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

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AN INVESTIGATION OF TALUS SLOPE DEVELOPMENT IN THE SIMILKAMEEN VALLEY NEAR KEREMEOS, B. C. by GEORGE A. WOROBEY B. Ed., University of B. C, 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS In the Department of Geography We accept this thesis as conforming to the required standard The University of British Columbia July, 197 2 In presenting t h i s thesis in p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library shall make it f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or p u b l i c a t i o n of t h i s thesis f o r f i n a n c i a l gain shall not be allowed without my written permission. Department of Geography The University of B r i t i s h Columbia Vancouver 8, Canada Date J u ly l> 1 9 7 2-- i -ABSTRACT Talus form and development i n the Similkameen V a l l e y near Keremeos, B r i t i s h Columbia was i n v e s t i g a t e d . I n i t i a l observa t ions suggested that t a l u s format ion i n the r e g i o n was e n t e r i n g a pas s ive stage and subsequent a n a l y s i s has conf irmed t h a t the t a l u s s lopes are tending towards s t a b i l i t y . V o l c a n i c ash exposed on one t a l u s s lope a l lowed the c a l c u l a t i o n o f r e l a t i v e r a te s of past and r e c e n t t a lu s accumulat ion which supported a ' d i m i n i s h i n g sediment y i e l d ' concept . A n a l y s i s of c l i m a t e data recorded a t Keremeos s i n c e 1930 r e v e a l e d a h i g h frequency of f r o s t c y c l e s . T h i s suggests the importance of f r o s t a c t i o n as a mechanism of weather ing a long the exposed headwal l s and i t i s thought t h a t the occurrence of abundant and massive t a l u s forms i n the r e g i o n i s b a s i c a l l y the r e s u l t of f r o s t weather ing i n a s s o c i a t i o n w i t h l i t h o l o g i c c o n t r o l s . A fence s t r u c t u r e designed t o capture r o c k f a l l d e b r i s y i e l d e d f a i r r e s u l t s and s u b s t a n t i a t e d the v a l i d i t y of u s i n g v e g e t a t i o n as an i n d e x of s t a b i l i t y on t a l u s s l o p e s . A weak but not monotonic i n c r e a s e i n sediment s i z e downslope was detec ted on a number of slopes, c o n t r a d i c t i n g an i n i t i a l v i s u a l impre s s ion . Debris sampled a long l a t e r a l p r o f i l e s on one t a l u s cone i s s i g n i f i c a n t l y l a r g e r a t the 1% l e v e l than d e b r i s sampled a l o n g the c e n t r a l p r o f i l e . Some c o r r e l a t i o n between s i z e and angle i s i m p l i e d , s i n c e the l a t e r a l p r o f i l e s are a l s o s t eeper ; i t i s hypothes ized that t r a n s p o r t mechanisms down the s ides are d i f f e r e n t from those a long the center of the cone . R e a d i l y observable c r o s s - s l o p e s o r t i n g , - i i -resulting i n the development of longitudinal strips of fine and coarse debris, is explained in terms of differential mass movement mechanisms. It is concluded that the talus slopes studied are complex and influenced by a variety of processes in addition to primary deposition. The mapping of one talus cone at a five foot contour interval provided the basis for a detailed analysis of talus form. A sample of the debris size taken simultaneously with the mapping of the surface allowed for the calculation and establishment of a fourth degree trend surface, an examination of which is made in conjunction with the map and photos of the cone. Practical implications of the development of talus as applied to this region are discussed. - i i i -TABLE OF CONTENTS Page ABSTRACT i LIST OF TABLES v i i LIST OF FIGURES v i i i LIST OF PHOTOS x LIST OF MAPS x i i i ACKNOWLEDGMENTS xiv CHAPTER I - INTRODUCTION 1 A. Regional Geology. 1 B. Mechanisms Involved in the Formation of Talus. 9 1. Mechanisms of weathering. 10 - physical 10 - chemical 12 2. Rockfall and.primary deposition. 12 - rockfall 12 - downslope movement and accumulation 13 - f a l l sorting 15 - angle of rest 16 3. Modification of the talus slope by mass movement mechanisms. 17 - spontaneous mass movement 17 - talus creep 18 - external disturbance 18 4. Morphology of talus development. 18 - the headwall 19 - chute formation 19 - talus forms 21 - depth of talus 21 - slope profiles 21 C. Problems Associated with the Study of Talus Dominated Landscapes. ' 24 1. Problems associated with mass movement mechanisms. 24 - accumulation versus mass movement 24 - observations of movement 25 - sta b i l i t y - 26 -iv-TABLE OF CONTENTS (cont'd) Page 2. Problems associated with the morphology and morphometry of talus. 26 - protalus ridges 26 - practical morphometric "problems 27 - sampling problems 27 CHAPTER II - HYPOTHESES AND METHODS OF INVESTIGATION 30 A. Lithologic and Topographic Controls. 30 B. Weathering Mechanisms. 32 - apparent effects 32 - frost action 33 - frost cycles 33 - chemical processes 35 - secondary physical processes 35 C. Rockfall Mechanisms. 35 D. Mass Movement Mechanisms. 36 - cross-slope sorting; formation of fine and coarse strips 36 - sampling fine and coarse strips 43 - painted lines 44 E. Morphometry and Morphology of Talus in the Similkameen Valley Near Keremeos . 45 1. Morphometry. 45 - s t a b i l i t y hypothesis 45 - diminishing sediment yield concept 49 - fences designed to capture rockfall debris 50 - Mazama ash deposit at CC44 56 - lateral and central profiles compared 56 - downslope sorting 58 - mapping TC26 59 - sampling TC26 62 2. Morphology. 62 - protalus ridges on TC67 64 - boulder aprons 64 - distribution of vegetation 69 - types of vegetation 71 CHAPTER III - OBSERVATIONS 73 A. Geologic Control. 73 -v-TABLE OF CONTENTS (cont'd) Page B. Weathering Mechanisms. 75 - frost action 76 - chemical action 84 - degrees of weathering 85 - root wedging 87 C. Rockfall and Primary Deposition. 88 - observations of rockfall 88 - fence samples 89 D. Mass Movement Mechanisms. 96 - evidence on painted lines 96 - water 101 - wind 102 - creep 102 - snow avalanche 103 - flowing water 103 - disturbance 103 - basal sapping 104 E. Morphometry and Morphology of Talus Development Near Keremeos, B.C. 104 1. Morphometry. 104 - stability 104 - diminishing sediment yield concept 105 - slope profiles 110 2. Morphology. 113 - classification of talus slopes in the region 113 - map and description of TC26 117 - miniature talus cone at CC44. 122 - basal sapping as the result of excavation 123 - chutes and funnels 124 CHAPTER IV - ANALYSIS AND INTERPRETATION 127 A. Profile Analysis. 127 - lateral and central profiles compared 127 B. Analysis and Interpretation of Downslope Sorting. 131 - running means along profiles 131 - traverse samples 137 C. Mass Movement as a Cross-Slope Sorting Mechanism. 144 - fine and coarse debris strips compared 144 - implications of uniform shape parameters 144 - v i -TABLE OF CONTENTS (cont'd) Page D. Morphometric Analysis and Interpretation. 150 - trend surface analysis on TC26 150 CHAPTER V - CONCLUSIONS 155 A. Summary. 155 B. Practical Recommendations for the Region. 158 BIBLIOGRAPHY 162 APPENDIX 170 A. Maps and Photographs Used. 170 B. Additional Notes for Map 2. 171 - v i i -TABLES Page I. Size-Angle Relationship (Behre, 1933). 24 II. Temperature Reading on Rock Headwall Below Fence #1 on TC25. November 24 - December 1, 1967. 77 III. Frost Cycles at Keremeos. 80 IV. Degrees of Weathering. 85 V. Displacement of Rocks on Line Painted on TC22. 97 VI. Classification of Talus Forms Near Keremeos, B.C. 114 VII. Cobble Analysis on Long Profiles TC21. 127 VIII, A. Comparable Slope Sections TC25. 128 B. Comparable Slope Sections TC21. 128 IX. Difference of. Means Test. 129 X. Trend Surface Analysis TC26; Analysis of Variance and Error Measures. 153 - v i i i -FIGURES Page 1-1. A Typical Cross-Section of the Similkameen Valley Near Keremeos, B.C. 7 1-2. Mean Monthly Temperature and Precipitation for Keremeos, B.C. 8 1-3. Evolution of a Chute or Funnel. 20 1-4. Compound Talus Slope. 22 II-1. Talus Development at Keremeos. 48 II-2. Fence No. 1 Across Chute at TC25. 52 II-3. Detail of Fence. 52 II-4. Detail of Boulder Apron Development. 68 I I I - l . Temperature Correlation Between Station at TC25 and A.E.S. Station at Keremeos. 79 III-2. Mean Monthly Frequency of Frost Cycles at Keremeos. 83 III-3. Sediment Sample from Fence No. 1. 95 III-4. Painted Line Along Coarse Strip on TC22. 98 III-5. Painted Line on TC22. 98 III-6. Mazama Ash Deposit in Talus Cone at CC44. 106 III-7 . Ash Deposit as Exposed Along Road Cut at CC44. 107 III-8. Model of Talus Cone at CC44. 107 III-9. Slope Profiles on TC21 and TC25. 112 IV-1. Mean Proportional and Cumulative Proportional Frequency Plots of b A:-xis Along Profiles on TC21. 130 -ix-FIGURES (cont'd) Page IV-2. Running Mean Plot of b Axes Along Center Profile on TC25. 132 IV-3. Running Mean Plot of b Axes Along Right Profile on TC21. 133 IV-4. Running Mean Plot of b Axes Along Center Profile on TC21. 134 IV-5. Running Mean Plot of b Axes Along Left Profile on TC21. 135 IV-6. Mean b Axis Plot of Traverse Samples on TC3. 138: IV-7. Mean b Axis Plot of Traverse Samples on TC26. 139 IV-8. Mean b Axis Plot of Traverse Samples on TC48. 140 IV-9. Mean b Axis Plot of Traverse Samples on TC67 . 141 IV-10. Proportional Frequency Plots and Cumulative Proportional Frequency Curves of. b Axes on TC3 . 142 IV-11. Within Cone Proportional and Cumulative Proportional Frequency Plots of b Axis . 143 IV-12. Plot of Mean b Axes Along Coarse and Fine Strips on CC52. 145 IV-13. Frequency Plots and Cumulative Proportional Frequency Curves of b Axes Along Fine Strip on CC52. 146 IV-14. Zingg Shape Distribution CC52. 147 IV-15. Flatness Parameter Along Fine and Coarse Strips on CC52. 148 IV-16. Sphericity Parameter Along Fine and Coarse Strips on CC52. 149 V - l . Rockfall Trajectories. 160 -x-PHOTOS Page 1-1. The Similkameen Valley at Keremeos Looking East. 5 I I - l . Headwall Near Old Tom Creek. 31 II-2. Headwall Near Keremeos. 31 II-3 . Maximum-Minimum Thermometer Installed in Rock Crevice at TC25. 34 II-4. CC52. 36 II-5. Detail of Surface on CC52. 37 II-6. TC67. 41 II-7. CC7. 41 II-8. Looking Up on TC67. 43 II-9. TC2. 47 11-10 Site of Fence #1 on TC25. 51 11-11. Site of Fence #2 on TC49. 51 11-12. Fence #1 on TC25. 53 11-13. Fence #2 on TC49. 53 11-14. Detail of Chute Above TC49 . 54 11-15. Headwall, Associated Talus, and Similkameen River at TC49 . 55 11-16. Mazama Ash Deposit at CC44. 57 11-17. Talus Resting on River Deposit at CC44. 57 11-18. TC48. 63 11-19. TC67. 65 11-20. TC67. 65 11-21. Detail of Boulder Apron at the Base of TC25. 66 -xi^ PHOTOS (cont'd) Page 11-22. Boulder Apron on TG42. 66 11-23. TC27 and TC28. 71 11-24. Closeup of Boulder Apron on TC28. 72 I I I - l . Weathered Rock Headwall at TC21. 75 III-2. Observed Solution on Headwall at TC25. 85 III-3. Weathering Degree No. 1 (Oilier, 1965). 86 III-4. Weathering Degree No. 2 (Oilier, 1965). 86 III-5 (a & b) Weathering Degree No. 4 (Oilier, 1965). 86 III-6. Possible Root Wedging Mechanism. 87 III-7. Broken Douglas F i r at Apex of TG67 . (Sept. 21/67). 89 III-8. Fence #1 on TC25. 91 III-9. Fence #1 on TG25. 91 111-10. Fence #1 on TC25. 91 I I I - l l . Fence #2 on TC49. 92 111-12. Painted Line Above Fence #1 at TC25. 100 111-13. Painted Line Above Fence #1 at TG25. 100 111-14. Al l u v i a l Gone Near TC43. 104 111-15. TC21. I l l 111-16. TG48. 117 111-17. TC26. 119 III-18. Along Headwall in Chute of TC26. 121 111-19. Miniature Talus at CC44. 123 - x i i -PHOTOS (cont'd) Page 111-20. Apex of Chute Above TC25. 125 111-21. Looking up at Funnel Above TC48. 126 V - l . Gathered Talus Rubble. 159 - x i i i -MAPS Page 1. Southwestern B.C. 2 2. The Similkameen Valley at Keremeos, B.C. 3 3. Geology of the Keremeos Region. 4 4A. TC26 With Overlay. 118 4B. TC26 With Trend Surface. 151 -xiv-ACKNOWLEDGMENTS Under the advice and guidance of Dr. M. A. Melton, formerly of the University of Br i t i s h Columbia, the investigation was initiated in the spring of 1967 . Observations were made during May through September of that year and again in January and the spring and early summer of 1968. Subsequent observations were made at irregular intervals in 1969 through 1971. Sincere appreciation is extended to Dr. Melton for his support. Particular thanks are expressed to the University of British Columbia and the Geography Department of the university for making available funds, in the form of research and travel grants, to carry out the fieldwork. The use of equipment supplied by the Departments of Geography, Geology, and C i v i l Engineering was appreciated. Credit is given to Brian Mennell and Lyle Finch who gave assistance in the f i e l d , more in the s p i r i t of research than for remuneration. The meteorological record for Keremeos (A.E.S.) was made available by Mrs. J. A. Russel whose observations of talus activity in the region were useful. Appreciation is extended to my sister and her husband for accomodation during the investigation. Many gave invaluable assistance with the compilation of the thesis. Dr. A. L. Farley of the University of British Columbia is thanked for his unfailing cooperation as advisor and suggestions for improvements . Sincere appreciation is extended to Dr. 0. Slaymaker of the University of British Columbia whose careful readings and criticisms lent coherence to the text. Peter Lewis of the Geological Survey of Canada gave much appreciated assistance in the calculation of pre- and post- Mazama rates - X V -of talus accumulation. No expression of gratitude could equal the efforts put forth by Dr. Mike Church of the University of British Columbia. His time, expertise, f a c i l i t i e s and encouragement made possible the analyses in Chapter IV. Suggestions he has made for the improvement to the whole work have been invaluable and i t is hoped that the thesis now has the desired "taughtness". Lastly, to my wife Berne Jean I extend my most heartfelt thanks for a job well done on the typing of the many drafts. Without her moral support the thesis would never have been written. 1 CHAPTER I - INTRODUCTION Near Keremeos in British Columbia the phenomenon of talus development is readily observable. I n i t i a l interest for the investigation was prompted by the abundance and great size of the talus forms found i n the region (see Map 2). Since preliminary observations suggested that talus development was entering a passive stage and that the rate of formation in the past must have been more rapid, the research was launched under the hypothesis that the talus slopes in the Keremeos area were tending towards st a b i l i t y . A. Regional Geology. The area studied (see Map 1) is properly a part of two major physiographic divisions of British Columbia that extend along the Similkameen River (see Holland, 1964). The area on the north side of the river is on the southern flank of the Thompson Plateau, part of the Interior System of British Columbia. The area on the south side of the river i s part of the Okanagan Range of the Cascade Mountains contained i n the Western System. Geology and structure (see Map 3) transcend the region, however, and being part of two major physiographic divisions seems to exert no geologic influence on the development of talus. It i s assumed that a l l of the slopes must have formed since the last retreat of the Cordilleran Ice Sheet from the area, giving them a geologic age of 10000 (^ ) years (see Fulton, 1971, p.v and p. 17.) The valley i s very steep-walled and deep and represents the incision of the Similkameen River into a plateau surface. The MAP 1. SOUTHWESTERN B. C. 3 MAP 2. SIMILKAMEEN VALLEY AT KEREMEOS, B. C. SCALE 1170000 REFERENCE 3000 6000 HIGHWAY OR ROAD COMPILED FROM B. C. AERIAL PHOTOGRAPHS TAKEN IN 1966 PERMANENT STREAM S INTERMITTENT STREAM \ j PIN CUSHION MOUNTAIN MAX.-MIN. TEMP.g INSTALLATION KEREMEOS TALUS CONES BOUNDARY OF FIELD AREA \ S 4 K MOUNTAIN 5 mean elevation at river level is 1500 feet a . s . l . rising steeply to an elevation of approximately 6000 feet on the north side of the river and approximately 7000 feet on the south side; thus average relief is of the order of 5000 feet. The U-shaped cross-section of the valley (see Photo 1-1) suggests that i t must have been shaped by the movement of ice through i t and the steepness of the valley walls is probably attributable to scouring by glaciers. The general Photo 1-1. The Similkameen Valley  at Keremeos Looking East. direction of movement of the Cordilleran Ice Sheet i n the area was from north to south but observed glacial striae along the valley walls indicate that the ice followed the course of the valley in this confinement, moving in a west to east direction. It seems that the major ice sheet sp l i t around the north end of the Okanagan Range near Princeton into two lobes, one of which turned to flow to the southeast 6 parallel with the Lower Similkameen Valley. After the retreat of the continental ice sheet a period of valley glaciation ensued, resulting in a steepening of the valley sides, redistribution of detrital material, and formation of cirques on some of the higher peaks. The steep rock faces thus produced along both sides of the valley in this stretch offer a situation geometrically ideal for the development of talus. The Similkameen River has a f a i r l y steep gradient, dropping 150 feet in the twelve mile stretch of valley studied. Some flood plain development has occurred on the postglacial valley f i l l but is not wide enough to accommodate extensive meander development. South of Keremeos the valley widens and an extensive flood plain with well developed meander loops can be observed. Figure 1-1 represents a typical section of the valley. The climate of the valley bottom is classed as BSk according to Koppen's classification ranging to Dfb on the uplands. A low annual total of precipitation and a high annual range of temperature prevails within the confines of the valley (see Figure 1-2). Keremeos averages ten inches of precipitation annually including about twenty-six inches of snow. Summers are hot with temperatures exceeding 100°F not uncommon. Typical vegetation i s of the parkland variety in the valley bottom, i.e., short grass with a scattering of Douglas f i r and ponderosa pine, ranging to sub-alpine coniferous forest on the higher cooler and wetter slopes . The dryness of the area is definitely reflected in the vegetation and,where overgrazing has occurred, sagebrush has replaced the natural grassland. The dryness is basically the result of a rainshadow effect produced by the Coast and Cascade F I G U R E I - l . A T Y P I C A L CROSS - SECTION OF 5000 6500 6000 5500 5000 4500 -•4000 3500 3000 2500 -2000 1500 1000 500 8 J A N F E B M A R A P R M A Y J U N J U L A U G S E P O C T N O V D E C FIGURE 1-2. MEAN MONTHLY TEMPERATURE AND PRECIPITATION  FOR KEREMEOS, B.C. The average was obtained from data for an eleven year period recorded on the Upper Bench Road, Keremeos, B.C. The f a i r l y high temperature range (45°F.) illustrates the continentality. Precipitation is low, however, having a mean annual total of 10 inches: i t is concentrated in June in the form of convectional storms. 9 Mountains to the west and is accentuated in the summer by the extension of hot, dry continental air from the south. The coastal mountains are also effective in producing a continental influence by cutting off the moderating effects any maritime air would have. A definite moisture deficit exists at lower elevations and most crops require irrigation. The rocks of the area studied are arranged in a closely folded band formation normal to the general east-west trend of the valley (see Map 3). They have been identified and mapped by Bostock (1939) as a succession of cherts, lavas, limestones, and other sedimentary forms of Permian age and younger. Colours are very drab and from a distance as well as close up give the rocks a dull appearance. As evidenced by the abundance and great size of talus forms observed the rocks along this stretch seem very susceptible to disintegration under the effects of weathering. B. Mechanisms Involved i n the Formation of Talus. Talus is by definition an accumulation of rock debris at the base of an exposed rock face or c l i f f . This accumulation is the net result of gradual decomposition and disintegration of the rock face by the processes of weathering and mass wasting. In time, the characteristically angular fragments produced become dislodged individually or en masse under the influence of gravity f a l l i n g free of the rock face to eventually assume a position of rest at the base of the c l i f f . With sustained weathering and rock f a l l activity the accumulation grows, assuming a slope referred to as the angle of repose. Rapp subdivides the advent of talus formation into three stages : 10 "1. Supply - f a l l of debris from the wall down to the surface of the talus. It is terminated by the primary deposition of the particles. 2. Shifting - the movement of the material down the talus slope after the primary deposition. 3. Removal or st a b i l i t y - movement of material away from the talus slope or stability of the slope by vegetation and eventual flattening of the profile and soil formation." (Rapp, 1960a, p. 6.) 1. Mechanisms of weathering. The weathering of rocks can be defined as the process whereby solid bedrock at or near the earth's surface i s reduced by physical and chemical means into sediment. Talus formation represents an i n i t i a l product along the continuum of the weathering process and both physical and chemical forces are involved at this stage. Although chemical weathering i s ultimately the more important of the two processes, mechanical breakdown during the i n i t i a l stages of weathering, eg. talus formation, can play a major or even dominant role. A number of weathering processes are recognized (see Reiche, 1962). Those of particular note for the present purposes are the physical processes of frost shatter, frost bursting and root wedging and the chemical processes of hydration, oxidation and solution. The importance of freeze-thaw cycles in association with water in rock weathering has been questioned and the definition of the effective limits for the same varies greatly. A frost cycle is defined as any fluctuation of temperature above and below 32°F. A freeze-thaw cycle implies a fluctuation of temperature above and below 32°F. of sufficient range for a definite freeze and thaw to occur. To exert a wedging action, the frequency of the cycle is obviously crucial but the duration and range of the cycle is important as well. Cook and Raiche (1962) noted that freeze-thaw cycles in the Arctic are much less frequent than thought to be and found that the frequency is much greater in Southern Canada. Boyd (1959) found that in order for a freeze-thaw cycle to be effective i t must occur through a range of 25° to 35°F. Fraser (1959) and others, however, set the effective range at 28° to 34°F. The implication of an effective range is that there must be a sufficient temperature fluc-tuation for a definite freeze and thaw to occur. But, much depends on the duration of the cycle. A frost cycle of a shorter duration will require a greater range in order to be effective. Wiman (1963) noted that most effective weathering occurred under so-called "Icelandic" conditions represented by one cycle every day rather than under "Siberian" conditions represented by colder temperatures but a cycle only every four days. It becomes apparent that the effective range probably varies a great deal. In reference to duration, Rapp (1957) classified frost cycles as follows: 1. Short frost cycle (several per day). 2. Daily frost cycle. 3. Fros t cycle of severa l days dura t ion . 4. Annual frost cycle. 5. Frost cycle of several years. Stock (1968) noted that the effectiveness of "frost-riving"is largely determined by the thickness and seasonal distribution of snow cover and the amount of water incorporated in the rock at time of freeze-up. Andrews (1961) concluded that the importance of frost as a weathering agent has been vastly overstated. The tremendous force exerted by the freezing of water confined within the interstices of rock, however, cannot be denied and within the recognized limits outlined above 12 cannot be discounted as a major mechanism of weathering. Some controversy over the effectiveness of root wedging exists. As yet, i t has not been conclusively demonstrated that the growth of plant roots can exert a force sufficient to fragment rocks. Of paramount importance in the processes of hydration, oxidation and solution i s the action of water on rock in association with oxygen and carbon dioxide in the a i r . Fragmentation of rock by physical processes greatly accelerates the rate of chemical decay but, so long as the rock can be penetrated by water, chemical weather-ing can occur. The rate and type of weathering is determined to a large degree by the characteristics of the rock in question. The susceptibility of the rock to fracture is an important control. The aspect of the beds and the degree of jointing as well as the resistance of the rock and i t s basic structure w i l l greatly affect the rate. How effective weathering mechanisms are on a given rock face in turn determines the rate of rockfall activity and associated talus development. 