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The Fraser Glaciation in the Cascade Mountains, southwestern British Columbia Waddington, Betsy Anne 1995

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THE FRASER G L A C I A T I O N I N THE CASCADE MOUNTAINS, SOUTHWESTERN B R I T I S H COLUMBIA By Betsy Anne Waddington B.Sc (Geology), The U n i v e r s i t y , of B r i t i s h Columbia (1986) A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT. OF GEOGRAPHY We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1995 © Betsy Anne Waddington, 1995 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Oeog^ pWy The University of British Columbia Vancouver, Canada Date f \ m \ \ Qt-i. Ici cl< DE-6 (2/88) ABSTRACT The o b j e c t i v e of t h i s study i s to r e c o n s t r u c t the h i s t o r y of g l a c i a t i o n from the s t a r t of Fraser (Late Wisconsinan) G l a c i a t i o n to the end of d e g l a c i a t i o n , f o r three areas i n the Cascade Mountains. The Cascade Mountains are l o c a t e d between the Coast Mountains and the I n t e r i o r Plateau i n southwestern B r i t i s h Columbia. The Coast Mountains were g l a c i a t e d by mountain g l a c i a t i o n f o llowed by f r o n t a l r e t r e a t , whereas the I n t e r i o r Plateau underwent i c e sheet g l a c i a t i o n f o l l o w e d by downwasting and stagnation. The Cascades were supposed t o have undergone a s t y l e of g l a c i a t i o n t r a n s i t i o n a l between these two. T e r r a i n mapping on a i r photographs f o l l o w e d by f i e l d checking was used to l o c a t e s u r f i c i a l m a t e r i a l s and landforms i n d i c a t i v e of g l a c i a t i o n s t y l e and p a t t e r n . A l l three study areas were g l a c i a t e d by mixed mountain and i c e sheet g l a c i a t i o n . At the s t a r t of Fraser G l a c i a t i o n , a l p i n e and v a l l e y g l a c i e r s formed around higher summits as occurred i n the Coast Mountains. At the g l a c i a l maximum the e n t i r e area was covered by the C o r d i l l e r a n Ice Sheet. D e g l a c i a t i o n was l a r g e l y by continuous downvalley r e t r e a t of a c t i v e g l a c i e r s , c o n t r a s t i n g w i t h downwasting and stagnation i n the I n t e r i o r P l a t e a u , and f r o n t a l r e t r e a t i n the Coast Mountains. The s c a r c i t y of f r e s h moraines i n the cirques suggests t h a t , u n l i k e i n the Coast Mountains, most cirq u e g l a c i e r s were not a c t i v e at the end of g l a c i a t i o n . Only the highest n o r t h f a c i n g c i r q u e s remained above the l o c a l snowline throughout d e g l a c i a t i o n and, as a r e s u l t , g l a c i e r s i n these v a l l e y s remained a c t i v e and r e t r e a t e d up v a l l e y . The p a t t e r n of g l a c i a t i o n i n the Cascade Mountains was s i m i l a r to t h a t of other areas which underwent mixed mountain and i c e sheet g l a c i a t i o n , such as the P r e s i d e n t i a l Range i n New Hampshire, the Green Mountains i n Vermont, mountain ranges i n west c e n t r a l Maine and the I n s u l a r Mountains on Vancouver I s l a n d . However, d e g l a c i a t i o n i n a l l areas was complex and depended s t r o n g l y on l o c a l c o n d i t i o n s . For t h i s reason l o c a l p a t t e r n s cannot be p r e d i c t e d e a s i l y on the b a s i s of g l a c i a t i o n s t y l e . The value of an understanding of g l a c i a t i o n s t y l e to improve the accuracy of t e r r a i n mapping was a l s o i n v e s t i g a t e d . I t was found that the model developed f o r the Cascade Mountains was of some use i n p r e d i c t i n g the presence of f i n e - t e x t u r e d m a t e r i a l i n v a l l e y bottoms and f o r the p r e d i c t i o n of g l a c i o f l u v i a l m a t e r i a l o v e r l y i n g t i l l . However f i n e - t e x t u r e d sediments were not found i n a l l v a l l e y s which were p r e d i c t e d to c o n t a i n them. The model appears to be most u s e f u l as an i n d i c a t o r of where to concentrate f i e l d checking i n order t o l o c a t e f i n e - t e x t u r e d sediments. TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS i v LIST OF FIGURES v i i i LIST OF MAPS x i ACKNOWLEDGEMETS x i i Chapter 1 INTRODUCTION 1 Chapter 2 ESTABLISHED STYLES OF GLACIATION 14 2.1 Mountain G l a c i a t i o n 14 2.1.1 Coast Mountains 16 2.2 Ice Sheet G l a c i a t i o n 18 2.2.1 Thompson Plateau 18 2.2.2 The Scandinavian Ice Sheet 21 2.2.3 Summary of Ice Sheet D e g l a c i a t i o n 21 2.3 Combined Mountain and Ice Sheet G l a c i a t i o n 22 2.3.1 Washington Cascade Mountains 2 2 2.3.2 I n s u l a r Mountains of Vancouver I s l a n d 25 2.3.3 The P r e s i d e n t i a l Range, New Hamphshire 26 2.3.4 Green Mountains, Vermont 28 2.3.5 West Ce n t r a l Maine 28 2.3.6 Summary of Combined Mountain and Ice Sheet G l a c i a t i o n 29 Chapter 3 METHODS OF DETERMINING STYLES AND PATTERNS OF GLACIATION 31 3.1 Landforms and Sediments I n d i c a t i v e of G l a c i a t i o n S t y l e s 31 3.1.1 E r o s i o n a l Landforms 31 i v 3.1.1.1 Cirques, Aretes and Horns 3 3 3.1.1.2 Troughs 34 3.1.1.3 Meltwater Channels 35 3.1.1.4 Streamlined Forms 3 7 3.1.2 Landforms and M a t e r i a l s of G l a c i a l D e p o s i t i o n 37 3.1.2.1 T i l l and E r r a t i c s 37 3.1.2.2 Moraines and other landforms composed of t i l l 39 