s m a y c a u s e c r y s t a l g r o w t h . 5) C r y s t a l s t e n d t o b e s m a l l i n s t e e p g l a c i e r s . 6) C r y s t a l s t e n d t o b e l a r g e i n l o n g g l a c i e r s . 7) C r y s t a l s g r o w s l o w l y a t l o w t e m p e r a t u r e s b u t r a p i d l y n e a r t h e m e l t i n g p o i n t . G r o w t h o f c r y s t a l g r a i n s i s c o n t r o l l e d b y t i m e , t e m  p e r a t u r e , a n d s t r e s s . T h e t e m p o r a l r e l a t i o n s h i p o f t h e v a r i o u s p a r t s o f a g l a c i e r c a n o n l y b e i n f e r r e d , b u t c o u l d b e i n d i c a t e d - so - by i s o t o p e s t u d i e s . G r a i n s i n some p a r t s o f a g l a c i e r may have a p o o r l y d e v e l o p e d d i m e n s i o n a l o r i e n t a t i o n . R i g s b y (I960, p. 605) n o t e d t h a t i n s t r o n g l y ' f o l i a t e d ' p o l a r g l a c i e r s t h e f i n e i c e g r a i n s t e n d t o be e l o n g a t e d p a r a l l e l w i t h t h e ' d i r e c t i o n o f movement' and p e r p e n d i c u l a r t o the c r y s t a l l o g r a p h i c C - a x i s . A c c o r d i n g t o Kamb (1959b, p. 1894) some t h i n s e c t i o n s of i c e f r o m t h e B l u e G l a c i e r c o n t a i n e d i n d i v i d u a l c r y s t a l s t h a t were narrow i n the d i r e c t i o n p e r p e n d i c u l a r t o the p l a n e of ' f o l i a t i o n ' and Gurm (1964) i l l u s t r a t e s f l a t t e n e d g r a i n s i n i c e s e c t i o n s f r o m the F ranz J o s e f G l a c i e r . Most w o r k e r s , however, r e p o r t t h a t t h e y have not o b s e r v e d d i m e n s i o n a l o r i e n t a t i o n , but i t i s p o s s i b l e t h a t t h e s e w o r k e r s cut i c e s e c t i o n s i n a p l a n e t h a t does not show a p r e f e r r e d o r i e n t a t i o n . C r y s t a l l o g r a p h i c E l ements At t h e p r e s s u r e s and t e m p e r a t u r e s t h a t e x i s t i n g l a c i e r s , i c e c r y s t a l l i z e s as an h e x a g o n a l m i n e r a l p r o b a b l y i n t h e d i t r i g o n a l - p y r a m i d a l c l a s s 3m ( P a l a c h e , Berman and F r o n d e l , 1944, p. 494), a l t h o u g h Rossman (1950) s u g g e s t s i t may b e l o n g t o the d i h e x a g o n a l - p y r a m i d a l c l a s s 6 mm„ F o r t u n a t e l y , because i c e i s o p t i c a l l y u n i a x i a l , i t s c r y s t a l l o g r a p h i c o r i e n t a t i o n may be measured r e a d i l y i n t h i n s e c t i o n and i l l u s t r a t e d i n much the same way t h a t q u a r t z o r i e n t a t i o n s a r e d e t e r m i n e d f o r t e c t o n i t e s . I n p e t r o f a b r i c s , i n d i v i d u a l r e a d i n g s a r e p l o t t e d as p o i n t s on the l o w e r hemisphere of an e q u a l a r e a p r o j e c t i o n , - g l  and then c o n t o u r e d a t t h e l e v e l s of 1, 2, 3, 4, 5% etc.. of the d a t a per 1% a r e a o f the p r o j e c t i o n . C o n c e n t r a t i o n s o f d a t a a re c a l l e d maxima, and t h e c o n t o u r e d p r o j e c t i o n i s r e f e r r e d t o as a f a b r i c diagram (Friedman, 1963) . S m a l l u n i f o r m g r a i n s c h a r a c t e r i s t i c o f t h e a c c u m u l a t i o n zone g i v e f a b r i c diagrams w i t h most d a t a c l u s t e r e d near t h e c e n t r e ( P e r u t z and Se l i g m a n , 1 9 3 9);(Fuchs, 1959) ; (Gow, 1963) . The c o n t o u r e d diagrams i n d i c a t e t h a t g r a i n s t e n d t o be o r i e n t e d w i t h t h e C v a x i s v e r t i c a l - normal t o t h e t e m p e r a t u r e i s o g r a d , o r g l a c i e r s u r f a c e . I c e i n t h e a b l a t i o n zone has r e c r y s t a l l i z e d under s t r e s s and f a b r i c diagrams commonly have two o r more maxima t h a t a re independent o f t h e g l a c i e r s u r f a c e ( R i g s b y , I960). The maxima are d i f f i c u l t t o e x p l a i n , f o r t h e y n e i t h e r c o i n c i d e e x a c t l y w i t h c r y s t a l l o g r a p h i c o r i e n t a t i o n s p r e d i c t e d by some t h e o r i e s , nor c o r r e s p o n d c l o s e l y w i t h any rnesoscopic s t r u c t u r e . B race (I960) examined p o s s i b l e o r i e n t a t i o n s f o r m i n e r a l s i n a s t r e s s f i e l d o f three,, non-zero, p r i n c i p l e s t r e s s e s and s u g g e s t s t h a t t h e s t a b l e o r i e n t a t i o n i s a f u n c t i o n o f c o n f i n i n g p r e s s u r e . He p r e d i c t s t h a t t h e s t a b l e C v o r i e n t a t i o n f o r u n c o n f i n e d i c e l i e s a l o n g a s m a l l g i r d l e 50° f r o m t h e main s t r e s s d i r e c t i o n . Kamb (1959a) b e l i e v e s t h a t m i n e r a l o r i e n t a t i o n depends o n l y on t h e s t r e s s d e v i a t o r s and i s independent o f h y d r o s t a t i c p r e s s u r e , and t h a t the f i n a l o r i e n t a t i o n i s i n f l u e n c e d by the'mechanism o f o r i e n t a t i o n . Kamb p r e d i c t s i c e g r a i n s w i l l o r i e n t t h e m s e l v e s so t h e C v a x i s i s normal t o - 82 - a mesoscopic ' f o l i a t i o n ' plane, but upon release of stress favourably oriented grains r e c r y s t a l l i z e so that the f a b r i c has C v axes arranged at the corners of a diamond pattern centred upon the o r i g i n a l maxima. Some diamond patterns have been obtained by numerous workers but the angles between opposite pairs of maxima do not appear to be constant. Reid (1964, p. 258) has compiled a table to show that angles between corresponding sets range from 37° and 110°, to 27° and 59°. Experimental inves t i g a t i o n and t h e o r e t i c a l considera tions indicate that i n d i v i d u a l ice grains should deform only by movement p a r a l l e l with the basal plane, a plane of weakness inf e r r e d from an atomic structure proposed by Bjerrum (1952). It has been assumed that; i f ice grains deform by movement along the (0001) plane, grains with the basal plane p a r a l l e l with the d i r e c t i o n of maximum resolved shear-stress should be i n a more favourable attitude than those that have the basal plane i n some other position. Based on t h i s premise, the ideal f a b r i c diagram for deformed p o l y c r y s t a l l i n e ice should have a concentration of C v axes normal to ice layers assumed to be formed p a r a l l e l with the plane of greatest resolved shear stress. Fabric's with C v axes concentrated about one point near the pole of some mesoscopic layer have been determined by Rigsby (I960) f o r ice in-the Tuto tunnel, and near the margin of an ice ramp near Thule i n Greenland. Fabric diagrams, - 83 - o b t a i n e d elsewhere on t h e ramp s u r f a c e , and on temperate g l a c i e r s i n o t h e r c o u n t r i e s , commonly have t h r e e or f o u r maxima t h a t do not always appear t o be r e l a t e d t o i c e l a y e r s . I n r e c e n t y e a r s , s e v e r a l a u t h o r s have s t u d i e d the r e l a t i o n between i c e f a b r i c s and i c e l a y e r s o b s e r v e d on t h e a b l a t i o n s u r f a c e of g l a c i e r s . Temperate g l a c i e r s have been s t u d i e d by P e r u t z and Seli g m a n (1939) i n t h e A l p s ; Bader (1951); R i g s b y (1953); A l l e n et a l . (I960); T a y l o r (1962) i n N o r t h A m e r i c a ; Gunn (1964) i n New Z e a l a n d ; Adie (I960) i n Norway, and Schwarzacher and U n t e r s t e i n e r (1954) i n S w i t z e r l a n d . P o l a r g l a c i e r s have been i n v e s t i  g a t e d by R i g s b y (1955); Fuchs (1959); R e i d (1963); and Gow (1964). I c e f a b r i c diagrams i l l u s t r a t e d by . t h e s e w o r k e r s a r e a l l s i m i l a r i n appearance but th e r e l a t i o n s h i p between maxima and l o c a l i c e l a y e r s i s s t i l l n o t c l e a r . The p r e s e n t a u t h o r made i c e f a b r i c d e t e r m i n a t i o n s , i n c o n j u n c t i o n w i t h a s t u d y o f i c e l a y e r s on t h e a b l a t i o n zone o f A t h a b a s c a G l a c i e r between t h e l o w e s t i c e f a l l and snout. The f a b r i c diagrams o b t a i n e d i n t h e p r e s e n t s t u d y have two o r more maxima w i t h d i s t r i b u t i o n s s i m i l a r t o t h o s e o b t a i n e d _ 84 - by other workers. The positions of these observed maxima cannot be related d i r e c t l y to mesoscopic structures but appear to be influenced by the method of sampling and the l i m i t a t i o n s of the manner i n which data are presented. PREVIOUS WORK Although g l a c i e r s have.been studied since the mid 1700's, most of the early work was concerned with the syste matic measurement of g l a c i e r movement and only speculations were made of the actual mechanism of ice flow. It i s only within the l a s t twenty years that .glacier studies have included measurements of the crystallographic orientation of ice grains. Tyndall (1858) explained how the crystallographic o r i e n t a t i o n of large c r y s t a l could be determined by measuring the attitude of figures which form within an ice c r y s t a l . These 'Tyndall-figures' are produced by a series of c l o s e l y spaced rounded to hexagonal discs, or s t e l l a t e bubbles, elon gated' i n the basal plane and r e s u l t from i n t e r n a l melting when an ice c r y s t a l i s exposed to 'infra-red r a d i a t i o n ' . The bubble planes or discs may appear on the surface of large c r y s t a l s as deeply etched grooves known as 'Forel s t r i p e s ' . Tyndall figures can only be detected i n large c r y s t a l s so the method cannot be used to determine the orientation of smaller grains. It was Klocke (1879) who suggested'that ice should be examined using optic aids but i t was not u n t i l 1895 that the nature of f i n e grained ice was examined by Deeley and / Fletcher (1895) when they used polarized l i g h t to indicate the crystallographic orientation of small ice grains. Crystal orientation studies of fine grained ice were f i r s t made i n the laboratory by Bader and others (1939),. and i n the f i e l d by Perutz and Seligman (1939). Since that time, p a r t i c u l a r l y in the la s t decade, the crystallographic orien t a t i o n of grains in several g l a c i e r s have been measured and the r e s u l t i n g f a b r i c diagrams compared with the orientation of mesoscopic structures v i s i b l e on the ice surface. Perutz and Seligman (1939) studied the MOnch and Jungfrau f i r n areas in Switzerland. Fabric diagrams of 50 to 100 grains measured i n specimens taken at a depth of 8 metres had most of the data clustered near the centre, i n d i  cating that most cry s t a l s were oriented with C v axes normal to the surface. Specimens from progressively deeper l e v e l s i n the f i r n had f a b r i c s with r e l a t i v e l y few grains oriented i n t h i s d i r e c t i o n . Fuchs (1959, p.16-17) investigated f i r n i n the Green land ice sheet. He found that f o r depths below 8 metres the C axes have a weak preferred orientation normal to the tempera ture isotherms, which were generally sub-parallel with the surface. Fabrics of polar i c e to a depth of 305 metres were obtained by Gow (1963, p. 781) from a v e r t i c a l hole at Byrd Station, Antarctica. At 71 metres the ice grains were very small and had no preferred crystallographic orientation, but ice sections from 163 and 305 metres contained larger grains ! - 86 - of ice that gave diagrams i n d i c a t i n g a well defined preferred o r i e n t a t i o n of sub-vertical C v axes. Reid (1964) measured the crystallographic orienta t i o n of f i r n grains in surface folds on the Ross Ice Shelf, Antarctica. The f a b r i c diagrams are d i f f i c u l t to interpret, but Reid claims that the preferred orientations are strongest i n diagrams from the f o l d limbs, where the shear stress i s t h e o r e t i c a l l y greatest. In the ' i d e a l ' f a b r i c , f o u r maxima are centred 21°, 26 Q , 27°, and 32° from the pole to the shear plane, and t h e i r d i s t r i b u t i o n i s said to r e f l e c t some rotation of the stresses r e l a t i v e to the present f o l d axis. Investigations of ice grains from the ablation zones of temperate and polar g l a c i e r s have shown that t h e i r f a b r i c s are similar (Rigsby, I960). These f a b r i c diagrams have two or more areas of concentration that do not appear to coincide with the pole position of mesoscopic structures. Authors of the most recent papers have suggested that the f a b r i c s of coarse ice are d i f f e r e n t from those ob tained from f i n e ice (Taylor, 1962Kamb, 1959b). Such a d i s t i n c t i o n , however, i s d i f f i c u l t to j u s t i f y , but in order to show that both types of ice give e s s e n t i a l l y the same f a b r i c i t i s necessary to discuss the way diagrams have been obtained and interpreted by d i f f e r e n t i n d i v i d u a l s . Bader (1951) investigated a small area of stagnant ice near the margin of the Malaspina Glacier i n Alaska. He i l l u s t r a t e s c l e a r l y , the in t e r l o c k i n g contacts of coarse ice grains and describes the d i f f i c u l t y in i d e n t i f y i n g i n d i v i d u a l - 87 - grains. He measured the C v axis orientation of 5& ice grains and represents the readings as uncont'oured data on .the upper hemisphere of an equal area projection. He found that the C v axes were clustered into four groups: "....One normal to the g l a c i e r surface.^, one' p a r a l l e l to the g l a c i e r surface i n the direc tion of flow, and two symmetrically l'ocated at angles of close to 20° to the normal of the plane of the banding.". Because the ice was overlain by vegetation covered moraine, Bader assumes that i t was e s s e n t i a l l y 'dead i c e ' but he concludes that the orientation pattern r e f l e c t e d the south- ward movement of the g l a c i e r by deformation under i t s own weight. (Ibid. p. 534). Rigsby (195 3) obtained s i m i l a r f a b r i c s , containing two or more maxima, from active ice within the Malaspina Gla c i e r , and from ice in the ablation zone of the Emmons Glacier on Mt. Rainier i n Washington, and from the Saskatchewan Glacier in Banff National Park. He measured C v orientations from ice sections cut p a r a l l e l with the ' f o l i a t i o n ' but i n a v e r t i c a l plane i n order to prevent rapid melting of the i c e . At each lo c a t i o n he measured 100 to 250 orientations that he l a t e r plotted and contoured on the lower hemisphere of an equal area projection. He made no d i s t i n c t i o n between f a b r i c s of fin e and coarse ice but rotated a l l the contoured data so that i n each diagram the perimeter represents a horizontal surface on the g l a c i e r . In each diagram two or more areas of concentration containing less than 15% of the data per unit area are vaguely - 88 - centered about the pole to the layering that i s represented by a great c i r c l e i n the diagram. To demonstrate the rel a t i o n s h i p between the ice l a y  ering and the d i s t r i b u t i o n of maxima, Rigsby constructed a composite or synoptic diagram by combining the data of several f a b r i c diagrams from the Emmons G l a c i e r . The composite d i a  gram was made by combining several rotated diagrams. To rotate the diagrams the 'pole to f o l i a t i o n ' was moved along a p r i n c i p l e axis u n t i l i t was at the centre and the maxima positions were rotated a similar amount. The r e s u l t i n g dia grams were then rotated about t h e i r new centre u n t i l the maxima positions were made to correspond. In the f i n a l synoptic diagram, the maxima appeared to cluster into four main groups forming a diamond pattern about the centre with oppo s i t e pairs of maxima having angular distances 84° and 52°. Rigsby suggests that t h i s type of diamond pattern might indicate that movement occurs on glide planes p a r a l l e l with the (1122) and (1012) crystallographic planes as well as the basal plane. However, subsequent laboratory.experiments have not demonstrated that ice c r y s t a l s w i l l deform along planes other than the basal plane. As an alternative hypothesis, Rigsby suggests the pattern may form by gliding'along four d i f f e r e n t shear d i r e c  tions within the g l a c i e r . He presumes that these directions w i l l occur at d i f f e r e n t times and thus, the maxima are of di f f e r e n t ages. Rigsby (1955, I960) l a t e r made observations on the - 89 - i c e sheet and a p o l a r g l a c i e r near Thule i n n o r t h w e s t Green l a n d . He measured 1 00 t o 2 00 g r a i n s at s e v e r a l l o c a t i o n s and a g a i n found i c e f a b r i c s w i t h more t h a n one maximum. Some f a b  r i c s had maxima c o n t a i n i n g 2 5 % o f t h e d a t a per one per cent a r e a , and i c e from the w a l l o f t h e Tuto t u n n e l had a s i n g l e maximum o f 39% near t h e p o l e o f a d i s t i n c t l a y e r e d s t r u c t u r e . A l l h i s o t h e r diagrams c o n t a i n e d one or more maxima c l u s t e r e d i n t o one q u a d r a n t , b u t ne a r the p o l e t o a ' f o l i a t i o n ' . R i g s b y ( I 9 6 0 , p. 6 05 ) concludes t h a t i n p o l a r g l a c i e r s the g l i d e p l a n e s of i c e g r a i n s a r e p a r a l l e l w i t h t h e ' f o l i a t i o n ' and have an i d e a l f a b r i c , b u t under m e l t i n g c o n d i t i o n s i n temper a t e g l a c i e r s , t h i s i d e a l f a b r i c t e n d s t o be changed to the c h a r a c t e r i s t i c 3 or 4 maxima t y p e by r e c r y s t a l l i z a t i o n near the s u r f a c e . A d i e ( i 9 6 0 ) worked on i c e specimens f r o m an a d i t w i t h i n t h e c i r q u e g l a c i e r o f V e s t - S k a u t b r e e n i n Norway. At s e v e r a l l o c a t i o n s i n the g l a c i e r , he c u t s u b - h o r i z o n t a l s e c t i o n s p a r a l l e l w i t h a p r o n o u n c e d ' s t r a t i f i c a t i o n ' Because he measured o n l y p o l a r o r i e n t a t i o n s , a l l C v axes were l e s s t h a n 4 5 ° f r o m the normal t o t h e l a y e r . He p r e s e n t e d h i s d a t a as a c o n t o u r e d d i a g r a m - t h e c o n t o u r s a re a l l w i t h i n 4 5 ° o f t h e diagram c e n t r e . These diagrams, s i m i l a r t o o t h e r i c e f a b r i c s , have two or more maxima w i t h up t o 7% o f t h e d a t a . A d i e i n t e r p r e t s h i s diagram as h a v i n g a main maximum w i t h l a t e r superimposed submaxima. He does not e x p l a i n the p r o c e s s t h a t caused the submaxima. - 90 - Schwarzacher and Untersteiner (1953) measured C y axes of grains i n the ablation zone of the Pasterze Glacier i n Switzerland. At several locations they measured 200 or more grains and obtained ice f a b r i c s with 3 or 4 maxima. These maxima are vaguely related to nearby layered ice but do not have the same d i s t r i b u t i o n as maxima i n f a b r i c s obtained by Rigsby. For the f a b r i c diagrams from the Pasterze,the authors postulate that the maxima correspond to several co-existing shear directions i n the g l a c i e r . They suggest that these directions correspond with three sets of f i n e grained layers observed elsewhere on the g l a c i e r surface, and further explain that the 4th maximum i n the diagrams corresponds with the pole to the plane.of the p r i n c i p a l crevasse system. Kamb (1959b),and A l l e n , Kamb, Meier and Sharp (I960) give ice f a b r i c s obtained from 14 locations on the ablation zone of the Blue Glacier, on Mount Olympus i n northwest Washing ton. At each l o c a l i t y they measured 100 to 250 C v axis orien tations i n ice sections cut i n s p e c i f i c planes. The orienta t i o n of these planes was determined by a l o c a l co-ordinate system of three mutually perpendicular axes arranged i n