2 . Rockfall and primary deposition. Rockfalls, and to a lesser degree rockslides and avalanches, are the major sources of debris resulting in the buildup of talus. Rapp (1960b) l i s t s a number of r o c k f a l l - i n i t i a t i n g mechanisms: frost bursting, thermal changes, heavy rains, snow block f a l l s , ice block f a l l s , chemical weathering, wind, creep, and earthquakes. Frost action is probably the most important of these mechanisms especially in climates characterized by frequent frost cycles. Rocks shattered and burst by frost action subsequently release fragments when the ice melts. Short term i.e., daily frost cycles, are important 13 especially in their effect on the shallower cracks . In this case rockfall by "frost-riving" (Rapp, 1960b) occurs. Some examples of rockfall i n i t i a t i n g thermal changes are expansion and contraction caused by daily temperature variations or differential expansion caused by solar heating where different rock types are interbedded or beside patches of snow. The localized movement associated with differential expansion and contraction of the rock as heating and cooling occur may be an effective dislodgement mechanism. Rainfall can be an effective i n i t i a t i n g mechanism by: 1. diminishing the internal f r i c t i o n along joints or other slip planes in the rock. 2. creation of high hydrostatic pressure in joints dammed by water transported debris . 3. thawing ice after previous frost bursting. (Rapp, 1960b) Debris incorporated i n snow or ice masses attached to the rock face ma be carried along when these masses are released. Debris avalanches associated with the buildup of hydrostatic pressure in joints under heavy or prolonged r a i n f a l l are rare but are important since such a great volume of debris i s released almost instantaneously. Wind can dislodge very loose fragments but is recognized as only of minor importance. Roots growing in cracks along the rock face may be an effective prying mechanism; especially when the trees are subjected to heavy winds. Creep of any material over the rock face eg. regolith snow, may disengage loose rocks. Finally, rocks already dislodged can knock others loose i f they bounce along the c l i f f face on their way down. Once dislodged, however, the individual rock fragments come under the exclusive control of gravity. Individual rocks move down slope by sliding, r o l l i n g , skipping and free f a l l . In general, larger rocks w i l l generate greater kinetic 14 energy because of their greater mass and thus wi l l travel farther down slope. Where the individual fragment eventually comes to rest on the talus slope depends on a number of factors. A rock which has great mass and momentum may r o l l beyond the talus. Such large rocks typically form an apron at the base of the talus. The distance the rock f a l l s from the headwall before encountering the talus slope can also affect the distance i t w i l l travel on the talus slope: rocks f a l l i n g further w i l l acquire greater momentum and w i l l tend to travel farther down the slope. The slope of the headwall and the talus slope below, however, can affect distance travelled by individual fragments. Rocks f a l l i n g from an essentially vertical c l i f f lose considerable momentum upon impact with the talus slope, especially i f the slope angle of the talus near the apex is relatively f l a t . If the headwall is sloping, however, fragments can gain a considerable horizontal momentum which is much less dissipated upon contact with the talus slope and, with a bounding action, travel comparatively farther downslope. Momentum buildup on flatter sloping headwalls i s also limited, however; especially i f the headwall surface is rough. As the talus deposit grows in response to rockfall activity the surface characteristics developed further affect the mode and distance of travel of rockfall fragments. Growth may take place i n layers parallel to the angle at which the materials come to rest. Distance travelled by each particle can range from a maximum equal to the total length of the slope down to a minimum of zero. Since the deposit rests against its source of debris, the headwall, some pieces obviously do not move downslope at a l l before they are covered under subsequent rockfalls. Rocks r o l l i n g down the surface w i l l be affected by the slope and degree of roughness of the surface i t s e l f . A given rock w i l l travel farther on a steep slope than a fla t t e r slope. A rock f a l l i n g at high speed along the inclined surface w i l l touch that surface only at the high points with i t s high points i f the rocks comprising the surfac are smaller than the rock r o l l i n g over them. According to Ritchie (1963) the size or shape of the rock has l i t t l e bearing on i t s r o l l i n g characteristics except i f i t is long like a pencil which tends to retard r o l l through eccentric action. Angular momentum of a rock r o l l i n g over a surface of smaller rocks tends to increase until two things tend to slow i t down: 1. a flatter slope and 2. larger materials to r o l l over. Energy is lost by impact as i t comes in contact with pieces of its own size. Progressive slowing down causes the rolling rock to sink lower into the irregularities of the surface losing more energy by virtue of more contact with the surface. Momentum is eventually totally dissipated and the rock becomes trapped i n a void between rocks of i t s own size or larger. F a l l sorting seems implicitly obvious, i.e., larger rocks have greater kinetic energy so should therefore r o l l further before coming to rest. Tinkler (1966) observed that the proportion of larger sediment sizes increases downslope on talus sampled in North Wales. He attributed this sorting to the effects of gravity. Gardner (1971a) noted a logarithmic decrease in the mean size of debris upslope on talus observed in the Lake Louise d i s t r i c t . Behre (1933), however, noted the exact opposite on talus slopes observed in the Rocky Mountains and Caine (1967) found a tendency for rock size to decrease slightly downslope on talus observed in Tasmania but noted that the differences are not s t a t i s t i c a l l y significant. In view of the discrepancies, therefore, the general law 16 of f a l l sorting should be seen as the statement of only one process on talus slopes. It is clear that primary deposition must be dominated by this process, but subsequent modification of the surface of the talus slope is controlled by other processes. The accumulation of rock debris in this way assumes an angle of rest referred to as the repose slope. The repose slope or angle of repose of unconsolidated material has been widely studied (Behre 1933, Meiner 1934, Van Burkalow 1945, Ward 1945, Andrews 1961, Melton 1965, Tinkler 1966, Rahn 1966). In the case of talus materials, large, angular, rough surfaced and densely packed rocks tend to support a higher angle of repose. The maximum angle of repose which can be attained by a given deposit of rock debris depends on the inertia required to overcome the internal f r i c t i o n . When the maximum repose slope is exceeded, the particles slide to readjust to a slope less than the maximum repose angle. The coefficients of sliding and static f r i c t i o n for rock debris have been placed at 28° and 34° respectively (Melton, 1965) and i t i s interesting to note that a consolidation of slope measure data on talus (Rapp 1960, Melton 1965, Caine 1967, Stock 1968, Gardner 1968, et al.) displays a range of 10.5° - 41.5° with modes at 28° and 33° respectively. Whether or not a given deposit w i l l assume the maximum angle of repose depends on the mode of deposition and the time elapsed after deposition. Deposits which are built up gradually with a minimum of disturbance w i l l attain slopes closer to the maximum. A deposit comprised of a certain shape of particles arranged in an interlocking matrix or imbricated fashion could support i t s e l f to achieve an angle of rest which would exceed the theoretical maximum repose slope. In natural debris deposits, the process of weathering can result in a 17 cementing of the individual particles which w i l l allow the deposit to exceed the theoretical maximum repose slope. Further, debris deposits held together by the root structure of a sufficiently dense vegetation cover could maintain slopes in excess of the theoretical maximum. Also, thin mantles of debris on a well bossed steep bedrock surface could be supported at angles exceeding the theoretical repose slope. As can be seen, however, some agent in addition to the internal f r i c t i o n of the particles must be operative before a debris deposit can exceed i t s theoretical maximum. The i n i t i a l establishment of a position of rest by rocks tumbling from the headwall may be only temporary; subsequent downslope movement may occur through mechanisms of mass movement. 3. Modification of the talus slope by mass movement mechanisms. Readjustment of a talus surface can occur i n a number of ways. The mechanisms involved come under the general heading of mass movement. Spontaneous mass movement or movement exclusive of the effects of a carrying medium occurs when the shearing limit of the material comprising the slope is reached. Failure is produced in a number of ways . The addition of water through melt or precipitation increases the pore water pressure resulting in failure referred to as "mudflow". Solifluction i s an important mechanism in permafrost environments. Water can also act as a lubricant. Behre (1933) noted that talus in the Rocky Mountains tended to remain stable in dry weather but became more mobile in wet weather. Icing along the points of contact has the same effect. If the slope becomes steepened by the addition of material, failure is eventually reached. Also, removal of material away from the base of the deposit i.e., basal sapping, produces failure. 18 Talus creep is another form of mass movement. The disturbance created by freeze-thaw action in water saturated talus results in a net downslope movement. Experiments and theoretical calculations by Scheidegger (1961) suggest that the expansion and contraction created by alternate daily heating and cooling are sufficient to cause net downslope movement referred to as "dry rock creep". External disturbance of the deposit can produce mass movement. The impact of f a l l i n g rock and raindrop impact have effect. The movement of any medium such as water, snow, or ice over the surface transports material downslope. Earth tremors and animal activity are additional sources of disturbance. Wind transport has been cited as a possible mechanism (Rapp, 1960b) but this is doubtful since most talus material is too large to be affected by wind. Finally, through "...the shifting and removal of the material the talus formation is levelled out, takes on a more concave profile and may be transformed, for example, into an a l l u v i a l cone." (Rapp, 1960,p.6) The characteristic forms associated with talus development, however, require some explanation. 4. Morphology of t a l u s development. Talus proper develops essentially from rockfall activity under the influence of gravity. The slope produced represents the aggregate deposition of fragments ro l l i n g , sliding, or bouncing to an eventual position of rest. As the importance of water or avalanching snow as a transporting medium increases, talus forms grade into alluvial cones or avalanche boulder tongues and rockslide tongues (see Rapp 1959) having a distinct concave-up longitudinal profile. A variety of talus forms per se, are recognized. 19 To i n i t i a t e the formation of a talus slope a rock face of steep slope must be exposed. Such a feature could be a c l i f f produced by f l u v i a l or glacial erosion. Tectonic activity resulting in escarpments and fault blocks are further examples. The steep rock slope produced, from which the weathered fragments move by free or bounding f a l l to build the talus below, is variously referred as the mountain wall, rock wall, headwall or rock headwall, free wall, free-face or c l i f f face. The headwall, to i n i t i a t e talus formation, must have a slope steep enough to allow for movement of fragments by sliding, r o l l i n g , bounding or free f a l l . Slopes much less than 40° w i l l result in l i t t l e or no talus formation since gravity is unable to overcome static f r i c t i o n at low angles. In general, the headwall has an inclination ranging from 40° to 90°. Obviously a headwall of greater height w i l l result in accelerated talus development since more area is exposed to weathering. The structure of the headwall controls the rate and mode of destruction by weathering. If zones of weakness exist a dissection of the headwall ensuesj. producing gullies or chutes (see Figure 1-3). Because weathering is concentrated along these zones of weakness rockfall activity is greatest here and becomes channelled along the gullies or chutes. Rapp (1960a) noted that the frequency of rockfall is directly related to the degree of dissection of the headwall. In comparison to a relatively undissected headwall the area of rock directly exposed to weathering processes on a dissected one is much greater. In addition, water from melt and precipitation is channelled along the gullies or chutes. The force of this flowing water and that which becomes frozen in the joints w i l l i n i t i a t e further rockfall activity. A dissected headwall, therefore, FIGURE 1-3. EVOLUTION OF A CHUTE OR FUNNEL STAGE I. Chute develops i n i t i a l l y as a c l e f t i n the headwall above the talus deposit. STAGE 2 . Talus grows as a r e s u l t of the r o c k f a l l concentrated by c l e f t above. As the headwall d i s -integrates the c l e f t i s widened and deepened to form a chute or funnel. CLEFT CHUTE TALUS Y T A L U S STAGE 3. Up b u i l d i n g of talus and downcutting STAGE 4. With conti nued talus growth, chute i n chute eventually r e s u l t s i n the merging of the becomes layered with mantle of debris producing two forms. a continuous debris covered slope from the apex of the chute to the base o 21 should have greater rockfall activity. whether a headwall retreats more or less uniformly over the whole of the free face or unequally by dissection with formation of gullies or chutes w i l l affect greatly the shape of talus developed below. In general, talus cones with a convex horizontal profile are associated with a concentrated rockfall source; sheet talus develops when a l l parts of the headwall supply material uniformly. A headwall undergoing dissection retreat might display a variety of forms. Sheet talus alternating with talus cones can occur. Individual cones may coalesce to form a compound talus slope (see Figure 1-4). Where a thin mantle of debris collects on a steep surface the feature i s called a debris slope. The debris remains much controlled by the underlying rock structure. The depth of talus deposits can vary greatly ranging from very shallow collections on debris slopes to substantial depths in larger formations. Rapp (1960a) reported a range in depth from 1 to 35 meters but noted that maximum depths never amount to more than about 1/10 of the height of the talus slope. Debris deposits which are composed of essentially homogeneous particles throughout should develop essentially straight slope profiles. The slope surface of such deposits approximates an inclined plane. Talus deposits, however, are never homogeneous throughout. Often, more than one rock type is present and the individual fragments are never exactly the same size or shape. Moreover, as a result of natural sorting which may occur along the transportation surface of a talus slope, different parts of the deposit may have distinctly different size and slope characteristics than others. The net effect of this heterogeneous FIGURE I*" 4. COMPOUND TALUS SLOPE- individual cones coalesce to form a continuous talus deposit. GULLY -cleft in a steep headwall through which debris is channelled by free or bounding f a l l to form a talus cone below. The gully usually remains detached from the actual talus accumulation. With sustained activity a gully becomes a chute. CHUTE - a cleft which concentrates debris to form a talus cone. Notice that the transportational surface of the talus extends well up into the chute. FUNNEL - a half funnel-shaped c l e f t in a headwall which i s wide at i t s top and narrower below through which debris is concentrated to form a talus slope. As with the chute the talus accumulation extends well up into the funnel. 23 composition is to produce not only a wide variation in the repose angle among talus slopes but, more importantly, a variable profile on each individual slope. The profile of a talus slope represents the complex and delicate adjustment of the debris to the many factors which affect slope development in varying degrees along the profile some of which are listed below: 1. The mode of and the duration since deposition. 2. Internal f r i c t i o n as controlled by the type, size and shape of debris. 3. The degree of sorting in the debris. 4. The amount, type and distribution of vegetation. 5. Thickness of the mantle and underlying surface characteristics. 6. Settling and redistribution of debris mechanisms, eg. creep, wash, compaction, weathering. Attempts to explain the characteristic concave longitudinal profile of talus slopes in terms of the size sorting and repose slope concepts have not been successful. Many inconsistencies are apparent. Machatschek (1952) attributed the concavity of the profile to the sorting of material on talus slopes, i.e., from smaller to larger sizes of material down the slope. The basic assumption he used was that fines are capable of supporting steeper angles than coarse material. Behre (1933) explained the concave profile in terms of talus he observed in the Rocky Mountains. In this case the observed sorting was from larger to smaller material downslope attributed to the effects of weathering. He assumed that larger fragments can achieve higher angles of rest therefore producing a slope which is steep at the top and flatter at the bottom resulting in a concave profile. This relationship is demonstrated in Table I below: 24 Table I Size-Angle Relationship (Behre, 1933). Average Diameter in Inches Average Slope i n Degrees 12 6 4 2 1 35° 35° 32° - 34° 31° - 32° 26° - 31° His is only one set of data, however, and the results cannot be taken as universal. Scheidegger (1970) suggested that i f the formation of a talus slope i s due to talus creep then angles near the top, where sliding is initiated, should be steeper than those near the base, where the materials come to rest, resulting in a concave profile. The difference in slope might also be attributed to the difference i n packing of the materials. Materials near the top of the slope may become more packed as a result of more concentrated rockfall activity. The materials with greater cohesion near the top would be capable of supporting steeper angles than the lesser packed materials downslope producing a concave profile. There seems to be no simple explanation for this phenomenon and observations of profiles which are essentially straight, composite concave - convex, and even convex (Rapp 1957) tend to complicate i t further . G. Problems Associated with the Study of Talus Dominated Landscapes. 1. Problems associated with mass movement mechanisms. on a talus slope is the determination of the following: is the talus surface basically the result of primary accumulation processes or does i t represent the modification of a surface by mass movement mechanisms after accumulation under rockfall activity? Whichever process The central problem in an explanation of the features exhibited 25 predominates greatly affects the type of surface produced. In youth , or times of accelerated rockfall activity, accumulation mechanisms would predominate; later, mass movement mechanisms w i l l exert an effect and a composite form may result. In the fin a l stages of development, or when rockfall activity abates, mass movement processes may come to predominate. Whatever the stage, the net effect of mass movement is to lower the slope. Perhaps slope can be taken as some indication of the process predominating,i.e., accumulation on steeper slopes; mass movement on gentler slopes. However, no limits have been established and a great deal more study w i l l be required to define them -- i f in fact they exist. Actual observations of movement on talus slopes are few. Most of the movement in i t i a t i n g mechanisms described in section B of this chapter are theoretical. Some insight into net and differential movement has been gained by driving steel stakes (Rapp 1960) into talus slopes at fixed locations and noting downslope movement over long intervals of time. Results indicate that the surface layers tend to move most quickly. Lines painted cross-axially on talus debris observed over long periods of time indicate differential movement along the surface especially on slopes where the debris is sorted into strips of fines and coarse material (eg. Stock, 1968). However, the cause of the sorting into strips and the reasons for differential movement noted are not understood. Scheidegger (1970) hypothesized that movement may take place as miniature landslips which occur when talus assumes a c r i t i c a l thickness and slope creating a c r i t i c a l toe c i r c l e along which the landslip w i l l occur. An observation by Rapp (1960a, p. 61) seems to confirm this theory. However, observations of failure on sand slopes 26 (Van Burkalow, 1945) indicated that sliding does not occur along a circular surface but i s , rather, laminar, being essentially parallel to the slope. Van Burkalow suggested that sliding on talus slopes must approximate this type of failure. A related problem is the recognition of the degree of activity on a talus slope. Stakes and painted lines as described above afford a rough measure of activity. If remaining unaltered over long periods of time the slope is considered to be stable. Vegetation is also used as an indicator: "A rough measure of the permanence of st a b i l i t y of a talus slope is also afforded by the growth of grasses or other small shrubs on i t . The unsatisfactoriness of this criterion comes largely from the fact that the time required for grass to advance up the slope results in a lag; on account of the need for s o i l accumulation the slope may be essentially 'at rest' several years before i t is even scantily occupied by the grass and may well stand for a decade before moderately carpeted."- (Behre, 1933, p. 624) Indirectly, rockfall activity is an indicator of the degree of activity or s t a b i l i t y on a talus slope. Substantial rockfall activity w i l l produce a very active surface. As rockfall abates the surface is better able to stabilize i t s e l f . Tarpaulin traps have been used as measures of rockfall activity (eg. Barnett 1966, Stock 1968); otherwise, l i t t l e quantitative data regarding s t a b i l i t y is available. 