3.1.2.3 G l a c i o f l u v i a l m a t e r i a l 39 3.1.2.4 G l a c i o l a c u s t r i n e m a t e r i a l 40 3.1.3 Su i t e s Of Landforms And M a t e r i a l s Expected With Each Type Of G l a c i a t i o n 41 3.2 F i e l d Techniques and A n a l y s i s Used To Determine Patterns and S t y l e s of G l a c i a t i o n i n the Cascade Mountains 42 3.2.1 A i r Photograph I n t e r p r e t a t i o n 43 3.2.2 F i e l d Program 43 3.2.2.1 S u r f i c i a l M a t e r i a l s 44 3.2.2.2 Rock Weathering 4 5 3.2.3 Reconstruction of G l a c i a l H i s t o r y 47 Chapter 4 MT. STOYOMA AREA 4 9 4.1 I n t r o d u c t i o n 49 4.2 Topography and E r o s i o n a l Landforms 4 9 4.3 D e p o s i t i o n a l Landforms and S u r f i c i a l M a t e r i a l s 54 4.3.1 T i l l 54 4.3.2 Moraines 56 v 4.3.3 Terraces, G l a c i o f l u v i a l and G l a c i o l a c u s t r i n e Deposits 59 4.4 Rock Weathering 61 4.5 G l a c i a l H i s t o r y 62 4.5.1 V a l l e y G l a c i e r Phase 62 4.5.2 Ice Sheet Stage 63 4.5.3 D e g l a c i a t i o n 66 4.5.3.1 Sediment Cores 70 4.6 N e o g l a c i a t i o n 70 Chapter 5 ANDERSON RIVER AREA 71 5.1 I n t r o d u c t i o n 71 5.2 Topography and E r o s i o n a l Landforms 71 5.3 D e p o s i t i o n a l Landforms and S u r f i c i a l M a t e r i a l s 75 5.3.1 T i l l 76 5.3.2 Terraces, G l a c i o f l u v i a l and G l a c i o l a c u s t r i n e Deposits 77 5.4 Rock Weathering 80 5.5 G l a c i a l H i s t o r y 82 5.5.1 V a l l e y G l a c i e r Phase 82 5.5.2 Ice Sheet Stage 84 5.5.3 D e g l a c i a t i o n 84 5.6 N e o g l a c i a t i o n 89 Chapter 6 MT. OUTRAM AREA 90 6.1 I n t r o d u c t i o n 90 6.2 Topography and E r o s i o n a l Landforms 93 6.3 D e p o s i t i o n a l Landforms and S u r f i c i a l M a t e r i a l s 96 6.3.1 T i l l 97 v i 6.3.2 Moraines 98 6.3.3 Terraces, G l a c i o f l u v i a l and G l a c i o l a c u s t r i n e Deposits 99 6.4 Rock Weathering 103 6.5 G l a c i a l H i s t o r y 107 6.5.1 V a l l e y G l a c i e r Phase 107 6.5.2 Ice Sheet Stage 110 6.5.3 D e g l a c i a t i o n 111 6.6 N e o g l a c i a t i o n 117 CHAPTER 7 DISCUSSION 118 7.1 G l a c i a t i o n of the Northern Cascade Mountains 118 7.2 P a t t e r n of G l a c i a t i o n i n areas w i t h Mountain and ICE SHEET g l a c i a t i o n 126 7.3 A p p l i c a t i o n of G l a c i a t i o n Models to T e r r a i n Mapping 127 7.3.1 Examples from the Northern Cascade Mountains 127 7.3.2 Conclusions 131 REFERENCES 133 APPENDIX 1: Schmidt hammer data f o r the Mt. Stoyoma area 14 0 APPENDIX 2: Schmidt hammer data f o r the Anderson R i v e r area 14 6 APPENDIX 3: Schmidt hammer data f o r the Mt. Outram area 152 v i i LIST OF FIGURES Figure 1.1: Loca t i o n map f o r the Cascade Mountains. 2 Figure 1.2: Sketch d e p i c t i n g f r o n t a l r e t r e a t . 3 Figure 1.3: Sketch d e p i c t i n g f r o n t a l r e t r e a t w i t h s t a g n a t i o n . 4 Figure 1.4: Sketch d e p i c t i n g downwasting and stag n a t i o n . 5 Figure 1.5: The four phases of g l a c i a t i o n 7 Figure 1.6: Four phases of d e g l a c i a t i o n . 8 Figure 2.1: Sketch d e p i c t i n g the four phases of g l a c i a t i o n . 15 Figure 2.2: The four phases of i c e sheet d e g l a c i a t i o n i n an area of moderate r e l i e f . 20 Figure 2.3: Lo c a t i o n map of the southern B r i t i s h Columbia and northern Washington Cascades. 23 Figure 2.4: Loca t i o n map of northeastern United S t a t e s . 27 Figure 4.1: Legend f o r Stoyoma area maps. 5 0 Figure 4.2: Loca t i o n map of the Mt. Stoyoma study area. 51 Figure 4.3: Plateau of the Mt. Stoyoma study area. 52 Figure 4.4: Summits at the head of Miner's Creek. 53 Figure 4.5: Map showing the extent of c l a y - r i c h t i l l . 55 Figure 4.6: Selected s t r a t i g r a p h i c s e c t i o n s . 57 Figure 4.7: Cabin Lake wi t h moraine. 58 Figure 4.8: R e l a t i o n between mean Schmidt hammer readings and e l e v a t i o n . 62 Figure 4.9: E a r l y Fraser G l a c i a t i o n a l p i n e g l a c i e r s i n the Mt. Stoyoma area. 64 Figure 4.10: P l o t of cirque area versus trough l e n g t h . 65 Figure 4.11: Ice form l i n e during deglaciation', based on moraines at Cabin Lake and Miner's Creek. 67 v i i i Figure 4 . 12 : Ice form l i n e during d e g l a c i a t i o n based on meltwater channels at 1580 m. 68 Figure 5 . 1 : Legend f o r Anderson R i v e r area maps. 72 Figure 5 .2 : L o c a t i o n Map of the Anderson R i v e r study area. 73 Figure 5 .3 : Horns between the North and South f o r k s of the Anderson Ri v e r . 75 Figure 5 .4 : Head of the North Fork of the Anderson R i v e r . 76 Figure 5 . 5 : Selected s t r a t i g r a p h i c s e c t i o n s . 78 Figure 5 . 6 : P l o t of mean Schmidt hammer values versus e l e v a t i o n . 81 Figure 5 . 7 : E a r l y Fraser G l a c i a t i o n a l p i n e g l a c i e r s . 83 Figure 5 . 8 : An i c e l e v e l during d e g l a c i a t i o n . 87 Figure 5 . 9 : An i c e l e v e l near the end of d e g l a c i a t i o n . 88 Figure 6 . 1 : Legend f o r Mt. Outram area maps. 91 Figure 6 . 2 : L o c a t i o n map of the Mt. Outram Study Area. 92 Figure 6 . 3 : Mt. Outram and surrounding south f a c i n g c i r q u e s . 93 Figure 6 .4 : Photo of Johnson Peak, showing rounded summit. 95 Figure 6 .5: Moraine damming lake on the south side of Mt. Outram. 98 Figure 6 . 6 : Selected s t r a t i g r a p h i c s e c t i o n s . 100 Figure 6 . 