the following manner. Two of the axes were i n the plane of the f o l i a t i o n which was always near v e r t i c a l , and the t h i r d was normal to t h i s plane. In the plane of the 'foliation', the nearly v e r t i c a l axis i n the dip d i r e c t i o n was l a b e l l e d up-dn and the axis which corresponded to the st r i k e d i r e c t i o n was la b e l l e d N-S or E-W depending on the approximate trend of the . - 91 - f o l i a t i o n , N being the geographic north, which i s downstream f o r most parts of the Blue Glaci e r . C v measurements are i l l u s t r a t e d .on equal area projec tions i n which the plane of f o l i a t i o n i s at the circumference or along one of the p r i n c i p a l diameters. This method of repre sentation has an obvious disadvantage, f o r some of the diagrams are .. d i f f i c u l t to compare d i r e c t l y . Uncontoured diagrams i l l u s t r a t e d by Allen' et a l . (I960) have more than one maxima and appear to be similar to f a b r i c diagrams obtained by workers from other g l a c i e r s . By casual inspection, Kamb (1959b)divided the diagrams into several types rel a t e d to d i f f e r e n t types of ice i n the following manner: Fabric diagrams of f i n e ice have 'multiple maxima', i n which the C v axes occur with no obvious concentration or a 'single broad maximum' with axes concentrated near the pole to the ice l a y e r i n g . Fabrics of the coarse bubbly i c e , interlayered with the f i n e ice described above, or near the margins of the g l a c i e r , may have 'multiple maxima'. Many diagrams f o r coarse ice have maxima in a group of three (L-type f a b r i c ) or in a group of four (4-maximum f a b r i c ) , s i m i l a r to the diamond pattern obtained by Rigsby. It should be noted, however, that Rigsby did not d i s t i n g u i s h c l e a r l y between the types of ice that he used to obtain his diagrams. Kamb states that the L-type f a b r i c of coarse ice i s an e a r l i e r stage of the 4-maxima or diamond pattern i n which the maxima appear to be centred about the pole to the f o l i a t i o n . The long axis of the diamond i s roughly p a r a l l e l with a shear-- 92 - stress vector acting across the f o l i a t i o n plane. Taylor (1962) measured 200 grain orientations at each of four s i t e s on the upper part of the ablation zone of the Burroughs Glacier, Alaska. Fabric diagrams obtained from these measurements have areas of concentration containing up to 6% of the data per unit area. Taylor considers that the ice f a b r i c s were produced by r e c r y s t a l l i z a t i o n just below the rupture layer near the ice surface and that the single maximum observed i n the f a b r i c of fin e grained ice i s normal to a gently dipping f o l i a t i o n plane. The same maximum also occurs i n f a b r i c diagrams obtained from in t e r c a l a t e d layers of coarse ice but the other two maxima i n the diagrams are said to correspond closely with poles of steeply dipping 'thrust f a u l t s ' and 'oblique shear fractures' v i s i b l e on the ice surface. In summary, C v measurements show that ice grains i n polar and temperate g l a c i e r s have a preferred o r i e n t a t i o n . Most f a b r i c diagrams have two or more maxima containing 5 or 7^ of the data per one per cent area, that are not commonly centred near the pole to the i c e - l a y e r s . To explain t h e i r d i s t r i b u t i o n , previous workers have related the position of i n d i v i d u a l maxima to other fracture planes (Taylor, 1962), sets of co e x i s t i n g shear planes (Schwarzacher and Untersteiner, 1953), c r y s t a l structure (Kamb, 1959b), or some r e c r y s t a l l i z a t i o n phenomenon (Rigsby, I960). Because the d i s t r i b u t i o n of C v maxima i n i c e - f a b r i c diagrams i s d i f f i c u l t to understand, more f i e l d data was obtained from Athabasca Glacier in order to f i n d a simple explanation. - 9 3 - METHOD OF FIELD STUDY During, the summers of 1961 and 1962, C v orientation of ice grains were determined at 25 selected s i t e s on the sur face of the ablation zone of the Athabasca G l a c i e r , Alberta. Because there were few suitable s i t e s on the western side of the g l a c i e r , most measurements were taken from the central and eastern side of the g l a c i e r , between the lowest ice f a l l and the toe. Each sample s i t e was located on an a e r i a l photo graph and i t s position i s given"in Figure 23v '• ''« Location s i t e s selected i n the ablation zone were confined to hummocky surfaces above the l e v e l of the melt water that runs over the ice surface. Debris and melted ice grains were chopped from the surface to expose a small pro j e c t i n g block of firm unmelted i c e . Two sides of the exposed block were cut v e r t i c a l l y in a north-south d i r e c t i o n and the top was cut i n a horizontal plane. The orientations of the sides and of a l l v i s i b l e mesoscopic structures within the block were measured with a Brunton compass. Horizontal slabs of ice were cut from the block at distances of one or two inches and the ice between them di s  carded. This was done to reduce to a minimum any chance that one ice grain would occur i n two successive sections. On exposure to a i r the ice melted along the grain contacts and i t was d i f f i c u l t to prevent the progressive melting of the block. In the l a t e r stage of the investigation,- ice sections were cut and then stored for a few hours i n an insulated cooler before grain orientations were obtained. FIGURE 23. OUTLINE MAP OF ATHABASCA GLACIER SHOWING LOCAT ION 8 OF ICE FABRIC M E A S U R E M E N T S . - 95 - Orientation of C v axes of c r y s t a l s within ice sec tions were measured using a 6" universal stage with four axes of r o t a t i o n . This stage was b u i l t by Mr. Peters of the Mining Department of the University of B r i t i s h Columbia,' following the design of Rigsby, as i l l u s t r a t e d by Langway (1958). Metal parts of the stage have b-een constructed from brass that has been n i c k e l plated to decrease e f f e c t s of weathering, and a l l washers and other f r i c t i o n surfaces have been made from t e f l o n A wooden box that encloses the stage can be opened on one side to form a support f o r a polaroid disc mounted above the stage. Opening the side also allows l i g h t to enter the box. This l i g h t i s r e f l e c t e d upwards through the stage from a s t a i n l e s s steel mirror screwed inside the box at the bottom. The stage has two 6 inch diameter discs of thi n p l a s t i c between which the ice specimen i s mounted. This speci men i s prevented from moving between the discs by l i n e s of a half centimetre g r i d scored into the underside of the top disc Thick slabs cut from the ice surface were reduced to l / l 6 inch thick by melting the ice with a cement trowel that had been previously warmed on a small o i l heater. To keep the o r i g i n a l o r i e n t a t i o n of the ice section, one of the oriented sides was aligned with one of the l i n e s of the gr i d cut into the top p l a s t i c d i s c . When an ice. section was f i r s t mounted, high i n t e r  ference colours of i n d i v i d u a l grains prevented accurate determination of the extinction p o s i t i o n , but as the ice thinned by melting, C v orientations could be r e a d i l y measured. - 96 - As no assistant was employed, i t was possible to measure only 10 to 20 grains before most sections disintegrated. Several sections-were cut and a t o t a l of 100 to 200 C y axes measured following the procedure;outlined by Langway (1958). Errors r e s u l t i n g from mechanical manipulations and other procedures w i l l be enumerated i n a discussion of ice f a b r i c s presented at the end of t h i s chapter. In the present study, no hemispheres were used and readings at high i n c l i n a  tions of the stage may be i n error as a r e s u l t of r e f r a c t i o n of l i g h t from a i r / p l a s t i c / i c e , etc. However, i t i s considered that, f o r duplicate readings of the same grain, errors i n r e f r a c t i o n and poor alignment of sight may give differences up to 05°. Errors i n the horizontal o r i e n t a t i o n of the ice section may be as great as 03°, but as several sections were used, some inaccuracies i n the measurements may have been partly compensated. RESULTS OF FIELD STUDY A description of the ice f a b r i c s determined from the ablation zone of the Athabasca G;lacier i s given i n t h i s part 6*f the thesis. The significance of the areas of concentration i n the f a b r i c diagrams and an i n t e r p r e t a t i o n of the r e s u l t s i s presented in the l a t e r part of the'-section e n t i t l e d "Discussion of Ice Fabrics". Over those parts of the g l a c i e r surface that were 'examined, the., ice grains varied considerably i n both size and shape, but most of the i n d i v i d u a l ice sections cut from the - 97 - surface could be described as fi n e or coarse ice (see Page 47) following the broad c l a s s i f i c a t i o n of Kamb (1959b, p.1893). He described ice on the Blue Glacier as fine i c e , coarse bubbly- ice,, and coarse clear i c e , but although these types were a l l ident i f i e d - o n the Athabasca Glacier, only the f i n e and coarse bubbly ice w£re examined i n d e t a i l . Fine ice occurs mainly near the c e n t r a l part of the g l a c i e r i n thick layers with intercalated minor layers of coarse bubbly i c e . In t h i n section fine ice i s composed of uniform grains 0.5'to 6 mm. i n diameter and r a r e l y up to 2 cm. i n s i z e . The grains are regular i n shape but tend to be sub- spherical, and have smooth contacts. Small bubbles within the ice mass may be concentrated into bubble r i c h layers indepen dent of any ice layering. The weathered surface of f i n e ice i s granular and si m i l a r in appearance to f i r n . . ( F i g u r e 15). Thick layers of coarse ice and thinner layers of. f i n e grained ice are c h a r a c t e r i s t i c of the marginal areas of the g l a c i e r . Coarse bubbly ice contains i r r e g u l a r ice grains that i n t h i n section have diameters from 3 cm. to 10.cm. and highly sutured margins. Within the grains are numerous spheri c a l and e l l i p s o i d a l bubbles, 1 mm. to 2 mm. in diameter, con tai n i n g water and a vapour phase. These bubbles may be concen trated within i n d i s t i n c t layers to give a weak f o l i a t i o n . Well defined layers may contain more numerous, larger bubbles and then the surface of the weathered ice appears whiter. Coarse clear ice i s formed by large c r y s t a l s 3 cm., to 12 cm., i n diameter. These grains contain few bubbles and - 98 - have int e r l o c k i n g contacts with surrounding c r y s t a l s . This type of ice i s found i n three d i f f e r e n t parts of the g l a c i e r as: 1) Large zones of stagnant ice at the margins of the g l a c i e r . 2) Thin layers int e r c a l a t e d with coarse bubble i c e . 3) Irregular pods and masses where ponded-meltwater has frozen i n cracks and crevasses. In a l l of the thin sections examined, neither granu lated nor brecciated ice was observed, and no strained c r y s t a l grains were recognized. C v measurements for each ice section were corrected fo r r e f r a c t i o n using the table given by Langway (1958, p. 7) and plotted on a diagram using the lower hemisphere of an equal area projection. The plane of the diagram represents a horizontal surface whose geographic orientation i s given by a small mark in d i c a t i n g north. C v axes plotted on the projection have been contoured to give a f a b r i c diagram i n the conventional method as described by F a i r b a i r n (1949, p. 285-289). .In the diagrams the plane of ice layering i s represented by a great c i r c l e . A l l the measured axes and t h e i r corresponding contoured diagrams are given as part of the Appendix at the end of t h i s t h e s i s . The s i t e of each f a b r i c determination i s indicated on an outline diagram of the g l a c i e r (Figure 23) and shown to gether with a l l diagrams i n a map enclosed i n the f o l d e r at the back of t h i s thesis. In most of the f a b r i c diagrams,the C„ measurements are clustered into a small section with two - 99 -r or more small areas containing more than 7% of the data per one per cent of the diagram area. , . A l l the diagrams from the Athabasca Glacier are similar to those obtained by workers from other g l a c i e r s (for example, Rigsby, 1955 and I960), but before any interpretation can be made of them, the geological significance of the data should be established. The v a l i d i t y of the diagrams i s discussed i n a l a t e r section, and evidence i s given to show that some maxima are not s i g n i f i c a n t - t h e i r p osition may be influenced by the system of sampling and numerous l i m i t a t i o n s i n the methods used to present the data. By casual inspection, f a b r i c diagrams from the Athabasca Glacier may be divided into two groups according to which quadrant of the diagram contains the majority of obser vations. Those diagrams with most of the axes plotted i n the southeast quadrant are designated Group I and those with most axes i n the northeast quadrant are designated Group I I . Group I Fabric diagrams, distinguished as Group I, were obtained from steeply dipping layers of coarse ice at several locations near the southeastern margin of the g l a c i e r . In each diagram C v axis readings generally occur near the periphery of the diagram i n the south eastern quadrant. In the diagrams, areas of concentration with up to 7% of the data are clustered near the pole to the great c i r c l e that represents ice layers. Most of the concentrations appear to - 100 - f a l l on the locus of a small c i r c l e of radius 30° to 50°. The centre of t h i s small c i r c l e l i e s close to the pole of the ice layering. Group I diagrams indicate that grains near the g l a c i e r margins tend to be oriented 30° to 50° from the pole to coarse ice layers that' dip steeply towards the c e n t r a l part of the g l a c i e r . Group II Fabrics assigned to Group II were obtained from sections cut from contorted layers of f i n e ice near the centre of the g l a c i e r . Some of the diagrams may not be s t r i c t l y accurate, because approximately o n e - f i f t h of-the grains i n some sections were too small to measure. However, for most diagrams, readings of G v axes are. confined to the northeast and southwest quadrants and are generally concentrated into two or three small areas containing up to 7% of the data per one per cent area of the diagram. In most diagrams, the maxima appear to be unrelated to the great c i r c l e that represents ice layering. Figure 2^4 and Figure 25 are sketch maps showing a small area of the g l a c i e r surface with contorted layers of f i n e ice. Samples taken at four d i f f e r e n t locations give f a b r i c diagrams containing two or more.maxima unrelated to ice layering but a l l occurring on a small c i r c l e of radius 30° to 50° . - 101 - w White area, no obvious layers Direction of glacier flow Fine layers Narrow crack open at surface Fabric location F - fine ice N° of readings-N* of sections • Pole to layering Contour interval I. 2.3.4,5 % ez£$ Contour depression Estimated small circle centre x FIGURE 24 M A P op F I N E L A Y E R S A N D F A B R I C D I A G R A M S F R O M L 0 C A T I 0 N 8 62-11, 62-12. - 102 - W White area.no obvious layers j)lreotion of glacier flow Fine layers S Narrow crack open at. surface Fabric location F - fine ice N° of readings—N° of sections A Pole to layering Contour interval 1 , 2 , 3 . 4 , 5 °/o «H3 Contour depression • • Estimated small circle centre x FIGURE 25 MAP OF FINE LAYERS AND FABRIC DIAGRAMS FROM LOCATIONS 6 2 - 1 4 . 6 2 - 1 5 . - 103 - The p o s i t i o n o f t h e maxima v a r y f r o m diagram t o d i a g r a m , b u t i n g e n e r a l , t h e y appear t o f a l l on t h e l o c u s o f a s m a l l c i r c l e o f r a d i u s 30° to 50°. The c e n t r e of t h i s c i r c l e r e p r e s e n t s a l i n e t h a t i s n e a r l y h o r i z o n t a l and s u b - p a r a l l e l w i t h t h e d i r e c t i o n o f g l a c i e r f l o w . The d i s t r i b u t i o n o f r e a d i n g s i n diagrams a s s i g n e d t o Grqup I I i n d i c a t e t h a t near t h e c e n t r e zone o f the g l a  c i e r , f i n e g r a i n s o f s u r f a c e i c e te n d t o be o r i e n t e d 30° to 50° from t h e d i r e c t i o n o f g l a c i e r f l o w . To d e t e r m i n e a r e l a t i o n s h i p between t h i s s m a l l c i r c l e and t h e i c e l a y e r s , d i a g r a m s were r o t a t e d , and recombined i n s e v e r a l d i f f e r e n t ways t o g i y e s y n o p t i c diagrams. The most s u c c e s s f u l attempt i s a s y n o p t i c diagram ( F i g u r e 2 6 ) i n which t h e c e n t r e r e p r e s e n t s t h e c e n t r e o f the s m a l l c i r c l e s f r o m a number o f diagrams. The s y n o p t i c d i a g r a m was c o n s t r u c t e d i n the f o l l o w i n g manner: on a s e l e c t e d group o f o r i g i n a l f i n e i c e f a b r i c s , s m a l l c i r c l e s were drawn t o pass t h r o u g h t h e maxima and the c e n t r e o f t h e c i r c l e on each d i a g r a m was l o c a t e d by i n s p e c t i o n . T h i s c e n t r e was t h e n r o t a t e d a l o n g t h e E-W-axis t o the c e n t r e o f t h e diagram.. D u r i n g t h i s m a n i p u l a t i o n t h e p o l e t o t h e l a y e r s and t h e c e n t r e o f g r a v i t y o f each maxima were r o t a t e d a s i m i l a r a n g u l a r d i s t a n c e . A l l t h e r o t a t e d diagrams were t h e n combined t o g i v e F i g u r e 2 6 . I n t h i s d i a g r a m the c e n t r e r e p r e s e n t s t h e c e n t r e of t h e e s t i m a t e d s m a l l c i r c l e s , the open c i r c l e s r e p r e s e n t t h e maxima t h a t g e n e r a l l y , f a l l a l o n g a s m a l l c i r c l e , and the t r i a n g l e s r e p r e s e n t t h e p o l e s t o t h e - 104 - o Maxima positions. y Centre of smal l c irc le A Pole to ice layering (note- all fall alone a great olrcle) FIGURE 26. S Y N O P T I C D I A C R A M O F R O T A T E D F A B R I C S OF FINE I C E FROM L O C A T I O N S 62~3 to 62-8. 