2. Problems associated with the morphology and morphometry of talus . Descriptions of the form and shape of weathered c l i f f faces and associated talus accumulations are readily available; those by Rapp are particularly comprehensive. Talus forms are easily distinguished from similar debris accumulations such as avalanche boulder tongues, rock glaciers and a l l u v i a l cones. On some talus slopes a mound of rock fragments in the form of a ridge separated by a slight depression from 27 the base of the talus proper has been observed (Behre 1933, Bryan 1934, Andrews 1961, Stock 1968). A generally acceptable explanation for this phenomenon, however, has not been advanced. Behre explains i t as the result of accumulated snow on the talus, between the c l i f f and the valley, which persists into late spring when most of the winter snow has melted. The snow on the talus is sheltered from the sun by the c l i f f . The wasting of debris from the c l i f f is active at this time of year because of the high frequency of freeze-thaw cycles. Debris accumulated on the snow pack slides and r o l l s easily off the snow pack and concentrates to form a ridge near the base of the talus called a "nivation ridge". Bryan (1934) does not agree with this terminology as i t implies formation in respect to snow accumulation. He does not see this as the general case and offers the term "protalus rampart" as being a more suitable name. A number of practical problems are encountered in morphometric analysis of talus slopes. Of significance is the depth of the talus deposit since shallow deposits can be much affected by the surface on which they rest. Determination of the depth of the deposit by excavation is d i f f i c u l t and indeed practically impossible on particularly deep deposits. Talus slopes in general are very steep and usually quite mobile. Survey work and especially mapping on such a surface is a particularly d i f f i c u l t undertaking. Sampling the debris also presents problems. The most valid method of sampling is usually the completely random method whereby each individual in the population has a known chance of being selected in the sample. This tends to eliminate bias from the sampling program due to the temptation on the part of the sampler to choose samples which are "good looking" or "typical". Often, however, in geomorphology the data have a systematic trend which renders 28 the data economically unfeasible for completely random sampling. In such cases, some systematic method is employed which utilizes random sampling at a point, along a line, or within an area based on some predetermined pattern or system. In many cases systematic sampling methods compare favourably with completely random sampling. However, as Cochran (1966) notes, the "...disadvantages are that they may give poor precision when unsuspected periodicity is present and that no trustworthy method The surface of a talus slope is a transportation surface along which debris is moving essentially in one direction, i.e., from the top to the bottom. Sampling on a systematic basis along this axis of transportation is particularly expedient on talus slopes especially, for example, to determine whether or not a significant downslope progression of debris size (sorting) exists. For size frequency analysis on the slope a two dimensional sampling grid is useful placing one axis of the grid parallel to the axis of movement on the slope and the other perpendicular to i t . On a talus cone a more representative sample would be obtained using a radial grid since the direction of transport is not constant but radiates from the apex of the cone. In this way, as many sample stations could be established near the apex of the cone as there would be near the base with the number of samples at each station varying as a function of the area of each graticule. Establishing the number of samples required in a particular program is another problem. The number has to be large enough to give valid results yet small enough to be reasonably accommodated within the limits of the program. A practical problem encountered in sampling debris on a talus slope is the mobility for estimating 1966, p. 230) known." (Cochran, 1 sy) is the error variance. 29 of the surface. To sample without disturbance of the surface is d i f f i c u l t and practically impossible in certain cases. 30 CHAPTER II - HYPOTHESES AND METHODS OF INVESTIGATION A . Lithologic and Topographic Controls . The investigation was confined to a 12 mile stretch of valley upstream from Keremeos where talus development was observed to be concentrated. This occurrence of abundant and massive talus forms is a result of three factors: rock type, structure, and glacial history. The f i r s t factor i s the susceptibility of the cherts, lavas, limestones and other sedimentary rocks in the area to weathering. It was observed that disintegration of the rocks was quite general and complete throughout the 12 mile stretch. To the south, however, the rock forms grade into more resistant quartzite, schist and granodiorite. Upstream, the same basic succession of rock noted above continues (see Rice, 1966, p. 8). However, as one proceeds northwestward out of the region the rocks become increasingly more resistant as the result of increased metamorphism: "A l l members of the group are more or less metamorphosed and near the contact with the Coast intrusions the alteration becomes intense. As the contact is approached the argillaceous sediments, particularly, become coarser grained; feldspar and biotite develop; and the schistose texture gives place, with a further coarsening of grain, to a gneissic texture so that the sediments grade into the granitoid rock of the main intrusive body." (Rice, 1966, p.8) It seems then, that the weaker rocks found in the 12 mile stretch under study are more susceptible to weathering than those found immediately to the northwest and south. The second factor is related to the general joint pattern exhibited by the rocks. The rocks dip steeply, usually greater than 60° (see Photo II-l), in a generally north to south direction (Map 3). Since the orientation of the valley of the Similkameen trends generally east-west along the stretch studied, the planes present vertical zones Photo I I - l . Headwall Near Old Tom Creek. The white bed of limestone in the rock face near Old Tom Creek illustrates the steep dip (72°) of the beds and the orientation of their strike normal to the valley. Photo II-2. Headwall Near Keremeos. Detail of rock headwall in the v i c i n i t y of Keremeos along the north side of the valley. Note the joint planes which aid the penetration by water and subsequent weathering. 32 of weakness along which weathering in association with water can effectively proceed perpendicular to the strike of the valley (see Photo II-2) . Northwest and south of the 12 mile stretch, the orientation of the joint planes matches that of the orientation of the valley thus presenting planes parallel to the valley walls. Such a pattern allows for fewer effective routeways along which weathering can proceed to produce wasting effective for talus formation. The third factor noted was the configuration of the valley. Along this stretch the valley is somewhat confined, having very steep sides with the bedrock exposed along both sides. Movement of the Cordilleran Ice Sheet in the area was basically from the north to the south. This would have produced more pronounced scouring - and hence broadening - in the north-south trending sections of the valley. The east-west trending section therefore remains more exposed and vulnerable to the processes of weathering and subsequent talus formation. Down-stream, the valley broadens appreciably and the walls are less steep with much of the bedrock protected with a mantle of t i l l . Upstream, the valley i s also somewhat broader and the rocks here, too, remain more protected by a t i l l mantle. B. Weathering Mechanisms. The rocks exposed to the effects of weathering exhibit some faulting and light folding. The net effect of the disturbance has been to produce a slight metamorphosis in the rocks . Some granitic intrusion has occurred but is rare in the region studied. Weathering has had a most deleterious effect on these rocks but in varying degrees of intensity. The cherts are most immune to decay and remain as the bolder bluffs exposed along the walls of the valley. Unequal dissection of 33 the headwall is most characteristic, being concentrated in the zones of weaker sedimentary and volcanic rock, especially where faulting has occurred. The net effect has been to produce a variety of talus forms the most common being successions of coalesced cones. Decomposition and disintegration of the rocks as the result of chemical and physical weathering respectively are readily observable in the rocks exposed. It i s suggested that disintegration due to frost action and decomposition as the result of chemical action are the chief mechanisms of weathering. "Frost bursting" and "frost shatter" as the result of water freezing within the interstices of the rocks are considered to be the dominant mechanisms of disintegration. . The following points support this claim: a) Water is available throughout the freeze-thaw period, (see Figure 1-2) b) The joint pattern, as discussed in section A. of this chapter, and the chemical weathering of the rocks (see Chapter III) provide for optimal penetration of the rocks by water . c) Frost action could b^ effective along the headwalls since the light snow cover during the winter provides a minimum of insulation. d) The shattered appearance of the headwall and the angularity and 'freshness' of much of the talus debris suggest frost action. The frequency of frost cycles (provided water is available) to a large extent determines the effectiveness of the mechanism. In general, the 2 Mrs. Russ el.,, recorder for the Met. Station at Keremeos notes that snow cover i n the area does not vary greatly from an average of about 12 inches. Also, from personal observations i t was noted that the headwall is kept essentially bare of snow by the wind. 34 more frequent the cycles the greater the destruction of the rocks affected. To determine the frequency of frost cycles in the region, an analysis of climate data obtained from the Atmospheric Environment Service of the Ministry of Transport (Canada) was made. A continuous record for Keremeos station on the Upper Bench Road of that municipality is available from the year 1930 to the present. To correlate with these records a maximum-minimum thermometer was installed in the headwall at TC25 (see Photo II-3) and a frost cycles record for the week November 24 to December 1, 1967 was obtained. The thermometer was Photo II-3. Maximum-Minimum  Thermometer (arrow) Installed in  Rock Crevice at TC25. The thermometer was placed about 3 feet from the surface. located on the headwall inside a rock crevice 150 feet below fence #1 (see following section) on the right side (interpret l e f t or right, facing in the direction of transport down the talus slope) of TC25 so as to give a 35 reading representative of the temperature affecting the rock. Analysis of both sets of frost cycle data is made in Chapter III. Decomposition due to chemical weathering is of primary importance in the region. The processes of oxidation, hydration, and solution seem most pronounced, as substantiated by observations in Chapter III. A number of secondary physical weathering processes have limited effect in the region, including splattering effect of raindrops and the wedging action attributed to the growth of plant roots along planes of separation in the rocks (see observations in Chapter III). C. Rockfall Mechanisms. Upon investigation i t was concluded that four rockfall mechanisms (Chapter I.B.2.) predominate. Of greatest importance would be release of fragments from rocks shattered and burst by frost action. Analysis of frost cycles in Chapter III supports this claim as well as the effectiveness of "frost-riving" as a mechanism. Rainfall could be an important release mechanism during June when precipitation, in the form of thunderstorms, in concentrated. Meltwater earlier in the spring .could have the same effect. Expansion and contraction associated with alternate heating and cooling is probably an important dislodgement mechanism in the summer when temperatures exceeding 100°F. are not uncommon and cooling under clear skies at night is effective. Since many of the headwalls observed exhibit a relatively dense growth of stunted Douglas f i r trees (see Photo III-6, p.87) root wedging could be important as well. Observations of the effectiveness of these mechanisms are included in Chapter III. Creep is not an important release mechanism since l i t t l e or no regolith develops on the very steep headwalls. Snow block and ice block 36 f a l l s would have l i t t l e or no effect in this area which has only a light snowfall most winters . Some observations of release caused by wind are included in Chapter III indicating that wind might be important. D. Mass Movement Mechanisms. It is suggested that differential shifting of debris due to mass movement mechanisms produces cross-slope sorting on the talus slopes studied and accounts for the development of strips of fine and coarse debris noted on most slopes (see Photos II-4 and II-5). Hypothetically, debris of a larger size is capable of greater mobility over the surface Photo II-4. CC52• Note the alternating strips of fine and coarse debris across the talus surface. of a talus slope by virtue of i t s greater mass, allowing the development of greater kinetic energy (Chapter I.B.2.). Further, the potential for mobility for a given rock increases i f the surface over which i t will move is composed of fragments smaller than i t s e l f . The mobility of smaller Photo II-5. Detail of Surface on  CC52. Note strip of coarse material in foreground and successive strip of fines in the background. The packsack gives the scale. 38 rocks, therefore, is much restricted due to their limited capacity to develop kinetic energy. Also, rocks which are relatively small w i l l most likely encounter rocks of the same size or larger on the slope over which they move. This further impedes their mobility. In view of this relationship between size and mobility and in light of observa-tions made on talus slopes in the region studied, i t is suggested that movement on these slopes occurs in two distinct ways. In general, movement downs lope for the larger rocks occurs on an individual basis. Smaller particles, however, are usually incapable of individual mobility and therefore must move en masse along s l i p planes i n response to spontaneous mass movement mechanisms . To explain the process i t must be hypothetically examined in detail. Rockfall activity from the headwall is the source of supply for the?, debris comprising the talus slope. Fragments both large and small are continuously added and in this way the deposit grows, maintaining a slope which, under normal circumstances, is commensurate with the angle of internal f r i c t i o n of the material. Rockfall debris w i l l encounter the talus slope at or near i t s summit (in the case of a cone near the apex and indeed, i f a chute or funnel has developed, far above the summit of the talus slope). To preserve a more or less constant slope on the talus deposit some of this debris must migrate downslope. Some of the larger rocks would be able to move immediately to the base of the slope. It was noted that an apron of larger boulders occurs at the base of most slopes observed in the region (see Morphology this Chapter) . Not a l l of the rockfall debris can move directly to the base of the talus, however, as do the boulders which accumulate to form the apron. Some become immobile almost as soon as they encounter the 39 surface of the talus deposit, especially the smaller rocks..., Some of the larger ones may move a fa i r distance downslope but a l l eventually become lodged at some point on the talus surface However, accumulation w i l l be greatest at or near the apex or summit of the talus where rockfall activity is concentrated. This disproportionate rate of accumulation w i l l produce the development of steeper slopes at the top of the talus deposit with a successive decrease in angle downslope. This may in part account for the concave profile observed on talus slopes studied in the valley (see observations Chapter III) . The angle near the top of the deposit cannot continue to increase indefinitely, however. At some point the shear stress within the material w i l l exceed the internal f r i c t i o n of the fragments and failure w i l l occur. The materials w i l l slide e_n masse or as individuals thus reducing the slope of the surface to one below that which produces failure. With successive rockfall the slope near the top of the talus may again be built up, only to be readjusted by fai l u r e . The readjustment probably never involves the entire talus slope at the time of a particular event. Rather, the readjustment is probably l o c a l i z e d and would alternate back and forth across the slope thus preserving the basic symmetry apparent on-any talus deposit. It is suggested that this readjustment due to spontaneous mass movement accounts for the sorting which produces a pattern of alternate strips of fine and coarse material observed on most talus slopes in the region (see Photos II-4 and II-5) . To explain the mechanism, a consideration of the mass movement process in detail w i l l be made. Upon release by spontaneous mass movement the size of the individual fragment w i l l be crucial i n determining how far i t w i l l move 40 before again coming to rest. The larger fragments, once mobile, are capable of moving greater distances downslope. The smaller fragments tend to move only short distances, i f at a l l , because of their small mass and i n a b i l i t y to move over the surface irregularities of a slope which is composed for the large part of fragments greater than or equal to their own size. In this way the larger pieces would tend to divorce the smaller ones near the summit of the deposit. The larger ones move downslope until contact with either a decreased slope or fragments of a comparable size reduces their momentum sufficiently to bring them to rest. Some of the larger ones may travel to the base to become incorporated as part of the boulder apron. In this way concentrations of fines would develop near the top of the slope. As these concentrations of fines develop, their potential for movement en masse increases. They may become released en masse in the form of miniature landslides, the whole being capable of greater mobility than any one of the individual fragments comprising the mass. The individual fragments would ride easily over one another, f i l l i n g in the surface irregularities they encounter to create fingers or strips of fine debris extending down the talus slope (see Photo II-6). On September 3, 1967 an observation of this phenomenon was made on CC7 (see Photo II-7). The mass of small-sized debris C~1.5"d.) shows up i n the photograph as a light brown patch which has moved downslope separating into four distinct fingers or lobes. The contrast in colour is due to the effects of weathering; the lighter fresher material had s l i d from above onto the drab weathered surface of the middle portion of the slope. A less recent but similar occurrence is v i s i b l e as a more weathered but s t i l l detectable darker patch further to the right in Photo II-7. By the 41 Photo II-6. TC67. Note the light coloured projections on the right side of the cone indicating recent downslope migration of fines. The banded appearance due to alternating strips of coarse and fine debris on the surface is characteristic of talus observed i n the region. Photo II-7. CC7. Note fresh slide of fine debris (arrow). 42 following year the very fresh patch had become weathered so as to become barely detectable on the surface. A closeup view of the fines indicated that the new material was a layer some eight inches in depth. At the leading edge where the mass came to rest a definite lobe had developed giving the deposit a 'snout' shaped front. Once this pattern of alternating bands of fine and coarse debris becomes established, successive readjustment due to mass movement would tend to accentuate i t . Any large rocks moving downslope w i l l be able to travel without much resistance over these deposits of fines and w i l l most probably not come to rest on them. The larger rocks, rather, would concentrate along the coarse strips where rocks of a comparable size would impede their movement downslope. Otherwise, the larger rocks would tend to move further downslope because of their increased momentum. Also, the i n i t i a l routeways established by the miniature'.landslides of fines become the most l i k e l y routes for successive en masse movement, these being the lines of least resistance in terms of a surface impediment. In this way the fine strips eventually extend their development to the very base of the talus deposit (eg. see Photo II - 8 ) . Another observation tends to confirm the theory of development presented above. In a l l cases, the coarse strips of debris are much more stable than the fine. Walking upslope on talus in the region was 1 relatively easy along a coarse strip but.practically impossible along a fine strip. The mobility of the fines made the exercise analagous to walking 'up' a 'down' escalator. The difference in mobility suggests a difference in the way in which the rocks were deposited. According to the theory, rocks along the coarse strips accumulate on an individual basis allowing for imbrication. This creates a greater degree of 43 Photo II-8. Looking Up on TC67. Note where lobe of fine debris has overridden coarse rubble near the base of the cone. Field book in foreground gives scale. compaction resulting in greater sta b i l i t y . The fines, however, coming to rest en masse, are not allowed to f i t together and remain very mobile under foot. The theory presented above attributes the observed pattern entirely to sorting, produced as the result of spontaneous mass movement, on the slope. To determine whether or not other controls such as shape of debris should be considered, a fabric analysis was made by sampling debris on CC52. Samples were taken on one fine and one coarse strip adjacent to one another on the slope. A systematic method was employed on each strip taking 25 samples at each of 10 sites located at 50 foot intervals along the st r i p . In this way a total of 250 samples over a distance of 450 feet was obtained on each strip. At each site, the samples were selected as randomly as possible by grabbing each with eyes closed. The a(long), b(intermediate) and 44 c(short) axes were measured and recorded for each rock. The analysis is included in Chapter IV. To detect net and differential movement to be used as a measure of the degree of activity on the talus slopes, a series of lines were painted. In particular any significant difference in behaviour on fine as compared to coarse strips of debris was sought. On December 3, 1966 two lines each 50 feet in length were painted on TC22, the largest talus cone observed in the region. Yellow paint i n pressurized tins was used. Similar lines 100 feet in length were painted on May 16, 1967 above and below fence #1 on TC25. In August, 1967 a line 750 feet in length was painted on CC52, the position of the line being established by telescopic alidade. The line transected a section of the series of coalesced cones on CC52 which exhibit a well developed pattern of fine and coarse strips. The observed disturbance of these lines and additional observations made on talus slopes in the region were used as a measure of the importance of other mass movement mechanisms including: talus creep, avalanche transport, water transport, and wind transport. The results of these observations are included in Chapter III. In order to paint a line on a talus slope one must necessarily disturb the surface. Any movement which subsequently occurs could be the direct result of the disturbance created. There seems to be no effective way of differentiating between movement attributable to natural mass movement mechanisms and that attributable to the disturbance created while painting the line. When walking over a talus surface, individual rocks become displaced downslope. Sometimes whole masses of debris slide to readjust to a lower angle. The net effect is to produce compaction of the debris immediately below the line being painted. Any movement 45 which occurs along the line may simply be an adjustment of the slope above in response to the disturbance below. Results, therefore, should be interpreted cautiously. E• Morphometry and Morphology of Talus i n the Similkameen Valley  Near Keremeos. 