7 : Road cut through upper end of g l a c i o f l u v i a l t e r r a c e i n Sowaqua Creek v a l l e y . 101 Figure 6 . 8 : S e c t i o n i n kame t e r r a c e along Nicolum Creek. 102 Figure 6 . 9 : P l o t of mean Schmidt Hammer readings w i t h e l e v a t i o n . 104 Figure 6 . 10 : E a r l y Fraser G l a c i a t i o n a l p i n e g l a c i e r s . 108 Figure 6 . 11 : P l o t of cirque area versus trough l e n g t h . 109 Figure 6.12: An i c e l e v e l near the s t a r t of d e g l a c i a t i o n . 112 Figure 6.13: A l a t e r i c e l e v e l . 114 Figure 6.14: An i c e l e v e l near the end of d e g l a c i a t i o n . 115 Figure 7.1: G l a c i a t i o n model f o r the northern Cascade Mountains. 119 Figure 7.2: Outram and Stoyoma cirq u e area versus trough l e n g t h 120 Figure 7.3: Probable routes f o r the e a r l y advance of i c e from the Coast Mountains. 122 x LIST OF MAPS Map 1: T e r r a i n Map of the Mt. Stoyoma Area Map 2: T e r r a i n Map of the Anderson R i v e r Area Map 3: T e r r a i n Map of the Mt. Outram Area x i ACKNOWLEDGMENTS Many thanks to-my supervisor June Ryder f o r her support and guidance throughout t h i s p r o j e c t . Her i n s i g h t s and ideas on many aspects of t h i s work were i n v a l u a b l e . Michael Church reviewed t h i s document and provided may u s e f u l suggestions f o r i t s improvement. Numerous f e l l o w students and f r i e n d s provided support and encouragement. A s s i s t a n c e i n the f i e l d was provided by C a r r i e Brown, L i z Leboe and B r i a n Waddington. Funding was provided by B r i t i s h Columbia M i n i s t r y of F o r e s t s , Cattermole Timber and a N a t i o n a l Research C o u n c i l of Canada matching funds grant. C H A P T E R 1 I N T R O D U C T I O N The Cascade Mountains, i n Canada, occupy a small area between the Coast Mountains and the Thompson Plateau (Figure 1.1). The o b j e c t i v e of t h i s study i s to determine the s t y l e and p a t t e r n of g l a c i a t i o n f o r three study areas i n the northern Cascade Mountains duri n g the Late Wisconsinan Fraser G l a c i a t i o n . Areas i n v e s t i g a t e d f o r t h i s t h e s i s are centred around Mt. Stoyoma, Anderson R i v e r and Mt. Outram i n the northern, c e n t r a l , and southern p a r t s of the Canadian Cascade Mountains (Figure 1.1). A f u r t h e r o b j e c t i v e i s to i n v e s t i g a t e whether or not an understanding of the g l a c i a l h i s t o r y of the Cascade Mountains can be used to improve the accuracy of t e r r a i n mapping i n the study areas. The s t y l e of g l a c i a t i o n i s determined by the type of i c e mass present, whether i c e flow d i r e c t i o n i s c o n t r o l l e d by u n d e r l y i n g topography or i c e surface slope, and whether i c e i s a c t i v e l y f l o w i n g or s t a t i o n a r y . The p a t t e r n of g l a c i a t i o n i s the s p a t i a l d i s t r i b u t i o n of i c e and i c e flow d i r e c t i o n . From d e s c r i p t i o n s of g l a c i a t i o n i n s e v e r a l l o c a l i t i e s (Sutherland and Gordon 1993; Clague 1989; Waitt and Thorson 1983; F u l t o n 1967; F l i n t 1971, 1951; Davis and Mathews 1944) three general s t y l e s of g l a c i a t i o n can be defined: 1. mountain g l a c i a t i o n , where i c e i s l o c a l and t o p o g r a p h i c a l l y c o n t r o l l e d ; 2. i c e sheet g l a c i a t i o n , where the i c e source i s o f t e n r e g i o n a l and i c e flow i s c o n t r o l l e d by i c e surface g r a d i e n t , not l o c a l topography; and 3. mixed mountain and i c e sheet g l a c i a t i o n , where both l o c a l and r e g i o n a l i c e sources e x i s t at 1 Figure 1.1: L o c a t i o n map f o r the Cascade Mountains, showing the l o c a t i o n of the three study areas. 2 d i f f e r e n t times throughout the g l a c i a l c y c l e . Ice flow i s c o n t r o l l e d by topography during mountain g l a c i a t i o n stages and by i c e surface gradient during the i c e sheet stages. These s t y l e s w i t h examples from B r i t i s h Columbia and elsewhere w i l l be discussed f u r t h e r i n Chapter 2. Three s t y l e s of d e g l a c i a t i o n are described from s e v e r a l l o c a l i t i e s i n North America, (Clague and Evans 1994; Clague 1989, 1984; Ko t e f f 1974; Fu l t o n 1967). The f i r s t i s f r o n t a l r e t r e a t , which occurs when a g l a c i e r remains a c t i v e throughout d e g l a c i a t i o n and the i c e t h i n s while the snout moves back i n the d i r e c t i o n from which i t advanced (Figure 1.2). This i s most common w i t h mountain g l a c i a t i o n , but a l s o occurs at the per i p h e r y of i c e sheets. The second s t y l e i s f r o n t a l b) c) active ice outwash plain Figure 1.2: Sketch d e p i c t i n g f r o n t a l r e t r e a t , a ) . Maximum extent of g l a c i e r , b ) . G l a c i e r t h i n s as snout r e t r e a t s , i c e i s a c t i v e , c ) . Continued r e t r e a t of a c t i v e i c e and d e p o s i t i o n of g l a c i o f l u v i a l outwash. d). Continued r e t r e a t of a c t i v e i c e . d) outwash plain 3 r e t r e a t w i t h s t a g n a t i o n of the g l a c i e r snout (Figure 1.3). This occurs w i t h both mountain and i c e sheet g l a c i a t i o n . F i n a l l y , the t h i r d s t y l e occurs when i c e becomes cut o f f from i t s source; i t e v