62-10 to 62-12, S 62-14 to 62-16. - 105 - r o t a t e d l a y e r s . P o l e s t o t h e f i n e l a y e r s tend t o f a l l a l o n g a g r e a t c i r c l e t h a t i s almost at 9 0 ° t o t h e c e n t r e of t h e s m a l l c i r c l e s c o n s t r u c t e d on the o r i g i n a l d iagrams. The r e a  son f o r t h i s a n g u l a r r e l a t i o n s h i p . i s not c l e a r . I n summary, C y measurements f r o m t h e a b l a t i o n s u r  f a c e o f the A t h a b a s c a G l a c i e r may be d i v i d e d i n t o two d i s t i n c t g r o u p s . Samples o b t a i n e d f r om c o a r s e i c e l a y e r s near t h e g l a c i e r margins g i v e diagrams w i t h most of t h e r e a d i n g s c l u s  t e r e d a l o n g a s m a l l c i r c l e 'normal' t o t h e l a y e r s (Group I ) . ": G v measurements o f f i n e i c e from near th e c e n t r e o f the g l a  c i e r g i v e f a b r i c diagrams i n which two or more maxima have no d i r e c t r e l a t i o n s h i p w i t h t h e a t t i t u d e o f t h e f o l d e d l a y e r s but a r e l o c a t e d a l o n g a s m a l l c i r c l e w i t h / c e n t r e ' s u b - p a r a l l e l w i t h t h e d i r e c t i o n o f g l a c i e r f l o w (Group I I ) . DISCUSSION OF ICE FABRICS In a l l g l a c i e r s t h a t have been examined, t h e i c e f a  b r i c diagrams show t h a t g r a i n s near t h e s u r f a c e i n the a b l a t i o n zone have a d e f i n i t e p r e f e r r e d c r y s t a l l o g r a p h i c o r i e n t a t i o n . A l t h o u g h t h i s p r e f e r r e d o r i e n t a t i o n i s c o n s i d e r e d t o r e s u l t f r o m g l a c i e r movement, f a b r i c diagrams do not commonly have maxima i n p o s i t i o n s i d e n t i c a l t o t h o s e d e t e r m i n e d i n l a b o r a  t o r y e x p e r i m e n t s o r i n f e r r e d by t h e o r y . As summarized i n t h e d e s c r i p t i o n o f p r e v i o u s i c e f a b r i c s t u d i e s g i v e n above, - p o s i t i o n s ^ o f i n d i v i d u a l maxima have been c o r r e l a t e d w i t h mesoscopic s t r u c t u r e s , p o s t u l a t e d c o - e x i s t i n g p l a n e s o f shear and w i t h some p r o c e s s o f r e c r y s t a l -- 106 - l i z a t i o n . Before any general i n t e r p r e t a t i o n can be made of ice f a b r i c diagrams,it i s necessary to outline the methods used to obtain the diagrams and also consider l i m i t a t i o n s i n the manner which data i s i l l u s t r a t e d . Mechanical errors and the inherent d i f f i c u l t i e s i n producing f a b r i c diagrams w i l l be described under the headings:' problems of sampling, observational errors, and methods of diagram construction. The v a l i d i t y of the i n d i v i d u a l maxima w i l l be discussed i n a l a t e r section r e l a t i n g to the interpreta t i o n of diagrams;. Sampling Problems Methods of obtaining.thin sections of ice vary accor ding to the investigator, but most workers cut horizontal slabs from ice near the g l a c i e r surface. 'To r e s t r i c t any melting, Rigsby (1953) preferred to cut'his sections v e r t i c a l but rotated a l l h i s data into a horizontal plane. Kamb (1959b)cut sections in the ' f o l i a t i o n ' plane or at right angles to i t , but the diagrams he i l l u s t r a t e s , are d i f f i c u l t to compare d i r e c t l y with the diagrams of others. However, his f i e l d techniques are not fundamentally d i f f e r e n t from the -more usual methods and they give similar r e s u l t s . To be s t a t i s t i c a l l y v a l i d , the f i e l d measurements must be s u f f i c i e n t to give a f a i r representation of the true orientation, not of the number of grains, but of .the volume of material with the C,r axis i n a certain d i r e c t i o n . The v 4 basic premise i n i c e - f a b r i c studies i s that there i s no change - 107 - i n bulk volume during deformation and that ice grains deform by movement only along the plane of maximum resolved shear stress.' Grains oriented with t h e i r basal-:.plane p a r a l l e l with the plane of maximum resolved shear stress should increase in number and size while those with the basal planes i n some other d i r e c t i o n s should be crushed and become smaller. Thus, one small grain should not be given the same emphasis i n the f a b r i c diagram as" a large grain, the l a t t e r presumably formed by the union of 'several grains now favorably oriented with res pect to the stress system. At present, there i s no convenient way to measure or represent the volume of oriented material. Allen et a l ; ; (I960) represent the r e l a t i v e size of oriented c r y s t a l s by the size of c i r c l e s plotted i n f a b r i c diagrams, but the highly i r r e g u l a r nature of coarse ice grains, as i l l u s t r a t e d by Bader (1951, Fig.2) would make any d i s t i n c t i o n on grain size d i f f i  c u l t to j u s t i f y . Because of melting, i t i s not possible to measure the orientation of a l l grains that form the t o t a l population •'' of any ice section. Instead, a sample population must be selected by measuring a l i m i t e d number of the grains in any thin section. This l i m i t e d number should be obtained by some constant procedure to eliminate errors and ensure that measure ments are obtained i n a systematic manner. There should be some s t a t i s t i c a l test to establish how closely the sample population resembles the t o t a l population. By convention i n petrofabrics, a sample population - 108 - of 200 i s g e n e r a l l y taken, not because i t has any s t a t i s t i c a l b a s i s but mainly because s i n g l e ' e r r a t i c ' readings may be ignored i f data are contoured at the one per cent l e v e l on a diagram. Although a sample po p u l a t i o n of two hundred,or per haps four hundred,may be s u f f i c i e n t to determine a f a b r i c , problems regarding the r e l a t i v e s i z e of the c o n s t i t u e n t g r a i n s cannot be r e s o l v e d . Observational E r r o r s A l l measurements of i c e g r a i n o r i e n t a t i o n w i l l be subject to operator bias , and any mechanical e r r o r s i n using the u n i v e r s a l stage. At sub-zero temperatures, t h i n s e c t i o n s of i c e do not melt and a l l g r a i n s i n a s e c t i o n can be measured. In f a b r i c s t u d i e s of temperate g l a c i e r s , however, the i c e sec t i o n s are c o n t i n u a l l y m e l t i n g and there i s time to measure only some of the g r a i n s . F a i r b a i r n (1949) l i s t s two main sources of observa t i o n a l e r r o r . i n p e t r o f a b r i c s t u d i e s . 1) Measurement of too few gr a i n s to giv e an average o r i e n t a t i o n . 2) A r b i t r a r y s e l e c t i o n and measurement of gr a i n s of c e r t a i n s i z e , o r i e n t a t i o n , c r p o s i t i o n and neglect of other g r a i n s equally, important i n the a n a l y s i s . P o s s i b l e e r r o r s using the u n i v e r s a l stage f o r i c e f a b r i c work have been l i s t e d by Langway (1958, p. 8) as: 1) P a r a l l a x e f f e c t when the eye i s not normal to the measured g r a i n . 2) - E r r o r s i n measuring exact e x t i n c t i o n p o s i t i o n s - 109 - at high angles. 3 ) Reading the orientation d i a l s on the stage. 4) Inherent mechanical errors i n the stage, for the reproduction of readings for the same grains i s usually between 1 or 2 degrees. As well as the possible errors l i s t e d above, i t i s d i f f i c u l t to determine accurately the orientation of grains which have the C y axis within the plane of the stage, and there may be addit i o n a l errors r e s u l t i n g from r e f r a c t i o n of light, at a i r , p l a s t i c , water and ice contacts. Other possible errors include the inaccurate orienta t i o n of sections and the measurement of two grains which are parts of the same i r r e g u l a r c r y s t a l . Errors i n section orienta t i o n and c r y s t a l measurement do not amount to more than 5°, but with the use of many sections, these errors may compensate each other i n part. When an ice section i s f i r s t examined, t h i c k grains have high birefringence colours and i t is-rhot easy to determine t h e i r exact extinction position. In sections of f i n e ice 20$ of the grains may be smaller than the thickness of the section so t h e i r orientation cannot be determined; consequently, only the larger grains can be measured. Because there i s only a li m i t e d time before any ice sections disintegrate, a f t e r each reading there i s a tendency to select the next grain from those that are already near extinction, in order to save time. When s u f f i c i e n t measurements have been taken, a l l readings are corrected f o r r e f r a c t i o n , following the table given by Langway (1959, p. 7). Kamb (1962) has pointed out - 110 - that t h i s table i s not s t r i c t l y correct, and has derived a d i f f e r e n t set of correction values. These values are not s i g n i  f i c a n t l y d i f f e r e n t from those given by Langway, and most workers continue to use the e a r l i e r tables so that t h e i r diagrams may be consistent with those of previous studies. Diagram Construction Most authors plot the corrected readings on a h o r i  zontal plane using the lower hemisphere of an equal area Schmidt net, and represent the orientation of ice layers by great c i r c l e s . Data on the projections may be contoured using a counting out method, but most wo,rkers contour t h e i r data i n the manner described by F a i r b a i r n (1949) to obtain the f i n a l diagram. Readings taken from ice sections that are not h o r i  zontal may be plotted on an equal area net and then rotated into a horizontal plane. It should be r e a l i z e d that a pattern obtained by ro t a t i n g a contoured diagram i s s l i g h t l y d i f f e r e n t from that obtained by contouring the same readings that have been rotated i n d i v i d u a l l y . Contouring as i t i s conventionally done i n the mariner described by F a i r b a i r n (1949) i s neither accurate nor exactly reproducible. The actual positions of the contours.depend upon the alignment of a g r i d used to locate the counter, and f u l l y accurate contouring would require that the shape of the counter change from c i r c u l a r at the centre of the diagram to an e l l i p s e near the circumference (Mellis,•1942). - I l l - Because of observation errors and sampling methods, (any group of readings may not represent the true f a b r i c . Con- tour diagrams constructed from the readings w i l l give a pattern influenced by the counter shape and the position of the g r i d . Despite a l l these discrepancies, most contoured diagrams of temperate and polar g l a c i e r s are remarkably similar Interpretation Before interpreting ice f a b r i c diagrams, i t i s neces sary to determine i f the sample f a b r i c does resemble the true f a b r i c , and then decide i f the maxima arise from various methods of sampling, or i f they t r u l y represent d i r e c t i o n s i n which C v axes are concentrated. In petrofabric studies, diagrams are appraised v i s u a l and those i n which there i s no obvious c l u s t e r i n g of data are said to be ' i s b t r o p i c ' or 'uniform'. I f the data are arranged in a d i s t i n c t pattern, with some element of symmetry, the dia^ grams are said to represent f a b r i c s that have a r e a l preferred o r i e n t a t i o n . Fabric diagrams with areas of concentrations contain ing l+Ofo of the data'In one per cent of the area do represent a f a b r i c which has a d e f i n i t e preferred o r i e n t a t i o n . Diagrams with concentration of only 5 to 7%, however, may represent a true f a b r i c with a weak preferred orientation, or they may r e s u l t from random sampling of a f a b r i c i n which there i s no preferred orientation of the C y axes. The terminology used to describe the orientation - 112 - of petrofabric diagrams i s not c l e a r l y defined, and some authors make no d i s t i n c t i o n between the terms ' i s o t r o p i c ' , 'uniform' and 'random'. An is o t r o p i c or uniform f a b r i c i s one i n which data are d i s t r i b u t e d evenly throughout a diagram such that, no matter how i t i s sub-divided into equal areas, the same amount of data occurs i n each sub-area. It i s unl i k e l y that a uni form d i s t r i b u t i o n occurs i n nature. A random f a b r i c i s one in which readings are di s t r i b u t e d i r r e g u l a r l y over the diagram and may give concentrations up to 5% of the data i n one per cent of the t o t a l area.. A random f a b r i c could r e s u l t from random sampling a hypothetical uniform f a b r i c or one with no preferred ori e n t a t i o n (See F l i n n , 1958, Diagram 1 ). To determine i f diagrams with scattered areas of low concentration do represent true f a b r i c s with preferred orien t a t i o n some test must be applied. Most of the tests that have been proposed f a l l n a t u r a l l y into three main types. 1) The most common test i s to compare mathema t i c a l l y , the actual d i s t r i b u t i o n of data with a hypothetical uniform d i s t r i b u t i o n . 2) Less commonly, a diagram i s compared with similar diagrams obtained -from a f a b r i c that has a known preferred orien t a t i o n . 3 ) In the least common method, a series of 'sub- diagrams' are obtained by p l o t t i n g small groups of readings from the same specimen. S i m i l a r i t i e s between the 'sub-diagrams' are considered evidence of a preferred orienta-- 113 - t i o n i n the t r u e f a b r i c . S e v e r a l s t a t i s t i c a l t e s t s have been d e s c r i b e d by Ghayes ( i n F a i r b a i m , 1949) i n c l u d i n g a g e n e r a l t e s t and a zone test proposed by Winchell. In most of the s e m a t h e m a t i c a l t e s t s a diagram i s d i v i d e d i n t o a number of sub-areas o r c e l l s o f e q u a l s i z e , and the observed, number o f r e a d i n g s i n each c e l l i s compared w i t h t h e number to be e x p e c t e d i f t h e f a b r i c were u n i f o r m . Any d i f f e r e n c e s between the observed and the ex p e c t e d number g i v e s a n u m e r i c a l f i g u r e termed a Chi-square v a l u e . I f the sum o f t h e s e v a l u e s from a l l s ub-areas i s g r e a t e r than a c e r t a i n a r b i t r a r y v a l u e , the diagram i s s a i d t o be 1 s i g n i  f i c a n t '. T h i s term does not i m p l y t h a t t h e diagram has any g e o l o g i c a l s i g n i f i c a n c e ; i t merely states t h a t t h e d i s t r i b u t i o n o f d a t a i n t h e diagram:, i s m a r k e d l y d i f f e r e n t from t h a t o f a u n i f o r m diagram. •» The a p p l i c a t i o n o f m a t h e m a t i c a l a n a l y s i s t o p e t r o - f abrics has .been d i s c u s s e d by F l i n n (1.958, p. 533 ) 'whose work i n d i c a t e s that most mathematical' t e s t s are v a l u e l e s s . For any diag r a m , t h e s i g n i f i c a n c e l e v e l o r Chi-square v a l u e o n l y i n d i  c a t e s t h e d i f f e r e n c e between a sample f a b r i c and a h y p o t h e t i c a l u n i f o r m d i s t r i b u t i o n o f p o i n t s , and c o n t r i b u t e s n o t h i n g t o the u n d e r s t a n d i n g o f a sample f a b r i c . F l i n n * s "work i n d i c a t e s t h a t diagrams s h o u l d be compared'with t h o s e o b t a i n e d from s a m p l i n g a n a t u r a l f a b r i c w i t h a known o r i e n t a t i o n . I t i s d i f f i c u l t to o b t a i n a true n a t u r a l f a b r i c f o r i t would r e q u i r e t h e measurement o f a l l elements i n a p a r t i  c u l a r p o p u l a t i o n . I n g e o l o g i c a l l i t e r a t u r e , t he b e s t f a b r i c f o r comparison i s that given by Rusnak (1957, p. 4 0 4 ) . Rusnak determined the o r i e n t a t i o n of sand grains placed i n a small trough with running water. He re g u l a t e d the flow of water so t h a t the sand gr a i n s could j u s t be moved. Neglecting drag e f f e c t s produced by the side of the trough, the moving water would tend to o r i e n t the g r a i n s so they become imbricate down stream. Rusnak measured the o r i e n t a t i o n of 100 grains but when the p l o t t e d data were contoured, the r e s u l t i n g diagram appeared to be a random f a b r i c with no obvious areas of con c e n t r a t i o n . A t o t a l of 200 measurements gave a sample f a b r i c w i t h f i v e areas of concent r a t i o n c o n t a i n i n g 3% of the data i n the imb r i c a t e p o s i t i o n , where one maximum was a n t i c i p a t e d by theory. This experiment by Rusnak i n d i c a t e s that sample f a b r i c s of 200 observations may have more than one maximum i n the genera 1 area of the t h e o r e t i c a l maximum. Ice f a b r i c s have maxima c l u s t e r e d i n t o one small s e c t i o n of the diagram, and because there i s no s u i t a b l e s t a t i s t i c a l t e s t to show that the d i s t r i b u t i o n i s g e o l o g i c a l l y s i g n i f i c a n t , the diagrams must be compared wi t h other f a b r i c diagrams. When i c e f a b r i c diagrams are compared with the random diagram constructed by F l i n n (1958, p. 533) i t i s obvious t h a t g l a c i e r i c e does have a s i g n i f i c a n t p r e f e r r e d o r i e n t a t i o n . Now, i t i s necessary t o decide i f the maxima i n i c e f a b r i c diagrams represent a c t u a l concentration o f C v axes i n a r e a l f a b r i c , or i f they r e s u l t from sampling techniques, f a b r i c r e p r e s e n t a t i o n s , or simply lack of adequate data. - 115 - Kamb (1959b) notes that diagrams wi t h l a r g e numbers of readings do not have c l e a r l y d e f i n e d maxima and concentra t i o n s are best developed i n diagrams that contain only a small number of readings. A l l e n et a l . (I960, p. 617) i l l u s t r a t e two diagrams c o n t a i n i n g C v measurements taken from the same l o c a l i t y on the Blue G l a c i e r . One of t h e i r diagrams (C-23) contains 155 readings c l u s t e r e d i n an i r r e g u l a r manner about the pole to the. ' f o l i a t i o n ' . The second diagram (C-24) con-' t a i n s only 59 C v axes which give a pronounced f a b r i c that they describe as a 4 maxima f a b r i c , w i t h the comment: "The r e s u l t s suggest that a diamond may be emerging. The C-24 diagram i s the more convincing, but i t s u f f e r s from inadequate sampling because measurements were hampered by bad weather." To show that some maxima are spurious and t h e i r p o s i t i o n s i n f l u e n c e d by s e l e c t i o n of a sample p o p u l a t i o n , one of the f a b r i c diagrams from the Athabasca G l a c i e r has been r e - p l o t t e d i n groups of 100 readings to give four s u b - f a b r i c s (Figures 27 and 28). The s u b - f a b r i c s were obtained i n the f o l l o w i n g manner: the sample p o p u l a t i o n c o n s i s t s of a t o t a l of 200 readings that were recorded i n a f i e l d notebook and numbered co n s e c u t i v e l y from 1 to 200. These readings were grouped i n t o 100 readings as (A) 1 to 100, (B) 100 to.200, (C) every odd numbered reading, and (D) every even numbered reading, and the groups p l o t t e d i n the sub*~fabric diagrams. From an i n s p e c t i o n of the f o u r s u b - f a b r i c s i n Figures 27 and 28, i t i s obvious that the maxima do not occur i n e x a c t l y the same p o s i t i o n i n each diagram, and i n some they are not even - 116 - 0 Totol fabric of 200 roadings * pole to roe layering A Sub fabric of flret 100 readings Contour Interval 1,2,3,4,5 % B Sub fabric of next 100 readings <0 Contour depression. FIGURE 27. F A B R I C D I A G R A M A N D S U B F A B R I C D I A G R A M S FROM LOCATION 6 2 - 5 . i - . 1 1 7 - 0 C D 0 Total fabric of 200 readings C Sub fabrio of 100 'odd' readings. D Sub fabrio of 100 'even' readings. A Pole to ice layering Contour Interval l.2.3.4.5V« <z£5 contour depression. FIGURE 28 FABRIC DIAGRAM AND SUB FABRIC DIAGRAMS FROM LOCATION 62~5. - 118 present. If the existence and position of maxima in a diagram are influenced by the number of readings and the l i m i t a t i o n s of the method of representation, can i n d i v i d u a l concentrations be considered s i g n i f i c a n t ? Maxima of 5 to 7% appear to be s i g n i f i c a n t with respect to the entire diagram, but they disap pear, i f the smaller area containing one per cent or more of the data i s contoured. Although maxima do not occupy the same positions in each f a b r i c diagram they tend to be r e s t r i c t e d to one sector of the diagram, and many appear to be di s t r i b u t e d along a small c i r c l e . Diagrams given i n Figures 29 to 34 show the t o t a l f a b r i c for fin e ice,and beside them,a more simple diagram with contours that outline areas containing 3 or 5% or more of the data. In each of the s i m p l i f i e d diagrams a small c i r c l e has been constructed so that i t passes through the maxima positions, and the estimated centre of t h i s c i r c l e i s indicated by a small cross. Inspection of the s i m p l i f i e d diagrams shows that; 1) the maxima do not occur i n the same r e l a t i v e positions even when the • • sample locations are i n the same area. 2) the centre of the small c i r c l e tends to be i n the same general position on each diagram. 