1. Morphometry. As a major hypothesis of this thesis i t is suggested that the talus slopes in the Similkameen Valley near Keremeos are entering the f i n a l stages of development and are tending towards st a b i l i t y . I n i t i a l observations of the talus forms investigated suggested that the talus slopes were entering a passive stage of development. It is assumed that a l l the talus forms in this region have developed since the retreat of the last Cordilleran Ice Sheet from the area since scour would have erased any talus previously developed. Therefore, the talus developed in this region probably has an age of about 10000 years (Fulton, 1971). Talus formation was probably rapid following the retreat of ice from the area. The headwalls, bared to the very floor of the valley would have presented a substantial weathering surface and in the cold humid post-glacial climate would have resulted in a rapid rate of ro c k f a l l . Since the i n i t i a l rapid growth, however, talus formation has probably undergone an ever decreasing rate of development. The main criterion used to substantiate this s t a b i l i t y hypothesis is the degree of vegetation cover. As noted in Chapter I.C . I . , vegetation can be a very useful and valid index. Very active slopes subject to frequent rockfall activity and mass movement do not, in general, have a vegetation cover. In this sense, the mobility of the surface serves as an impediment to the establishment and growth of plants. As rockfall 46 activity abates and, as the surface of the talus slope becomes more stable, vegetation is able to establish a foothold. The establishment of a vegetation cover does not, however, imply the cessation of activity. Indeed, the talus slope may continue to grow i f rockfall activity continues. What is implied, rather, is that activity is on the decline indicating an approach towards at least temporary i f not permanent sta b i l i t y . A l l talus slopes observed had some form of vegetation cover on them. For most, the cover was not complete being concentrated near the top and/or near the base of the slope. Some slopes observed had a complete cover indicating a high degree of s t a b i l i t y and essentially the completion of the talus phase (see Photo II-9). The establishment of some form of plant cover on a l l talus slopes observed is interpreted as an indication that the rate of talus development near Keremeos is decreasing. Further-more, this passive stage of development is not considered to be a temporary phase with rejuvenation to occur sometime in the future; rather, i t is interpreted as the approach of the f i n a l stages of talus development. To substantiate this claim, i t is necessary to consider the probable evolution which has occurred since the talus phase began. After the last retreat of ice from the area (10000* B.P.) the headwalls along the valley were probably bared to their maximum extent; probably to the floor of the valley. It can be assumed for the purposes of this theory that the profile of the valley was essentially U-shaped this being characteristic of a glaciated valley and, with certain modifications, the basic profile observable at the present time. I n i t i a l l y , therefore, the headwall i n cross-section probably appeared as illustrated in stage 1 of Figure I I - l . Rate of talus development would be rapid at this stage since a maximum surface along the headwall would be exposed to the effects of weathering and the post glacial climate 47 Photo I I - 9 . TC2 . Note the complete v e g e t a t i o n cover and the t r a i l c r o s s i n g the cone i n d i c a t i n g a h i g h degree of s t a b i l i t y . L i t t l e of the headwal l remains exposed most hav ing been covered by the t a lu s b u i l d i n g up aga ins t i t . R o c k f a l l a c t i v i t y w i l l cont inue but a t a subdued and ever decreas ing r a t e . T h i s t a l u s has entered i t s f i n a l s tage of development. 48 FIGURE H-l. TALUS DEVELOPMENT AT KEREMEOS A. STAGE MAXIMUM EXPOSURE OF HEADWALL R O C K H E A D W A L L MINIMUM SURFACE OF ACCUMULATION S I M I L K A M E E N R l V E R B. STAGE 2 R O C K H E A D W A L L - * \ EXPOSURE OF HEADWALL DECREASES SURFACE AREA OF TALUS INCREASES s ^ - T A L U S S I M I L K A M E E N R I V E R 49 would favour a rapid rate of weathering due mainly to frost shatter. Also, the area of accumulation on the talus i t s e l f would be small allowing for a rapid growth rate. As soon as a talus deposit begins to form, however, the rate of growth would decrease as illustrated in stage 2. It can be seen that the rate of development at this stage would be much reduced as compared to stage 1. A concept of 'diminishing sediment yield' can be applied. As the talus deposit grows in size i t covers more of the headwall from which i t derives i t s supply of debris. The rate of supply, therefore, decreases. Also, as the talus deposit increases in size so does i t s surface area. At any successive level of development the talus requires more debris for a specified increment of growth than i t did for the previous level. But, the rate of supply decreases at each successive level producing a net decelleration in the rate of growth. At some point the effectiveness of rockfall activity, now at a much reduced ratejbecomes much reduced having to cover a talus surface which has increased greatly i n area. At this point the talus would be entering its f i n a l stage of development and the establishment of vegetation on i t s surface would serve as an indication of approaching sta b i l i t y . The degree of stability noted in the region varies a great deal, however. Some of the slopes yet appear to be active. Certainly, rockfall activity continues along the headwall exposed. However, these talus slopes have grown to vast proportions and have covered the greater portion of the headwall that was originally exposed. For example, TC22, one of the larger cones, extends through approximately 1500 feet of rel i e f and measures some 2500 feet along i t s base and 3000 feet along i t s longitudinal profile. Talus slopes of this magnitude can reduce the 50 effects of even substantial rockfall activity. A measure of the degree of present activity on talus slopes in the region was obtained from two fences designed to capture rockfall debris constructed on TG25 and TC49 in the latter part of May, 1967. To test the hypothesis, one fence was constructed on a talus cone which was judged to be relatively active (see Photo 11-10) and the other on a cone considered to be more stable (see Photo 11-11). The main s t a b i l i t y criterion used was vegetation cover; a more dense growth considered indicative of greater s t a b i l i t y . TC25, considered to be the more active cone, was also the larger of the two. As can be seen in Photo 11-10, a well developed chute extending far back into the headwall complements this cone. Fence #1 was constructed at the entrance to the chute near the apex of the cone. So positioned the fence would capture that debris f a l l i n g from the headwall in the v i c i n i t y of the apex of the cone as well as that debris travelling through the chute en route to the talus slope. Galvanized chicken wire six feet wide with a two inch mesh was used to construct this fence which measured 188 feet in length (see Figures II-2 and II-3). Rockfall and transportation through the chute is most concentrated along i t s outer edges, the center remaining more stable as a result of the vegetation (trees, shrubs, grasses) which has become established there. Part of fence #1 is illustrated in Photo 11-12. Fence #2, constructed on TC49 is 185 feet long and of the same design as fence #1 (see Photo 11-13). TC49, however, was judged to be less active than TC25 and i n this respect served as a basis for comparative study. TG49 proved to be a transitional form of talus, however. 51 Photo 11-10. Site of Fence #1  on TC25. The fence was constructed just above the largest Douglas f i r tree at the apex of the cone where i t grades into the chute above i t . Note how the configuration of the chute tends to accentuate the major joint pattern in the rock comprising the headwall. Photo 11-11. Site of Fence #2 on TG49. The fence was constructed at the apex of the cone at the point where i t coincides with the headwall in the photograph. Note heavy growth of vegetation indicating greater degree of s t a b i l i t y . 52 FIGURE H-2. FENCE NO. I ACROSS CHUTE AT TC 25 i V FIGURE H-3. DETAIL OF FENCE 53 Photo 11-12. Fence #1 on TC25. Note the headwall in the background and more stable central portion of chute. 54 Observations of a channel near the apex of the cone indicated that f l u v i a l action was affecting development on the cone. An inspection of air photos confirmed this (see Photo 11-15). A substantial catchment basin has developed above TC49 which would serve to concentrate the flow of water onto the talus. The chute above TG49 was essentially void of debris indicating that water must flow through i t (see Photo 11-14 below). Photo 11-14. Detail of Chute  Above TC49 . Note how much of the loose debris has been removed from the chute by flu v i a l action. Modification and deposition due to f l u v i a l effects, however, are minor on TC49. Both fences were sampled on two separate occasions. On September 5 and 6, 1967 fences #1 and #2 respectively were sampled. Since the accumulation period ran from the end of May until the beginning of September a sample for the frost-free season was obtained. On Photo 11-15. Headwall, Associated Talus, and  Similkameen River at TC49. Note degree of vegetation cover on TC49 indicating a stable slope. Note also the well developed catchment basin above the cone resulting in the development of a f l u v i a l channel at the apex of TC49 (see arrow). 56 June 12 and 13, 1968 they were again sampled. The accumulation period from September to June provided a sample for the period of frost activity in the region. The results of this sampling program are included in Chapter III. An ash deposit observed on CC44 near the confluence of the Ashnola and Similkameen Rivers afforded a rough measure of the rate of past talus development in the area and was used to test the validity of the 'diminishing sediment yield concept' advanced in this thesis. On CC44 at a point where a cut for the Southern Trans-Canada Highway truncates a series of cones of this group a layer of volcanic ash preserved at depth on the largest cone (see Photo 11-16) has been identified (Ryder, 1970, p. 196) as that of the Mazanaeruption which occurred to the south of the region 6600 years B.P. (Powers & Wilcox, 1964, Westgate et a l . , 1970, Fulton, 1971). The ash deposit neatly divides the talus deposit (of which i t is a part) into that debris which was deposited in the interval 10000 - 6600 B.P. (3400 years) and that deposited since deposition of the ash (660CT years). The contact between the talus deposit and the river terrace on which i t has developed is clearly defined i n the road cut (see Photo 11-17). Therefore, a record of the evolution of at least one of the talus slopes i n the area is available. Employing a telescopic alidade and stadia rod the cone in question was surveyed to obtain a rough measure of the volume of debris built up prior to the deposition of the ash as compared to the volume built up since the ash deposit. The results of this analysis are included in the observations of Chapter III. It was hypothesized that a talus cone, especially one with a chute or funnel extending up from i t s apex,should have different slope Photo 11-16. Mazama Ash Deposit at CC44. Arrow shows contact between talus and terrace of the Similkameen River on which i t rests . Photo 11-17. Talus Resting on River  Deposit at CC44. Zone of contact between talus of CC44 and terrace of the Similkameen River, on which the talus rests, is clearly v i s i b l e . Note degree of compaction of talus debris which allows i t to support a near vertical slope in the road cut. 58 and debris distribution characteristics along the sides of the cone as compared to the middle. Any talus slope is a transportation surface over which debris is moving in a downslope direction. On a cone, however, movement is most concentrated and consistent along the central axis. To note any significant difference, therefore, a number of profiles were established employing the abney level and measuring tape method. (A simple technique was chosen that would allow for a simultaneous sampling of the debris size on a systematic basis. King (1966) notes that slopes measured by this method are accurate to 1/2°.) A l l profiles were obtained starting at or near the apex of each cone and then measuring slope segments at 100 foot intervals downslope (or shorter i f the irregularity of the terrain warranted i t ) . The slope angle for each segment was obtained by siting from station to station with an abney level while standing erect. Suitable natural targets above and below were chosen to keep the profile oriented in as straight a line as possible. On TC21 three profiles were established (one medial and two lateral) and debris size (a,b, and c axes) was sampled at ten foot intervals along each. On TC25 two profiles were taken; one down the center and the other down the right side of the cone. Debris size was sampled only along the central profile of this cone. Observations made suggested that no downslope sorting occurs on talus slopes in the region. Methods to validate this hypothesis were sought. The samples of debris taken in association with the establishment of the profiles discussed above served as one method to test for downslope sorting. Another used was the establishment of a series of traverse grab samples on a number of cones. In a l l , four talus cones were sampled employing a systematic method. A number of cross-slope walks 59 were made on each cone taking samples at ten step intervals. On each of TG48 and TG67 a total of four traverses were made; on TC3 and TC26 a total of six and seven traverses respectively were made. The traverses were evenly spaced on each cone to include one traverse at or near the apex, one at or near the base, and two or more in between. Samples were taken at each ten step interval by reaching behind and selecting the f i r s t rock touched. The lengths of the a, b, and c axes for each rock were measured and recorded. The data collected are analyzed in Chapter IV. To serve as a basis for detailed slope analysis, debris sampling, and talus morphometry, a talus cone of intermediate size was mapped at a large scale. A cone (TC26 on Map 2) with a south-facing aspect was chosen since the south-facing slope of the valley exhibits a greater degree of talus development. Also, the amount of vegetation cover on the cone suggested that i t was intermediate between very stable and active cones, both of which are found in the valley. TC26 has a rockfall chute (see Chapter I.B.4.) leading up from i t s apex which is characteristic of most cones in the area. Finally, a cone rather than some other talus form was chosen since the cone form is most prevalent in this valley. A cone of intermediate size was chosen to f a c i l i t a t e mapping. (Much larger cones are present in the area but the task of mapping TC26 alone took the writer and a rod man two weeks to complete.) The cone mapped is 1800 feet long, 1200 feet wide (at the base) and extends through 1000 feet of r e l i e f . Mapping was accomplished during the summer of 1967 (June 27-30; July 4,5; August 22-25; August 30 - September 3) by plane table survey employing a telescopic alidade. A large scale map (1 inch to 100 feet) with a 5 foot contour interval (^  1 foot assumed accuracy level) was obtained (see Map 4A, p. 118). A baseline (see I,II,III,IV on Map 4A) 60 was established along the level talus apron by measurement with a steel tape (accurately as possible by using a spring balance to give readings under constant tension, and measurement in a short time interval so that temperature flux effects would be minimal) and levelling with the telescopic alidade and plane table. The four stations along the baseline were flagged with permanent wooden markers and were used as reference points to establish subsequent triangulation stations in order to complete the survey. Station II was chosen as the datum and assigned an arbitrary elevation of 100 feet. Thirty-one triangulation stations, to serve as a grid reference to establish a network of points of elevation from which contours could be drawn, were chosen. Elevation was calculated for each from the stadia intercept and angle reading on the rod. The plane table was then set up at each baseline station and triangulation station in turn. Correct orientation was maintained by siting back to at least three other reference points. The number and location of triangulation stations were strategically chosen so that no one alidade shot determining the elevation and location of a point would be at a distance greater than 150 feet or at an angle exceeding 25°. The positions of the f i r s t eleven triangulation stations were established by reference to at least three other reference points, at least two of which were baseline reference points, giving the lower third of the map the most accurate readings. As the survey proceeded upslope, i t became increasingly d i f f i c u l t and eventually impossible to refer back to the baseline reference points in order to f i x triangulation stations. By careful reference back to at least three adjacent triangulation stations subsequent triangulation stations were established with what was thought to be a fair degree of accuracy. In light of this fact, however, accuracy probably decreases 61 upslope on the map. The confinement of the rock walls in the chute above the apex of the cone obscured most of the downslope reference points resulting in probably the lowest degree of accuracy for this section of the map. Wooden lathe targets flagged with cardboard faced with a fluorescent orange emulsion served very well as markers for each of the triangulation and baseline stations. At each of the four baseline stations and thirty-one triangulation stations, a minimum of four and a maximum of 52 points of elevation were established by rod readings employing the telescopic alidade. Three hundred fifty-four such points were established. Elevation and position of a total of 389 points, then, were determined and served as the basis for the map. The f i e l d sketch was permanently fixed to an 18" x 24" plane table mounted on a removable tripod and was conveniently drawn on a sheet of frosted acetate. The survey was initiated at baseline point II. Rays were drawn from II to I, III, and IV and the proportionate map distance was scaled off thereby fixing the points on the map. Elevations of points I, III and IV were then determined by levelling in reference to station II arb i t r a r i l y established as the 100 foot datum. The most frustrating and time consuming part of the survey was to keep the plane table level and correctly oriented at each station. This was especially d i f f i c u l t on the higher slopes of the cone where the angle exceeded 37° and the debris was very mobile. At each reference station a network of points was established at a density required to draw five foot contours with relative ease. The correct planimetric distance and elevation of each point were calculated from the alidade readings on the rod. The correct position was then established for each point on the map by scaling off the proportionate distance with a pair of dividers along a ray established by the alidade siting on the rod. 62 Each rod station was selected to f a c i l i t a t e maximum expression of the terrain. The contours were drawn in the f i e l d as the survey proceeded and as much of the s u r f i c i a l detail as possible was noted some of which is contained in the overlay to Map 4A in Chapter III. No insurmountable obstacles were encountered, but the survey was not without problems, including the steep and unstable surface, the presence of trees and the gustiness of the wind. On Map 4A only the contours which express the debris covered slope of the talus cone and associated chute were established by this survey. Those contours expressing the detail of the rock headwall, except for the rock spur (noted on the overlay), were extrapolated from air photos and serve to il l u s t r a t e the basic form only of the rock headwall in the immediate vic i n i t y of the talus cone, and should not be taken as correct. A detailed sample of the debris on TC26 was taken in conjunction with the survey. One rock at each rod station was grabbed with eyes closed and its intermediate (b) axis was measured. An interpretation of the data collected is included in Chapter IV. In passing, i t can be noted that very large rocks (> 3 f t . dia.) were observed only rarely on the talus slopes in the region. As already noted these larger rocks generally travel to the bottom of the slope where they accumulate to form a boulder apron. The few large ones observed at rest higher up on the talus slope were usually very f l a t or elongate in shape (see Photo 11-18) which accounted for their unusual position on the slope. 2. Morphology. The phenomenon labelled "nivation ridge" (Behre, 1933) "protalus rampart" (Bryan, 1934) and "protalus boulder accumulation" (Stock, 1968) 63 Photo 11-18. TC48. Note very large boulder at rest on talus slope in association with characteristically smaller sized fragments. This boulder has a long axis of 10 feet, its very f l a t shape accounting for its unusual position on the slope. 64 was observed on one talus slope in the region. On TC67 near the base of the cone a transitional zone of crescent-shaped ridges can be observed leading out onto the boulder apron (see Photos 11-19 and 11-20) . This phenomenon does not exist on any of the other talus slopes in the region and a reasonable explanation for its occurrence cannot be given. If i t has developed according to the hypothesis advanced by Behre, 1933 (see Chapter I.C.2.) i t must then be a r e l i c t form because of the following: 1. At no time during the investigation (1966 - 1972) was a substantial snowpack observed on TC67 (or any other slope) . 2. Climate data since 1930 indicate that snowfall is characteristically light in this region. It is feasible that these ridges could have developed according to Behre's theory but only in a climate regime characterized by heavier snowfall. As mentioned, this phenomenon occurs only on TC67. Because of i t s northern exposure and the existence of a substantial ridge to the east of the cone, TC67 remains sheltered a great deal of the time from the sun. On September 21, 1967 i t was observed that TC67 remained entirely in shadow until 1:00 p.m. that day. A similar situation would exist during the spring months which could allow any substantial snow pack accumulated during the winter to persist late into the spring. It was observed that parts of some of the ridges have become buried as the result of more recent talus development which suggests that they might be a r e l i c t accumulation. Boulder aprons have developed at the base of almost a l l talus slopes in the region (see Photo 11-21) . These aprons are the accumulation of those rocks which by virtue of their large size are able to move uninterrupted a l l the way to the bottom of the deposit.. I n i t i a l l y most of these boulders would probably travel a f a i r distance beyond the talus 65 Photo 11-19. TC67• The arrow shows the location of protalus ridges near base of TC67. Note also the river terrace near the base of the talus cone and well developed alluvial fan on the opposite side of the Similkameen River. Photo 11-20. TC67. Arrow shows the location of one of the protalus ridges on TC67 . Note that the ridge occurs at the base where the character-i s t i c a l l y sharp break in slope occurs . Note also the large size of debris comprising the ridge. Photo 11-21. Detail of Boulder Apron at the  Base of TC25. Note the sharp break in slope where apron begins . The excavation in the foreground illustrates that the boulders extend at depth beneath the talus proper. Photo 11-22. Boulder Apron on TC42. Note the very sharp boundary between the boulder apron and the talus proper. Hard hat l e f t of center gives scale. 