e n t u a l l y loses p l a s t i c i t y and ceases to flow and downwasting and stagnation occurs. (Figure 1.4). Figure 1.3: Sketch d e p i c t i n g f r o n t a l r e t r e a t w i t h s t a g n a t i o n of the snout, a) Maximum extent of g l a c i e r . b ) . G l a c i e r t h i n s as snout r e t r e a t s , i c e i s a c t i v e , c) Snout stagnates as g l a c i e r r e t r e a t s . A c t i v e i c e i s present behind the snout, d ) . Continued r e t r e a t ; i c e blocks become i s o l a t e d from stagnant f r o n t . G l a c i o f l u v i a l outwash and i c e contact d e p o s i t s formed. Each s t y l e of g l a c i a t i o n produces a c h a r a c t e r i s t i c s u i t e of landforms and deposits which w i l l be discussed f u r t h e r i n chapter 3. In p a r t i c u l a r the s t y l e of d e g l a c i a t i o n , has the l a r g e s t i n f l u e n c e on the type of s u r f i c i a l m a t e r i a l deposited. The most recent g l a c i a t i o n during which the C o r d i l l e r a n Ice Sheet covered much of B r i t i s h Columbia was the Fraser G l a c i a t i o n . I t has been c h a r a c t e r i z e d as mountain g l a c i a t i o n 4 Figure 1.4: Sketch d e p i c t i n g downwasting and s t a g n a t i o n , a) Maximum extent of g l a c i e r , b ) . Ice mass t h i n s i n p l a c e , surface gradient i s s t i l l maintained and l o c a l flow i s present, c ) . Continued t h i n n i n g , surface gradient i s l o s t and i c e i s stagnant, d). F i n a l stages of r e t r e a t , i c e separates i n t o b l o c k s of dead i c e . Ice contact g l a c i o f l u v i a l and g l a c i o l a c u s t r i n e m a t e r i a l deposited. and f r o n t a l r e t r e a t i n mountain ranges such as the Coast Mountains and i c e sheet g l a c i a t i o n w i t h downwasting and s t a g n a t i o n i n the lower areas such as the Thompson Plateau (Clague 1989). E x i s t i n g evidence (Saunders et a l . 1987; Mathews 1968; Holland 1964) suggests that elements of both of these s t y l e s are present i n the Cascade Mountains. Thus the e x i s t i n g models of g l a c i a t i o n i n B r i t i s h Columbia may not f u l l y d e s c r i b e g l a c i a t i o n i n the Cascade Mountains. Fraser G l a c i a t i o n s t a r t e d roughly 29,000 years BP w i t h the formation and expansion of a l p i n e g l a c i e r s i n mountainous areas throughout the Canadian C o r d i l l e r a . These continued t o grow, and coalesced to form i c e caps. Continued growth l e d t o 5 the formation of the C o r d i l l e r a n Ice Sheet at the Fraser Maximum roughly 14,500 years BP. This covered a l l but the highest summits i n the Coast, Columbia and Rocky Mountains, and a l l l o w l y i n g areas between mountain ranges (Figure 1.5) (Ryder et a l . 1991; F l i n t 1971; F u l t o n 1971; Davis and Mathews 1944) . D e g l a c i a t i o n began s h o r t l y a f t e r the i c e sheet reached i t s maximum extent w i t h t h i n n i n g of the i c e sheet (Figure 1.6). The i c e mass over the I n t e r i o r separated from that over the mountains due t o the emergence from beneath the i c e of i n t e r v e n i n g r i d g e s . A f t e r t h i s , continued t h i n n i n g of Coast and Columbia Mountain i c e l e d to separation i n t o v a l l e y g l a c i e r s and f r o n t a l r e t r e a t continued u n t i l g l a c i e r s receded to roughly t h e i r present day extent (Clague 1989). In the I n t e r i o r , i c e downwasted and upland areas became i c e f r e e before low l y i n g areas. Continued t h i n n i n g l e d to widespread s t a g n a t i o n (Ryder et a l . 1991; Tipper 1976, 1971; F u l t o n 1967). By 11,500 years BP (Ryder et a l . 1991) g l a c i e r s had r e t r e a t e d t o roughly t h e i r present day extent. Further d e t a i l s of the Fraser G l a c i a t i o n i n southern B r i t i s h Columbia w i l l be d i s c u s s e d i n Chapter 2. Snowline r i s e s from southwest to northeast across the Coast Mountains (Evans 1989). At B r i t t a i n R i v e r , on the coast, contemporary g l a c i a t i o n l e v e l i s 1900 m while at Yalakom R i v e r on the east side of the mountains i t i s 2700 m. This 800 m r i s e i n g l a c i a t i o n l e v e l over 150 km i s due t o a steep d e c l i n e i n s n o w f a l l eastward. As a r e s u l t of t h i s gradient areas t o 6 a) C O A S T ^ / C O L U M B I A M O U N T A N S M O U N T A I N S INTERIOR P L A T E A U b) C O A S T ^ / C O L U M B I A M O U N T A N S M O U N T A I N S INTERIOR P L A T E A U INTERIOR P L A T E A U Figure 1.5: The four phases of g l a c i a t i o n ( a f t e r Clague 1989; Ryder 1982; Tipper 1976; Davis and Mathews 1944). a) Growth of a l p i n e g l a c i e r s , b) V a l l e y g l a c i e r s begin to coalesce, c) Piedmont complexes form around the Coast and Columbia Mountains. d) An i c e sheet i s formed over the I n t e r i o r P lateau. 7 a) C O A S T y C O L U M B I A M O U N T A N S M O U N T A I N S INTERIOR P L A T E A U b) C O A S T _y C O L U M B I A M O U N T A N S M O U N T A I N S INTERIOR P L A T E A U c) / C O A S T / C O L U M B I A M O U N T A N S fj M O U N T A I N S INTERIOR P L A T E A U d) ' C O A S T - ~ / C O L U M B I A M O U N T A N S M O U N T A I N S INTERIOR P L A T E A U Figure 1.6: Four phases of d e g l a c i a t i o n ( a f t e r Clague 1989; Ryder 1982; Tipper 1976; Fu l t o n 1967). a) Maximum i c e l e v e l s T b) Ice sheet begins to t h i n over both the mountains and I n t e r i o r P lateau, c) Ice sheet separates i n t o trunk g l a c i e r s i n the mountains, downwasting continues over the I n t e r i o r P l a t e a u , d) V a l l e y g l a c i e r s continue to r e t r e a t up v a l l e y i n the mountains, i c e stagnates i n v a l l e y s of the I n t e r i o r P l a t e a u . 