3')"" few readings occur near the estimated -' 119 - 61-4 F 200-14 Fabric location Type of ice F fine N° of readings N° of sections A Pole to ice layering Contour interval 1,2,3,4,5% <22> Contour depression Postulated small circle X Estimated centre of circle F I G U R E 29 FABRIC DIAGRAMS OF FINE ICE WITH SIMPLIFIED DIAGRAM SHOWING LOCUS AND CENTRE OF POSTULATED SMALL CIRCLE. Fabric location A Pole to ice layering Type of ice F fine Contour interval 1,2,3,4,5 58 N ° of readings N° of sections Contour depression ~ Postulated small circle X Estimated eentre of circle FIGURE 30. FABRIC DIAGRAMS O F F I N E ICE WITH SIMPLIFIED D I A G R A M S H O W I N G ' L O C U S A N D CENTRE O F POSTULATED SMALL CIRCLE. 121 - Fabric location A Pole to ice layering Type of ice F fine Contour interval 1,2,3,4,5 85 N° of redding* N° of sections Contour depression Postulated small circle X Estimated eentre of circle FIGURE 3I. FABRIC DIAGRAMS OF FINE ICE WITH SIMPLIFIED DIAGRAM SHOWING LOCUS AND CENTRE OF POSTULATED SMALL CIRCLE. - 122 - 62-9 F 22-4 Fabric locotion A Pole to ice layering Type of ice F fine Contour interval 1,2,3,4,5 58 N° of readings N° of sections <22) Contour depression «•-"" Postulated small circle X Estimated eentre of circle FIGURE ^2. FABRIC DIAGRAMS OF FINE ICE WITH SIMPLIFIED DIAGRAM SHOWING LOCUS AND CENTRE OF POSTULATED SMALL CIRCLE. - 123 - Fabric locotion A Pole to ice layering Type of ice F fine Contour interval 1,2,3,4,5 58 N° of readings N° of sections Contour depression Postulated small circle X Estimated centre of circle FIGURE 33 FABRIC DIAGRAMS OF FINE ICE WITH SIMPLIFIED DIAGRAM SHOWING LOCUS AND CENTRE OF POSTULATED SMALL CIRCLE• Fabric location * Pole to ice layering Type of ice F fine Contour interval 1,2,3,4.5 58 N° of readings N° of sections <32> Contour depression , ' ~ Postulated small c irc le X Est imated centre of circle IGURE 34. FABRIC DIAGRAMS OF FINE ICE WITH SIMPLIFIED DIAGRAM SHOWING LOCUS AND C E N T R E OF POSTULATED SMALL CIRCLE* - 125 centre of the constructed c i r c l e . 4 ) the maxima are i r r e g u l a r l y d i s t r i b u t e d along the small c i r c l e . The d i s t r i b u t i o n of maxima along a small c i r c l e i s even more obvious i f the s i m p l i f i e d diagrams are combined d i r e c t l y i n t o a synoptic diagram (Figure 3 5 ) . The maxima show no obvious concentrations but tend t o occur w i t h i n a narrow zone, th a t represents a small c i r c l e . Few readings occur'near the estimated centre and the c i r c l e i t s e l f does not seem to be r e l a t e d to the i c e l a y e r i n g . F a b r i c diagrams of f i n e i c e i n d i c a t e that C v axes of g l a c i e r i c e do not occur i n a s i n g l e maximum near the pole p o s i t i o n of the i c e l a y e r s , but tend to c l u s t e r as a small cone about a unique a x i s . i t i s assumed, that the C v axes of g l a c i e r i c e are c l u s t e r e d at random w i t h i n t h i s cone, and the exact p o s i t i o n of any i n d i v i d u a l maximum i s not d i r e c t l y con t r o l l e d by the s t r e s s system. The a c t u a l p o s i t i o n s of maxima i n most diagrams r e s u l t from random sampling a f a b r i c i n which the C v axes appear to be randomly d i s t r i b u t e d w i t h i n a small c i r c l e , a type of sample f a b r i c t h a t could a l s o r e s u l t from random sampling a uniform g i r d l e ( F l i n n , 1958, p. 538). The f a b r i c diagrams obtained from the Athabasca G l a  c i e r are not unique. They c l o s e l y resemble f a b r i c diagrams given by Taylor (1962) f o r the c e n t r a l part of the Burroughs G l a c i e r , and those i l l u s t r a t e d by Rigsby (I960) f o r the Emmons, Saskatchewan, and other g l a c i e r s . Most diagrams may be - 126 - Areas of concentration CP 3 * X Estimated centre of small circle A Pole to ice layering F I G U R E 35 SYNOPTIC DIAGRAM OF FINE ICE FABRICS FROM LOCATIONS 62-3 t.O 6 2 - 8 . 62-10 to 62-12, fcY 62-14 to 62-16. - 12? - i n t e r p r e t e d t o r e p r e s e n t a f a b r i c i n which the C y axes a r e con f i n e d t o a s m a l l cone whose a x i s i s s u b - p a r a l l e l w i t h t h e g l a  c i e r f l o w o r a t r i g h t a n g l e s t o c o a r s e l a y e r s . The b e s t examples t h a t can be used here a r e diagrams from t h e M o l t k e G l a c i e r ( R i g s b y , I960, F i g . 6), r e p r o d u c e d here as F i g u r e 3 6 , On each diagram a s m a l l c i r c l e has been c o n s t r u c t e d t o pass t h r o u g h t h e maxima. Diagrams o b t a i n e d f r o m l a y e r e d i c e near the g l a c i e r m argins ( c f . Group I o f the diagrams o b t a i n e d f r o m the A t h a b a s c a ) have most r e a d i n g s p l o t t e d i n t h e s m a l l a r e a w i t h maxima o f 5 t o 7% a l o n g t h e l o c u s o f a s m a l l c i r c l e whose c e n t r e i s near t h e p o l e p o s i t i o n of s t e e p l y d i p p i n g i c e l a y e r s . I n t h e d i a g r a m f r o m an u n l a y e r e d sample o f i c e near the c e n t r e o f the M o l t k e G l a c i e r ( c f . Group I I f rom the A t h a b a s c a G l a c i e r ) most r e a d i n g s are r e s t r i c t e d t o one quadrant and c l u s t e r e d i n t o t h r e e maxima. These maxima appear t o f a l l on t h e l o c u s o f a s m a l l c i r c l e whose c e n t r e c o r r e s p o n d s c l o s e l y w i t h a l i n e s u b - p a r a l l e l w i t h t h e d i r e c t i o n o f g l a c i e r f l o w . SUMMARY G v measurement of i c e g r a i n s on t h e a b l a t i o n zones of. t h e A t h a b a s c a and o t h e r g l a c i e r s g i v e f a b r i c diagrams t h a t have d a t a c l u s t e r e d i n t o a s m a l l p a r t o f t h e p r o j e c t i o n w i t h more t h a n one maxima c o n t a i n i n g 5 t o 7% o f the d a t a . The maxima appear t o be randomly d i s t r i b u t e d a l o n g a s m a l l c i r c l e of r a d i u s 3 0 t o 5 0 ° , and i n many diagrams t h e y have no o b v i o u s r e l a t i o n w i t h t h e p o l e t o the i c e l a y e r i n g . F a b r i c diagrams FIGURE 3 6 ICE F A B R I C D I A G R A M S F R O M M O L T K E G L A C I E R . ( ofter R I C S B Y 1955 ) 129 - may be divided into two main types. Diagrams from fine ice near the g l a c i e r centre have maxima, unrelated to any layering, that f a l l on the locos of a small c i r c l e whose centre corresponds to a l i n e that i s sub- p a r a l l e l with the d i r e c t i o n of g l a c i e r flow. Diagrams from coarse ice near the gl a c i e r margin have maxima along a small c i r c l e whose centre l i e s near the pole to steeply dipping layers. In the central part' of a g l a c i e r , ice may be under compression or tension, but near the g l a c i e r margin a shear stress i s caused by confining wall rocks. Angular r e l a t i o n  ships between stress systems and ice f a b r i c s are not well understood, but Cy.measurement of ice stressed under known conditions may help to determine how C v axes become oriented. Results of laboratory experiments on ice are described in the next chapter. - 130 - CHAPTER.IV EXPERIMENTAL 'STUDIES GENERAL STATEMENT One o f the major problems i n s t r u c t u r a l g e o l o g y i s t o e s t a b l i s h the a n g u l a r r e l a t i o n s h i p , between s t r e s s s y s  tems and t h e secondary s t r u c t u r e s t h e y produce. A r e l a t i o n  s h i p between d i f f e r e n t secondary s t r u c t u r e s can be e s t a b l i s h e d r e a d i l y by d e t a i l e d e x a m i n a t i o n s o f f o l d e d r o c k s , but i t i s i m p o s s i b l e t o d e t e r m i n e t h e o r i e n t a t i o n o f a s t r e s s system t h a t no l o n g e r e x i s t s . When l a y e r e d r o c k s a r e d i s t o r t e d , t h e o r i e n t a t i o n o f the s t r e s s system may p r o g r e s s i v e l y change, w i t h t h e r e s u l t t h a t , a f t e r d e f o r m a t i o n , i t s o r i g i n a l o r i e n t a  t i o n i s d i f f i c u l t t o d e t e r m i n e . I n f a c t , once deformation- has o c c u r r e d , it'may not even be p o s s i b l e t o deduce t h e o r i g i n a l a t t i t u d e o f t h e l a y e r s , • - • " L a t e stage f o l d i n g o f l a y e r e d t e c t o n i t e s commonly o c c u r s by displacement;, a l o n g c o n j u g a t e f a u l t p l a n e s or j o i n t s . To deduce t h e o r i e n t a t i o n "of the s t r e s s system t h a t causes t h e d e f o r m a t i o n , c o n j u g a t e p l a n e s have been compared w i t h t h e f r a c t u r e s _ p r o d u c e d by b r i t t l e f a i l u r e o f r o c k s i n m e c h a n i c a l t e s t s . •However, i t i s not c o r r e c t t o e x p l a i n a l l . r o c k d e f o r m a t i o n by some p r o c e s s o f b r i t t l e f a i l u r e i f s t r a i n r e s u l t s , from creep o r some p r o c e s s " o f ' p l a s t i c ' f l o w . I n l a b o r a t o r y ' t e s t s i t t i s not easy to d u p l i c a t e t h e t e m p e r a t u r e - 131 - and pressure conditions under which a rock w i l l deform and i t i s impossible to continue such tests u n t i l the material behaves as a 'Rheid'. Most rocks have a rheid-value of 10-4 years, and they are not suitable test materials f o r labora tory experiments. Ice, however, i s more suitable f o r i t deforms r e a d i l y i n short term mechanical tests, and i t i s r e l a t i v e l y easy to duplicate i n the laboratory many of the stress conditions that exist i n g l a c i e r s . Since the turn of the century, many d i f f e r e n t bending, tension, extrusion, compression and shear tests have been con- ' ducted.upon i c e , but most o f them have been to determine a flow law f o r single ice cr y s t a l s or p o l y c r y s t a l l i n e aggregates. Although i n d i v i d u a l test r e s u l t s are not exactly reproducible, and some d e t a i l s remain uncertain, the main features of ice flow are now well recognized and the general properties have been summarized by Glen (1958 a, c ) . Single c r y s t a l s of ice are b r i t t l e , but they have' no detectable fundamental strength. Under the smallest stress,• an ice specimen w i l l deform but, with time, the rate of s t r a i n may increase rapidly to approach a steady value. Most of the st r a i n apparently occurs by 'translation' along the c r y s t a l  lographic basal plane, and no other glide planes have been p o s i t i v e l y identified.by experiment. Several workers have demonstrated, that movement occurs in zones p a r a l l e l with the basal plane (McConnel, 1891), and recently, Nakaya (1958) deformed single ice c r y s t a l s and determined that movement occurs i n s l i p bands that are concen-- 132 - trated into a series of zones about 0.06 mm. apart, and paral l e l with the basal plane. To determine the d i r e c t i o n of easiest g l i d e , Steinemann (1954) sheared c r y s t a l s in various directions within the OOOl plane. He did not detect any glide l i n e , but suggests.' that one alternate p o s s i b i l i t y i s the 1120 d i r e c t i o n . Creep of single ice c r y s t a l s has been measured by Griggs and Coles (1954), Steinemann (1954), J e l l i n e k and B r i l l (1956), Butkovitch and Landauer (1958, 1959), and others. They obtained e s s e n t i a l l y the same creep curves, ir r e s p e c t i v e of whether the ice was deformed in tension, compression or shear experiments. Their r e s u l t s indicated that a f t e r 20 to 30 hours the rate of s t r a i n becomes constant and may be related to the applied stress according to the flow law: € » K T ° K i s a constant that depends upon the temperature, and for most experiments, the value of n ranges from 1.5 to 3.9 with a mean of about 2.5 For any.given stress the rate of s t r a i n for a single c r y s t a l increases with time and the ice i s said to become 'softened'. In contrast, the s t r a i n rate f o r p o l y c r y s t a l l i n e ice under constant load decreases with time. This decrease i s a ttributed to the mutual interference of adjacent grains and a vaguely defined process c a l l e d ' s t r a i n hardening'. Creep curves f o r p o l y c r y s t a l l i n e ice specimens de formed by Glen (1955), Steinemann (1958a, b), Butkovitch and Landauer (1958, 1959) Vialov (1958) and Mellor (1959) are similar i n appearance and indicate that a steady rate of s t r a i n _ 133 - i s reached aft e r about 10 hours. It i s not possible to duplicate the r e s u l t of i n d i  vidual experiments and differences between various workers may be a r e s u l t of variations i n the shape, size, or f a b r i c of test specimens. Glen (1955) compressed small cylinders 1 to 2 inches i n diameter, and J e l l i n e k and B r i l l (1956) extended small rectangular blocks 2.5 cm. . square and 10 cm. long. It i s possible that in some tests i f the load was applied f o r less than 10 hours, the s t r a i n rate did not reach a steady value. The flow law f o r p o l y c r y s t a l l i n e aggregates has the same form as the law f o r single c r y s t a l s with almost the same value of n. Glen (195 2) obtained values of 3.2 or 4.2, Steinemann (1958a) using commercial i c e , determined a value of 1.9 f o r stresses' at 1 bar and a value of 4.2 at 15 bars. Butkovich and Landauer (1959) stressed blocks of commercial and g l a c i a l ice and obtained a value of n f o r two sets of experiments, one with stresses between 0.5 to 3 bars, the other f o r stresses between 7 to 28 bars. The specimens were at -5°C. i n a l l t e s t s and both groups indicated a'- power law. with n = 2.96. Different r e s u l t s were obtained by Vialov (1958) who found a great increase i n the value of n for stresses above 5 bars. A change i n the flow law at high'stresses may not be too s i g n i f i c a n t i n glaciology for most g l a c i e r s appear to deform under stresses of l e s s than 2 bars. However, any change i n the flow law at a stress of one bar would be of - 134 considerable importance. Glen (1955, p. 536) has suggested that there may be a s l i g h t bend i n the s t r e s s - s t r a i n graph at 1 bar to indicate some s l i g h t change i n the flow law. More recently, Tegart (1964) suggested that any difference i n the stress exponent may be due to some fundamental change from basal s l i p to some other plane of movement i n the individual' ice grains. For stresses below 1 bar, Steinemann (1958a, p. 25) obtained a value of n r 1.9, and Vialov (195 8) and Mellor (1959) a value of 1.5. Th(e tests of Steinemann, however, may be c r i t i  cized, f o r i n his experiments, the s t r a i n rate'may not have reached a steady .value. Descriptions of the tests by Vialov and by Mellor do not indicate c l e a r l y that the specimens reached a steady rate of s t r a i n . Theoretical flow laws that are power laws with indices between 2.5 and 4.5 have also been deduced from consi deration of d i f f e r e n t d i s l o c a t i o n mechanisms. (Weertman, 1955, 1957a, b) I?;) . Constant K i n the flow law i s temperature dependant. Glen (1955, P. 532) showed that his re s u l t s f i t t e d a v a r i a t i o n Q of the form ( - RT) where R i s the gas constant, T i s the absolute temperature- and Q i s the creep a c t i v a t i o n energy f o r ice.. Early values f o r Q were given as 31.8 K cals/mol. but a value of 14 K cal/mol. has been obtained from the data of J e l l i n e k and B r i l l (1956), and Raraty and Tabor (1958), Although temperature has a marked eff e c t -on £he rate of glacier' flow, changes in hydrostatic pressure do not appear - 135'- to a l t e r s i g n i f i c a n t l y , t h e rate of ice deformation. Rigsby, (1958), deformed solid, blocks ' and Higashi (1959), t h i n walled cylinders of ice under confining pressures up to 350 bars. They were unable to show that the rate of deformation was affected by changes i n the confining pressures f a r i n excess of those calculated f o r g l a c i e r s . Laboratory t e s t s give flow laws that agree well with those obtained from f i e l d observations, but g l a c i e r ice f a b r i c are not the same as.those determined by fin d i n g the c r y s t a l  lographic orientation of grains i n deformed ice test specimens Many laboratory experiments have been carried out to determine a precise mathematical rela t i o n s h i p between stress and s t r a i n , but r e l a t i v e l y few studies have been made to deter mine the actual mechanics of ice deformation. A short summary of previous q u a l i t a t i v e work i s given below. PREVIOUS WORK Most of the e a r l i e s t experiments on ice deformation were carried out about the turn of the century, using very crude apparatus. In many of the experiments, no attempt was ever made to control temperature f l u c t u a t i o n s , so the re s u l t s cannot be used f o r quantitative interpretations. McConnel (1891) stressed bars of coarse p o l y c r y s t a l  l i n e i c e f o r one to eight hours. He took no measurements, but demonstrated that s t r a i n was confined to movement planes p a r a l l e l with the basal plane of the c r y s t a l s . - 136 Von Engeln (1915) compressed fragments and small blocks of ice i n a s t e e l cylinder under stresses up to 1,400 l b s . but he did not measure the s t r a i n . In o r i g i n a l speci mens, grains were elongated p a r a l l e l with the cylinder axis, but a f t e r several days they r e c r y s t a l l i z e d so that t h e i r longest dimension was across the cylinder. Although von Engel took several photographs to i l l u s t r a t e the shape and size of the grains, he did not determine t h e i r crystallographic orien t a t i o n . Bader, Haefeli and others (1939) deformed snow speci mens and ice specimens and measured the orientation of twenty to f o r t y grains from each sample. There was no well defined f a b r i c for snow samples i n compression or tension .tests, but for a specimen i n simple shear,27 of the 35 measured grains were oriented within 45° of the pole to the shear plane. In contrast to the snow specimen, a sample of ice i n compression had a preferred orientation; a l l the 26 measured grains were within 20 to 45° of the unique stress. For an ice specimen i n tension for 49 days, most' of the readings were le s s than 45° from the inferred true axis of tension. In a specimen sheared f o r six days at 4 Kg/cm the axes were arranged i n four d i r e c t i o n s , two of them i n the plane that contained the di r e c t i o n of shear. From t h e i r r e s u l t s , the authors concluded .that in compression experiments the 'translation-plane' f o r ice i s normal to the unique stress axis; i n shear i t i s p a r a l l e l ' with the plane, of shear, and i n tension i t i s p a r a l l e l with - 1 3 7 the tension axis. Steinemann (1958a) subjected a cylinder of poly c r y s t a l l i n e i c e to a torsion shear t e s t . The f a b r i c of- the r e c r y s t a l l i z e d specimen had two strong, and one weak maxima. After the load had been released f o r some time, post-kinematic r e c r y s t a l l i z a t i o n processes produced a f a b r i c with one maximum normal to the plane of shear. Steinemann also determined that f a b r i c diagrams of r e c r y s t a l l i z e d ice from compression tests had most readings within a small c i r c l e about the stress axis. He.constructed several histograms to show c l e a r l y that, C v axes tend to be in c l i n e d 20° to 50° from the stress axis. To determine how shear stress affected the c r y s t a l  lographic orientation of ice grains,•Rigsby (I960) sheared a small h inch thick square of p o l y c r y s t a l l i n e ice under a stress of 50 to 75 l b s / i n 2 (3 to 5 Kg/cm2) at a temperature of -2°C. The o r i g i n a l slab was composed of 16 i n d i v i d u a l blocks cut from single grains of i c e , and frozen together to resemble a checker board four inches square. During the tes t s , the o r i g i n a l square was distorted into a parallelopiped. To i l l u s t r a t e a progressive change in the f a b r i c , Rigsby took a series of photographs. These showed that the 16 o r i g i n a l blocks broke down into smaller fragments with new grains tending to ..crystallize along the o r i g i n a l boundaries. After l g to 2 months, the block contained 135 grains, and had a f a b r i c with a preferred orientation - the C axes tended to - 1 3 8 - be p a r a l l e l with the short diagonal of the deformed 'square.' Rigsby also deformed a 2 inch square slab of fine gr'ained ice grown from water seeded with snow. The f a b r i c of the deformed block did not show any obvious preferred orien ta t i o n but by shearing the specimen back and forth along the 'same plane' Rigsby produced a stronger pattern with concent rations of C v axes at the poles to two shear d i r e c t i o n s . Not a l l laboratory experiments r e s u l t i n r e c r y s t a l  l i z a t i o n . In most of them,strain i s by b r i t t l e f a i l u r e . Under a high stress, ice blocks develop a maze of i n t e r n a l cracks and fractures that become progressively longer and more numerous with time.. In a series of compression t e s t s , Brown (1926) noted that fractures appeared i n the specimens accompanied by audible 'crackling' sounds. Ivanov and Lavrov (1950) describe a simi l a r phenomenon and show that , i n t h e i r tests, s t r a i n occurred in a series of discontinuous jerks. The strain-time curve they i l l u s t r a t e i s not a smooth curve, but a series of d i s  continuous steps suggesting that ice flow occurs as i n d i v i d u a l increments of s t r a i n . To investigate microseismic e f f e c t s i n greater d e t a i l Gold (1962) compressed a number of ice blocks f o r three hours and recorded a l l the noises they made, using a p i e z o e l e c t r i c c r y s t a l frozen to one face of each block. Compression tests 2 with a x i a l stresses up to 15 Kg/cm gave the customary s t r a i n - time curves in which the s t r a i n rate decreased with time. For stresses greater than 17 Kg/cm4' the s t r a i n rate increased. - 139 - C o n c u r r e n t m i c r o s e i s m i c r e c o r d i n g s i n d i c a t e d t h a t f o r s t r e s s e s l e s s t h a n 10 K g / c m 2 t h e r e w a s v e r y l i t t l e i n t e r n a l c r a c k i n g , b u t a b o v e 10 K g / c m 2 t h e s t r a i n w a s a s s o c i a t e d w i t h a c o n t i n u o u s c r a c k i n g n o i s e . A b o u t . 