67 deposit i t s e l f depending on the slope of the substratum. As the deposit grows, however, the rocks themselves serve as impediments to other rocks r o l l i n g to the base and a fringe deposit of these boulders would accumulate at the base. In a l l cases, the boundary between the talus slope proper (composed of much smaller debris) and the boulder apron is very sharp (eg. see Photo 11-22); an abrupt change of slope can be noted as well. (Usually about 10°, i.e., at point of contact the talus would have a slope ranging from 30°-35°; the boulder apron correspondingly 20°-25°). The sharp break in slope indicates that the boulder apron must be controlled by mechanisms exclusive of those developing the slope above i t since the difference in angle cannot be attributed to the difference in size of debris (see Chapter I.B.2). The materials comprising the talus slope by virtue of the greater depth of the deposit are more controlled by their internal f r i c t i o n and have a characteristically high angle at or near the angle of repose of the material. The apron, however, is a shallow deposit of boulders tending to be controlled by the slope of the substratum which is characteristically low in angle. (Most talus slopes in the area are built out onto a river terrace which bounds the valley on both sides. See Map 2.) There are not enough boulders available to build the deposit deep enough to allow i t to develop a slope controlled by the internal f r i c t i o n of the rocks. The apron would be sustained as a leading edge of the talus extending farther out onto the surface as the talus deposit grows. It would be buried at i t s point of contact with the talus proper at the same rate as i t would be extending i t s e l f out onto the surface. Figure II-4 illustrates in cross-section this mode of development. Observations (see Photo 11-21) of a number of talus cones (TC5, TC21, TC22, TC25) which have been excavated at the FIGURE IE-4. DETAIL OF BOULDER APRON DEVELOPMENT 69 base to obtain riprap tend to confirm this mode of development. The layer of boulders comprising the apron extends beneath the talus deposit uninterrupted as far back as the excavations have been made It was noted that vegetation tended to be concentrated in two places on the talus slopes in the region: near the top of the slope and along the base in association with the boulder apron. A l l talus slopes have some form of vegetation cover extending usually from about 3/4 of the way up to the top of the slope (see Photo II-4). The cover varies from a f a i r l y dense growth of Douglas f i r (dominant) and ponderosa pine to a low mat of grass, weeds and sage. The following hypotheses are advanced as an explanation for this distribution: a) There is more moisture available for plant growth near the summit of the talus slope due to the concentration of runoff from precipitation and melt along the headwall. The effect would be greatest at the apex of talus cones where concentration through the c l e f t or chute in the headwall above occurs. Downslope, the effect is lost as the moisture percolates quickly through the permeable talus deposit. Also, any precipitation that does f a l l on the lower slopes of the talus i n f i l t r a t e s quickly and completely creating a dearth of vegetation. b) If the debris size near the top of the talus slope is smaller (yet to be tested in this thesis) then i t would be better able to support the growth of vegetation since s o i l formation i s accelerated and plant growth is more possible in finer textured deposits. c) Movement of debris on an individual basis near the top of the deposit as compared to movement en masse on the lower slopes would create less disturbance to vegetation attempting to establish i t s e l f on the slope. Therefore, conditions favour growth near the top of the slope. d) Potential damage to vegetation by debris r o l l i n g over the talus surface probably increases downslope as the debris gains momentum on i t s trip down. On a number of occasions rocks were purposely set loose in the v i c i n i t y of the apex of a number of talus cones. In a l l cases, the rocks set loose either came to rest after a short r o l l or continued r o l l i n g 70 with acceleration until reaching the boulder apron at the base. As the boulders accelerated downslope their apparent potential for damage to vegetation increased. Obviously, this effect would pertain to only large debris capable of sustaining mobility to the bottom of the slope and i t should be noted that a l l rocks set loose were the largest ones available. Small rocks are incapable of sustained r o l l over the rough surface of the talus. It is suggested that a l l four hypotheses exert influence. The effect discussed in hypothesis (a), however, is considered to be very important and in the f i n a l analysis probably of greatest influence. To further substantiate hypothesis (c), i t was noted at a point about 1/2 way up the slope on TC21 where a solitary sage bush, which had been able to establish i t s e l f along the upslope edge of a f l a t boulder, had been destroyed when overrun by mass movement of relatively fine debris. Additional evidence was observed on TC3. Vegetation strips consisting of saskatoon bushes and juniper trees extending quite far downslope on that cone were observed to coincide with the strips of coarse debris on the slope. The unvegetated surface between the strips of vegetation consisted of small sized fragments 3" d.). It is suggested that movement along the strips of coarse rock would be on more of an individual basis. The saskatoon bushes and juniper trees are gnarled and contorted, indicating some damage, but the plants are able to sustain growth. The strips of fine debris, however, remain unvegetated since movement probably occurs en masse in the form of miniature landslides. On a l l boulder aprons a concentration of Douglas f i r and ponderosa pine trees can be noted (see Photo 11-23). This dense growth does not extend out beyond the boulder apron ending rather abruptly at i t s edges. 71 Photo 11-23. TC27 and TC28. Note concentration of Douglas f i r trees in association with the boulder aprons of these cones . This concentration is best explained in terms of the following: a) Water which has i n f i l t r a t e d the talus deposit may seep out along the base of the talus in the proximity of i t s boulder apron. This additional supply of water may be the require-ment necessary to sustain a dense vegetation cover in the semi-arid environment. b) Rather than having the meagre r a i n f a l l distributed evenly over the surface, the boulders of the apron by channelling the runoff may tend to concentrate i t effectively thereby creating a network of favourable sites for tree growth between the rocks. This concept is illustrated in Photo 11-24. It is suggested that the effects outlined i n (a) and (b) above account for the distribution noted. An analysis of vegetation type on talus slopes in the area was made. The vegetation is of the dry parkland variety, i.e., short grass with scattered Douglas f i r and ponderosa pine trees. The occurrence of Douglas f i r as the dominant tree species is a reflection of i t s pioneer property of shade intolerance. On the talus slopes themselves, a total of what appeared to be 41 varieties of vegetation were observed including: 5 grasses, 27 weeds, 6 shrubs and 3 trees. Next to Douglas f i r (Pseudosuga menziesii), ponderosa pine (Pinus ponderosa) was the most common tree species. Some juniper trees (Juniperus scopulorum) were observed as well. The most common shrubs were: saskatoon (Amelanchier sp.), sage (Artemisia tridentata) and sumac (Rhus glabra). In general, the south side of the valley exhibits a more dense vegetation cover but the difference is not too significant. Talus slopes, however, on the south side of the valley exhibit a distinctly denser growth especially i n the form of Douglas f i r trees. This difference is attributed to aspect; a southern exposure being drier produces a more sparse vegetation cover. "Photo 11-24. Closeup of Boulder iiApron on TC28. Note ponderosa pine tree growing between large rocks comprising the apron. 73 CHAPTER III - OBSERVATIONS A. Geologic Control. A number of controls exerted by the basic geology of the rocks on rate of rock weathering and associated talus development are discussed in Chapter II. Two basic rock formations predominate, i.e., the Shoemaker Formation and the Old Tom Formation (Bostock, 1939). Variations between the two were noted but i t was found that these variations produced no discernible difference in the basic form or degree of development of the talus observed. There is some variation in the distribution of development, however (see Map 2). In general, the south-facing slopes exhibit a greater degree of talus development than the north-facing slopes . The difference could be the result of a climate difference between north-facing as compared to south-facing slopes. Also, the headwall along the north-facing slopes is less continuous, being dissected frequently by streams tributary to the Similkameen River. At many points the bedrock remains covered under a layer of glacial t i l l . These factors in conjunction with a more dense growth of vegetation have tended to inhibit talus development on the north-facing slopes. Two exceptions are worth mentioning. Some of the largest and most active slopes are included in the series of eleven talus cones which have developed along the north-facing slopes of K Mountain. The dissection of the headwall has produced the development of two large talus cones with chutes which have merged to form a distinct "K" shape which gives this peak i t s name. The rocks of the Old Tom Formation exposed here exhibit a set of well-developed joints having a dip of 85° and a strike perpendicular to the exposed face. 74 Water is able to penetrate these joints, resulting in rapid disintegration and substantial talus buildup. Another zone of concentrated talus development along the north-facing slope occurs just downstream from the mouth of the Ashnola River. Here, a series of six impressive talus cones (TG65 - 70) has developed along the rocks of the Shoemaker Formation exposed at this point. The south-facing slope of the valley exhibits a relatively continuous succession of talus forms. The only significant break in the succession occurs where Shuttle, Keremeos, and Armstrong Creeks converge to broaden the valley immediately to the north of the Keremeos townsite. A succession of talus cones on the south-facing slope from Manuel Creek to Armstrong Creek occurs as an isolated group along the rocks of the Old Tom Formation and the a r g i l l i t e of the Barslow Formation. Talus development is again encountered on the slopes of Pincushion Mountain located to the northwest of the Keremeos townsite. Here, the most substantial and most impressive development in the area can be observed. The development on TC21 (see Photo 111-15) and TC22 is spectacular. In a l l , nine large and several small talus cones form this group which have developed from the weak rocks of the Shoemaker Formation exposed here. Further examples are TC48 (see Photo 111-21) where a huge funnel has developed in association with this cone and the large coalesced cone groups at CC51 and CC52. An anomaly can be observed at CC38 near Old Tom Creek. At this point, the headwall remains essentially intact exhibiting only a very limited development of talus at its base. An inspection of Map 3 shows that the joint planes in the rock exposed here are parallel to the trend of the valley. So aligned, they present an aspect unfavourable 75 for weathering and the rocks remain l i t t l e affected by weathering processes. No dissection has occurred along the headwall. The debris comprising the small amount of talus which has developed is generally large in size, an indication that dislodgement occurs in large plates parallel to the exposed face. The observation confirms the hypothesis that the aspect of the joints in the bedrock exposed along the valley exerts a significant influence on the degree of talus development since the remainder of the south-facing slope exhibits impressive talus development. B. Weathering Mechanisms. It was hypothesized that a variety of weathering processes is active in the region, resulting in the advanced state of disintegration observable on most headwalls (see Photo I I I - l ) . As discussed in Chapter II i t is thought that both physical and chemical processes have Photo I I I - l . Weathered Rock Headwall at TC21. produced a rapid destruction of the headwalls forming the bold and abundant talus forms observable. A number of observations substantiate the effectiveness of these processes. 76 Frost shatter and frost bursting are considered to be the dominant weathering processes in the region. Climate data were examined to determine the frequency and magnitude of frost cycles. The data recorded on the maximum-minimum thermometer installed inside the headwall at TC25 are found in Table II. To serve as a check, a standard thermometer was placed outside the headwall and it s record is included i n the table as well. Some difference between the temperature recorded at the times of observation between the maximum-minimum thermometer and the standard thermometer was noted. This was expected since one was placed inside a crevise on the headwall and the other outside. I n i t i a l l y , however, i t was found that some difference existed between the standard thermometer and the maximum-minimum thermometer readings under identical conditions. The reading for the standard thermometer was assumed correct and the maximum-minimum records were adjusted as noted in Table II. Coincidentally, a most opportune week was chosen to make the observation since frost cycles occurred on six of the seven days of record; two of these (November 26 and 30) exceeded the effective range of 28°F and 34°F as defined by Fraser (1959). The observations serve to i l l u s t r a t e that frost cycles do in fact occur along the headwall. On the day of the November 25th inspection i t was noted that ice had formed along the rock face the night before; this ice was already in the process of melting at eleven o'clock that morning indicating that freezing and thawing were occurring in association with the frost cycles. The readings obtained from this record correlate very well with the record for the same interval at the meteorological station (A.E.S., Canada) on the Upper Bench Road at Keremeos. The comparison is Table II. TEMPERATURE READING ON ROCK HEADWALL BELOW FENCE #1 ON TG25 • NOVEMBER 24 - DECEMBER 1, 1967 . Date 1967 Time Air Temp. °F. Stan. Thermometer Maximum* Minimum** Max.* °F. in Previous 24 Hours Min.** °F. in Previous 24 Hours 1. Nov.24 11:30 am 42.5 42.0 41.5 -- --2. Nov.25 11:30 am 33.0 34.5 34.5 42.0 31.4 3. Nov.26 4:00 pm 26.5 28.0 28.5 37.o*** 21.5*** 4. Nov. 27 4:30 pm 29 .0 31.0 29.5 32.0 25.0 5. Nov.28 4:30 pm 29.5 29.0 29.5 33.0 28.0 6. Nov.29 4:30 pm 33.5 33.0 33.0 34.0 29.0 7 . Nov. 30 4:20 pm 32.0 33.5 32.5 35.5 26.5 8. Dec. 1 4:10 pm 32.0 32.5 31.5 35.5 28.5 * A l l maximum readings i adjusted -1 ,5°F. obtained as the mean discrepancy with standard thermometer. ** A l l minimum readings adjusted -. 5°F. obtained as mean discrepancy with standard thermometer. *** Maximum and minimum over a 28.5 hour period. 78 illustrated in Figure I I I - l . In general, the readings at Keremeos tend to exhibit a greater range. The difference is not great, however, being in the order of magnitude that could be attributed to the difference in temperature that would be expected within the shelter of the rock at TC25 as compared to the open air temperature recorded at Keremeos. Although the sample for purposes of comparison is small i t does indicate that temperatures recorded at Upper Bench Road station in Keremeos are representative of those experienced along the headwall in the immediate vici n i t y of Keremeos. (TC25 is located approximately four miles upstream from the Upper Bench Road station) . The frequency of frost cycles (see Chapter I.B.I.) was t a l l i e d to obtain the monthly totals for the years 1930 through 1971 and the results appear in Table III. Each monthly total was subdivided into categories as follows: 1. FC = a frost cycle in the range 29°-33°F. inclusive. 2. FD = a frost cycle in the range outside the limits established in (1) above but within the range 26°-34°F. inclusive in accordance with the effective range of 28°-34°F. as defined by Fraser (1959). 3. BD = a frost cycle of the magnitude 25°-35°F. inclusive or greater as defined by Boyd (see Fraser 1959) as the effective range. What is implied by both Fraser and Boyd i s that the outside air temperature w i l l have to drop significantly below 32°F . before water trapped inside rocks w i l l freeze and, correspondingly, w i l l have to rise significantly above 32°F. in order to melt any ice which has formed. In essence, they define the limits required to i n i t i a t e ice wedging resulting in eventual shatter in rocks affected. However, much depends on the duration of the cycle. For short cycles even greater ranges would be required. FIGURE HE" I. TEMPERATURE CORRELATION BETWEEN STATION AT TC 25 AND A.E.S. STATION AT KEREMEOS Table III. FROST CYCLES AT KEREMEOS. Year October November December January Februar y March April Tot. Tot. Tot. Tot. f o r 19 FC FD BD FC FD BD FC FD BD FC FD BD FC FD BD FC FD BD FC FD BD FC FD BD Season 30-31 9 3 2 8 4 10 5 1 3 3 1 0 25 9 15 49 31-32 1 0 0 6 2 4 6 7 2 2 10 1 1 1 7 3 3 7 0 0 0 19 23 21 63 32-33 4 0 0 7 1 1 5 3 4 7 4 4 3 6 2 6 2 5 2 0 0 34 16 16 76 33-34 1 1 0 5 2 1 8 2 4 7 5 2 1 10 8 4 1 0 0 0 0 26 21 15 62 34-35 2 0 0 9 0 0 5 7 2 7 1 1 8 4 7 7 3 9 3 1 3 41 16 22 79 35-36 7 2 0 6 4 7 7 2 1 7 8 4 0 1 2 6 8 3 2 1 2 35 26 19 80 36-37 2 0 0 4 6 12 6 3 7 0 0 0 1 1 10 5 0 2 2 0 0 20 10 31 61 37-38 0 0 0 5 3 2 5 2 2 6 3 5 6 5 3 10 4 2 1 1 0 33 18 14 65 38-39 1 0 0 2 8 4 4 2 3 9 12 3 5 4 9 7 7 2 2 0 0 30 33 21 84 39-40 3 0 1 8 0 3 6 2 1 5 2 4 12 1 3 1 3 1 0 0 0 32 8 13 53 40-41 1 0 0 7 3 3 3 2 2 5 3 1 0 3 10 3 2 1 0 0 0 19 13 17 49 41-42 3 0 0 4 1 3 7 5 2 6 1 0 9 3 6 9 6 2 0 0 0 38 16 13 67 42-43 4 0 0 5 6 2 5 5 2 1 0 1 5 7 3 3 3 12 1 0 0 24 21 20 65 43-44 3 2 0 7 3 2 5 3 4 4 4 3 4 3 13 11 1 9 0 0 0 34 16 31 81 44-45 0 0 0 4 4 4 6 2 2 6 6 2 8 5 3 9 3 3 6 1 0 39 21 14 74 45-46 2 3 0 7 5 4 2 1 2 7 6 5 6 1 8 5 2 1 2 0 0 31 18 20 69 46-47 4 6 0 6 3 9 3 3 1 4 2 4 7 2 4 4 0 5 1 0 0 29 16 23 68 47-48 1 0 0 10 6 2 8 6 5 9 2 9 5 3 4 7 6 6 4 2 1 44 25 27 96 48-49 5 4 0 13 0 3 2 3 4 0 0 3 2 0 7 11 1 4 0 0 0 33 8 21 62 49-50 6 0 1 5 2 0 7 8 5 0 0 2 3 2 5 5 5 2 2 2 0 28 19 19 66 50-51 4 0 0 6 4 7 7 2 2 9 4 4 3 6 12 3 2 4 1 1 1 34 19 30 83 51-52 0 2 3 5 4 7 3 3 1 5 1 2 7 8 4 9 7 4 0 0 0 29 25 21 75 52-53 0 0 0 4 4 5 4 5 5 5 3 5 7 8 4 5 3 1 1 1 0 26 24 20 70 53-54 0 0 0 4 2 2 14 5 3 4 2 1 5 0 3 4 3 10 5 3 1 36 15 20 71 54-55 3 2 1 5 1 0 4 10 4 5 5 4 6 6 9 6 3 11 12 1 0 41 28 29 98 55-56 3 1 0 2 4 2 1 0 5 7 3 4 1 2 10 7 5 4 1 1 0 22 16 25 63 56-57 0 0 0 6 3 6 10 3 1 3 1 1 2 1 9 6 4 3 0 0 0 27 12 20 59 57-58 2 0 0 6 9 2 9 8 1 8 3 1 6 1 1 5 4 4 0 0 0 36 25 9 70 58-59 2 0 0 2 5 1 7 5 1 0 5 3 4 8 7 4 3 0 2 2 0 21 28 12 61 (over) Table I I I . (continued) Year October November December January February March April Tot. Tot;. Tot. Tot.for 19 FC FD BD FC FD BD FC FD BD FC FD BD FC FD BD FC FD BD FC FD BD FC FD BD Season 59-60 1 0 0 2 6 4 5 8 5 5 1 0 7 5 4 4 3 4 1 0 0 25 23 17 65 60-61 1 0 0 10 5 5 5 3 3 3 4 5 4 4 2 5 1 4 2 0 0 30 17 19 66 61-62 3 1 1 4 7 6 3 5 4 1 4 3 4 3 1 4 4 4 1 0 0 20 24 19 63 62-63 1 0 0 3 2 3 0 4 4 5 3 2 7 5 5 9 2 0 1 0 0 26 16 14 56 63-64 2 4 0 4 5 2 5 8 2 4 6 6 5 10 9 5 4 2 2 0 0 27 37 21 85 64-65 2 1 0 4 4 2 4 1 1 4 1 2 10 12 1 6 4 11 1 0 0 31 23 17 71 65-66 2 0 0 3 3 1 7 1 1 3 1 4 11 6 3 7 1 3 2 0 0 35 12 12 59 66-67 0 0 0 5 5 1 5 5 4 5 4 6 9 2 1 9 6 2 2 0 . 0 35 22 14 71 67-68 0 0 0 5 4 2 5 4 3 6 1 4 6 3 10 4 1 0 2 0 1 28 13 20 61 68-69 0 0 0 7 0 4 6 1 6 2 1 1 4 8 7 7 2 5 0 0 0 26 12 23 61 69-70 3 1 0 4 3 1 9 2 0 5 1 2 8 8 2 1 4 4 1 0 0 31 19 9 59 70-71 3 4 0 4 2 2 6 3 6 4 4 2 7 4 3 3 8 4 3 1 0 30 26 17 73 Total 82 34 7 225 141 151 221 144 118 194 131 119 217 175 231 234 135 163 71 19 9 1230 791 780 2801 Mean 2.05 .65 .18 5.62 3.52 3.78 5.52 3.60 2.95 4.85 3.28 2.98 5.42 4.38 5.78 5.85 3.38 4.08 1.78 .48 .22 Mean Total 3.08 12.92 12.07 11.11 15.58 13.31 2.48 30.75 19.78 19.50 70.03 82 Cycles extending over days or weeks may require a fluctuation of only one or two degrees above and below 32°F. in order to be effective. Much, too, depends on the depth of penetration of the water. A much greater range of longer duration would be required to freeze and thaw water locked deep inside the rock. Water near the surface would be affected by cycles of a much smaller range and shorter duration. Ultimately, a l l frost cycles are important since "frost-riving" occurs when water on the surface of an exposed rock surface freezes and thaws producing dislodgement of previously loosened fragments resulting in rockfall activity. A fluctuation in temperature one degree above and below 32°F. is usually sufficient for this mechanism to operate. During the forty year record at Keremeos, a total of 2801 frost cycles has occured for an average of 70.0 cycles per year. Of these, a total of 1571 or an average of 39.3 cycles per year were greater than or equal to the effective range of 28°-34°F. as defined by Fraser. A total of 780 or an average of 19.5 cycles per year equalled or exceeded the effective range of 25°-35°F . as established by Boyd. The results support the assumption that frost shatter is an important mechanism of disintegra-tion of the rocks exposed in the region. Figure III-2 illustrates that the cycles occur with high frequency throughout the late f a l l , winter, and early spring seasons. As previously noted, precipitation is available in a l l months of the frost season. Disintegration by frost shatter could be sustained throughout the frost season but concentrated activity may occur during the late winter and early spring intervals. February and March are the months of highest frequency of freeze-thaw cycles. During these months more water from snow melt is available which would render freeze-thaw cycles at this time particularly effective. Concentrated 83 FIGURE 3K-2. MEAN MONTHLY FREQUENCY OF FROST CYCLES AT KEREMEOS F R O S T S E A S O N 84 rockfall activity during the spring season, according to the observations of local residents of Keremeos, tends to confirm this assumption. Frost bursting is probably an important mechanism as well. Freeze-thaw cycles are not required to i n i t i a t e this mechanism; rather, low freezing temperatures of a long duration (eg. several days or weeks) are required to freeze the water confined in porous rock. A study of the records for Keremeos indicate that temperatures do drop to very low levels (on occasion below 0°F.) and at times for intervals of a week and longer. At these times rocks which are saturated with water would be very susceptible to frost bursting. Observations suggest that chemical action i s an important weather-ing mechanism in the region. At many points along the unevenly dissected headwall and especially i n the clefts where chutes have formed the rock is found to be i n an advanced state of decomposition. The rock appears to be essentially 'rotten' and pieces could be broken off easily with the hands. Reddish-brown stain is readily visible along the planes of separation indicating oxidation. The crumbly texture is indicative of a volume increase which can be attributed to the process of hydration. This is most prevalent in the clefts where water from precipitation and melt would be most concentrated to react chemically with the rock in association with the oxygen and carbon dioxide of the a i r . The effects of solution are considered important as well. Some evidence for this is illustrated in Photo III-2. A zone of mineral precipitation where a spring emerges on the headwall at TC25 was observed. It was concluded that the mineral here precipitated is derived by solution along the joints in the headwall above. Of a l l the rock types exposed in the valley, limestone would probably be most susceptible 85 Photo III-2. Observed Solution on  Headwall at TC25. The photo shows the course of a small stream which emerges as an intermittent spring further up along the headwall. The dark coloured band is a zone of precipitation of mineral probably derived by solution from the headwall above. No water was flowing at the time of photography. Pack sack gives scale. to this process. Various degrees of chemical weathering (Melton 1965; Oilier 1965) have been defined. Ollier's progression is given in Table IV below. Table IV. DEGREES OF WEATHERING. (after O i l i e r , 1965) Degree No, 1 2 3 Description Fresh; hammer tends to bounce off. Easily broken with hammer. Rock can be broken by a kick with the boots but not by hand. Can be broken in hands but does not disintegrate in water. Soft clay with grit ; disintegrates i f immersed in water. Examples of rocks considered to be representative of Ollier's degrees 1, 2 and 4 are illustrated in Photos III-3, III-4 and III-5 (a and b) 87 r e s p e c t i v e l y . No r o c k s h a v i n g O l l i e r ' s d e g r e e 5 w e r e o b s e r v e d o n t h e t a l u s s l o p e s o r h e a d w a l l s i n v e s t i g a t e d . F i n a l l y , t h e g r o w t h o f t r e e s a l o n g t h e h e a d w a l l s may p r o d u c e s o m e d i s i n t e g r a t i o n t h r o u g h t h e a c t i o n o f r o o t w e d g i n g . P h o t o III-6 i l l u s t r a t e s t h e e s t a b l i s h m e n t o f s t u n t e d D o u g l a s f i r t r e e s o n o n e o f t h e P h o t o III-6. P o s s i b l e R o o t  W e d g i n g M e c h a n i s m . M o s t r o c k f a c e s i n t h e a r e a h a d s o m e t r e e s ( u s u a l l y D o u g l a s f i r ) g r o w i n g o n t h e m . T h e w e d g i n g a c t i o n o f t h e r o o t s o f t h e s e t r e e s m i g h t p r o d u c e s o m e p h y s i c a l w e a t h e r i n g . h e a d w a l l s i n t h e r e g i o n . W h e t h e r o r n o t t h e g r o w t h o f r o o t s c a n e x e r t a f o r c e s u f f i c i e n t t o d i s i n t e g r a t e r o c k s a s y e t h a s n o t b e e n d e m o n s t r a t e d . H o w e v e r , t h e f o r c e i s c e r t a i n l y g r e a t e n o u g h t o d i s l o d g e r o c k s a l r e a d y d i s i n t e g r a t e d , a n d , i n a s s o c i a t i o n w i t h t h e p r y i n g a c t i o n p r o d u c e d a s t r e e s s w a y i n t h e w i n d , m u s t b e c o n s i d e r e d a s a n i m p o r t a n t r o c k f a l l i n i t i a t i n g m e c h a n i s m . G. Rockfall and Primary Deposition. Personal observations and accounts by local residents substantiate the occurrence of rockfall activity in the region. Local residents report activity frequently. The slope at TC14 and TC15 on K Mountain immediately to the south of the Keremeos townsite is referred to most often as the site of these observations. Substantial f a l l s reaching almost to river level have been observed. Residents agree that rockfall activity is concentrated during the spring season. In the spring of 1966 a section of the wooden pipeline at the base of TC25 was torn out by debris travelling down this slope. A number of observations of rockfall events were made: 1. May 27, 1967. A rock about 5 inches in diameter f e l l from the l e f t headwall during inspection of fence #1 on TC25. 