8 the east of the Coast Mountains, such as the Cascade Mountains and Thompson Plateau are much d r i e r and l e s s l i k e l y to support g l a c i a t i o n . The landforms of the Coast Mountains are dominated by g l a c i a l e r o s i o n . Horns, aretes, and deep steep w a l l e d troughs are common. The highest summits were nunataks during Fraser G l a c i a t i o n and as a r e s u l t are extremely steep and sharp. This area contains the highest peaks i n B r i t i s h Columbia, w i t h many summits over 3000 m, the highest being 4016 m Mt. Waddington. As a r e s u l t of the l a r g e amount of winter s n o w f a l l and c o o l summer temperatures there are c u r r e n t l y thousands of g l a c i e r s i n the Coast Mountains (Evans 1989) i n c l u d i n g extensive i c e f i e l d s around Mt. S i l v e r t h r o n e , Mt. Waddington, and the head of the L i l l o o e t R i v e r (Ryder 1981; Holland 1964). The Thompson Plateau i s dominated by a r o l l i n g upland surface d i s s e c t e d by deep broad v a l l e y s . Most of the Thompson Plat e a u l i e s between 12 00 m and 1500 m w i t h a few summits to 2250 m (Holland 1964). As a r e s u l t of the dry c l i m a t e and low e l e v a t i o n s , snowline i s c u r r e n t l y above a l l summits. Even durin g Fraser G l a c i a t i o n there were no s i g n i f i c a n t a l p i n e g l a c i e r s w i t h i n the southern i n t e r i o r . The Cascade Mountains have been d i v i d e d i n t o four ranges: Okanagan, Hozameen, Skagit, and an unnamed northern range (Figure 1.1). In B r i t i s h Columbia they are lower than the Coast Mountains; the highest peaks are between 1800 m and 2400 m. Throughout the Cascade Mountains there are s c a t t e r e d remnants of a Late Miocene e r o s i o n surface (Ryder 1981; 9 Mathews 1968), which has been d i s s e c t e d by c i r q u e s and troughs. The higher summits show the e f f e c t s of a l p i n e g l a c i a t i o n , while lower peaks are rounded and c l e a r l y were overridden by i c e (Holland, 1964). As the Canadian Cascades l i e east of the Coast Mountains, they r e c e i v e l e s s p r e c i p i t a t i o n , and as a r e s u l t of the r i s e i n snowline across the Coast Mountains, snowline i s c u r r e n t l y above most peaks i n the northern Cascades. In B r i t i s h Columbia and northern Washington only a few small g l a c i e r s remain i n the Skagit and Hozameen Ranges, which are l a r g e l y south of the Coast Mountains. These ranges are l o c a t e d where v a l l e y s cut through the Cascade Mountains from the coast, a l l o w i n g moist c o a s t a l a i r masses to penetrate f u r t h e r i n t o the range (Porter 1977). In Washington g l a c i e r s are extensive o n l y on the l a r g e volcanoes. In the north and east the Cascades grade i n t o the Thompson Plateau. In these areas summits are low and rounded. The highest summits are l e s s than 2000 m and t o t a l r e l i e f i s between 900 m and 1400 m. In the south and west peaks are sharper. Summits are up to 2400 m i n the Skagit area and r e l i e f i s 1700 m t o 1800 m. The g l a c i a l h i s t o r y of the Cascade Mountains has been s t u d i e d mostly i n Washington, near the periphery of the C o r d i l l e r a n Ice Sheet ( H e l l e r 1980; P o r t e r 1976; Waitt 1977, 1975; C r a n d e l l 1963; Mackin 1941). Daly (1912) made observations of g l a c i a t i o n along the 49th p a r a l l e l as p a r t of a bedrock mapping p r o j e c t . Matthews (1968) s t u d i e d g l a c i a t i o n 10 of the L i g h t e n i n g Lakes area i n southern B r i t i s h Columbia and Saunders et a l . (1987) s t u d i e d d e g l a c i a t i o n i n the C h i l l i w a c k V a l l e y . No st u d i e s e x i s t f o r the area north of the Skagit R i v e r except that of Ryder (1981) i n the northernmost Cascade Mountains. The Washington st u d i e s show th a t , as i n the Coast Mountains, a l p i n e g l a c i e r s formed at the s t a r t of the Fraser G l a c i a t i o n , but, u n l i k e i n the Coast Mountains these r e t r e a t e d before the Fraser Maximum. Then, at the Fraser Maximum the C o r d i l l e r a n Ice Sheet overtopped most summits as i n the I n t e r i o r Plateau (Ryder 1981; Waitt 1977, 1975) . A l p i n e g l a c i e r s were g e n e r a l l y not a c t i v e during d e g l a c i a t i o n (Waitt 1977, 1975; Mackin 1941) and mountain v a l l e y s were i c e f r e e w h i l e C o r d i l l e r a n Ice remained i n main v a l l e y s . The C h i l l i w a c k v a l l e y g l a c i e r l o c a t e d f u r t h e r n orth was l i k e l y confluent w i t h the C o r d i l l e r a n Ice Sheet (Saunders et a l 1987), but i t began to r e t r e a t up v a l l e y while a c t i v e C o r d i l l e r a n i c e remained i n the Fraser v a l l e y . As a r e s u l t a lak e was dammed i n the lower C h i l l i w a c k v a l l e y and a l a r g e sandur prograded to the west as the v a l l e y g l a c i e r r e t r e a t e d u p v a l l e y . This study demonstrates that drainage i n one v a l l e y i n the Cascade Mountains was d i s r u p t e d by C o r d i l l e r a n Ice pushing up i n t o the lower reaches of the v a l l e y . I t i s p o s s i b l e that drainage i n other Cascade v a l l e y s was a l s o dammed by C o r d i l l e r a n Ice, r e s u l t i n g i n the formation of lakes i n v a l l e y s which were d e g l a c i a t e d by f r o n t a l r e t r e a t of Cascade Mountain a l p i n e g l a c i e r s . 