6 0 $ o f t h e t o t a l n o i s e o c c u r r e d i n t h e f i r s t h o u r , b u t i n o n e t e s t t h e n o i s e a g a i n i n c r e a s e d . A f t e r e a c h e x p e r i m e n t , G o l d e x a m i n e d t h e s t r e s s e d b l o c k s a n d n o t e d t h a t m o s t o f t h e f r a c t u r e s i n t h e m w e r e p a r a l  l e l w i t h t h e s t r e s s a x i s , a n d t h a t n o f r a c t u r e p l a n e w a s i n c l i n e d m o r e t h a n 45° f r o m t h i s d i r e c t i o n . F o r m o s t c r a c k s , t h e l o n g d i r e c t i o n w a s p a r a l l e l w i t h g r a i n b o u n d a r i e s a n d 12 o f 41 m e a s u r e d p l a n e s w e r e e i t h e r p a r a l l e l w i t h , o r p e r p e n d i  c u l a r t o , t h e c r y s t a l l o g r a p h i c a x i s o f t h e g r a i n s i n w h i c h t h e y o c c u r r e d . R e c e n t l y , K a m b (1964) s h e a r e d a s p e c i m e n o f f i n e ' g r a i n e d i c e u n d e r s t r e s s o f 1 K g / c m 2 f o r a p e r i o d o f t h r e e m o n t h s . D u r i n g t h e e x p e r i m e n t t h e f i n e g r a i n e d i c e r e c r y s t a l  l i z e d i n t o a n a g g r e g a t e o f l a r g e i n t e r l o c k i n g g r a i n s s i m i l a r i n a p p e a r a n c e t o g l a c i e r i c e . A l t h o u g h K a m b g i v e s n o d e t a i l s h e i l l u s t r a t e s t h a t , i n t h e r e c r y s t a l l i z e d s p e c i m e n , t h e C v a x e s w e r e c o n c e n t r a t e d i n t w o d i r e c t i o n s , o n e n o r m a l t o t h e s h e a r p l a n e a n d t h e o t h e r 30° f r o m t h e f i r s t b u t s t i l l i v i t h i n t h e d i r e c t i o n o f m o v e m e n t . T h e p r e f e r r e d o r i e n t a t i o n s o f C v a x e s o f r e c r y s t a l  l i z e d i c e i n d e f o r m e d t e s t s p e c i m e n s a r e n o t i d e n t i c a l t o t h o s e o b t a i n e d f r o m g l a c i e r i c e , n o r a r e t h e y s i m i l a r t o t h e f a b r i c s p r e d i c t e d b y t h e o r y . B e c a u s e m o r e i n f o r m a t i o n i s n e c e s s a r y , t h e a u t h o r c o n d u c t e d a s e r i e s o f l a b o r a t o r y e x p e r i m e n t s . T h e - 1 4 0 - purpose of the p r e s e n t s e r i e s o f e x p e r i m e n t s was not t o e l a b o r a t e on the f l o w laws f o r i c e but to d e t e r m i n e t h e r e l a  t i o n s h i p between s t r e s s systems and m i c r o s c o p i c s t r u c t u r e s . METHODS OF LABORATORY STUDY I n t h e p r e s e n t s e r i e s o f e x p e r i m e n t s , u n c o n f i n e d c y l i n d e r s o f i c e were deformed w i t h i n a domestic deep f r e e z e . The c y l i n d e r s were compressed under a c o n s t a n t l o a d and t h e s t r a i n r e c o r d e d so t h a t t h e r e s u l t s c o u l d be compared w i t h t h o s e o b t a i n e d by p r e v i o u s w o r k e r s . A f t e r each t e s t t h e deformed c y l i n d e r s were s e c t i o n e d and the c r y s t a l l o g r a p h i c o r i e n t a t i o n d e t e r m i n e d f o r 1 0 0 t o 2 0 0 g r a i n s . A p p a r a t u s Because o f the l a c k o f s u i t a b l e f a c i l i t i e s , i c e c y l i n d e r s were compressed i n s i d e a do m e s t i c deep f r e e z e . Dur i n g each t e s t , e v e r y e f f o r t was made t o keep a l l c o n d i t i o n s c o n s t a n t but t h e deep f r e e z e had a range o f about 2°C. per c o o l i n g c y c l e . A c o n s t a n t a x i a l l o a d was m a i n t a i n e d w i t h a s i m p l e h y d r a u l i c system, c o n s i s t i n g o f an e i g h t t o n j a c k f e d w i t h h y d r a u l i c f l u i d f r o m a b o o s t e r ram .connected t o a c y l i n d e r o f compressed n i t r o g e n ( F i g u r e 3 7 ) . The system was c a l i b  r a t e d a g a i n s t a B a l d w i n U n i v e r s a l t e n s o m e t e r and t h e t o t a l l o a d d e t e r m i n e d f o r v a r i o u s a i r p r e s s u r e s on the ram, measured "with a Bourdon-tube p r e s s u r e gauge co n n e c t e d t o t h e o u t l e t s i d e o f t h e r e g u l a t o r on t h e n i t r o g e n c y l i n d e r . - 141 - The o r i g i n a l c a l i b r a t i o n measurements showed that' gas pressure was d i r e c t l y proportional to the load, and that the hydraulic system was not instantaneous. The system had a time lag of about two and one-half minutes before the jack came under f u l l load, but once the load had been applied, i t remained constant to within 5 l b s . despite any gas leakage. Procedure Test cylinders of p o l y c r y s t a l l i n e ice used i n the experiments were made from large blocks of commercial ice purchased from a l o c a l ice company. The blocks were sawn into a series of small rectangular bricks that were c h i s e l l e d into rough cylinders about 5 i inches i n diameter. The rough cylinders were rounded to a diameter of 4 or 5 inches and then cut to the required length. Because of the small working space, ice specimens had to be transferred into and out of the freezing unit, and i t was impossible to keep t h e i r temperature constant. After a cylinder had been cut to size, i t was placed i n the deep freeze unit and allowed to stand f o r 2 4 hours. Then, i t was placed upright on a s t e e l block and f i t t e d into an i r o n frame above the hydraulic jack. The jack was pumped by hand and the s t e e l block raised u n t i l the test cylinder was secure between the block and the top of the frame (Figure 3 7 ) . A d i a l gauge was then attached to the supporting frame and the entire assembly allowed to stand f o r several hours i n order to attain a steady temperature. press u re domestic deep freeze. FIGURE SCHEMATIC DIAGRAM SHOWING APPARATUS TO C O M P R E S S I C E - ' 1 4 3 - To start each experiment, the nitrogen cylinder was opened and the regulator adjusted u n t i l the Bourdon-tube gauge recorded the pressure necessary to produce the required load. Because the hydraulic .system was not instantaneous, i t was not possible to obtain an i n i t i a l reading of the s t r a i n gauge at the start of any t e s t . For the f i r s t few minutes, the ice deformed rapidly but a f t e r a few hours, the rate of s t r a i n steadier decreased. Strain readings were taken at one minute i n t e r v a l s , but as the s t r a i n rate became less, the i n t e r v a l s were increased. Readings taken over a period of 3 0 hours gave strain-time graphs with curves similar to those obtained by other workers. After each experiment, the gas pressure was released, the ice removed, and the deformed specimen cut to give three sections for f a b r i c analysis. In order to reduce any 'Schnitt- e f f e k t ' two sections were cut about four- inches apart, normal to the stress axes, and the t h i r d was cut from the intervening block, but at right angles to the d i r e c t i o n of c r y s t a l growth i n the o r i g i n a l block (Figure 3 8 ) . Corrected readings were plotted on an equal area net and those of the v e r t i c a l section were rotated so that a l l data could be represented i n a common diagram. The f i n a l contoured diagrams represent horizontal sections cut normal to the stress axis. In each diagram the stress axis i s at the centre, and the o r i g i n a l growth d i r e c t i o n i s indicated by a small mark at the perimeter. - 144 - Direction of original growth. Stress axle. Stress oxis Direction ot original growth. Horizontal sect I on. Vertical section. Horizontal seotlon. View looking down on deformed ice cylinder showing relation between growth direction, compression axis and toe sections. FIGURE 38. DIAGRAM SHOWING RELATION BETWEEN FABRIC DIAGRAM AND SECTIONS OF ICE CYL INDER. RESULTS OF LABORATORY STUDY Although the main purpose of the present series of compression tests was to determine.the f a b r i c of compressed p o l y c r y s t a l l i n e i c e , creep curves were also obtained i n order to correlate the experimental data with the r e s u l t s of other workers. In an i n i t i a l series of experiments, car r i e d out at - 5 ° G. over a range of a x i a l stress 20 l b s . to 136 l b s . ( 1 . 5 -to 10 Kg/cm2), unconfined cylinders of ice were .compressed fo r more than 30 hours. It was not possible to determine e l a s t i c s t r a i n , and because of l i m i t a t i o n s i n the apparatus, no measure ment could be made of the i n i t i a l length of the tes t cylinders. The absolute s t r a i n could, not be determined accurately, but to compare stra i n s obtained i n t y p i c a l experiments, creep curves have been constructed to pass through a r b i t r a r y point's of 10 minutes and one hour on the graphs representing test s t r a i n s f o r 90 minutes (Figure 39) and 25 hours (Figure 40), .. Individual curves,, s i m i l a r i n appearance to the c h a r a c t e r i s t i c creep curves obtained by a i l other workers, may be divided into two d i f f e r e n t parts: 1) an i n i t i a l steep section representing a transient creep that diminishes_ with'.time (primary creep). 2) a 'straight' portion showing a constant rate of deformation or steady creep, (secondary creep). Secondary creep i s d i f f i c u l t to determine; the creep curve i s f Time irT hours. FIGURE 40 S T R A I N - T I M E GRAPHS FOR COMPRESSION T E S T S . - 1^8 - straight i n Figures 39 and 40, and i t seems that the value for steady creep i s to some extent a function of the time scale chosen for the graph. In any s p e c i f i c test the stra i n curve does not appear to be consistent with respect to other curves at a smaller stress. In some tests the rate of s t r a i n i s less than a n t i  cipated and may be lower than the st r a i n rate determined f o r a smaller stress. Because the creep curves are not consistent and the absolute s t r a i n .........can not be ascertained, i t i s d i f f i c u l t to determine a mathematical solution f o r them. Several unsuccess f u l attempts were made to resolve the creep curve into a series of component flow laws similar.to the flow laws resolved by Carey. A more extensive discussion of the creep curves i s given i n the Appendix at the back of t h i s t h e s i s . Test specimens deformed f o r .less than 30 hours did not r e c r y s t a l l i z e . Individual grains were strained, but compared with grains of unstressed i c e , there was no. obvious difference in t h e i r shape, siz e , or crystallographic o r i e n t a t i o n . Fabric diagrams f o r some stressed cylinders given i n Figure 41 are not d i f f e r e n t from the diagrams obtained from C v measurements of undeformed samples. Blocks of undeformed ice are composed of elongate cr y s t a l s with C v axes that tepid to be almost at right angles to t h e i r d i r e c t i o n of growth. Samples used i n the present experiments were selected from 300 l b . blocks of commercial - 149 - ice made by freezing tap water i n large s t e e l tanks suspended i n brine. Ice formed i n i t i a l l y on the walls of the tank and grew towards the centre, forming elongate grains 5 to 10 cm, long and 1 cm. i n diameter. Fabric diagrams of commercial ice have most data within a broad g i r d l e that i s 60° to 90° from the growth d i r e c  t i o n (Figure 41). Within the g i r d l e , readings are generally d i s t r i b u t e d at random, and may be clustered into maxima with up to 5 or 7$. A l l diagrams indicate that G v axes of grains i n undeformed i c e are i n c l i n e d more than 55° from the 4 i r e c t i o n of growth. Thin sections cut from most test specimens contain grains that have not r e c r y s t a l l i z e d . A l l grains look undeformed and the f a b r i c diagrams are similar to those of undeformed i c e . In contrast, specimens deformed at high stresses f o r a long time had r e c r y s t a l l i z e d . In thin section, the elongate grains are strained or broken, and along t h e i r contacts small i r r e g u l a r grains have c r y s t a l l i z e d . C v measurements of the grains give diagrams that are d i f f e r e n t . Generally, the difference i n f a b r i c i s not easy to recognize, p a r t i c u l a r l y i f the r e c r y s t a l  l i z a t i o n has been incomplete. Re c r y s t a l l i z e d specimens give f a b r i c diagrams in which C v axes form an incomplete g i r d l e (Figure Llt experiment 64:15) that has a d i s t i n c t break near the perimeter.. The general d i s t r i b u t i o n of data indicates that G v axes tend to be i n c l i n e d to the stress axis and occur with random d i s t r i b u t i o n along a small c i r c l e . The change between the f a b r i c of - 150 - Sample Number t Direction of cry eta I growth £3> Contour depression • 'Stress axis Contour Interval 1,2,3,4,5% FIGURE 41. FABRIC DIAGRAMS OF COMPRESSED ICE. - 151 - undeformed and stressed ice i s emphasized i f data are rep resented i n a series of histograms. Histograms (Figures 42 to 44) show the i n c l i n a t i o n of C y axes from the d i r e c t i o n of growth, and from the stress axis. Histograms of undeformed ice are very similar to a h i s t o  gram showing a uniform d i s t r i b u t i o n of data. Sligh t differences between diagrams may arise from inadequate sampling or Schnitt- effekt „ A l l histograms showing the i n c l i n a t i o n of C v axes to growth d i r e c t i o n appear to be si m i l a r , but the figures for r e c r y s t a l l i z e d specimens are d i f f e r e n t . Histograms f o r experi ments 64:14 and 64:15 showing the i n c l i n a t i o n of C v axes from the stress axis have comparatively few readings normal to the stress axis and more between 30° and 50°. These figures for r e c r y s t a l l i z e d ice are i d e n t i c a l to those obtained by Steinemann (1958a, p. 48). They c l e a r l y i n d i  cate that under compression, ice tends to r e c r y s t a l l i z e so that Cy axes are i n c l i n e d to a unique axis, and f a l l along a small c i r c l e of radius 20° to 50°. A preferred ori e n t a t i o n of C v axes i n c l i n e d at 45° to the stress d i r e c t i o n could be produced i f ice grains r e c r y s t a l  l i z e d so that t h e i r basal plane was sub-parallel with the d i r e c t i o n of maximum resolved shear s t r e s s . However, the same orientation could r e s u l t i f ice grains were oriented with basal planes aligned with the d i r e c t i o n of rheid flow, 1 5 2 - • undeformed 90 % - 3 0 - - 20 - - 10 - - 0 - uniform 90 <T 90 6 3 - 2 90 0 °/o - 30 - — 2 0 - 10 90 - O 6^-3 90 0 90 % 64-5 90 0 90 — 30 - - 2 0 - 10 64-6 S 90 0 90 Each histogram shows % of c v axes inclined from direction of growth (o) and direction of stress axis (S) F I G U R E 4 2 HISTOGRAMS SHOWING INCLINATION OF C v AXES OF COMPRESSED ICE CYLINDERS - 153 - % Each histogram shows % of Cy axes inclined from direction of growth (o) and direction of stress axis ( 8 ) FIGURE 4 3 H I S T O G R A M S SHOWING INCLINATION OF C v AXES OF COMPRESSED ICE C Y L I N D E R S - 1 5 4 - 64-13 P - 3 0 - - 20 - „ n 64 " To - 10 - - 0 - J G_ % n e 4~ 1 5 90 0 - 30 - - 20 - 10 90 6 5 - 2 90 0 r2 90 Vo 6 5 - 3 90 0 — 30 - - 2 0 - - 10 - - . 