2. May 30, 1967. While working on fence #1 at TC25 much debris was seen and heard f a l l i n g from the headwalls. Rain was f a l l i n g at the time. 3. May 31, 1967. Rain which started the previous day continued f a l l i n g throughout this day of observation. Much debris was observed f a l l i n g from the right headwall while working on fence #2 at TC49. 4. June 15, 1967. Rocks could be heard tumbling down headwall while climbing up TC49 to inspect fence #2. Rain was recorded the day before. 5. Recently damaged Douglas f i r trees attributed to rockfall activity were observed on TG25 (June 1968) and TC67 (September 1967), eg. see Photo III-7. 6. July 26, 1971. A large ponderosa pine tree located about 50 feet from the headwall about one-half way up TC26 was observed to have been damaged by recent rockfall activity. Five large branches had been broken from the tree. In retrospect i t should be noted that very l i t t l e rockfall activity was observed in proportion to the time spent in the f i e l d . The record above, however, illustrates the importance of r a i n f a l l as a release mechanism 89 Photo III-7 . Broken Douglas F i r  at Apex of TC67 (Sept. 21/67). The damage was attributed to rock-f a l l activity. Note loose rocks at base of tree. Hardhat gives scale. in the region. Rain storms were recorded on only a few occasions during the investigation; observed rockfall activity occurred almost invariably in association with these storms. Debris captured in the two fences constructed provided some measure of the rate of rockfall activity in the region and substantiated the hypothesis that vegetation could be used as an effective index of st a b i l i t y . At the commencement of each sample, the fences were prepared by clearing out any debris in or on the chicken wire barricade. To keep the wire mesh flush with the surface, several large rocks were placed along the upslope edge of the fence. These rocks were sprayed l i b e r a l l y 90 with yellow paint in order to be able to identify them i f they became incorporated in the sample. Any that were, were excluded. In this manner both fences were set up for the f i r s t sample beginning May 31, 1967. Fence #1 was subsequently inspected on September 5, 1967. Much evidence of rockfall activity and/or debris transport through the chute on TC25 was observed. The fence was considerably damaged on both sides near the headwall indicating the effects of rockfall activity. The i n i t i a l assumption that the right side of the chute seemed most active was confirmed by the fact that most damage occurred on this side where about 35 feet of fence had been levelled. Two of the steel pipe posts had been considerably bent downslope and four of the 2" x 2" wooden stakes had been ripped out (see Photo III-8). It was concluded that this damage had been caused by a substantial avalanche of debris from the adjoining headwall on this side. In a l l , 139 rocks were captured during the interval May 31 through September 5, 1967. No estimate can be made of the sample lost where the fence had been levelled. Also, some rocks travelling at high speeds l e f t only a hole in the fence as evidence (see Photo III-9). In these cases the diameter of the hole was taken as representative of the size of the rock and this was recorded as the measurement of the intermediate axis . A number of very large rocks were captured as illustrated in Photo 111-10. Obviously, these rocks were not travelling at very high speeds when coming into contact with the fence. 3 Total volume captured was calculated at 213,486 i n . by taking the cube of the intermediate axis as representative of the volume of the rocks (this provides an overestimate of the volume; see Gardner, 1970) or approximately 123 cubic feet of debris. On September 6, 1967 fence #2 was inspected. More rocks were 91 Photo III-8. Fence #1 On TC25. Observation Sept. 5/67 showing damage to fence attributed to rockfall. Note steel pipe post bent downslope. Photo III-9. Fence #1 on TC25. Photo 111-10. Fence #1 on TC25. Note hole about 12" d. in fence Note large boulder captured by observed Sept. 5/67 indicating fence, rock travelling at high speed. 92 captured but these were generally small in size. As expected the larger portion of the sample and the largest rocks were captured by that section of the fence extending across the fluvial channel near the apex of TC49 (see Photo 11-14, p.54). It was concluded that the existence of this f l u v i a l channel accounted largely for the apparent st a b i l i t y of the rest of TC49. Rockfall debris would be effectively concentrated by this channel allowing the remainder of the slope to stabilize i t s e l f . The channel is V-shaped in profile, some 20 feet deep and 40 feet wide and extends about one-half way down the cone. There is not a substantial buildup of debris at the terminous of this channel, however, indicating that rockfall activity must be limited on this slope. Photo I I I - l l shows large debris captured by fence #2 at the bottom of the fluvial channel. The fence broke when an attempt was made to clear these boulders out after they were measured. In a l l , 275 rocks were captured. The combined 3 volume of these rocks was calculated at 77,356 in. or approximately 93 45 cubic feet of debris. This volume was substantially less than that captured for the same period at fence #1 and supports the hypothesis that TC49 is more stable than TG25. After sampling, both fences were cleared of a l l debris and the damage done to them repaired. Both were again prepared for sampling; this time for the period extending through the frost season. Fence #2 was again inspected on June 12, 1968 after nine months had elapsed. Unfortunately, the sample obtained in fence #2 for this .second interval cannot be taken as representative. A much larger sample was obtained -- 589 as compared to 275 rocks in the previous interval --but a major portion of the sample was lost. The section of fence extending across the f l u v i a l channel had become completely levelled by debris moving down the channel. Since a major portion of the previous sample -- and especially a l l the larger boulders -- had been captured by the fence in the channel, i t is assumed that the bulk of the volume was lost in the second attempt. Total volume in the absence of any large 3 boulders was only 20,771 in. or approximately 12 cubic feet of debris, considerably less than the f i r s t sample. '. Some estimate of the volume lost can be made. In the f i r s t sample the volume of debris captured by that section of fence through the channel alone represented approximately 507o of the total sample. If this same relationship is applied to the second sample, then an adjusted total volume can be calculated: adjusted volume (approximate) = volume captured 0.5 = 41,000 i n . 3 = 24 cubic feet On June 13, 1968, fence #1 was inspected and sampled. A previous inspection without sampling had been made on November 24, 1967. At this 94 time, a number of large holes were patched up and an estimate of the size of the intermediate axis of the rocks making the holes was recorded and included in the June 13, 1968 sample. On June 13, the fence was found to be essentially intact although about 20 feet of fence again on the more active right side of the chute -- had been torn out by rockfall activity. It was not f e l t that a major portion of the sample had been lost, however. Measurement was completed as in the other three samples and a total of 1492 rocks was recorded. In the interval 3 September 5, 1967 to June 13, 1968 a total volume, therefore, of 907,283 i n . or approximately 519 cubic feet of debris had been captured. The results of this sample tend to confirm the hypothesis that rockfall activity is concentrated during the frost season since the volume is more than three times as great as the previous sample. Compared to the adjusted volume calculated for the sample at fence #2, the second sample from fence #1 supports the i n i t i a l assumption that TC25 is more active than TC49 . A frequency plot of the sample obtained from fence #1 (June 13, 1968) is shown in Figure III-3 (plots of the other samples exhibit a similar distribution). The plot illustrates that the distribution i n size of intermediate axes would probably have a mode somewhere below 3 inches. Unfortunately, the mesh size of the wire used in the fences was 2 inches in diameter. Rocks having an intermediate axis of 2 inches or less could easily escape through the mesh. In view of this i t is f e l t that no reliable way of estimating the mode can be employed. Chicken wire of a heavier gauge and smaller mesh size is available but was not used because of the cost factor. In retrospect, much better results would probably have been obtained using the more expensive wire. More of the smaller-sized debris would have been captured and the heavier gauge would have 95 FIGURE HT-3. SEDIMENT SAMPLE FROM FENCE NO. I (AT TC 25 SEPT. / 67 - JUNE/68) 400-i 380 H 360-j 340-320-300-280-260 240-4 220-j >-O UJ 200-| z> o £ 180 H u. 160-140-120-100-80-60-40-20-T — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i i I I i—r=i—| I I l—r 0 I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 INTERMEDIATE AXIS IN INCHES 96 provided a more sturdy fence. The observations confirm the r e l i a b i l i t y of using vegetation as an indicator of s t a b i l i t y . This index was used in determining the location of the two fences constructed. The more dense and complete vegetation cover on TC49 was interpreted as an indication of a more stable slope. Since the fences were approximately the same in length (fence#l, 188 feet; fence #2, 185 feet); and since the intervals of sampling were.identical the results substantiate the assumption. The volume captured by fence #1 was significantly greater for both sample intervals. Since the results obtained represent only a crude estimate of the actual rockfall which occurred and, r e a l i s t i c a l l y , represent only that year for which a sample was taken, they cannot be taken as conclusive. However, in view of the fact that fence #1 has since been a l l but completely levelled by rockfall activity while fence #2 remains essentially intact, i t is f e l t that the index can be used with some confidence. D. Mass Movement Mechanisms. Movement was detected on lines painted on TC22, TC25 and CG52 but i t is f e l t that the results must be interpreted very cautiously (see Chapter II.D.). Two lines each 50 feet in length were painted cross-slope on TC22 on December 3, 1966. These lines were subsequently inspected on May 12, 1967. Only the lower line could be found. Being only 50 feet in length, the possibility of the upper line being wiped out by sliding debris is likely. TC22 appears to be a relatively active talus cone and evidence of slides of the magnitude required to erase the line are visible on this cone. The lower line exhibited only minor disturbance over the five month interval. A few rocks had moved on an individual 97 basis but the line had remained essentially intact. No bending indicative of differential movement had occurred. On June 11, 1968 the lower line on TC22 was again inspected. On this occasion, some thirteen months after the i n i t i a l inspection, the line exhibited widespread disturbance. The line transects four distinct strips of fine and coarse debris on the slope, i.e., fine, coarse, fine, and coarse from right to l e f t across the slope. It was noted that more disturbance had occurred on the coarse strips as compared to the fine strips. A l l rocks along the coarse strips had at least moved out of position as illustrated in Figure III-4. A number of individual rocks had been displaced and had moved downslope as far as 113 inches from the line. The line painted across the fine strips did not exhibit as much disturbance although a number of individual rocks had moved varying distances downslope. Table V below is a summary of the displacement of rocks observed. Table V. Displacement of Rocks on Line Painted on TC22. Number of Rocks ^ f n ^ f °^ T, . ~. . , Displacement Position Displaced  1. Fine s t r i p #1 12 1" to 29" 2. Coarse strip #1 15 2" to 14" 3. Fine strip #2 33 3" to 113" 4. Coarse strip #2 14 2" to 20" Differential movement had occurred as well. The line on both coarse strips had become appreciably bent downslope as illustrated in Figure III-5, On May 16, 1967 two lines each 100 feet in length were painted above and below fence #1 on the chute leading up from the apex of TC25. Both lines were located on the right side of the chute which appeared to be the most active part. These lines were inspected 3% months later 98 F I G U R E ILT-4. PAINTED LINE ALONG COARSE STRIP ON TC 22 ORIGINAL LINE :AS OBSERVED JUNE 11/68 F I G U R E HI-5. PAINTED LINE ON TC 22 (AS OBSERVED JUNE/68) FINE STRIP I COARSE STRIP I FINE STRIP 2 COARSE STRIP 2 99 on September 5, 1967. The lower line had remained essentially intact, although part of the line had become bent about one foot downslope. The upper line was essentially obliterated during the same interval (see Photos 111-12 and 111-13). The installation of fence #1 no doubt contributed to the difference in the degree of disturbance between the two lines since debris travelling through the chute was being captured by fence #1 during this interval. In the latter part of August 1967, a line 750 feet in length was painted on CC52 (see Map 2 and Photo II-4). To maintain an accurate level, the position of the line was established using a Keuffel and Esser telescopic alidade and stadia rod. The line was fixed to a suitable bench mark located at the base of a huge Douglas f i r tree on the l e f t side of the slope of CC52. The line was resurveyed on June .12, 1968. Readings along the line were compared to the bench mark reading of 4.76 feet by sighting onto the rod at approximate nine foot intervals along the line. A total of 89 readings made along the 750 foot line indicated a definite net downslope movement of the line. The difference in elevation was converted from feet to inches and these readings in turn were converted to net downslope movement according to the following relationship: Net downslope movement i n inches = vertical difference in inches .57358 where: .57358 = sin. of 35°, taken as the average slope of talus along the line. Net downslope movement ranged from a minimum of .9 inches to a maximum of 15.6 inches with a mean displacement of 6.14 inches along the line. One negative reading (-1.3") was obtained. This anomaly i s interpreted as an error in the survey rather than a net upslope movement. Again, as with the observations of the line painted on TC22 greatest movement Photo III-12. Painted Line Above  Fence #1 at TC25. As observed May 16, 1967. Photo 111-13. Painted Line Above  Fence #1 at TC25. As observed Sept. 5/67. Note almost complete destruction of line. Note also distance large boulder has moved as indicated by arrows . 101 occurred along the coarse strips of debris . Assuming this differential movement is exclusive of the effects of the disturbance created by walking over the talus surface when painting the line then some difference in the mechanisms of mass movement affecting coarse debris strips as compared to fine debris strips is implied in the observations. Perhaps a variation i n mode of deposition, degree of compaction, or fragment characteristics exerts some influence; but, no inference can be made at this time. An analysis of fragment parameters as related to coarse and fine strips of debris is included in Chapter IV. Observations of mass movement mechanisms in the region are now presented. Water in the form of melt or precipitation is assumed important as a movement i n i t i a t i n g mechanism. In this case the water serves as a lubricant along the points of contact i n the deposit. If the deposit i s resting at or near i t s c r i t i c a l angle and becomes saturated with water, the internal f r i c t i o n of the mass may be sufficiently reduced to i n i t i a t e spontaneous mass movement in the deposit. Such failure was never actually observed during the investigation but indirectly i t was substantiated on two occasions. On May 30, 1967 TC25 was climbed in order to inspect the fence which had been established on that cone. The normal route, which follows a strip of coarse debris along the right margin of the cone, was used. As always, the rocks remained f a i r l y stable under foot providing for a good access route. While working on the fence above, a f a i r l y heavy rain storm was experienced. Following the same route down i t was noted that the coarse strip of rocks had become extremely mobile. Every rock stepped on, moved, and in some instances a whole section of the slope gave way when stepped on. Obviously, the rain had been in-strumental in reducing the internal f r i c t i o n of the deposit. A similar 102 situation was recorded on the same slope on November 24, 1967 when the rocks which had become wetted by melting snow were observed again to be very unstable underfoot. 3 Mrs. Russel reports observing some very substantial debris slides on TG3 above her place of residence on the Upper Bench Road. She notes that debris moves down as a mixture of rock and snow during the winter season when snow covers the talus slope. Otherwise, releases have been observed as rocks r o l l i n g and bouncing over the surface at a high velocity creating a cloud of dust en route to the base of the talus. She further notes that the debris avalanches occur usually i n association with a f a l l of rain or wet snow and none have been observed occurring during the summer season. Wind has been considered a possible mass movement-initiating mechanism. On a number of occasions winds gusting at very substantial velocities were experienced while working on the talus slopes in the region. Most intense winds occurred late in the afternoon on particularly hot days during the summer in the form of convectional updrafts. These updrafts become concentrated into intense gusts near the apex of the cones especially where chutes or funnels have developed in the headwall. No actual disturbance of debris on the talus surface was ever observed, however. Creep may be an important mass movement mechanism and may have been detected by the lines painted on TC22, TC25 and CC52. Freeze-thaw cycles might be an important creep-initiating mechanism in view of the high frequency of cycles in this area. In order to be effective, however, the debris must have a high water content. The dry Keremeos climate, 3 Recorder at A.E.S. Met. Station at Keremeos. 103 therefore, may tend to limit the effectiveness of this mechanism. Dry rock creep, the result of thermal expansion and contraction as postulated by Scheidegger (1961), may be important. Diurnal temperature ranges during the summer can be high providing ideal conditions for the operation of this mechanism. As mentioned, debris slides composed of a mixture of snow and rock have been observed on TC3. Snow avalanche, therefore, may be another important mass movement mechanism but would be limited by the character-i s t i c a l l y light snows recorded in the valley. Evidence of flowing water acting as a transporting mechanism of debris was observed on TC49 and a number of the talus slopes along K Mountain. TC49 has already been identified as a transitional talus form which w i l l probably eventually become an all u v i a l cone. Well developed catchment basins in the chutes and funnels above the slopes along K Mountain effectively channel the flow of water onto the slopes and evidence of wash is apparent. The characteristically dry climate, however, limits the effectiveness of this mechanism in the region. A number of all u v i a l cones were observed in the area but these forms are considered to be distinct from talus (see Photo 111-14). Disturbance of the talus surface by animals and people in the region must be considered an important movement-initiating mechanism. A sizeable population of goats and deer which inhabit the region were observed frequently on the slopes. Many of the talus slopes have game t r a i l s on them. Hunters, prospectors and mountain climbers frequent the talus slopes as well. The very mobile strips of fine debris found on most slopes provide ideal downslope routes for climbers. Natural basal sapping of talus deposits does not occur in this 104 Photo 111-14. Alluvial Cone Near TC43. Note the water-scarred gentler-sloped surface which identifies this feature as an all u v i a l cone. The dense vegetation cover indicates a greater availability of water. Arrow shows recent mudflow scar near center of photo. region since most of the talus is perched high above river level on a terrace which bounds the valley on both sides along this stretch. Basal sapping has occurred on TC5, TC21, TC22, and TC25 where excavations to obtain riprap have been made. On these slopes, the talus immediately above the excavations has failed along sl i p planes extending several hundred feet upslope. The mass movement of the debris has resulted in the formation of slopes much steeper than those on the adjacent undisturbed talus . E. Morphometry and Morphology of Talus Development Near Keremeos, B.C. 1. Morphometry. Indications of st a b i l i t y on the talus slopes investigated were sought. A few of the slopes had well established game t r a i l s on them, eg. one was observed on TC25 just below the weed and grass cover found near the apex of that cone; a game t r a i l observed on TC2 can be seen 105 in Photo II-9; about midway on the slope of TC22 another of these t r a i l s indicates a certain degree of stability since such features could not develop on active slopes. The chutes and funnels which complement more than one-half of the talus slopes in the region provide another indication. In themselves, the chutes and funnels are an expression of the variable nature of the headwall exhibiting alternate zones of weak and resistant rock. The degree to which these features have evolved, however, indicates a late stage of development (see Chapter I.B.4.). A l l chutes and funnels observed in the region have reached the final stage of development. This observation i s interpreted as an indication of impending s t a b i l i t y and as such supports the st a b i l i t y hypothesis advanced in this thesis. Calculations of respective rates of accumulation before and after the deposition of Mazama Ash at CC44 support the 'diminishing sediment yield concept' advanced in Chapter II to explain the impending s t a b i l i t y of talus slopes in the region. A number of assumptions are made. It is assumed that a l l of the talus debris at the site has accumulated since the last retreat of continental ice from the region. According to the hypothesis advanced, the rate prior to ash deposition (6600 years B.P.) should significantly exceed the rate after ash deposition. Figure III-6 illustrates in cross-section the situation at CC44. As exposed in the roadcut the Mazama ash occurs at an average depth of 10 feet below the surface of the talus although the depth varies greatly as illustrated in Figure III-7. Beneath this, an average of 15 feet additional talus material rests on the river terrace. Before rates of deposition can be calculated, some assumption regarding the nature of the subsurface must be made. The exact profile FIGURE HT-6. MAZAMA ASH DEPOSIT IN TALUS CONE AT CC 44 ROAD CUT -HEADWALL F RIVER TERRACE (MAXIMUM POSSIBLE DEPTH OF TALUS) B 647' H 107 FIGURE HT-7. A S H D E P O S I T A S E X P O S E D A L O N G R O A D C U T 522' FIGURE E I-8.M O D E L O F T A L U S C O N E A T C C 44 IW,TH A S H DEPOSIT ) 108 of the boundary between talus and the surface on which i t rests cannot be defined without excavation of the entire talus deposit. Some limits can be established, however. A maximum depth would be defined by an extension of the river terrace back to a vertical headwall, i.e., along line AB in Figure III-6. This situation is unlikely, however. A minimum depth is defined by line EF. It is assumed that the talus deposit must be at least this deep as defined by the depth exposed along the road cut i f the observed slope of 34.8° is taken as representative throughout i t s development. This situation, too, is unlikely in view of the expected profile of a glaciated valley. The actual profile probably lies somewhere between these limits. A precise definition of the profile is not required for the present purposes, however. To test the hypothesis, a maximum and minimum volume of accumulation prior to ash deposition w i l l be calculated and compared with the volume accumulated after ash deposition occurred. with the following assumptions: 1. The talus cone represents a segment of a right circular cone. 2. The talus cone is bounded by vertical faces of coalescence, i.e., the talus cone in question coalesces with adjacent talus cones. 