11 The Canadian Cascade Mountains thus provide an o p p o r t u n i t y t o study p a t t e r n s of g l a c i a t i o n which may d i f f e r somewhat from the models of mountain g l a c i a t i o n f o l l o w e d by f r o n t a l r e t r e a t and i c e sheet g l a c i a t i o n w i t h downwasting and s t a g n a t i o n , which have been developed f o r the Coast Mountains and I n t e r i o r Plateau r e s p e c t i v e l y . The areas s t u d i e d are c l o s e r to the centre of the C o r d i l l e r a n Ice Sheet than the Washington s i t e s and thus may have experienced d i f f e r e n t p a t t e r n s of g l a c i a t i o n . This study w i l l add more d e t a i l to the understanding of Fraser G l a c i a t i o n i n B r i t i s h Columbia. The three study areas are spread over a d i s t a n c e of 80 km from near the northern l i m i t of the Cascade Mountains to the Skagit R i v e r (Figure 1.1). Each area encompasses between 100 and 200 km . The study areas were s e l e c t e d to encompass some of the topographic v a r i a b i l i t y present w i t h i n the B r i t i s h Columbia Cascades. The northern and southern areas were known to c o n t a i n l a t e r a l moraines of the C o r d i l l e r a n Ice Sheet (Dr. J.M. Ryder, personal communication 1992) and thus one i c e marginal p o s i t i o n was already known i n each area. The study boundaries were d e l i m i t e d to i n c l u d e the high summits, l a r g e troughs and p l a t e a u areas near the moraines. The c e n t r a l area, at the head of Anderson R i v e r , was s e l e c t e d t o i n c l u d e s e v e r a l w e l l developed horns and l a r g e troughs, which are rare i n other p a r t s of the Cascades. D e t a i l s of each area w i l l be d i s c u s s e d i n chapters 4 to 6. The s t y l e of g l a c i a t i o n was determined by study of e r o s i o n a l and d e p o s i t i o n a l features created during the l a s t 12 g l a c i a t i o n . Each s t y l e of g l a c i a t i o n creates a c h a r a c t e r i s t i c s u i t e of d e p o s i t s and landforms. Many of these can be i d e n t i f i e d on a i r photographs, so t h i s study r e l i e d h e a v i l y on a i r photograph i n t e r p r e t a t i o n f o r i n i t i a l i d e n t i f i c a t i o n of landforms and d e p o s i t s . This was accomplished by t e r r a i n mapping u s i n g the B r i t i s h Columbia system (Howes and Kenk 1988). F i e l d work allowed more d e t a i l e d examination of each area, i n c l u d i n g the c o l l e c t i o n of s t r a t i g r a p h i c i n f o r m a t i o n and the c o n f i r m a t i o n of data obtained from a i r photographs. Once the landforms and m a t e r i a l s were mapped i t was p o s s i b l e to determine the s t y l e of g l a c i a t i o n which best f i t the e x i s t i n g evidence. This methodology i s discussed f u r t h e r i n Chapter 3. The r e s u l t s from t h i s study demonstrate that the B r i t i s h Columbia Cascades have undergone mixed mountain and i c e sheet g l a c i a t i o n . Thus the patterns of g l a c i a t i o n i n the study areas were compared to those of other areas that have evidence of both l o c a l g l a c i e r s and an o v e r r i d i n g i c e sheet, such as the I n s u l a r Mountains on Vancouver I s l a n d and the Green Mountains and P r e s i d e n t i a l Range i n New England, to determine which f a c t o r s c o n t r o l the p a t t e r n of g l a c i a t i o n i n areas where mixed mountain and i c e sheet g l a c i a t i o n occurs. F i n a l l y the t e r r a i n maps constructed f o r t h i s study are reexamined i n l i g h t of the Cascades model to determine i f an understanding of the g l a c i a l h i s t o r y of the Cascade Mountains can improve the accuracy of a i r photo i n t e r p r e t a t i o n . 13 CHAPTER 2 ESTABLISHED STYLES OF GLACIATION The three s t y l e s of g l a c i a t i o n , mountain, i c e sheet and mixed, are d e s c r i b e d i n t h i s chapter, w i t h examples from B r i t i s h Columbia, Washington, northeastern United States and Scandinavia. 2.1 Mountain G l a c i a t i o n Mountain g l a c i a t i o n occurs i n areas which have only a l o c a l source of i c e . These areas are g e n e r a l l y the highest and wettest areas present, such as the Coast Mountains of B r i t i s h Columbia, the S c o t t i s h Highlands (Sutherland and Gordon 1993), or the Scandinavian mountains ( F l i n t 1971). Davis and Mathews (1944) i d e n t i f i e d four phases of g l a c i a t i o n , three of which occur during mountain g l a c i a t i o n . Phase one i s the a l p i n e phase: r e l i e f of the land surface g r e a t l y exceeds i c e th i c k n e s s , and i c e flow i s c o n t r o l l e d by topography (Figure 2.1a). In phase two, the intense a l p i n e stage, v a l l e y g l a c i e r s coalesce to form branching systems and i c e t h i c k e n s u n t i l r e l i e f only s l i g h t l y exceeds