0 _ X ll 65-4 J U 1 90 0 1 90 Each histogram shows % of C v axes inclined from direction of growth (0) and direction of stress axis (S) F I G U R E 44 HISTOGRAMS -SHOWING INCLINATION OF C v AXES OF COMPRESSED ICE CYLINDERS - 155 - DISCUSSION OF ICE FABRICS A l t h o u g h c r e e p c u r v e s o f most i c e e x p e r i m e n t s have been s y n t h e s i z e d i n t o a g e n e r a l i z e d f l o w law f o r i c e , t h e r e s u l t s o f w o r k e r s are not e x a c t l y s i m i l a r . One r e a s o n may be t h e d i f f e r e n c e i n shapes and s i z e s o f specimens used by each worker. Even i n a s e r i e s o f e x p e r i m e n t s under i d e n t i c a l c o n d i  t i o n s , i t i s not p o s s i b l e t o d u p l i c a t e a creep c u r v e o r r e p r o d u c e a r e c r y s t a l l i z a t i o n f a b r i c . T h i s may be due t o d i f f e r e n c e s i n t h e o r i g i n a l c r y s t a l l o g r a p h i c o r i e n t a t i o n o f g r a i n s i n any t e s t specimen. . D e s p i t e t h e s e d i f f e r e n c e s , creep c u r v e s , f o r s h o r t t e r m t e s t s , a l l have t h e same g e n e r a l f o r m and i n d i c a t e t h a t t h e s t r a i n d e c r e a s e s w i t h t i m e . Commonly, t h e a x i a l s t r a i n i s v e r y s m a l l and t h e r e are no r e a l changes i n t h e a r e a of c r o s s s e c t i o n . I n t e s t s a t h i g h s t r e s s e s , o r i n t h o s e c o n t i n u e d f o r a l o n g t i m e , the a x i a l s t r a i n may be c o n s i d e r a b l e , and the a rea of c r o s s s e c t i o n change p r o g r e s s i v e l y so t h a t the e f f e c t i v e s t r e s s i s a l t e r e d . I f any t e s t i s c o n t i n u e d f o r many days, t h e s t r e s s system w i l l p r o g r e s s i v e l y a l t e r and the s t r a i n r a t e may i n c r e a s e . I n a c o m p r e s s i o n t e s t s by G l e n (1955) the s t r a i n r a t e i n c r e a s e d , and a l t h o u g h he took no f a b r i c measurements, he a t t r i b u t e s t h e i n c r e a s e t o a r e c r y s t a l l i z a t i o n p r o c e s s . S t r a i n and r e c r y s t a l l i z a t i o n o f m a t e r i a l under s t r e s s a r e a f f e c t e d by numerous f a c t o r s , i n c l u d i n g : t e m p e r a t u r e , i m p u r i t i e s , g r a i n s i z e , and t i m e . There i s no doubt t h a t t e m p e r a t u r e has a g r e a t e f f e c t - 156 ~ on r e c r y s t a l l i z a t i o n . Near the freezing point, ice r e c r y s t a l - . l i z e s so that the grain size increases rapidly, p a r t i c u l a r l y i n a stress-free environment (Rigsby, I960,- p. 606). At lower temperatures c r y s t a l growth i s retarded, but below -10°C. i t i s almost n e g l i g i b l e , unless the ice i s under stress. Bader et a l . (1939, p. 54-55) state that deformation causes an increase i n grain si z e , and Steinemann notes that the grains increase under stress and again increase when the load i s removed. In contrast, Shumskii (1958, p. 246) considers that r e c r y s t a l l i z a t i o n under stress reduces the average grain size. These contrasting e f f e c t s may result from differences i n tem perature conditions of each, experiment. Effects of impurities have not been studied, but Rigsby (I960, p. 602) suggests that bubbles i n h i b i t c r y s t a l growth by absorbing s t r a i n and preventing migration of grain boundarie s. Very l i t t l e i s known about the importance of time i n the s t r a i n and growth of i c e . Demorest proposed that the l a t t i c e of d i s t o r t e d c r y s t a l s reorganizes very r a p i d l y to produce instantaneous r e c r y s t a l l i z a t i o n . Time lapse photographs des cribed by Knopf (1953, p. 297) show that reorganization occurs within a 'few minutes'. In the f i r s t few hours, under high loads., creep results from small scale displacements along cracks, and f i s s u r e s . I f a test continues f o r several tens of hours, the ice may recrys- t a l l i z e and the f a b r i c change. Sections of unstressed ice have grain contacts that give an i r r e g u l a r network, l i k e a f r o t h of - 157 - bubbles sectioned at random. In contrast, stressed ice i s 'com posed of in t e r l o c k i n g grains.' Changes i n general appearance are readi l y distinguished but changes i n the crystallographic f a b r i c are not easy to re cognize, p a r t i c u l a r l y when r e c r y s t a l l i z a t i o n i s incomplete. Small t e s t specimens contain a lim i t e d number of grains and, because only a few of them can be measured, the re s u l t i n g f a b r i c diagrams do not contain many readings. A l l diagrams are subject to the same errors and mis representations as i n other petrofabric studies. Concentrations of 20% are highly s i g n i f i c a n t but maxima of 5 or 7% may have no r e a l meaning, p a r t i c u l a r l y when a diagram contains only 50 or 60 readings. Several f a b r i c diagrams have been obtained for deformed ice but they are d i f f i c u l t to in t e r p r e t , and the maxima do not occur i n the po s i t i o n indicated by theory. I f ice grains only deform along the basal plane, p o l y c r y s t a l l i n e ice should have most grains with the C v axis normal to the plane of maximum resolved shear stress. For ice i n shear, Rigsby (I960, p. 603) obtained a f a b r i c with a weak maximum in the t h e o r e t i c a l position,, but most other workers have obtained f a b r i c s with two or more maxima i n c l i n e d from the pole to the shear plane. Reid (196/+-, p. 258) compares the r e s u l t s obtained by many workers and suggests that the ' i d e a l ' f a b r i c contains four maxima arranged i n a diamond pattern, Kamb (1959a) suggests that in stressed i c e , the C v axes are a l l normal to the-shear - 158 - plane, but on the release of stress the orientation changes rap i d l y to a diamond pattern. The development of a diamond pattern from a single maximum has not been proven and ice f a b r i c s could just as e a s i l y be interpreted as a true stress f a b r i c produced by random con- centrations of axes within a small c i r c l e of radius 20° to 50°. The most consistent r e c r y s t a l l i z a t i o n f a b r i c s have been obtained from unconfined samples i n compression. Generally, the readings are clustered about the unique stress axis, but few of them are actually p a r a l l e l with i t . In a diagram con t a i n i n g 45 readings, Bader et a l . (1939) found most C v axes were between 20° and 45° from the stress axis. Steinemann (1958a, p. 48) obtained the same type of f a b r i c and shows that most axes are 20° to 50° from the unique axis. In the present series of experiments, diagrams of specimens r e c r y s t a l l i z e d under stress, have data within a small c i r c l e about the stress axis and maxima of 3 or 5$ are considered to represent random concentrations of C v axes i n  clined 30° to 50° from the stress axis. Inclinations of 45° to the stress axis would r e s u l t - i f grains tended to c r y s t a l l i z e with the basal planes oriented p a r a l l e l with the plane of maximum shear stress. In a test cylinder, t h i s plane would be a conic surface about the stress axis. In practice, planes of f a i l u r e are much less than 45° , and i f the basal planes were p a r a l l e l to such planes, the eF axes should be i n c l i n e d 45° to 75° from the stress a x i s . The C v i n c l i n a t i o n of 20° to 50° i s more r e a d i l y explained i f the - 159 - basal plane i s • • assumed to be sub-parallel with 'planes' of rheid flow. Few fabrics'have been determined for ice r e c r y s t a l l i z e d i n tension experiments. Generally, the C v axes tend to be in c l i n e d at high angles to the tension axis. SUMMARY In most creep t e s t s , s t r a i n r e s u l t s from small cracks and fractures and there i s no s i g n i f i c a n t change i n the speci men f a b r i c . I f a high load i s applied for a long time, r e c r y s t a l l i z a t i o n may occur and the preferred orientation of the new grains depends upon the stress system. Fabric diagrams from many experiments have maxima that are d i f f i c u l t to i n t e r  pret, but the diagrams indicate that C v axes are not always normal to predicted planes of maximum resolved shear stress. R e c r y s t a l l i z e d ice from tests i n tension have C v axes at high angles to the stress axis. For ice i n compression, the C v axes are randomly d i s t r i b u t e d about the stress axis, i n a small c i r c l e of radius 20° to 50°. C v axes of specimens i n shear, are concentrated into a small c i r c l e of radius at 20° to 30° from the normal to the shear plane. - 160 - CHAPTER V RELATION BETWEEN ICE .STRUCTURES AND STRESS SYSTEMS GENERAL STATEMENT In studies of deformed rocks, the geometric r e l a t i o n between distorted structures i s determined from projections and used to i n f e r the orientation of the stress system. The most common stress orientation i n f e r r e d f o r tectonites i s based on the premise that the d i r e c t i o n of compression i s normal to the a x i a l plane of a f o l d . This plane i s thought to represent a compromise position between two conjugate planes that form p a r a l l e l with t h e o r e t i c a l planes of maximum resolved shear stress determined from b r i t t l e ' f a i l u r e . If f o l d i n g occurs while the rock i s i n a ' p l a s t i c ' condition, t h i s inference may not be correct. Glacier ice deforms as a ' p l a s t i c ' body but ice structures are commonly compared with features produced by b r i t t l e f a i l u r e . It has been inferred that the basal plane of ice c r y s t a l s w i l l become oriented so they are p a r a l l e l with the d i r e c t i o n of maximum resolved shear stress. If t h i s were true, the C v axes of ice grains would a l l be clustered about one d i r e c t i o n that i s normal to a plane of shear. Fabric diagrams of stressed ice have more than one maximum, and they are not e a s i l y explained by assuming the g l i d e plane of ice i s p a r a l l e l with a plane of maximum resolved shear stress. The actual f a b r i c i s due to displacement along any l o c a l plane of movement. - 1 6 1 - In order to show how ice f a b r i c s are produced, i t i s necessary to know the mechanics of g l a c i e r flow, MECHANICS OF ICE MOVEMENT Glacier flow results from large scale movements over bedrock surfaces, along planes within the i c e , and from small scale movements of the ice grains. Small scale movements include displacement between grains ( i n t e r c r y s t a l l i n e ) and movements within i n d i v i d u a l c r y s t a l s ( i n t r a c r y s t a l l i n e ) but i t i s d i f f i c u l t to d i s t i n g u i s h c l e a r l y between the two types f o r they are complex, interdependent mechanisms that are complicated by regelation. Creep mechanisms fo r i c e , described by Shumskii ( 1 9 5 8 ) and Gold ( 1 9 6 3 ) include: 1 ) movement along s l i p planes. 2 ) d i s t o r t i o n of s l i p planes, and the formation of kink bands that r e s u l t in polygonization.• 3 ) formation of cracks and c a v i t i e s . k) d i s t o r t i o n of grain boundaries, c a t a c l a s i s . 5 ) grain boundary migration. 6 ) r e c r y s t a l l i z a t i o n . Movement Along S l i p Planes S l i p planes in i c e , s i m i l a r to structures described i n detailed works on metallurgy, were recognized by early g l a c i o - l o g i s t s ( 1 8 9 0 ) . Experiments by Nakaya ( 1 9 5 8 ) show that, in single c r y s t a l s , s t r a i n r e s u l t s from movement along cl o s e l y - 162 - spaced t r a n s l a t i o n planes, p a r a l l e l with the basal plane. The c r y s t a l l a t t i c e orientation on each side of the t r a n s l a t i o n plane remains unchanged and no twinning i s produced. A l l move ment i s continuous, and any displacement i s through an in t e g r a l number of ionic distances. D i s t o r t i o n of S l i p Planes Gold (1963) noted t h a t , i n ice strained less than 1%, s l i p planes of many c r y s t a l s become bent or even twisted. At the bend, a contact develops at r i g h t angles to the o r i g i n a l s l i p _ plane - the plane of contact i s referred to as a small angle boundary. With further deformation, the s l i p planes buckle at the contact and the boundary may develop into a kink band. Kink bands appear to be .best developed in crystals, oriented with the basal plane p a r a l l e l with the shear d i r e c t i o n . • Highly distorted grains may eventually break into small units, each with s l i g h t l y d i f f e r e n t crystallographic orien- t a t i o n . Commonly, only one or two fragments are produced, but '• 9 extensive fragmentation i s possible (polygonization of Shumskii, 1958). Formation of Cracks and Cavities Under stress, minute d i s l o c a t i o n s develop .about cry s t a l imperfections and at sit e s of inhomogex'eous s t r a i n , and they migrate through the grain u n t i l they are blocked. Concen- • tra t i o n s of blocked dislocations cause stress that may exceed the l o c a l strength of the ice and produce a t r a n s c r y s t a l l i n e - 1 6 3 - crack related to the crystallographic orientation. Gold ( 1 9 6 3 ) measured the orientation of small cracks in deformed ice blocks and found that over 6 7 % were t r a n s c r y s t a l l i n e , and three- quarters of them were p a r a l l e l or at right angles to the basal plane. With further increase "in'strain, t r a n s c r y s t a l l i n e cracks may propagate across grain boundaries. Where they pass into ' •  an adjacent grain, the orientation changes so the plane i s p a r a l l e l with or at right angles to the basal plane of the new grain. Small dislo c a t i o n s , or microscopic holes i n the atomic structure may migrate through a c r y s t a l l a t t i c e and coalesce on the grain boundaries to form a series of c a v i t i e s or a single column large enough to be v i s i b l e . D i s t o r t i o n of Grain Boundaries As deformation continues, movement and d i s t o r t i o n of s l i p planes become more intense and the c r y s t a l s begin to break up. Fragmentation.occurs along small' angle boundaries and along the o r i g i n a l contacts of the grains. Gold ( 1 9 6 3 ) examined grain boundaries.of p o l y c r y s t a l l i n e ice under compression, and found that, at some contacts, steps and small fractures develop. Grain Boundary Migration Movement of grain boundaries i s one of ttie f i r s t signs of deformation in ice specimens (Gold, 1 9 6 3 , p. 1 3 ) . Under stress, part of a c r y s t a l l a t t i c e may change i t s position, so that the l a t t i c e structure has the same orientation as an - 164 - a d j a c e n t g r a i n , and i o n s on b o t h s i d e s o f a c o n t a c t u n i t e t o fo r m one g r a i n ( K r a u s z , 1961). G r a i n boundary m i g r a t i o n i s one o f t h e more i m p o r t a n t s t r a i n mechanisms c l o s e l y a l l i e d w i t h r e c r y s t a l l i z a t i o n . E xcept f o r t r a n s l a t i o n g l i d i n g on the b a s a l p l a n e , none of the s t r a i n mechanisms c o u l d cause any r e o r i e n t a t i o n o f t h e c r y s t a l l o g r a p h i c axes. R i g s b y (1953) d i s c u s s e d t h e p o s s i b i l i t y o f movement a l o n g o t h e r c r y s t a l l o g r a p h i c p l a n e s , but c o n s i d e r s t h a t none o f t h e p l a n e s c o u l d g i v e t h e obser v e d C y a x i s o r i e n t a t i o n s . To account f o r r e o r i e n t a t i o n , S h u m s k i i (1958) proposes t h a t l e a s t s t r e s s e d g r a i n s t a k e t h e p l a c e o f h i g h l y s t r e s s e d c r y s t a l s w h i c h d i s i n t e g r a t e by a p r o c e s s of p o l y g o n i - z a t i o n , o r by a p r o c e s s o f m i g r a t o r y r e c r y s t a l l i z a t i o n . RELATION. BETWEEN FABRIC AND STRESS ORIENTATION P r e f e r r e d o r i e n t a t i o n can r e s u l t e i t h e r f r o m the e l i m i n a t i o n o f some u n f a v o u r a b l e g r a i n s o r f r o m w h o l e s a l e r e  c r y s t a l l i z a t i o n . I f u n f a v o u r a b l e g r a i n s a re e l i m i n a t e d , and t h e i r i o n s ' t r a n s f e r r e d ' t o o t h e r g r a i n s , f a v o u r a b l y o r i e n t e d g r a i n s s h o u l d become p r o g r e s s i v e l y l a r g e r , and t h e i c e f a b r i c more d e f i n i t e l y o r i e n t e d down the i c e tongue. I n most g l a c i e r s , g r a i n s have almost t h e same s i z e , and the degree o f p r e f e r r e d o r i e n t a t i o n appears t o remain c o n s t a n t , i n d i c a t i n g t h a t i c e movement i s p r o b a b l y a p r o c e s s o f c o n t i n u a l r e c r y s t a l l i z a t i o n , D u r i n g g l a c i e r f l o w , a l l g r a i n s , even the most f a v o u r a b l y o r i e n t e d , are c o n t i n u a l l y broken and the f r a g m e n t s r e c r y s t a l l i z e d . T r a n s l a t i o n g l i d i n g w i t h i n f a v o u r a b l y o r i e n t e d c r y s -- 165 - t a l s may be prevented by adjacent grains, and stresses r e l i e v e d by buckling of glide planes and formation of small angle boun daries and kink bands. Crystals reduced to two or more frag ments of s l i g h t l y d i f f e r e n t orientations may be r e a d i l y united with adjacent fragments V Q £ , , I s i m i l a r orientation by a process of boundary migration. Most f a b r i c diagrams have two or more concentrations of C v aXes•inclined from the normal to the inferred plane of shear. These concentrations are not produced by some relaxa t i o n process but are a, d i r e c t . r e s u l t of r e c r y s t a l l i z a t i o n under stress. In laboratory experiments, the axes seem to be i n c l i n e d from the normal to the l o c a l plane of movement (or rheid flow) and not from the normal to the resolved shear stress. Within a g l a c i e r , probably the greatest shearing forces are applied "along the bottom and sides, but towards the centre, shear decreases and most gl a c i e r s are i n compression. Fabric diagrams from coarse ice near the margins show most C v axes are i n c l i n e d from the layer which i s sub-parallel with the shear plane. C v axes from surface i c e near the g l a c i e r centre are independent of any layering, but are i n c l i n e d from the d i r e c t i o n ' of compression. Problems of r e l a t i n g ice f a b r i c s to the stress systems, arise from assuming a stress orientation and then postulating that ice c r y s t a l s have t h e i r basal plane sub-parallel with t h e o r e t i c a l planes of shear.' For the central part of any g l a c i e r , these planes are v e r t i c a l and 45° from the l i n e of flow. Axial planes of f o l d s i n fine layers at the surface - 166 - indicate that the actual plane of movement i s v e r t i c a l and transverse. This plane of laminar flow resembles the 'lines of Rheid Flow' postulated by Garey ( 1 9 5 4 ) . I f g l a c i e r ice behaves as a rheid body, flow w i l l tend to occur along planes of easiest r e l i e f normal to the major stress axis i n order to decrease the maximum stress, and increase the minimum. The plane of flow i s normal to the compression axis i n laboratory t e s t s , and for Athabasca Glacier, i t i s a transverse sub-vertical plane normal to the general d i r e c t i o n of flow. This transverse v e r t i c a l plane controls the orienta t i o n of the c r y s t a l axis, and i s also the plane of f o l d i n g f o r the l o n g i t u d i n a l layers of f i n e i c e . Down the length of Atha basca G l a c i e r , fine layers are deformed into s i m i l a r f o l d s about v e r t i c a l transverse a x i a l planes. These a x i a l planes are sub- p a r a l l e l with j o i n t s and fractures that commonly separate f o l d limbs.. Because fractures are considered a near surface feature, the fol d i n g must also occur near the surface as a re s u l t of compression of f i n e layers formed i n a v e r t i c a l plane at depth. There i s l i t t l e information about structures at depth within any temperate g l a c i e r . Kamb and Shreve (1962a, b) examined d r i l l cores to a depth of 114 m., but they have not published any f a b r i c diagrams. They describe the f a b r i c as being d i f f i c u l t to inter p r e t , but I assume that unless ice has di f f e r e n t orientation under increased hydrostatic stress, grains should tend to orient themselves so the basal plane i s sub- p a r a l l e l with 'planes' of rheid flow* At depth, i n the centre ' • - 167 - of the g l a c i e r , the planes would be v e r t i c a l and lo n g i t u d i n a l , •• and the cr y s t a l s oriented i n a small c i r c l e normal to the '• •direction of flow. SUMMARY . The r e l a t i o n between secondary structures i n g l a c i e r s i s summarized i n Figure 45. At the margins, i c e layers are sub-parallel with the contact walls". The layers generally form sub-parallel with the d i r e c t i o n of shear and the coarse c r y s t a l s become oriented so the C y axes f a l l along a small c i r c l e (radius 120° to 50°) with a centre normal to the ice layers. L i t t l e i s known about the ice at depth, but i t i s presumed jthat layers near the base may be coarse and sub-parallel with the walls. Ice near the centre has no contact e f f e c t s and the ice i s in.pure tension of compression. At depth, the layers are probably v e r t i c a l and l o n g i  t u d i n a l . As ice i s brought nearer the surface by ablation and upward movements, i t becomes compressed and the layers become folded about a transverse v e r t i c a l plane, which i s the true d i r e c t i o n of movement. The fin e ice grains are not oriented with respect to the f i n e layers, but have a preferred orienta t i o n i n a small c i r c l e centred on the compression axis. FIGURE 45. SCHEMATIC DIAGRAM OF PART OF A GLACIER TO SHOW THE DISTRIBUTION OF LAYERS AND ORIENTATION OF ICE GRAINS, (laminar flow ot centre ot surface due to compression.) - 169 - • CHAPTER VI CONTRIBUTIONS AND RECOMMENDATIONS SUMMARY 0? CONTRIBUTIONS: The main topics of the thesis concern a study of Athabasca Glacier to determine the o r i g i n of secondary structures produced by g l a c i e r flow and to relate the pre f e r r e d crystallographic orientation of g l a c i e r i.ce c r y s t a l with s i m i l a r f a b r i c s determined for laboratory test specimens that have r e c r y s t a l l i z e d under known stress conditions. The following are considered to be o r i g i n a l contribu t i o n s : 1. A detailed description of contorted layers of fin e ice previously referred to as long i t u d i n a l layers. Fine layers did not occur on a l l g l a c i e r s and where they have been observed i n previous studies, descriptions are generally incomplete and t h e i r r e l a t i o n s h i p s with other structures have not been_di-scussed. 