3. H/L - --a. constant, i.e., the cone has maintained a constant slope where, A(h) = the area of any one segment as a function of height and, dh = the increment of height. In Figure III-8 the area of the sector of a c i r c l e of radius r which A model of the talus cone at CC44 w i l l be used (see Figure III-8) of 34.8°. The total volume in Figure III-8 i s : H V = / A(h) ..: dh 109 subtends on angle of 0< r ad ians i s 2 A = T r " . o< 2TT l/20<r b u t , r = L(H-h) H t h e r e f o r e V = 1/2 o •I L(H-h) n 2 H d h . o r , V = 1/60CL H , which i s the formula f o r a segment of a r i g h t c i r c u l a r cone. Now,c<= 4 4 . 4 ° = 0.77445 rad ians and, i n F i g u r e III-8 (see F i g u r e III-6 a l s o ) : H T - 465 L T = 647 H M = 455 hi = 633 440 L B = 612 Then, t o t a l p o s s i b l e volume accumulated i n 10,000 years i s : V T = 1/6 0<:(L T ) 2 (H T ) = l / 6 < * ( 6 4 7 ' ) 2 ( 4 6 5 ' ) 2i 25.1 x 1 0 6 f t . 3 Maximum p o s s i b l e volume accumulated i n 3400 years p r i o r to ash d e p o s i t i o n i s : V max. = 1 / 6 * V <«M> = l ^ c x ^ S ' ) 2 ^ ' ) 23.5 x 1 0 6 f t . 3 110 And, minimum probable volume accumulated prior to ash deposition i s : V . = V - V„ min. max. B where, V g = 1 / 6 0 ^ ) 2 ( H B ) = 1/6(X^612 »)2(440«) ^ 21.3 x 10 6 f t . 3 therefore V . = 23.5 x 1 0 6 f t . 3 - 21.3 x 10 6ft. 3 min. = 2.3 x 106 f t . 3 The volume accumulated in 6600 years (post-Mazama time) i s : PM T max. 25.1 x 10 6 f t . 3 - 23.5 x 10 6ft. 3 1.6 x 10 6ft. 3 Therefore, the maximum possible rate of accumulation prior to ash deposition 3 is V /3400 or 6921 f t . /year. The minimum probable rate before ash max. 3 deposition is V . /3400 or 664.9 f t . /year. And, the rate of accumulation min. } 3 since ash deposition i s V^/6600 or 241 f t . /year (this compares reasonably 3 with the amounts captured on TC25 and TC49 i n 1967-68, i.e., 642 f t . and 3 69 f t . respectively for fence #1 and fence #2). At best, the rate of accumulation before ash deposition was approximately 30 times that after ash deposition; at least, about three times greater. The results support the 'diminishing sediment yield concept' and substantiate that the rate of accumulation on at least one talus slope i n the region has decreased during post-glacial time. Longitudinal slope profiles established on TG21 (see Photo 111-15) and reproduced in Figure III-9 i l l u s t r a t e that lateral profiles, in general, are steeper than central profiles (see Chapter IV). As illustrated, the profiles appear to be nearly rectilinear. A l l five profiles, however, Photo 111-15. TC21 • FIGURE IE-9. SLOPE PROFILES ON TC 21 AND TC 25 P R O F I L E S ON T C 25 RIGHT (950' ) CENTER (1180') P R O F I L E S ON T C 21 RIGHT (1570') CENTER (1500') L E F T ( 1 3 5 5 ' ) -113 are slightly concave gradually decreasing from 36°-37° near the apex to 33°-34° near the base. A sharp break in slope occurs where the boulder apron begins, a phenomenon observed in association with a l l boulder aprons investigated in the region. The profiles were established on two separate talus slopes but they are very similar throughout. Other observations of slope were made on talus slopes in the region and in general the slopes are steepest near the apex. Although additional profiles were not established i t is concluded that the concave profile is the general case in the region. 2. Morphology. The talus slopes observed in the region were classified according to a number of c r i t e r i a . Basically, only two forms of talus have developed in the region. The very uneven dissection of the headwalls has resulted in the formation of either distinct talus cones (coded as TC on Map 2) or groups of cones which have become coalesced (coded as CC on Map 2). Talus slopes observed in the region have been classified in Table VI. The following c r i t e r i a were used to classify the slopes according to size: 1. Huge (H) = slopes measuring > 2500 feet across the base and extending through > 1500 feet of r e l i e f . 2. Very Large (VL) = 2000 - 2500 feet across the base and extending through 1200-1500 feet of r e l i e f . 3. Large (L) = 1500-2000 feet across the base and having 1000-1200 feet of r e l i e f . 4. Medium (M) = 1000-1500 feet across the base and 500-1000 feet .of r e l i e f . 5. Small (S) = < 1000 feet across the base and < 500 feet of r e l i e f . Stability was judged according to the apparent degree of activity on the slope and the degree of vegetation cover. According to vegetation distribution, many slopes had more than one area of concentration, 114 Table VI. CLASSIFICATION OF TALUS FORMS NEAR KEREMEOS, B.C. Identi- Headwall Veg. Veg. Boulder fication Configuration Size Aspect Stability Type Dist. Apron 1 2 3 4 5 6 7 8 CC1 D M S S S CC _ TC2 D L S TTS S CC -TC3 C VL\ S A T T -TC4 D M S RA T M B TC5 D L S A T T,S,B B TC6 C M S RA T B B TC7 D L S A T T B TC8 C S N RA T T B TC9 C S N RA T T B TC10 C S N RA T T B TC11 C S N RA T T B TC12 C M N A T T B TC13 F L N A T B ,M B TC14 F H N A T S B TC15 F VL N A T M,T B TC16 C L N S T CC B TC17 C M N RA T T B : TC18 c M N RA T T B CC73 D M N TTS T CC B TC72 c VL N TTS T T,B B CC71 D M N TTS T T,B B TC70 C S N A T T B TC69 C M N A T T B TC68 C S N RA T T,S . B TC67 F VL N RA T T,M B TC66 C S N RA T T B TC65 C VL N A T T B CC64 D S W TTS T T B CC63 D M E A T T,B B TC62 D L E RA T T,B B TC61 D L E RA T CC B CC60 D M N TTS T T B CC56 D S N TTS T CC -CC57 D S N TTS T CC -CC58 D L N RA T T,B B CC59 D S N TTS T CC -TC55 C VL S RA T T,B B CC54 C H S RA T T,B B CC53 D H S A T T,B B CC52 D H S A T T,B B TC51 D L S S T CC B TC50 D S S TTS T CC B TC49 F L S TTS T CC -TC48 F H S A W T,B B TC47 C M S TTS T CC B (over) 115 Table VI. (continued) Identi- Headwall Veg. Veg. Boulder fication Configuration Size Aspect Stability Type Dist. Apron 1 2 3 4 5 6 7 8 TC46 C M S TTS T T B TC45 C M S TTS T T B CC44 D M S TTS S CC B TC43 F VL S S T T,B B TC42 C H S S T M B TC41 C M s S T T,B B TC40 c L s A T T,B B TG39 c M s TTS T T,B B CC38 D S s RA T CC -TC37 C M s RA T T,B B TC36 F VL s RA T T,B B TC35 C H s RA T T,B B TG34 F VL s S T T,B B CC33 D S s A T T,B -TC32 C L s S T T,B B CC31 D S s RA T CC -CC30 C M s RA T T,B B CG29 D S s RA T CC B TC28 D S s RA T T,B B TC27 D S s TTS T T,B B TC26 C M s TTS T CC B TG25 C L s A S T,B B TG24 C L s RA S T,B B TC23 F VL s A W T,B B TC22 C H s A W T,B B TG21 D H s A w T,B B TC20 D VL s A w T,B B GG19 D L E S S CC -Notes: 1. Identification (see Map 2). a) TC indicates a distinct talus slope. b) CC indicates a coalesced group of cones. 2. Headwall configuration. a) C indicates that a chute complements the cone or cones. b) F indicates that a funnel complements the cone. c) D indicates that the headwall is dissected . but that no chute or funnel has developed. 3. Size. a) H indicates a huge talus slope. b) VL - very large. c) L - large. d) M - medium. e) S - small. (over) 116 Table VI. (continued) 4. Aspect. a) N indicates a north-facing slope. b) S - south-facing. c) E - east-facing. d) W - west-facing. 5. Stability. a) S indicates a stable slope. b) TTS - tending towards s t a b i l i t y . c) RA - relatively active. d) A - active. 6. Vegetation type. a) T indicates predominantly trees with weeds and grass. b) S - predominantly shrubs with weeds and grass. c) W - predominantly weeds and grass. 7. Vegetation distribution. a) T indicates a concentration at the top of the slope. b) B - concentration at bottom. c) S - concentration along side or sides. d) M - concentration in middle. e) CC - a complete cover of vegetation. 8. Boulder apron. B indicates that a boulder apron has developed at the base of the slope. 117 i.e., T,B,S for this criterion in Table VI would imply concentration of vegetation at the top, bottom and along the sides of the slope. A good example of a huge coalesced cone is shown in Photo II-4. Photo 11-10 shows a very large talus cone complemented by a well developed chute. Photo 111-15 illustrates a huge distinct cone without a chute or funnel above it.TC48 with a well developed funnel is illustrated in Photo 111-16. Photo 111-16. TG48 . Note well developed funnel extending far into the headwall. TC26 was mapped (see Map 4A) as outlined in Chapter II, and as shown in Photo 111-17 is medium is size and complemented by a well developed chute. A boulder apron skirts the base of the cone and as illustrated on the overlay to Map 4A is distinguished by a sharp break in slope which is typical for boulder aprons observed in the region. The boulders comprising the apron on the l e f t side are very large (some > 25 f t . dia.). The talus rests on the surface of a river terrace which is exposed along the lef t side as illustrated on the overlay. TC26 is bounded on both sides by adjacent talus cones with which i t has coalesced the line of demarcation indicated by a definite V-bend in the contours C O N S T R U C T E D F R O M 1 9 6 7 P L A N E T A B L E S U R V E Y C O N T O U R I N T E R V A L - 6 F E E T C O M P I L E D B Y 0 . A . W O R O B E Y I 0 Q 8 119 Photo 111-17. TC26. upslope. The trough produced where they join is f i l l e d with large boulders. In essence, therefore, the boulder apron extends from headwall to headwall on TC26. As can be seen in Photo III-17 an uneven growth of Douglas f i r and ponderosa pine trees has become established on the talus surface. The oldest trees were estimated to be about 100 years of age indicating a certain degree of s t a b i l i t y on the slope. As can be seen in the photo the growth is concentrated near the apex where a continuous mat of bush, weeds and grass extends from about 2/3 the way up to the entrance to the chute (see overlay). Many dead trees are s t i l l standing but, as can be seen in the photo, many logs are strewn over the surface. Below the zone of continuous vegetation, the talus surface is sorted into distinct strips of fine and coarse debris which is characteristic of talus slopes in the region. The coarse strips are 120 usually quite narrow with the wider finer strips of debris between. The transition from coarse to fine, however, is abrupt. Longitudinal profiles of the cone are quite rectilinear but an inspection of Map 4A indicates that they are slightly concave, being steepest near the apex. The steep slope is maintained in the chute where a maximum of 38° is recorded. Debris was noted as being least stable near the apex and in the chute where slopes are steepest. Some interesting isolated features were noted. Near the base on the right side two auxiliary cone-like features can be observed (see overlay). The one on the extreme right is most distinct and forms the boundary between TC26 and the adjacent talus cone. Both are covered with a dense growth of bush, shrubs, weeds and grass . The one on the right has a definite convex longitudinal profile, being steepest at i t s base where i t merges with the boulder apron. The origin of these features presents an interesting problem. Both are covered with talus debris and are distinguishable only by their morphometric characteristics and their vegetation cover. Extending above the one furthest to the right to the rock spur on the right side of the chute are two distinct gullies separated by ridges on the talus surface. These gullies and ridges show up very well on Map 4A and are noted on the overlay. The features suggest f l u v i a l action. Water channelled by the chute above during a particularly intense storm would be most concentrated along the cleft separating the rock spur from main headwall on the right. So concentrated, i t could have produced the gullies observed either by channel flow or mudflow. The auxiliary cone-like feature at the base could represent the net accumulation of any debris transported downslope by the water. Near the base on the l e f t side a depression was observed on 121 the talus surface. This depression can be attributed to either compaction of the talus debris or, more probably, an irregularity on the surface beneath since the depth of the talus would be quite shallow at this point. The unequal dissection has produced a rock spur which protrudes a fa i r distance downslope as shown on the overlay and forms the right margin of the chute for about 1/3 of its extent. A c l e f t between the rock spur and the headwall on the right,which is bare of debris, channels some of the debris transported down the chute. An interesting phenomenon was noted on the l e f t side of the chute where i t joins with the headwall at the 900 foot level . At this point i t appears that the level of the rubble which mantles the surface of the chute has suddenly dropped about 18". As Photo 111-18 illustrates the surface of the headwall is covered with a f a i r l y complete growth of lichens which ends abruptly about 18" above the debris indicating that the headwall has been recently exposed as a result of a drop in level of the debris . An explanation for the • -Photo 111-18. Along Headwall in  Chute of TC26. Note discontinuity of lichen growth on headwall at about 18" above debris indicating settling of debris in the chute. 122 occurrence could be a sudden sliding away of a considerable portion of the debris in this part of the chute or a relatively instanteous compaction of the same. A claim stake marker is located on a ponderosa pine stump at this point and a cache of blasting caps and assorted mining tools were found in the headwall nearby. It is concluded that a prospector was doing some blasting along the headwall and that the shock of the explosion could have created the sliding or settling resulting in a lowering of the debris surface. The debris maintains a very steep slope at this point and is very mobile underfoot. It is feasible that the sudden shock of an explosion could have produced the settling observed. On June 15, 1967 an interesting phenomenon was observed at CC44. The cut of the Southern Trans-Canada Highway through the base of these cones is an essentially perpendicular wall composed of talus debris. Through compaction and soil formation as the result of weathering the talus debris has become most cohesive being able to support a slope near 90°. At one point along the cut, loose talus debris on the surface of the talus slope immediately above the cut was being dislodged by a particularly gusty wind noted that day. The debris being dislodged was in the process of actively forming a miniature talus cone at the base of the cut. The debris was being channelled by a cleft which had formed at this point along the cut (see Photo 111-19). As the debris came into .contact with the apex of the miniature cone, i t tended to spread i t s e l f out evenly preserving the characteristically symmetrical shape of the cone. Most of the debris dislodged was fine and most stopped before travelling more than one-half way down the miniature talus slope. The larger rocks moved directly to the base of the deposit forming an apron at the base. The sorting of the debris downslope was striking. Photo III-19. Miniature Talus at  GC44. Dust t r a i l l e f t by debris dislodged by wind from the talus surface of CG44 is visible at top of photo. Miniature cone formed from talus debris dislodged,which appears at the base of the cut, is about 6 feet high. Note coarser rubble at the base of the cone. Note also the very cohesive talus deposit through which the highway cut has been made. Sand-sized particles remained at the top becoming covered as subsequent fa l l s of debris occurred. From time to time masses of debris, already deposited near the apex,slid to readjust the slope. The slope of the deposit was measured by placing a survey rod f l a t on the surface and laying an abney level on the rod. It was found to have a constant slope of 34.9°. At the base of a number of talus slopes in the region excavations to obtain a suitable riprap have been made. As a result of this basal 124 sapping, the loose surface layers immediately above the excavations have s l i d away exposing a much stabler talus surface beneath. The newly exposed surfaces rest at angles exceeding 38° as compared to 33°-34° for the adjacent undisturbed areas of the talus slopes . The material comprising the newly exposed steeper surfaces was found to be in a state of chemical decay. Soil formation had already begun and the debris in general tended to be more compacted. This greater degree of consolidation allows these materials to support much steeper angles. The debris covered surfaces of the chutes and funnels which have formed above many of the talus slopes in the region are dist i n c t l y different from the talus surfaces below them. In general, the slopes of the chutes and funnels are greater than those on the talus slope below. Angles of rest are usually > 37°. This may be a reflection of the shallow depth of the debris in the chute or funnel allowing i t to be supported at a higher angle determined by the slope of the bedrock surface on which i t rests. In general, no observable downslope or cross-axial sorting is v i s i b l e in the debris and a high degree of activity is indicated by the lack of vegetation on the surface of chutes and funnels (eg. see Photo 111-20). The surface remains very active as this debris is conveyed down onto the talus surface below. Since the slope of the surface in chutes and funnels is steep, debris cannot accumulate to very great depths before sliding and removal from the chute or funnel takes place. It was noted that the cross-axial profile of the funnel complementing TC48 is concave-up as compared to the convex-up profile of the talus cone i t s e l f (see Photo 111-21) . At this point, the aspect of the bounding headwalls i s such that the rockfall trajectories onto either side of the funnel are basically perpendicular to the axis of 125 t r a n s p o r t d o w n s l o p e t h r o u g h t h e f u n n e l . A c r o s s - a x i a l s l o p e l e a d i n g d o w n a n d p e r p e n d i c u l a r l y o u t f r o m t h e h e a d w a l l s o n e i t h e r s i d e o f t h e f u n n e l h a s d e v e l o p e d , p r o d u c i n g t h e c o n c a v e p r o f i l e o b s e r v e d . Photo 111-20. Apex of Chute Above  TC25. Note the l ack of v e g e t a t i o n on the sur face of the chute and the in tense d i s i n t e g r a t i o n of the ad jacent h e a d w a l l . Photo 111-21. Looking up at Funnel Above TG48. Note the concave-profile (arrows) of the funnel in the background as compared to tt convex-up profile of the talus surface in the foreground. 127 CHAPTER IV - ANALYSIS AND INTERPRETATION A. Profile Analysis. Profiles established on TC21 and TC25 were used to test for a suggested difference between lateral and central profiles on talus cones. As plotted in Figure III-9 some difference in slope was detected. Table VIII illustrates the comparisons downslope for comparable slope sections on TC25 and TC21. The lateral profile on TC25 is an average of 1° steeper than the central profile; on TC21 the right and l e f t profiles are an average of 0.8° and 0.3° steeper respectively than the central profile. In a l l three cases, therefore, the lateral profile was found to be steeper than the central profile. The error of individual slope measurements is * 0.5° (King, 1966). However, the standard errors of the means of 10 measurements on TC25 and 15 and 14 measurements on TC21 listed in Table VIII are - 0.15°, - 0.12°, and - 0.13° respectively. Lateral profiles, therefore, are steeper than central profiles measured. Cobble a, b, and c axes were measured at 10 foot intervals along each profile on TC21. A definite difference in mean cobble size was detected between the lateral and central profiles. Cobbles, in general, are larger on the lateral profiles (see Table VII). Table VII. COBBLE ANALYSIS ON LONG PROFILES TC21 Mean along Mean along Mean along Measure Right Profile Center Profile Left Profile a axis 4.9" 2.6" 4.0" b axis 3.1" 1.7" 2.8" c axis 1.8" 1.0" 1.7" A difference of means test (see Blalock 1960, pp. 173-176) was applied, the results of which are tabulated below: Table VIII. A. COMPARABLE SLOPE SECTIONS TG25 Downslope Difference in Slope: Position Right-Center 100 feet (in degrees) 1 37.0 - 36.0 = +1.0 2 37.5 - 35.0 = +1.5 3 35.5 -• 35.0 = +0.5 4 36.0 -• 34.5 = +1.5 5 35.0 -• 35.0 = 0.0 6 36.0 - 34.5 = +1.5 7 35.0 - 34.5 = +0.5 8 35.5 - 34.0 = +1.5 9 35.0 - 34.0 = +1.0 10 35.5 - 34.5 = +1.0 B. COMPARABLE SLOPE SECTIONS TC21 Downslope Difference in Slope: Difference in Slope: Position Right-Center Left-Center x 100 feet (in degrees) (in degrees) 1 36.0 - 35.7 = +0.3 37 .0 " • 35.7 - +1.3 2 38.0 - 37 .0 = +1.0 36.7 -• 37 .0 = -0.3 3 37 .0 " 35.7 = +1.3 36.2 -• 35.7 = +0.5 4 36.5 - 35.5 = +1.0 35.7 -• 35.5 = +0.2 5 36.5 - 35.7 = +0.8 36.5 -• 35.7 = +0.8 6 36.5 - 35.5 = +1.0 36.0 -• 35.5 = +0.5 7 37.0 - 35.5 +1.5 35.5 -• 35.5 = 0.0 8 36.0 - 35.0 = +1.0 35.2 -• 35.0 = +0.2 9 35.0 - 34.8 = +0.2 35.0 -• 34.8 = +0.2 10 35.0 - 34.5 = +0.5 35.0 -• 34.5 = +0.5 11 35.0 - 34.4 = +0.6 34.2 -• 34.4 = -0.2 12 35.0 - 34.2 = +0.8 34.0 -• 34.2 = -0.2 13 34.5 - 34.0 - +0.5 34.0 -- 34.0 = 0.0 14 34.0 - 33.7 = +0.3 34.0 -• 33.7 = +0.3 15 33.5 - 31.7 = +1.8 129 Table IX. DIFFERENCE OF MEANS TEST 2 Tailed Test Means T*t*i df t at 1% Level 4 (a axis) right vs center 0.194 248 11.83 different right vs. l e f t 0.455 262 1.87 not significantly d i f f , l e f t vs. center 0.345 258 4.20 different (b axis) right vs. center 0.278 236 5.22 different right vs. l e f t 0.309. 278 1.14 not significantly d i f f , l e f t vs. center 0.235 235 4.67 different (c axis) right vs. center 0.165 245 4.95 different right vs. l e f t 0.182 280 0.77 not significantly d i f f . l e f t vs. center 0.143 240 4.73 different Means along lateral profiles are significantly different at the 170 significance level from means along the central profile but not from each other, even at the 5% level. Mean"' proportional and cumulative proportional frequency plots of the b axes according to Wentworth divisions i n inches (Figure IV-1) further i l l u s t r a t e the difference. The similarity of the plots for the lateral profiles is most apparent whereas the plot for the central profile where the mode lies in a much smaller size category is strikingly different. A Rolmogorov-Smirnov test (Miller and Kahn, 1962, pp. 464-470) for goodness of f i t validates this visual difference. Both the plots for the lateral profiles are significantly different from the plot for the central profile at the 170 significance level; the lateral profile plots are not significantly different at the 1% level from each other, however. The results indicate that some difference does exist in the characteristics between lateral as compared to central profiles along 4 t . Q 5 = 1.960 and t Q 1 = 2.576 for > 120 df. 5 Running means based upon 15 sample groups with a 5 sample overlap downslope on each profile. 130 FIGURE X2> I. MEAN PROPORTIONAL AND CUMULATIVE PROPORTIONAL FREQUENCY PLOTS OF b AXIS ALONG PROFILES ON TC 21 100 -i RIGHT T— i — r .31 .63L25 2.5 5 10 20 40 80 WENTWORTH DIVS.(ins.) 100 -i 80-60-z UJ o Ul 0_ 40-2 0 -C E N T E R T—1 1 I I I 31 .63 1.25 2.5 5 10 20 40 80 WENTWORTH DlVS.(ins) L E F T I I ! .31.63 1.25 25 5 10 20 4080 WENTWORTH DIVS.