i c e t h i c k n e s s (Figure 2.1b). Ice flow i s s t i l l c o n t r o l l e d by topography. During the t h i r d phase, the mountain i c e sheet stage, i c e thi c k n e s s s l i g h t l y exceeds r e l i e f , a continuous i c e sheet i s formed, but flow i s s t i l l l a r g e l y i n f l u e n c e d by u n d e r l y i n g topography (Figure 2.1c). The f o u r t h phase i s reached when a c o n t i n e n t a l g l a c i e r i s formed (Figure 2.1d) and i c e flow i s no longer c o n t r o l l e d by r e l i e f . The d e t a i l s of g l a c i a t i o n i n the 14 Figure 2.1: Sketch d e p i c t i n g the four phases of g l a c i a t i o n i n mountainous areas ( a f t e r Davis and Mathews 1944). a. A l p i n e phase: a l p i n e g l a c i e r s form around higher summits; r e l i e f g r e a t l y exceeds i c e t h i c k n e s s , b. Intense a l p i n e phase: v a l l e y g l a c i e r s coalesce to form branching systems; r e l i e f s l i g h t l y exceeds i c e t h i c k n e s s , c. Mountain i c e sheet phase: i c e t h i c k n e s s s l i g h t l y exceeds r e l i e f and a continuous i c e sheet i s formed; flow i s c o n t r o l l e d by u n d e r l y i n g topography, d. C o n t i n e n t a l i c e sheet phase: i c e thi c k n e s s g r e a t l y exceeds r e l i e f and flow i s c o n t r o l l e d by i c e surface g r a d i e n t . 15 Coast Mountains are described i n the f o l l o w i n g s e c t i o n as an example of mountain g l a c i a t i o n . 2.1.1 Coast Mountains The Coast Mountains along w i t h the Columbia and Rocky-Mountains were the source areas f o r much of the southern p a r t of the C o r d i l l e r a n Ice Sheet during Fraser G l a c i a t i o n . G l a c i a t i o n s t a r t e d w i t h the growth of a l p i n e g l a c i e r s roughly 29,000 years ago. (Ryder et a l . 1991; Clague 1981; Ryder 1981). These grew i n t o l a r g e v a l l e y g l a c i e r s and i c e caps, which were l a r g e l y confined to the Coast Mountains u n t i l 20,000 to 25,000 years ago (Clague 1989) . With continued growth the v a l l e y g l a c i e r s coalesced i n t o piedmont g l a c i e r s along the f l a n k s of the mountains, and expanded over the Thompson Plateau. Continued expansion created the C o r d i l l e r a n Ice Sheet over the I n t e r i o r , and i t e v e n t u a l l y covered a l l but the highest peaks i n the Coast, Columbia and Rocky Mountains. The i c e surface was g e n e r a l l y above 2300 m and l o c a l l y over 2500 m (Ryder et a l . 1991; Clague 1989). The maximum extent occurred between 14,000 and 14,500 years BP (Clague 1989). Retreat began immediately a f t e r the Fraser Maximum at 14,500 years BP. The i c e cap covering the mountains thinned and separated from the C o r d i l l e r a n Ice Sheet, and f u r t h e r t h i n n i n g l e a d to separation i n t o i n d i v i d u a l v a l l e y g l a c i e r s . (Ryder et a l . 1991; Tipper 1976, 1971). D e g l a c i a t i o n throughout the Coast Mountains was p r i m a r i l y by f r o n t a l 16 r e t r e a t . The absence of dead i c e topography such as hummocky a b l a t i o n moraine, i n d i c a t e s that i c e was a c t i v e throughout r e t r e a t . The l a c k of r e c e s s i o n a l moraines i s evidence of continuous r e c e s s i o n . Several s t u d i e s document the p a t t e r n of d e g l a c i a t i o n on the coast (Clague 1984, 1985; Armstrong 1981), where sea l e v e l s s t r o n g l y i n f l u e n c e d d e g l a c i a t i o n . There are fewer s t u d i e s of Fraser d e g l a c i a t i o n i n more i n l a n d areas. Desloges and G i l b e r t (1991) and G i l b e r t and Desloges (1992) used a c o u s t i c methods to study the sediments i n Ha r r i s o n and Stave Lakes. The lower l a y e r s of sediment i n Ha r r i s o n Lake are c o n s i s t e n t w i t h a high energy ice-proximal environment, but upward the p a t t e r n of sedimentation q u i c k l y becomes uniform, c o n s i s t e n t w i t h a more d i s t a l i c e source. The sediment record, combined w i t h a la c k of end moraines, i s taken as evidence of continuous r a p i d r e t r e a t of the L i l l o o e t V a l l e y G l a c i e r . S i m i l a r r e s u l t s were obtained from Stave Lake. F r o n t a l r e t r e a t continued u n t i l about 11,000 years ago, when lakes i n the lower and mid p o r t i o n s of Kwoiek Creek v a l l e y , on the eastern side of the Coast Mountains, were i c e fr e e (Souch 1989) . There i s abundant evidence throughout the Coast Mountains (eg. Ryder and Thompson 1986) that more recent g l a c i a l advances have g e n e r a l l y been followed by f r o n t a l r e t r e a t . Large l a t e r a l and te r m i n a l moraines are common and a c t i v e g l a c i e r s can be seen to be r e t r e a t i n g up v a l l e y s . Some l a r g e v a l l e y g l a c i e r s , such as the Tiedemann, have dead i c e at the 17 snout and are t h e r e f o r e receding by f r o n t a l r e t r e a t w i t h s t a g n a t i o n of the snout. I t i s l i k e l y that s i m i l a r p a t t e r n s of r e t r e a t were followed at the end of Fraser G l a c i a t i o n . 