2. Surface v e l o c i t y measurements have been used to show that the outcrop pattern of layers cannot res u l t from the progressive d i s t o r t i o n of a layer formed at the base of the ice f a l l . Because the layers do not change in size , or attitude down the g l a c i e r they must be produced at or near t h e i r present loca t i o n . 3 . S u f f i c i e n t diagrams have been obtained to show that - 170 - there are two d i s t i n c t types of ice f a b r i c , and that i n d i  vidual maxima may be spurious and have no geological s i g n i  f i c a n c e . Previous workers have related maxima to the structure of ice or to mesoscopic planes in the g l a c i e r , but diagrams from Athabasca Glacier, c l e a r l y show that C v axes tend to be oriented i n a small c i r c l e about a d e f i n i t e axis. 4. The ice "fabric f o r f i n e layers near the g l a c i e r center i s shown to be consistent with a f a b r i c that r e s u l t s from compression near the g l a c i e r surface. 5. Cylinders of i c e have been compressed u n t i l they re c r y s t a l l i z e d . Grains within r e c r y s t a l l i z e d specimens have a d e f i n i t e preferred orientation of C v axes that tend to f a l l along a small c i r c l e of 20° to 50° radius about the unique stress axis. Previously, very few r e c r y s t a l l i z e d laboratory specimens have been examined and the f a b r i c diagrams obtained were d i f f i c u l t to explain. 6. The orient a t i o n of most secondary structures i n g l a c i e r s i s shown to be more readi l y related with the type of viscous flow suggested by-Carey than with a th e o r e t i c a l plane of maximum resolved shear stress. RECOMMENDATIONS FOR FURTHER -WORK Secondary ice' structures exposed on ablation surfaces have been investigated, but there i s l i t t l e information about ice at deeper l e v e l s . Future g l a c i o l o g i c a l studies should - 171 - include detailed measurements of ice layers and f a b r i c s i n oriented cores from bore holes deep within the i c e , follow-\ ing the methods pioneered by Kamb and Al l e n (1962a and b) and Gow (1963). C v axis orientations should be determined in a cold room so that a l l the~constituent.grains can be measured and diagrams constructed to show angular r e l a t i o n s h i p s between adjacent grains. Ice sections should be cut i n more than one plane to reduce any 'Schnitteffekt•, and a l l data rotated, so they can be presented with reference to the common plane. This plane should be horizontal so that a l l diagrams can be re a d i l y compared. In order to show that diagrams are ge o l o g i c a l l y s i g n i f i c a n t , data should be presented as subdiagrams or i n a complete diagram containing more than 400 readings. To prove the r e l a t i o n between ice f a b r i c s and systems of stress, more test specimens should be deformed u n t i l they r e c r y s t a l l i z e under known conditions of stress. To show that r e c r y s t a l l i z a t i o n has occurred the specimens should be large enough' so that s u f f i c i e n t grains can be measured, both before and a f t e r each t e s t . Present r e s u l t s indicate that r e c r y s t a l l i z a t i o n does not occur i n short term t e s t s . Laboratory tests should be continued f o r many hundreds of hours or u n t i l the strain-time curves show t e r t i a r y creep. This creep probably represents the r e a l condition under which g l a c i e r s flow. - . 1 7 2 - BIBLIOGRAPHY The following abbreviations are used: Geog. Ann. - Geographiska Annaler. Geol. Mag. - Geological Magazine. Geol. Soc. Am. - Geological Society of America. J. Geol. - Journal of Geology. J. Glac. - Journal of Glaciology. I.A.S.H. 47 - International Association of S c i e n t i f i c Hydrology, Publication 4 7 , Proceedings of Symposium at Chamonix, 1 9 5 8 , Physics of the movement of i c e . P h i l . Mag. - Philosophical Magazine. P.R.S. - Royal Society (London) Proceedings, Series A. R.G.S. - Royal Geographical Society. SIPRE. - U.S. Army Corps of Engineers, Snow, Ice and Permafrost Research Establishment. Adie, R.J., I 9 6 0 , Ice f a b r i c investigations at Vesl-Skautbreen: Norwegian Cirque Glaciers, R.G.S., Research Series No. 4 , p. 25-38. Agassiz., L., 1 8 4 7 , Systeme Glaciere. Nouvelle etudes et experiences sur les g l a c i e r s actuels: Paris, Victor Masson, 5 9 8 p. Agassiz, L., I896, Geological Sketchs, London, Houghton M i f f l i n Co... Ahlmann, H.W:son., 1 9 3 6 , The f i r n structures on Isachsen's Plateau. S c i e n t i f i c r e s u l t s of the Norwegian-Swedish Spitsbergen Expedition, 1 9 3 4 , pt. VII: Geog. Ann., Bd. 1 8 ,"p. 4 8 - 7 3 . Ahlmann, H.W:tson., 1 9 4 8 , G l a c i o l o g i c a l research on the North A t l a n t i c coasts: R.G.S., Research Series 1 , 83 p. •Ahlmann, H.W:son., and Droessler, E.G., 1 9 4 9 , Glacier ice ' c r y s t a l measurements at Kebnekajse, Sweden; J. Glac., v. 1 , p. 2 6 9 - 2 7 4 . -173 - Ahlmann, H.Wrson., and Thorarinsson, S. , 1938, S c i e n t i f i c r e s u l t s of the Swedish-Icelandic investigations: Geog. Ann,, Bd. 20, p. 171-233. (1939, other r e s u l t s given i n Geog. Ann. Bd. 21, p. 39-66., p. 171-242.) Al l e n , C.R., Kamb, W.B., Meier, M.F., and Sharp, R.P., I960, Structure of the lower Blue Glacier, Washington: J.'-Geol., v. 68, p. 601-625. Atherton, D., 1963, Comparisons of ogive systems under various regimes: J. G l a c , v. 4, p. 547-557. Bader, H., Haef e l i , R., Bucher, E., Neher, J., Eckel, 0., and Thams, Chr., 1939, Der Schnee und seine Metamorphose: Beitrage zur Geologie der Schweiz, Geotechnische Serie Hydrologie, Lieferung. 3. Bern, 1939. (also SIPRE Translation No. 14, 1954.) Bader, H., 1951, Introduction to ice petrofabrics: J. Geol. v. 59, P. 519-536. Bjerrum, N., 1952, Structure and properties of i c e : Science, v. 115, p. 385-390. Brace, W.F., I960, Orientation of anisotropic minerals i n a stress f i e l d : Geol. Soc. Am., Memoir 79, p. 9-20. Brace, W.F., 1963, B r i t t l e fracture of rocks: in International Conference on State of Stress i n the Earth's Crust, The Rand Corporation, p. 2.1-2.103. Brown, E., 1926, Experiments on strength of i c e : St. Lawrence Waterway Project, Report of Joint Board of Engineers, Appendix F. 423-453. Butkovich, T.R., and Landauer, J.K. , 1958, The flow law for i c e : I.A.S.H. 47, p. 318-325. Butkovich, T.R., and Landauer, J.K., 1959, The flow law for ic e : SIPRE, Research Report No. 56. Carey, S.W., 1954, The rheid concept i n geotectonics: Journal of Geological Society of A u s t r a l i a , v. 1, p. 67-117. Chamberlin, R.T., 1928, Instrumental work on the nature of g l a c i e r motion: J. Geol., v. 36, p. 1-30. Chamberlin, T.C.., 1904, A contribution to the theory of g l a c i e r motion: Univ. Chicago, Decennial Pub., v. 9, p. 193-205. Chamberlin, T.C., and'Salisbury, R.D., 1909, Geology, geologic processes and t h e i r r e s u l t s : v. 1, New York, Henry Holt and Co., 684 p. - 174 - de Charpentier, J., I 8 4 I , Essai sur les g l a c i e r s et sur l e te r r a i n erratique du bassin du Rhone: Lausanne, 363 p. C o l l i e r , E.P., I960, Study of g l a c i e r s i n Banff and Jasper National Parks. I960: Water Resources Branch, Department of Northern A f f a i r s and National Resources. l e Compte, P., 1965, Creep i n rock s a l t : J. Geol., v. 73, p. 469-484. Crammer, H., 1904, Eis und Gletscher-studien: Neues Jahrbuch Mineralpgie Geologie .Beilage. Bd. 18, p. 57-116. Deeley, R.M. and Fletcher, G., 1895, The structure of g l a c i e r - ice and i t s bearing upon glacier-motion; Geol. Mag.,v. 2, p. 152-162. Demorest, M.H., 1938, Ice flowage as revealed by g l a c i a l s t r i a e : J. Geol., v. 46, p. 700-725. Demorest, M.H., 1943, Ice sheets: Geol. Soc. Am. B u l l e t i n v. 54, P. 363-400. Dobrowolski, A. B., 1923, Glaciers, structure and movement theories: Supplement No. 1 to the B u l l e t i n of the Polish Geophysical Society. (Polskie Towarzystao Geofizyczne) Part 16, Warsaw, 1939-1948, 191 p. (A t r a n s l a t i o n from Mianowski Inst. Adv. S c i . , Warsaw, 1923). von Drygalski, E., 1897, Gronlands Eisund sein Vorland, Gronland-Expedition der Gesellschaft f u r Erdkunde zu B e r l i n , 1891-1893, v o l . 1, 555 p. von Drygalski, E., I898, Die Eisbewegung, ihre physikalischen Urachen und ihre geographischen Wirkungen: Petermanns Geographische Mitteilungen,. Bd. 44, p. 55-64.. Emden, R., 189P, Ueber das Gletscherkorn: Neue. Denkschr. allgem. schweiz. Ges. f.d.ges. Naturw., Bd. 33, p. 1-44. von Engeln, O.D., 1915, Experimental studies and observations on i c e structure: American Journal of Science, v. 40, p. 439-473. # F a i r b a i r n , H.W., 1949, Structural petrology of deformed rocks: Addison-Wesley Press, Inc., 344 p. F i e l d , W.O., and Heusser, C.J., 1954, Glacier and botanical studies i n the Canadian Rockies, 1953: Canadian Alpine Journal, v. 37, p. 128-140. - 175 - Finsterwalder, S,, 1897, Der Vernaglferner: Wirsenschaftliche Ergonzungshefle zur Z e i t s c h r i f t der deutsch und osterreich, Alpenvereine, Bd. 1, p. 1-112. Fisher, J.E., 1947, Forbes' and Alaskan ' d i r t bands' on g l a c i e r s and their o r i g i n s : American Journal of Science, v. 245, p. 137-145. Fisher, J.E., 1962, Ogives of the Forbes type on alpine g l a c i e r s and a study of t h e i r o r i g i n s : J. G l a c , v. 4, p. 53-61. Fisher, 0 . , 1879, On the thermal conditions and on the s t r a t i f i c a  tion of the Antarctic i c e : P h i l . Mag.,'v. 7, p. 381-393. F l i n n , D., 1958, On tests of significance of preferred orien t a t i o n i n three dimensional f a b r i c diagrams: J. Geol., v. 66, p. 526-539. Forbes, J.D., 1842, On a remarkable structure observed by the author i n the ice of g l a c i e r s : Edinburgh New Philosophical Journal, v. 32, p. 84-91. Forbes, J.D., 1847, Thirteenth l e t t e r on g l a c i e r s : Edinburgh New Philosophical Journal, v. 42, p. 136-154. Friedman, M., 1963, Petrofabrics: i n International Conference on State of Stress i n the Earth's Crust, Rand Corporation, p. 10.1 - 10.128.. Fuchs, A., 1959, Some s t r u c t u r a l properties of Greenland snow: SIPRE, Research Report No. 42. Gerrard,•J.A.F., Perutz, M.F., and Roch, A., 1952, Measurement of the v e l o c i t y d i s t r i b u t i o n along a v e r t i c a l l i n e through a g l a c i e r : P.R.S., v. 213, p. 546-558. Gibb's, J.W. , 1906, On the equilibrium of heterogeneous substances: in Collected Works of J. Willard Gibbs, New Haven, Yale . University Press. Godwin, H., 1949, Pollen analysis of g l a c i e r s i n special r e l a t i o n to the formation of various types of g l a c i e r bands: J. G l a c , v. 1, p. 325-332. "Griggs, D.T., and Coles, N.E., 1954, Creep of single c r y s t a l s of i c e : SIPRE, Report No. 11. H a e f e l i , R., 1963, Observations in ice tunnels and t'he flow law of i c e : i n Ice and Snow, Ed. Kingery, Mass., The M.I.T. Press, p. 162-186. Glen, J.W. , 1952, Experiments on the deformation of i c e , J. G l a c , v. 2, p. 111-115. - 176 - Glen, J.W,, 1955, The creep of p o l y c r y s t a l l i n e i c e : P.R.S. v . 228, p. 519-538. Glen, J.W. , 1958a, The mechanical properties of ic e , 1. The p l a s t i c properties of i c e : Advances i n Physics, v. 7, p. 254-265. Glen, J.W. , 1958b, The s l i p of a g l a c i e r past i t s side walls: J. Glac. , v . 3, P. 188-192. Glen, J.W., 1958c, The flow law of i c e : I.A.S.H., 47, p. 171-183. Gow, A.J., 1963, Results of measurements i n the 309 metre bore hole at Ityrd Station, Antarctica: J. G l a c , v. 4, p. 771-784. Gunn, B.M-. , 1964, Flow rates and secondary structures of Fox and Franz Josef Glaciers, New Zealand: J. G l a c , v. 5, p. 173-190. Gold, L.W., 1958, Some observations on the dependence of s t r a i n and stress f o r i c e : Canadian Journal of Physics, v. 36, p. 1265-1275. Gold, L.W. , I960, The cracking a c t i v i t y i n ice during creep: Canadian Journal of Physics, v. 38, p. 1137-1148. Gold, L.W., 1963, Deformation mechanisms i n i c e : i n Ice and Snow, Ed. Kingery, Mass., The M.I.T. Press, p. 9 - 27. Hagenbach-Bischoff, E., 1899, Discussion of paper i n Arch. S c i . Phys. Nat., 3rd Ser., v. 22, p. 368-369. Hamberg, A., 1932, Struktur und Bewegungsvorgange im Gletschereise: Naturwissenshaftliche Untersuchungen des Sarekgebirges i n Schwedisch-Lappland, Bd. 1, p. 69-124. Harker, A., 1932, Metamorphism: a study of transformations of rock masses, London, Methuen and Co.., Ltd. 36O p. Hawkes, L., 1930, Some notes on the structure and flow of i c e : Geol. -Mag., v . 6 7 , 1930, p~. 111-123. Helmholtz, H., 1865, Eis und Gletscher: i n Populare wissenschaf- t l i c h e Vortrage, F. Vieweg und Sohn. Hess, H., 1904, Die Gletscher: F. Vieweg und Sohn., Braun schweig, 426 p. Hess, H., 1933, Das Eis der Erde: Handbuch d. Geophys., v. 7, Sec. 1, p. 1-121. - 177 - Heusser, C J . , 1956, Post g l a c i a l environments i n the Canadian Rocky Mountains:. Ecological Monographs, v. 26, p. 263-302. Higashi, A., 1959, P l a s t i c deformation of hollow ice cylinders under hydrostatic pressure: SIPRE, Research Report No. 51, 10 p. . Hopkins, W., 1862, On the theory of the motion of g l a c i e r s : Royal Society of London, Philosophical Transactions, v. 152, .p. 677-745. Hubbert, M.K., 1937, Scale models and geologic structures, Geol. Soc. Am., B u l l e t i n , v. 48, p. 1459-1519. Hugi, F.J., 1842, Ueber das Wesen der Gletscher: Stuttgart und Tubingen, J.G.Cotta, 135 p. Ivanov, K.Ye., and Lavrov, V.V., 1950, Ob odnoy osobennosti mekhanizma plasticheskoy deformatsii I'da: Zhurnal Tekhnicheskoy F i z i k i , Tom. 20, Vyp. 2, p. 230-231. (English t r a n s l a t i o n by SIPRE, Translation No. 10). Kamb, W.B., 1959a, Theory of preferred c r y s t a l orientation developed by c r y s t a l l i z a t i o n under stress: J. Geol. v. 67, p. 153-170. Kamb, W.B., 1959b, Ice petrofabric observations from Blue Glacier, Washington, i n r e l a t i o n to theory and experiment: Journal of Geophysical Research, v. 64, p. 1891-1909. Kamb, W.B., 1962, Refraction corrections f o r universal stage measurements. I. Uniaxial c r y s t a l s : American Mineralogist, v, 47, p. 227-245. Kamb, W.B., 1964, Glacier geophysics: Science, v. 146, p. 353-365. Kamb, W.B., and Shreve, R.L., 1963a, Structure of ice at depth in a temperate g l a c i e r tabs.): American Geophysical Union, Transactions, v. 44, p. 103. Kamb, W.B., and Shreve, R.L., 1963b, Texture and f a b r i c of ice at depth i n a temperate g l a c i e r (abs,): American Geophysical Union, Transactions, v. 44, p. 103. J e l l i n e k , H.H.G., and B r i l l , R., 1956, V i s c o e l a s t i c properties of i c e : Journal of Applied Physics, v. 27, p. 1198-1209. Kanasewich, E.R., 1964, Gravity measurements on the Athabaska Glacier, Alberta, Canada: J. G l a c , v. 4, p. 617-631. Kehle, R.O., 1964, Deformation of the Ross Ice Shelf, Antarctica:. Geol. Soc. Am., B u l l e t i n , v. 75, p. 259-286. - 178 - King, C.A.M., and Lewis, W.V., 1961, A tentative theory of ogive formation: J. G l a c , v. 3, p. 913-939. Kloc'ke, F., 1879, Uber die Optische Structur das Eises: Ber. Verh. naturf. Ges. Freiburg. i.B., Bd. 7, p. 17. Knopf, E.B., 1953, Processes of ice deformation within g l a c i e r s , by the late Max Harrison Demorest: J. Glac. v. 2, p. 297.::. Krausz, A.S., 1961, Etching technique to study p l a s t i c defor mation of i c e : J. G l a c , v. 3, p. 1003-1005. Lagally, M., 1934* Mechanik und Thermodynamik das stationaren Fletschers: L e i p z i g . Langway, C.C.,1958, Ice f a b r i c s and the universal stage: .SIPRE, Technical Report No. 62, 16 p. Leighton, F.B., 1951, Ogives of the East Twin Gl a c i e r , Alaska- t h e i r nature and o r i g i n : J. Geol., v. 59, p. 578-589. Lliboutry, L., 1957, Banding and volcanic ash on Patagonian g l a c i e r s : J. G l a c , v. 3, p. 20-25. Lliboutry, L., 1958, Studies of the shrinkage a f t e r a sudden advance, blue bands and wave ogives on Glacier Universidad: J. G l a c , v. 3, p. 261-268. MacDonald, G.J.F., 1957, Thermodynamics of so l i d s under hydrostatic stress with geologic applications: American Journal of Science, v. 255, p. 266-281. MacGregor, A.G., 1951, Ice cry s t a l s i n g l a c i e r s compared with quartz c r y s t a l s i n dynamically metamorphosed sandstones: J. G l a c , v. 1, p. 564-571. McConnel, J . C , 1890, On the p l a s t i c i t y of an ice c r y s t a l : P.R.S., v. 48, p. 259-260. McConnel, J . C , 1891, On the p l a s t i c i t y of an ice c r y s t a l : P.R.S., v. 49, p. 323-343. Mathews, W.H., 1959, V e r t i c a l d i s t r i b u t i o n of ve l o c i t y i n Salmon Glacier, B r i t i s h Columbia: J. G l a c , v. 3, p. 468-474. McCall, J.G., I960, The flow c h a r a c t e r i s t i c s of a cirque g l a c i e r and t h e i r effect on g l a c i a l structure and cirque forma t i o n : Norwegian Cirque Glaciers, R.G.S. Research Series No. 4, p. 39-62. Meier, M.F., I960, Mode of flow of Saskatchewan Glacier, Alberta, Canada: U.S. Geological Survey. Professional Paper No. 351, 70 p. - 179 - M e l l i s , 0 . , 1942, Gefugediagramme in stereographischer Projection: '.'inllcor, Min. Pet. Mitt., v. 53, p. 330-353. Mellor, M., 1959, Creep tests on Antarctic g l a c i e r i c e : Nature, v . 