(ins.) 131 talus slopes investigated. This substantiates the hypothesis formulated in Chapter II. Some correlation between size of debris and angle of slope may exist which would suggest some difference in the mechanism of transport along central as compared to lateral profiles. It was earlier suggested that transport down the center of a cone would probably be more rapid and concentrated than transport along the sides. In this event, coarse debris would tend to accumulate more along the sides of the cone where i t s momentum would be reduced. Also, a steeper slope may be achieved along the sides where there is less disturbance. The results, however, are based essentially upon the observations on a single talus cone in the region. B. Analysis and Interpretation of Downslope Sorting. With the exception of the boulder aprons noted, i t appeared that no observable downslope sorting occurs on the slopes studied, this being stated as a hypothesis in Chapter I I . Running mean plots of the b axes as measured along the profiles on TC21 and TC25 tend to contradict the hypothesis. The plots (Figures IV-2, IV-3, IV-4 and IV-5) indicate that a slight increase of grain size occurs upslope and downslope from the 200-400 foot position on a l l profiles. However, the 9570 confidence range illustrates that only on TC25 is the difference s t a t i s t i c a l l y significant in an upslope direction. Downslope from the 200-400 foot position means are significantly different on a l l profiles at the 57o level. The change, however, is not monotonic and, as illustrated, is only a weak trend. It is interesting to note that a mat of grass and sage covers the upper third of both slopes and that the smallest mean b axes recorded on both TC21 and TC25 occur midway along this band of vegetation. This is probably best interpreted as an indication that vegetation is better able to establish i t s e l f at this point in 132 F I G U R E E C - 2 . RUNNING MEAN PLOT OF b AXES ALONG CENTER PROFILE ON TC 25 14 13 -1 12 H CO LU O 81 7 H C O X < LU 6 H 5 H i H 95% CONFIDENCE RANGE (FOR THE MEANS) B O U L D E R A P R O N B E G I N S H E R E ~ ~ 1 1 1 1 1 — 1 1 1 1 1 1 1 — 75 175 275 375 475 575 675 775 875 975 1075 1175 DOWNSLOPE DISTANCE IN FEET 133 FIGURE 12-3. RUNNING MEAN PLOT OF b AXES ALONG RIGHT PROFILE ON TC 21 DOWNSLOPE DISTANCE IN FEET 134 FIGURE 121-4. RUNNING MEAN PLOT OF b AXES ALONG CENTER PROFILE ON TC 21 135 F I G U R E 1 2 - 5. RUNNING MEAN PLOT OF b AXES ALONG LEFT PROFILE ON TC 21 DOWNSLOPE DISTANCE IN F E E T 136 association with the smaller grain size of the debris rather than as a control exerted by vegetation on the distribution of grain size. In this light the observation tends to confirm an hypothesis made earlier about the concentration of vegetation near the apex of talus cones in the region. As illustrated in Figure III-9, the slope angle decreases slightly downslope from the 200-400 foot position with a corresponding increase in grain size. Some correlation between grain size and angle may exist in this respect which could explain the downslope trend. But, the results tend to contradict the correlation between larger-sized debris and steeper angle existing on the lateral profiles already discussed. The results suggest that different transport mechanisms are operational on different parts of the talus slope. On TG25 the mean at the 1175 foot position is significantly larger (see Figure IV-2) than a l l others on that plot with the exception of the one at the 575 foot position. The debris at the 1175 foot position i s part of the boulder apron and this significant difference would be expected. Included with the plots on TC21 (Figures IV-3, IV-4 and IV-5) are the population confidence ranges of the material at each downslope position. It is interesting to note that these overlap on a l l three profiles suggesting that the differences which have been detected are weak. Distributions of a l l samples are positvely skewed and kurtosis varies between slightly platykurtic and leptokurtic but no downslope trend is discernable. Sorting (as indicated by the Trask sorting coefficient) is good for a l l plots and shows no downslope trend; neither do Zingg shape and flatness and sphericity parameters. In particular, flatness and sphericity are remarkably uniform downslope. 137 A downslope difference in mean cobble size was detected through an analysis of the traverse samples on TC3, TC26, TC48, and TC67. However, the differences detected were weak and did not occur on a l l cones sampled. Downslope plots of mean b axis according to cross-slope traverse samples are shown in Figures IV-6, IV-7, IV-8 and IV-9. The 957<> confidence range for the means indicates that debris sampled along the boulder aprons is significantly larger in a l l cases, as expected. Other weak downslope differences are indicated by the plots but no definite general trend exists. Again, as with the data collected along the profiles on TC21 and 25, the 9570 confidence ranges for the populations of debris at each traverse overlap, indicating l i t t l e correlation between size .and downslope position. Of the four cones sampled by traverse, TG3 exhibited the most pronounced trend of downslope sorting. The proportional frequency and cumulative proportional frequency plot of b axes on TC3 in Figure IV-10 illustrates the general increase in size downslope. Within cone plots are shown for TC3, TC26, TC48 and TG67 in Figure IV-11. A Kolmogorov-Smirnov test indicates that the distribution on TC3 is significantly different from that on TC26 at the 5% level; no other significant differences between cones exists. The difference detected would be related to the lesser progressive increase o£ grain size downslope on TC26 (Figure IV-7) as compared to that on TC3 (Figure IV-6). Also, TC26 has a significant; proportion of grain sizes recorded in the smallest categories of the Wentworth divisions (Figure IV-11) which are''lacking on TC3. The results suggest a difference in cobble characteristics between TG3 and TC26 which may be related to geology. Skewness, kurtosis, Zingg shape, and flatness- and sphericity 133 FIGURE 32!-6. MEAN b AXIS PLOT OF TRAVERSE SAMPLES ON TC 3 2 3 4 5 6 DOWNSLOPE TRAVERSE POSITION 139 FIGURE IZ-7. MEAN b AXIS PLOT OF TRAVERSE SAMPLES ON TC 26 15 1 1 1 1 - i r 2 3 4 5 6 7 DOWNSLOPE TRAVERSE POSITION F I G U R E I f f - 8 . MEAN b AXIS PLOT OF TRAVERSE SAMPLES ON TC 48 , j 1 , 1 2 3 4 DOWNSLOPE TRAVERSE POSITION F I G U R E W- 9 . MEAN b AXIS PLOT OF TRAVERSE SAMPLES ON TC 67 DOWNSLOPE TRAVERSE POSITION F I G U R E 32-10 P R O P O R T I O N A L F R E Q U E N C Y P L O T S A N D C U M U L A T I V E P R O P O R T I O N A L F R E Q U E N C Y C U R V E S O F b A X E S O N T C 3 0 0 TRAVERSE 1 TRAVERSE 2 31.631.252.5 5 10 20 40 31 63 1.2525 5 10 20 40 b AXIS IN . INCHES TRAVERSE 5 TRAVERSE 6 b AXIS IN INCHES ( WENT. DIVS.) TRAVERSE 3 TRAVERSE 4 F I G U R E E M I . WITHIN CONE PROPORTIONAL AND CUMULATIVE PROPORTIONAL FREQUENCY PLOTS OF b AXIS J f i i — i — i — i — l 1 r— i i i i — i i I f—i—i—i—i—i—r—• r I i — i — i — i — i — i .31 .63 1.25 25 5 10 20 40 .31 .631.25 25 5 10 20 40 .31 .63 1.25 2.5 5 10 20 40 .31 .6312525 5 10 20 40 b AXIS IN INCHES (WENTWORTH DIVISIONS) BETWEEN CONES b AXIS IN INCHES 144 parameters calculated for the traverse samples indicate no downslope trend. Again, flatness and sphericity show remarkable uniformity downslope. C. Mass Movement as a Cross-slope Sorting Mechanism. Plots of mean b axis along the fine and coarse strips on CC52 are illustrated in Figure IV-12. The plots are of adjacent strips of debris on the same slope and serve to i l l u s t r a t e that cross-slope sorting of debris exists. Also, a slight increase in size downslope is significant at the 570 level on the fine s t r i p . As illustrated in Figure IV-13 this can be attributed to a progressive reduction in the frequency of the smallest sizes down the fine strip. This progression suggests sorting in conjunction with mass movement processes whereby smaller fragments come to rest f i r s t where debris moves downslope en masse, and tends to substantiate the hypothesis that movement occurs en masse along the fine strips. Since the same progression i s lacking along the coarse strip a different mechanism of transport, as already postulated, is suggested. Additional calculations from the data suggest no fragment characteristics which would tend to exert influence on the formation of fine and coarse strips. As expected, good sorting exists at a l l points along both strips. (Mean Trask sorting = 1.309 for the fine strip; 1.264 for the coarse strip.) Distributions are positively skewed and markedly platykurtic in general. Distribution of Zingg shape (Figure IV-14) displays no marked trends. The uniformity of flatness and sphericity as noted on a l l other downslope plots occurs on the fine and coarse strips as well as indicated by Figures IV-15 and IV-16. A l l plots of flatness and sphericity parameters calculated from the data, which were collected using a variety of techniques on a number of slopes, indicate definite uniformity downslope. In addition, plots 145 F I G U R E E E - 12 . PLOT OF MEAN b AXES ALONG COARSE AND FINE STRIPS ON CC 52 D O W N S L O P E D I S T A N C E IN F E E T FIGURE E Z H 3 . F R E Q U E N C Y P L O T S A N D C U M U L A T I V E P R O P O R T I O N A L F R E Q U E N C Y C U R V E S O F b A X E S A L O N G F I N E S T R I P O N C C 5 2 (downslope in feet) b AXIS IN INCHES (WENTWORTH DIVISIONS) 147 FIGURE EZr 14. Z I N G G S H A P E D I S T R I B U T I O N C C 5 2 COARSE STRIP NUMBER OF COBBLES 0 5 10 o o z CO r -o -o m o 50 100 150 7 2a p ~ 25( 30( o co z R z TI m m 1^ 350^ 400 15 20 25 4 1 4 5 0 ^ i PERCENT 20 40 60 80 100 _ l I . , i , J, i , L. K E Y MEAN TOTAL BLADE ROLLER DISC /a. FINE STRIP NUMBER OF COBBLES 0 5 10 15 20 25 PERCENT 9 , MEAN OTAL FLAT ; ELONGATE ELONGATE BUT SQUARE BLOCKY OR ROUND FLAT BUT SQUARE OR ROUND F I G U R E E Z H 5 . F L A T N E S S P A R A M E T E R A L O N G F I N E A N D C O A R S E S T R I P S O N C C 5 2 COARSE STRIP ( mean = .556) 95% CONFIDENCE RANGE FLATNESS = gc (limits are o to i ) a+b IF CLOSE TO 0, THEN VERY FLAT; IF CLOSE TO I, THEN MORE OF A CUBE • FINE STRIP (mean= .509) - i i i • i 1 1 1 1 1— 0 50 100 150 200 250 300 350 400 450 DOWNSLOPE DISTANCE IN FEET — i 1 1 1 1 1 1 1 1 1— 0 50 100 150 200 250 300 350 400 450 DOWNSLOPE DISTANCE IN FEET \.o-t CO CO .8 -LU 150 of Zingg shape indicate no discernable progression of change downslope, though a l l shapes are present. These observations tend to confirm Ritchie's hypothesis (Chapter I) that mobility of debris is independent of shape, i.e., shape of a rock does not inhibit i t s r o l l i n g a b i l i t y unless i t is elongate, eg., shaped like a pencil. If shape exerted a control then some progressional change downslope in the parameters calculated would be expected; no change was detected, however. Further, the flatness and sphericity parameters calculated (see representative values in Figures IV-15 and IV-16) suggest that no eccentric shapes predominate in the debris which has accumulated in the form of talus slopes in the region. This suggests that jointing of the headwall exerts a uniform effect resulting in a non-eccentric pattern of fragmentation. This inference is further augmented by the basic balance in the distribution of Zingg shape exhibited by a l l plots. The results coincide with the observations made of the jointing along the headwalls in the region. In general, the rocks exhibit a very complete joint pattern as a result of the intersection of at least three distinct planes of jointing. D. Morphometric Analysis and Interpretation. The debris comprising the surface of TC26 was sampled in conjunction with the mapping program. The b axis of one cobble was measured at each rod station (a total of 276 measurements). In this way, a f a i r l y complete--i f not random -- sample of the talus surface was obtained. From the detailed surface data collected a trend surface analysis was made. F i r s t through sixth degree regression equations involving x and y (independent position variables) and z (the dependent cobble measure (b axis) variable) were calculated. The fourth degree equation was chosen to plot a trend surface (see overlay to Map 4B) since the equation had a coefficient of 152 determination of .466 and was significant at the 170 level on the F test. The 6th degree equation explains 49.77» of the variance. The increased explanation, however, is not worth the increase in complexity involved with the higher order equations (see Table X). What is most striking is the upward slope of the trend surface in the lower l e f t portion of the cone. This is obviously the result of a concentration of very large-sized boulders in association with the boulder apron at this point (see discussion Chapter III.E.2.). In general the surface indicates larger cobbles a l l along the apron with a fringe extending up along the right side where TC26 merges with an adjacent cone. As already discussed, the trough of intersection where the cones coalesce is f i l l e d with larger cobbles as indicated by the trend surface. On the talus proper the trend surface indicates a zone of coarser cobbles down the center of the slope bounded on either side by zones of fines. It is interesting to note with an inspection of Photo III-17 that the zones of fines correspond closely to areas of concentrated tree growth as one would expect. As can be seen, the generalized distribution of fines and coarse material on the talus proper is oriented parallel to the axis of transportation down the cone. This suggests some control exerted by variable mass movement mechanisms on the slope. Larger cobbles, being capable of individual movement downslope may tend to accumulate along the central axis where transport is concentrated. The fines, incapable of individual movement downslope, could tend to accumulate near the apex i n i t i a l l y . Upon assuming a c r i t i c a l angle, however, readjustment could occur by release en masse in the form of miniature slides which would tend to avoid the coarser accumulations along the central axis moving, rather, to accumulate along the lateral portions of the cone. This, of Table X. TREND SURFACE ANALYSIS TC26; ANALYSIS OF VARIANCE AND ERROR MEASURES Sum of Mean Residual Residual Coeff. of Surface Squares DF Square DF Mean Sauare F Determination 1 increment .34 2 .17 29.83 total .34 2 .17 276 .57 29.83* .177 2 increment .28 3 .92 19.17 total .61 5 .12 273 .48 25.79* .321 3 increment .18 4 .45 10.85 total .80 9 .89 269 .42 21.22* .415 4 increment .98 5 .20 5.05 total .90 14 .64 264 .39 16.47* .466 5 increment .38 6 .63 1.64 total .94 20 .47 258 .38 12.19** .485 6 increment .22 7 .31 0.82 total .96 27 .35 251 .39 9.20** .497 Standard 23.87 - 21.69 + 20.13 - 19.23 + 18.87 18.66 * significant at the 17o level. ** not significant at the 170 level. 154 course, contradicts the observations in section A of this Chapter where i t was found that debris sampled along lateral profiles on TC21 was coarser than that sampled along the central profile. It should be noted, however, that the lateral profiles taken on TC21 were along the extremities of the cone where, as already noted in a discussion of the surface characteristics of TC26 (Chapter III.E.2.), a boulder fringe has developed. As illustrated by the trend surface on the overlay to Map 4B, however, the finer debris on TC26 is located between the coarser deposits along the center and the extremities of the cone. No profiles were established along comparable sections on TC21. The results suggest that accumulation and readjustment mechanisms on the slopes are complex and wi l l require further study before they are completely understood. 155 CHAPTER V - CONCLUSIONS A. Summary. The massive and abundant talus forms in the Similkameen Valley near Keremeos, B.C. were investigated. It is assumed that a l l of the talus has accumulated in the last 10000 years and i t is concluded,that talus formation in the region is entering a passive stage of development. The slopes observed have grown to near maximum proportions,covering to a great extent the headwalls from which sediment is derived. A 'diminishing sediment yield concept' was applied and calculations of rates of accumulation afforded by the incorporation of Mazamaash in one talus cone support the concept. The net effect has been a reduction in the rate and influence of rockfall activity resulting in a tendency towards sta b i l i t y . This is substantiated by the establishment of vegetation on a l l talus slopes observed; samples obtained from fences designed to gauge rate of rockfall i n the area confirmed the valid i t y of using vegetation as an index of st a b i l i t y . Lithologic control largely accounts for the form and degree of the talus development noted. The exposure of resistant cherts inter-bedded with weaker volcanic and sedimentary rocks has resulted in an uneven dissection of the headwalls under the influence of weathering. Talus cones occurring in isolation or as coalesced groups are the net result of the uneven dissection; south-facing slopes of the valley display greatest development. The frequency of frost cycles suggests the importance of the mechanisms of frost shatter and frost bursting, these being considered the dominant weathering mechanisms in the region. Observations indicate 156 that the chemical processes of oxidation, hydration and solution are important as well. A number of secondary physical processes, including root wedging, may have limited effect. Observed concentration of rockfall activity during the spring season suggests the importance of "frost-riving" as a release mechanism. Lubrication and buildup of hydrostatic pressure by water is also considered effective. The expansion and contraction associated with the character-i s t i c a l l y high diurnal range of temperature in summer may be a sufficient force to set rocks loose. Attempts to measure rates of rockfall activity met with f a i r success in the construction of fences on TC25 and TC49. The loss of a substantial portion of certain samples, however, limits the effectiveness of the method. Net and differential downslope movement of debris was detected on lines painted on three talus slopes in the region. In general, more disturbance and greater net downslope movement was recorded on coarse as compared to fine strips of debris. The r e l i a b i l i t y of this method of detecting mass movement on the slope is questioned in light of the disturbance to the slope when the line i s painted. Notwithstanding, the observations made suggest that mechanisms of mass movement differ between fine and coarse strips. Further study of the phenomenon is warranted. Spontaneous mass movement as the result of lubrication by water ( r a i n f a l l and melt) was indirectly observed. A number of other mass movement mechanisms are recognized as important, including talus creep, flowing water, snow avalanche, animal and human disturbance and basal sapping. It i s thought that reasonable explanations have been given for the occurrence of boulder aprons and the distribution of vegetation 157 on talus cones observed in the region. A satisfactory explanation for the occurrence of "protalus boulder accumulations" on TC67 could not be given but i t is thought that the ridges may represent a r e l i c t accumulation. Measurements on TG21 indicate that debris along lateral profiles is significantly larger at the 170 level than debris sampled along the central p r o f i l e . Also, some correlation between size and angle is implied since the lateral profiles are steeper than the central p r o f i l e . The results substantiate the hypothesis that transport mechanisms down the center are different from those along the sides of the cone. Further study in this direction might be worthwhile. According to i n i t i a l observations made, i t was hypothesized that no downslope sorting of the debris exists on talus slopes in the region. Analysis of data collected on longitudinal profiles and traverse samples contradict the hypothesis; a slight increase in cobble size downslope was detected. The trend is weak and not monotonic but an associated downslope decrease in angle suggests a correlation between size and angle. This contradicts the correlation between size and angle determined by comparison of central and lateral profiles on TC21. The results indicate that different transport mechanisms operate on different parts of the slope. Fine and coarse strips of debris found on most talus slopes observed displayed no significant differences in fragment characteristics which might account for the sorting observed. It is concluded that the cross-slope sorting into fine and coarse strips of debris is a function of variable mass movement mechanisms. It is suggested that the larger cobbles accumulate on an individual basis along the slope whereas the fine materials accumulate en masse in the form of miniature slides as strips 158 adjacent to the coarse material. Calculation of Zingg shape and flatness and shericity parameters from data collected in a variety of ways indicates no detectable downslope trend. This observation tends to confirm Ritchie's hypothesis that mobility of debris is independent of shape. The lack of a predominant shape type is a reflection of the very complete jointing of the headwall. The mapping of TC26 on a large scale for the purposes of morphometric analysis was attempted. A useful map was produced which verified some of the assumptions made regarding talus morphology in the region. Trend surface analysis based on sampling of the debris in conjunction with the mapping of TC26 provided good results. The fourth degree surface plotted explains 46.670 of the variance in the data and portrays the gross s u r f i c i a l detail of the cone very well. The generalized distribution of fines and coarse material portrayed by the trend surface on TC26 suggested control exerted by differential mass movement mechanisms. The distribution has been explained in terms of individual and en masse movement of debris on the slope. The investigation has produced some interesting as well as worthwhile results. The attempt, however, i s really only a beginning. Since the occurrence of abundant and impressive talus forms is rare in accessible regions i t is thought that the Similkameen Valley near Keremeos, B.C. affords an ideal opportunity for an expanded study of the distribution, form and mechanics of talus development. B. Practical Recommendations for the Region. The occurrence of a substantial number of talus slopes near Keremeos presents advantages and disadvantages to the residents of the area. Both past and present talus activity have effect. 159 Perhaps the most welcome advantage is the ready supply of suitable riprap, located at the base of most slopes, which is used to protect the banks of the Similkameen River during peak flows. This debris would be ideal, as well, to use as f i l l i n the construction of railway and highway beds. Construction of highways in close proximity to talus slopes, however, can prove to be dangerous. At CC44, the course of the Similkameen River hugs the north side of the valley very closely. At this point the Southern Trans-Canada Highway has a cut which truncates a series of coalesced talus cones. This is potentially dangerous for any passerby in line with debris moving down the talus slope. A ditch skirts the edge of the highway between i t and the cut but such a ditch would not be effective in containing the debris as such ditches are where cuts are made through shear rock faces (see Figure V-l). Ritchie (1963) suggested a series of fencing techniques to accomodate the Photo V - l . Gathered Talus Rubble F I G U R E Y - l . ROCKFALL TRAJECTORIES 161 various trajectories of debris encroaching upon highways. Rockfall produces additional problems in the valley. The accumulation of large boulders at the apron or base of talus slopes occurs frequently on level terrace land which is potentially arable. This land usually remains unproductive since removal of the boulders is costly. An exception appears in Photo V-l which shows talus rubble gathered into strips near the base of talus cones at CC7. The land reclaimed in this way was planted in a l f a l f a . 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Premier Rapport de la Commission Pour 1'Etude des Versants, University of Amsterdam, 1958. . "Slope Profile Analysis." Zeitschrift fur Geomorphologie, Supplementband 5, 1964, pp. 17-27. 170 APPENDIX. A. Maps and Photographs Used. Terrestrial photo coverage was obtained in the form of black and white prints and coloured slides using a 35 mm. camera. Air photo interpretation and the construction of a base map for the area were accomplished employing B.C. Government (Department of Lands, Forests and Water Resources, Victoria, B.C.) air photos list e d below in Table 1: Table U LIST OF AIR PHOTOS Scale at Date of Photo # River Level Exposure 1. B.C. 5007 - 65-84 1:10900 May 31/59 2. B.C. 5208 - 020-028 041-045 1:35700 Sept.3/66 3. B.C. 5214 - 001-003; 037-039; 097-104; 125-127; 178, 179 1:35700 Sept.3/66 Suitable topographic map coverage was available (Surveys and Mapping Branch, Department of Mines and Technical Surveys, Ottawa) and a l i s t of the maps used is found in Table 2. Table 2 LIST OF TOPOGRAPHIC MAPS Ti t l e of Map Number Scale Date 1. Keremeos Map 341A (82E/4) 1:50,000 1939 2. Ashnola 92H/1-E 1:50,000 1960 3. Penticton (advanced print) 82E/S-W 1:50,000 1965 4. Hedley (advanced print) 92H/8.-E & W 1:50,000 1966 171 B. Additional Notes for Map 2. The rocks as indentified by Bostock (1929, 1930) are as follows: 1. Independence Formation: chert, greenstone. 2. Shoemaker Formation: chert; some tuff, greenstone. 3. Old Tom Formation: greenstone; basalt flows, s i l l s , bosses; some diorite. 4. Springbrook Formation: mainly conglomerate; some sandstone, shale. 5. Marron Formation: mainly basaltic laval; some breccia, tuff, conglomerate. 6. Olalla pyroxenite. 7. Olalla syenite. 8. Barslow Formation: a r g i l l i t e . 9. Blind Creek Formation: limestone. 10. Kobau Group: quartzite, schist, greenstone. 


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