184, p. 717. M e r r i l l , W.M., 1963, Glacier ice - a natural laboratory for metamorphic pe t r o l o g i s t s : Geol. Soc. Am., Special Paper 68, p. 230. Moseley, H., 1869, On the mechanical i m p o s s i b i l i t y of the descent of g l a c i e r s by t h e i r weight only: P h i l . Mag., Ser. 4, v. 37, p. 363-370. Mugge, 0., 1895, Uber die P l a s t i c i t a t der E i s k r y s t a l l e : Neues Jahrbuch fur Mineralogie, Geologie und Palaeontologie, Bd. 2, p. 211-228, Mugge, 0 . , 1900, Weitere Versuche uber die Translationsfahigkeit des Eises, nebst Bemerkungen uber die Bedeutung de Structur das gronland ischen Inlandeises: Neues Jahrbuch fur Mineralogie, Geol., Bd. 2, p. 80-98. Muguruma, J., and Higashi, A., 1963, Non-basal gl i d e bands i n ice : Science, v. 1 9 8 , p. 573. Nakaya, U., 1958, Mechanical properties of single c r y s t a l s of i c e : SIPRE, Research Report No. 28, 46 p. Nak&ya, U. , and Matsumoto, A., 1953, Evidence of the existence of a l i q u i d - l i k e f i l m on ice surfaces: SIPRE, Paper 4, 6 -p. Nye, J . F i , 1951, The flow of g l a c i e r s arid ice-sheets, as a problem i n p l a s t i c i t y : P.R.S., v. 207, p. 554-572. Nye, J.F., 1959, The deformation of a g l a c i e r below an ice f a l l : J. G l a c , v. 3, p. 387-408. Nobles, L.H., I960, G l a c i o l o g i c a l investigations on the Nanatarssuaq ice ramp, northwestern Greenland: SIPRE, Technical. Report No. 0 6 , 57 p. Palache, C , .Berman, H., and Frondel, C , 1944, The System of Mineralogy, v. 1, New York, John Wiley and -Sons, Inc,, 834 p. Paterson, M.S., and Weiss, L.E., 1961, Symmetry concepts i n the structural analysis of deformed rocks: Geol. Soc. Am., B u l l e t i n , v. 72', p. 84I-882. - 180 - Paterson, W.S.B., 1962, Observations on Athabaska Glacier and t h e i r r e l a t i o n to the theory of g l a c i e r flow: Doctoral Dissertation, The University of B r i t i s h Columbia, Vancouver. Paterson, W.S.B., 1964, Variations i n ve l o c i t y of Athabasca Glacier with time: J. G l a c , v. 5, p. 277-285. Perutz, M.F., and Seligman, G.A., 1939, A crystallographic investigation of g l a c i e r structure and the mechanism of gl a c i e r flow: P.R.S., v. 172,. p. 335-360. P h i l l i p p , H., 1905,'Ueber Gletscherbewegung undvMoranen: Neues Jahrbucn f u r Mineralogie, Geol., v.: 2, p. 33-42.. Quincke, G., 1905, The formation of ice and the grained struc tures of g l a c i e r s : Nature, v, 72, p. 543-545- Rambe,rg, H., 1964, Note on model studies of f o l d i n g of moraines in piedmont g l a c i e r s : J. G'lac , v. 5, P- 207-218. Raraty, L.E., and Tabor, D,, 1958, The adhesion and strength properties of ice, P.R.S., v. 245, p. 184-201. Reid, J.R, , 1964., Structural glaciology of an ice layer i n a f i r n f o l d , Antarctica; Antarctic Research Series, v. 2, p. 237-266. Reid, H.F., I896, The mechanics of g l a c i e r s : J. Geol., v. 4, p., 912-928. RenaUd, A., 1949, A contribution to the study of the g l a c i e r grain, J". G l a c , v. 1, p. 320-324. Rigsby, G.P., 1953, Studies of cr y s t a l f a b r i c s and structures i n g l a c i e r s : Doct.pral Dissertation, C a l i f o r n i a Institute of Technology, 51 p. Rigsby, G.P., 1955, Study of ice f a b r i c s , Thule area, Greenland: " SIPRE, Report 26,.6 p. Rigsby, G.P., 1958, E f f e c t of hydrostatic pressure on vel o c i t y of shear deformation of single ice c r y s t a l s : J. G l a c , v..3, p. 2 7 I - 2 7 8 . Rigsby, G.P., I960, Crystal orientation i n g l a c i e r and i n experimentally deformed i c e : J. G l a c , v. 3, p. 589-609. Rossmann, F.. , 1950, Polare K r i s t a l l f o r m und Elektrische Erregung des Eises: Experientia, v. 6, p. 182. Rusnak, G.A., 1957,' The orienta t i o n of sand grains under condi tions of 'u n i d i r e c t i o n a l ' f l u i d flow: J. Geol., v. 65, p. 384-409. - 181 - Rutter, N., 1962, F o l i a t i o n of Gulkaria Glacier, Central Alaskan Range, Alaska: Geol. Soc. Am., Special Paper No. 68, p. 119. Savage, J . C , and Paterson, W.S.B., 1963, Borehole measure ments i n the Athabasca Glacier: Journal of Geophysical Research, v. 68, p. 4521-4536. Schwarzacher, W., and Untersteiner, N., 1953, Zum Problem der Banderung des Gletschereises: sitzungsberichte der Osterreichischen Akad. der Wissenschaften, M-n. Klass, Abt. 2a, Bd. 162, p. 111-145. Seligman, G., 1949a, Research on g l a c i e r flow: an h i s t o r i c a l o u t l i n e : Geog. Ann., Bd. 31, p. 228-238. Seligman, G.,"1949b, The ,growth of the g l a c i e r c r y s t a l : J. Glac., v. 1, p. 254-266. Seligman, G., 1950, The growth of the g l a c i e r c r y s t a l . Some further notes: J. G l a c , v. 1, p. 379-381. Sharp, R.P., 1951, Features of the f i r n on upper Seward Glacier, St. E l i a s Mountains, Canada:- J. Geol., v. 59, p. 599-621. Sharp, R.P., 1953, Deformation of borehole i n Malaspina Glacier, Alaska: Geol. S o c Am., B u l l e t i n , v. 64, p. 97-100. Sharp, R.P., 1954, Glacier flow - a review: Geol. S o c Am., B u l l e t i n , v. 65. , p.-821-838. Shumskii, P.A., 1955, P r i n c i p l e s of s t r u c t u r a l glaciology (osnovy strukturnogo ledovedeniia): Moscow, Izdatel 'stvo Akademii Nauk U.S.S.R., 1955. (Translated by D. Kraus for Geophysics Research Directorate, A i r Force Cambridge Research Center, Cambridge, Mass., also Dover Publications., Inc., New York, 1964, 497 p.) Shumskii-, P.A. , 1958,- The mechanism of ice straining and ice r e c r y s t a l l i z a t i o n : I.A.S.H. 47, p. 244-248. de S i t t e r , L.U., 1956, S t r u c t u r a l Geology: New York, McGraw- H i l l , 552 p. Somigliana,,. C. , 1921, Sulla profondita dei g h i a c c i a i : Rendiconti d e l l a accademia nazionale dei L i n c e i , No. 30. Steinemann, S., 1954, Results of preliminary experiments on the p l a s t i c i t y of ice c r y s t a l s : J. G l a c , v. 2, No. 16, p. 404-413. - 182 - Steinemann, S., 1958a, Experimentelle Untersuchungen zur P l a s t i z i t a t von E i s : Beitrage zur Geologie der Schweiz Geotechnische Serie, Hydrologie, No. 10. Steinemann, S., 1958b, Resultats experimentaux sur l a dynamique de l a glace et leur correlations avec le mouvement et l a petrographie des g l a c i e r s : I.A.S.H. 47, p. 184-198.. Streiff-Becker, R., 1938, Zur Dynamik des Fi r n e i s e s : Z e i t s c h r i f t fur Gletscherkunde, Bd. 26, p. 1-21. Streiff-Becker, R., 1943, Beitrag zur Gletscherkunde Forschungen an Clariden f i r n : im Kt. Glarus. Schweiz. Nat. Geselle Denkschr., Bd. 75, p. 111-132. S t u t f i e l d , H.E.M., and C o l l i e , J.N., 1903, Climbs and Explorations in the Canadian Rockies: London, Longmans, Green and Co. Sverdrup, H.O., 1935, S c i e n t i f i c r e s u l t s of the Norwegian- Swedish Spitzbergen Expedition, 1934: Geog. Ann. Bd. 17, p. 145-166. Tarr, R.S., and von Engeln, O.D., 1915, Experimental studies of ice with reference to g l a c i e r structure and motion: Z e i t s c h r i f t fur.Gletscherkunde, Bd. 9, p. 104-106. Tamman, G., 1929, Die Bildung des Gletscherskorns: Naturwissen- schaften, Bd. 17, p. 851-854. Taylor, L.D., 1963, Structure and Fabric on the Burroughs Gla c i e r , southeast Alaska: J. Glac. v. 4, 731-758. Tegart, W.J.McG., 1964, Non-basal s l i p as a major deformation process in the creep of p o l y c r y s t a l l i n e i c e : J. G l a c , v. 5, P. 251-254. Thomson, J., 1857, On the e f f e c t of pressure in lowering the freezing point of water, and on the p l a s t i c i t y of i c e : Proceedings of Belfast Natural History and Philosophical Society, Dec. 2. Turner, F.J., and Weiss, L.E., 1963, Structural Analysis of Metamorphic Tectonites: New York, McGraw-Hill, 545 p. Tyndall, J. , I858, On some physical properties of i c e : P.R.S., v. 9, p.76-80. Tyndall, J., 1859, On the veined structure of g l a c i e r s : Royal Society of London, Philosophical Transactions, v. 151, p. 279-307. Tyndall, J., i860, The g l a c i e r s of the Alps: London, John Murray, 444 p. - 183 - Tyndall, J., 1874, The Forms of Water: London, Henry S. King and Co., 192 p. Untersteiner, N., 1955, Some observations on.the banding of g l a c i e r i c e : J. G l a c , v. 2, p. 502-506. Vialov, S.S., 1958, Regularities of ice deformation: I.A.S.H. 47, p. 383-391. Weertman, J., 1955, Theory of steady state creep based on dis l o c a t i o n climb: Journal of Applied Physics, v. 26, No. 10, p. 1213-1217. Weertman, J., 1957a, Steady state creep through d i s l o c a t i o n climb: Journal of Applied Physics, v. 28, No. 3, p.. 362-364. Weertman, J., 1957b, Steady state creep of c r y s t a l s : Journal of Applied Physics, v. 28, No. 10, p. 1185-1189. Weertman, J., 1964, The theory of g l a c i e r s l i d i n g : J. G l a c , v. 5, p. .287-303. Winterhalter, R.U., 1944, Probleme der Gletscherforschung: Les Alpes, v. 54, p. 185-192. - 184 - APPENDIX I. ICE FABRIC DATA AND CONTOURED DIAGRAMS FOR ATHABASCA GLACIER - 185 - Fabric location. Plane of loe layers. Type of ice F tine. * Pole to loe layers. C. 8. coarse bubbly. contour Interval 1,23.4.5% N« ot rendinau N* of eeotlons. Contour depression. FIGURE ^ 6 ICE FABRIC DATA AND CONTOURED 0IAQRAM8 FOR ATHABA8CA GLACIER. - 186 - Fabric location. Type of loe F f ine. C.B. coarse bubbly. N * of readings. - N * of seotlons. FIGURE 47 ICE F A B R I C DATA AND C O N T O U R E D D IAGRAMS F O R ATHABA8CA G L A C I E R . , — Plane of ice layers. * Pole to loe layers. Contour Interval 1.23.4.5% Contour depression. - 187- Fabric location. Type of Ice F t ine. C. B. coarse bubbly. iM° ot readings. - N° of seotlons. x—' Plane of ice layers. &> Pole to ice layers. Contour interval 1.23.4.5% contour depression. FIGURE 48. ICE FABRIC DATA AND CONTOURED DIAGRAMS FOR ATHABASCA GLACIER. - 188..- 6 2-2 C B 190-25 Fabric location. Type of ice F f ine. C. B. coarse bubbly. N° of readings. - N° of seotions. Plane of ice layers. A Pole to ice layers. Contour interval 1.23.4,5% Contour depression. FIGURE 49. ICE FABRIC DATA AND CONTOURED 01 AG RAMS FOR ATHABASCA GLACIER. Fabric location. Type of loe F f ine. C.B. coarse bubbly. N" of readings. - N° of seotlons. pione of loe layers. * Pole to loe layers. Contour interval 1.23.4.6% Contour depression. F IGURE r i O . ICE FABRIC DATA AND CONTOURED 0IAGRAM8 FOR ATHABASCA OL AC IE R • - 190 - Fabric location. Type of ice F f Ine. C. B. coarse bubbly. N° ot readings. - N* of seotions. F I G U R E 51. Plane of ice layers. A Pole to ice layers. Contour interval 1,23.4,5% Contour depression. ICE FABRIC DATA AND CONTOURED DIAGRAMS FOR ATHABA8CA GLACIER. - 191 - Fabric looation. Plane of ice layers. Type of ice F f ine. A Pole to ice loyers. C B . coarse bubbly. contour interval 1,23.4.5% N° ot readings. - N° ot seotions. contour depression. FIGURE 52. ICE FABRIC DATA AND CONTOURED DIAGRAMS FOR ATHABASCA GLAC IER . - 192 - FIGURE 53. I C E F A B R I C D A T A A N D C O N T O U R E D DIAGRAMS F O R A T H A B A S C A G L A C I E R . - 193 - Fabric location. Plane of ice layers. Type of ice F fine. ^ Pole to ice layers. C.B. coarse bubbly. Contour interval 1 , 2 3 . 4 . 5 % N° ot readings. - N° of seotions. Contour depression. FIGURE 54. I C E F A B R I C D A T A A N D C O N T O U R E D D I A G R A M S FOR ATHABASCA GLACIER. - 1 9 4 - APPENDIX I I . ICE FABRIC DATA AND CONTOURED DIAGRAMS OF COMPRESSED ICE CYLINDERS - 195 - Sample Number f Direction of crystal growth. A x l a i -stress In lbs. ' • Stress axis. N° of read ings -N° of sections Contour interval 1,2,3,4,5 % Cu3 Contour depression. F I G U R E 5 5 I C E F A B R I C DATA A N D C O N T O U R E D D I A G R A M S O F C O M P R E S S E D ICE C Y L I N D E R S . - 1 9 6 - Sample Number f Direction of crystal growth. AXlaf stress in Ibe. • Stress axis. N» of readings-N° of sections Contour interval 1,2,3,4,5 Jtf Contour depression. FIGURE 56 ICE FABRIC DATA AND CONTOURED DIAGRAMS OF COMPRESSED ICE CYLINDERS. ] Q7 - Somple Number f Direction of crystol growth. Axlat -stress in lbs. • Stress axis. N° of readings-NO of sections Contour interval 1,2,3,4,5 % Contour depression. F IGURE 57. I C E F A B R I C DATA A N D C O N T O U R E D D I A C R A M S O F C O M P R E S S E D ICE C Y L I N D E R S . Sample Number f Direction of crystal growth. Axlai'-stress in lbs. • Stress axis. No of readings-N<> of sections Contour interval 1,2,3,4,5 # Cu3 Contour depression. FIGURL 58 I C E F A B R I C DATA A N D C O N T O U R E D D I A G R A M S O F C O M P R E S S E D I CE C Y L I N D E R S . - 1 9 9 - ( a f t e r 2 0 0 hours) ( a f W 2 00 ! h b u r s ) Sample Number f Direction of crystal growth. Axial -stress in lbs. • Stress axis. N ° of readings-N° of sections Contour interval 1,2,3,4,5 # Contour depression. FIGURE 59 . I C E F A B R I C DATA A N D C O N T O U R E D D I A G R A M S O F C O M P R E S S E D ICE C Y L I N D E R S . - 200 - Sample Number f Direction of crystal growth. Axial-stress in lbs. • Stress axis. N ° of readings-N° of sections Contour interval 1,2,3,4,5^ Contour depression. FIGURE 60. I C E F A B R I C DATA A N D C O N T O U R E D D I A G R A M S O F C O M P R E S S E D ICE C Y L I N D E R S . - 201 - APPENDIX I I I . CREEP CURVES FOR COMPRESSION TESTS FIGURE 62. 8TRA1N-T IME CURVE FOR AXIAL 81 R E 8 8 148 lbs. TEST 84-14. - 208 - APPENDIX IV INTERPRETATION OF CREEP CURVES GENERAL STATEMENT It i s convenient to describe creep of a deformed body- i n terms of some simple mathematical concept. Generally, such terms r e l a t e to an i d e a l body that deforms i n a c h a r a c t e r i s t i c and predictable manner. Most natural substances, however, are not i d e a l , they do not deform i n a simple manner, and t h e i r creep appears to be a combination of d i f f e r e n t types of flow. Carey (1954) considers that s t r a i n i s a combination of at least four components: (1) an e l a s t i c s t r a i n , (2) a transient s t r a i n that diminishes with time, (3) a time independent 'pl a s t i c s t r a i n ' , and (A) a time dependent 'viscous s t r a i n ' that i s pro por t i o n a l to the load. Although these components can be recog nized in most creep curves, i t i s d i f f i c u l t to resolve the curves into a simple mathematical formula that includes these components. Numerous laboratory t e s t s on ice show that i t has no fundamental stress and that i t w i l l creep under the smallest loads. Any e l a s t i c component i s very d i f f i c u l t to measure for the e f f e c t s l a s t only about 10 seconds (Gold, 1958). If a load i s applied f o r more than a few seconds, ..deformation i s permanent. The generalized creep curve f o r i c e , l i k e that of many metals, may be divided into small sections: 1) I n i t i a l steep portion of the curve (primary s t r a i n ) . 2) Straight portion of the curve (secondary s t r a i n ) , 3) A f i n a l increase i n the rate of s t r a i n ( t e r t i a r y s t r a i n ) . - 209 - The early portion of any graph i s dominated by tran sient s t r a i n , but i t s e f f e c t s decrease with time. The time for transient s t r a i n to become n e g l i g i b l e i n any p a r t i c u l a r test appears to be a function of the duration of the experiment and the construction of the graph. In the present series of tests, a l l graphs of the creep for a period of 90 minutes, appear to have a constant rate of s t r a i n a f t e r about 40 minutes (Figure 39), but i f these t e s t s are continued for 30 hours (Figure 40) the rate of s t r a i n becomes constant aft e r about 8 hours. In a compression test at 1 Kg/cm2, Haefeli (1963) found that the strain-rate became constant a f t e r 9 days. Glen (1955, p. 529) assumes that i f the s t r a i n i s small and the curves f i t Andrades law, any transient term w i l l be proportional to Most workers neglect any e f f e c t s of transient s t r a i n and use only the data from the straight portions of the curves, to obtain a flow law of the form: e = K T " where e = e f f e c t i v e s t r a i n rate ^ -= constant T = e f f e c t i v e shear stress r\ - constant This power law appears to be a good approximation, but the value f o r n does not appear to be constant. Values deter mined for n range from 1.0 to about 4.5. Such a wide va r i a t i o n could arise from experimental error due to some difference i n the siz e , shape or f a b r i c of the test specimens, or i t could a r i s e from some difference i n the process of ice deformation - 210 - (Tegart, 1 9 6 4 ) . Not a l l workers are convinced that the flow law f o r ice i s a simple power law. Gow ( 1965 ) measured the closure of a bore hole near Byrd Station, Antarctica, and considers that the power increases with both increase of stress and increase of time. Glacier flow r e s u l t s from continued stress over very long periods of time, and may well correspond with t e r t i a r y creep of experimental t e s t s . Few tests, however, have been continued long enough to obtain s u f f i c i e n t data to investigate t e r t i a r y creep. Glen ( 1 955 ) continued some t e s t s u n t i l the s t r a i n rate increased, and for one of the present experiments (Figure 62) the increase i n s t r a i n rate was associated with r e c r y s t a l l i z a  t i o n (Figure 4 4 ) . Most of the data from the present series of creep t e s t s are not consistent and the r e s u l t s are d i f f i c u l t to interpret. Due to limitations of the apparatus, i t was not possible to ob t a i n the i n i t i a l length of the t e s t specimens and the i n i t i a l section of creep curves given i n Figure 61 may not be accurate. Some tes t s have s t r a i n rates that are lower than tests with smaller stresses. Because of these discrepancies and the f a c t that the t o t a l s t r a i n cannot be determined, the creep curves have not been resolved into any mathematical law f o r the flow of i c e . To obtain more accurate data, a second group of ice cylinders were compressed under more rigorous conditions. APPARATUS To obtain accurate creep measurements, unconfined - 211 - 8 inch by 4 inch diameter ice cylinders were compressed at -10.5°C. under a x i a l loads from 200 to 1,000 lbs. on a Baldwin Universal Testing Machine for periods up to 10 hours. The speci mens were within a re f r i g e r a t e d temperature jacket at a constant temperature that was stable to less than 1°C. A l l measurements of these t e s t s have the same order of accuracy as conventional engineering t e s t s on concrete, and the general r e s u l t s compare favourably with the standards accepted by Le Gomte (1965) f o r the creep of rock s a l t . Ice cylinders placed within the apparatus, were l e f t overnight, and allowed to reach equilibrium. A load of 20 lb s . was applied, and the i n i t i a l s t r a i n reading obtained with a Rambold s t r a i n gauge accurate to .001 inch. F u l l load was applied i n about 5 to 10 seconds and then maintained f o r just over 10 hours. RESULTS Several cylinders were compressed under a x i a l loads of 200, 400, 600, 800, and 1,000 l b s . , and the r e s u l t i n g creep curves are given i n Figures 63 to 6$. No in d i v i d u a l curves can be reproduced exactly, but the graphs are thought to be s u f f i c i e n t l y r e l i a b l e to j u s t i f y some mathematical i n t e r p r e t a t i o n . Some curves were plotted as semi-log and log-log graphs i n order to obtain a simple expression to r e l a t e s t r a i n and time. The best solution obtained with creep curve f o r a load of 1,000 l b s . , gave the rate of a x i a l s t r a i n proportional to the square rate of the time. To show the dependence of s t r a i n upon the applied load, - 212 - the e f f e c t i v e creep rate has been plotted against the effec t i v e shear stress i n Figure 67. The figure shows the log shear stress and the log s t r a i n rate corresponding to the time i n t e r v a l s of 1, 2, 3, A, 5, and 10 hours. For each time i n t e r v a l the graph i s a straight l i n e i n d i c a t i n g .a power law of the form e - KT" . The slope of the l i n e progressively decreases with time, indicating that the value of the exponent changes with time from I .56 at 1 hour to 1.0 at 10 hours when the rate of creep appears to become constant. A graph of log n against log time gives a straight l i n e that suggests a power law with -o-a (Figure 68). If n i s a function of time, variations i n the value of n determined by various workers may re s u l t from difference i n duration of t h e i r experiments. In order to duplicate conditions of g l a c i e r flow i t would be necessary to continue laboratory t e s t s u n t i l t e r t i a r y creep occurred. Acceleration of the creep rate i s r e a d i l y attained under high stresses, but te s t s at low stresses must be continued f o r a considerable time. -213. - 4 I hour x 2 hours « 3 hours + 4 hours « 5 hours • 10 hours SHEAR STRE88(bars) FIGURE 67 . SHEAR STRAIN RATE Vs SHEAR STRESS. - 214 -500 1000. metre ATHABASCA GLACIER, ALBERTA, CANADA OUTLINE M A P S H O W I N G S A M P L E L O C A T I O N S & F A B R I C D I A G R A M S Figures by diagram Contour interva l 1,2 LEGEND Location Type of ice. F. f ine C.B. coarse bubbly N° of measurements N° o f sections 3, 4, 5 % . 1 - • 1% 2 9b 3% A - 5 % A ' Pole to ice 'layers. 

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
China 9 14
United States 8 0
Japan 4 0
United Kingdom 3 0
New Zealand 1 0
Ukraine 1 0
Czech Republic 1 0
City Views Downloads
Beijing 6 0
Ashburn 5 0
Tokyo 4 0
Shenzhen 3 14
Los Angeles 2 0
Chesterfield 2 0
Unknown 2 0
San Francisco 1 0
Prague 1 0
Cheadle 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}
Download Stats

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0053046/manifest

Comment

Related Items