2.2 Ice Sheet Gla c i a t i o n Ice sheet g l a c i a t i o n occurs i n lower areas adjacent to mountains, such as the I n t e r i o r Plateau of B r i t i s h Columbia or the lowlands to the east of the Scandinavian Mountains ( F l i n t 1971). Ice sheet g l a c i a t i o n corresponds to phase four of Davis and Mathews phases of g l a c i a t i o n , and i s most common i n areas of low t o moderate r e l i e f (Davis and Mathews 1944). During t h i s phase i c e i s much t h i c k e r than r e l i e f and flow i s u n a f f e c t e d by topography. G l a c i a t i o n on the Thompson Pla t e a u dur i n g Fraser G l a c i a t i o n and the Scandinavian Ice Sheet d u r i n g Weichsel G l a c i a t i o n are described i n the f o l l o w i n g s e c t i o n s as examples of i c e sheet g l a c i a t i o n . 2.2.1 Thompson Plateau V i r t u a l l y a l l the i c e covering the Thompson Plateau o r i g i n a t e d i n the Coast and Columbia Mountains (Ryder et a l . 1991) . The area was overridden by the C o r d i l l e r a n Ice Sheet a f t e r about 21,000 years BP. Expansion continued u n t i l 14,000 to 14,500 year BP (Ryder et a l . 1991). At i t s southern margin i n n o r t h - c e n t r a l and northeastern Washington the C o r d i l l e r a n i c e sheet began to r e t r e a t i t s margins, the i c e sheet receded by f r o n t a l r e t r e a t (Clague 1981), but elsewhere downwasting and stagnation dominated. By 18 11,500 t o 10,000 years ago the plateaus and v a l l e y s of the i n t e r i o r system were completely d e g l a c i a t e d (Clague 1981) . Fu l t o n (1967) i d e n t i f i e d four phases of d e g l a c i a t i o n i n the Kamloops area which summarize the s t y l e of i c e sheet d e g l a c i a t i o n f o r areas of moderate r e l i e f . The f i r s t phase was i c e sheet g l a c i a t i o n . Ice was a c t i v e , t h i c k e r than r e l i e f , and the r e g i o n a l i c e surface gradient c o n t r o l l e d flow (Figure 2.2a). During t h i s stage a blanket of basal t i l l was deposited. Once I n t e r i o r and Coast Mountain i c e separated and upland areas began to be exposed, phase 2 or the T r a n s i t i o n a l Upland Phase, was reached (Figure 2.2b). There was s t i l l minor r e g i o n a l flow, which was now c o n t r o l l e d by l o c a l topography. Phase 3 or the Stagnant Ice Phase began when continued t h i n n i n g allowed the exposed uplands to i s o l a t e i c e i n v a l l e y s (Figure 2.2c). Ice was s t i l l t h i c k enough to behave p l a s t i c a l l y , l o c a l surface drainage was s t i l l present and i c e marginal drainage was developed. The f i n a l , Dead Ice Phase occurred when i c e was too t h i n to flow any longer and the surface gradient was l o s t (Figure 2.2d). E n g l a c i a l and s u b g l a c i a l drainage were common r e s u l t i n g i n the d e p o s i t i o n of hummocky g r a v e l and eskers. As i c e downwasted major v a l l e y s were dammed by i c e , drainage was d i s r u p t e d and numerous g l a c i a l lakes formed (Ryder and Clague 1989; F u l t o n 1969, 1967; Armstrong and Tipper 1948; Mathews 1944). Tipper (1971) found s i m i l a r patterns of i c e r e t r e a t i n c e n t r a l B r i t i s h Columbia. 19 Figure 2.2: Sketch d e p i c t i n g the four phases of i c e sheet d e g l a c i a t i o n i n an area of moderate r e l i e f ( a f t e r F u l t o n 1967). a ) . Ice sheet g l a c i a t i o n : i c e i s much t h i c k e r than r e l i e f and flow i s c o n t r o l l e d by i c e surface g r a d i e n t , b ) . T r a n s i t i o n a l upland phase: uplands become i c e f r e e ; flow i s c o n t r o l l e d by l o c a l topography, c ) . Stagnant i c e phase: v a l l e y i c e i s cut o f f from i t s source, but s t i l l behaves p l a s t i c a l l y , d) . Dead i c e phase: i c e i s too t h i n to flow. 20 2.2.2 The Scandinavian Ice Sheet The Scandinavian Ice Sheet o r i g i n a t e d i n the Scandinavian Mountains at the s t a r t of Weichsel G l a c i a t i o n w i t h the growth of a l p i n e g l a c i e r s . G l a c i e r s f l o w i n g eastward from the mountains expanded and coalesced i n t o piedmont g l a c i e r s on the Bothnian lowlands ( F l i n t 1971). Further expansion and t h i c k e n i n g l e a d to the formation of an i c e sheet which b u r i e d the mountains and extended n e a r l y 13 00 km to the southeast, where flow was unimpeded. The maximum extent corresponds to c o n t i n e n t a l g l a c i a t i o n or phase 4 of Davis and Mathews. During d e g l a c i a t i o n the i c e sheet thinned r a p i d l y and r e t r e a t e d back toward the mountains, l e a v i n g a s e r i e s of end moraines (Eronen and V e s a j o k i 1988; F l i n t 1971). The t h i n n i n g i c e caused upland areas i n northeastern F i n l a n d and s e v e r a l northeast d r a i n i n g v a l l e y s to become i c e f r e e w h i l e t h i c k i c e remained i n v a l l e y bottoms (Johansson 1988; F l i n t 1971). As a r e s u l t numerous l a r g e lakes were dammed i n v a l l e y s by i c e i n t h e i r lower reaches, as occurred i n the Kamloops area of B r i t i s h Columbia. Highlands i n southern Sweden are very f l a t and i c e here downwasted and stagnated, l e a v i n g dead i c e topography of hummocky a b l a t i o n t i l l , kames, and k e t t l e s ( H i l l e f o r s 1979) 2.2.3 Summary of Ice Sheet Deglaciation Ice sheet d e g l a c i a t i o n i s l a r g e l y i n f l u e n c e d by l o c a l topography and p r o x i m i t y to the edge of the i c e sheet. Near the margins, f r o n t a l r e t r e a t i s common. Elsewhere, i c e 21 downwastes. Areas w i t h moderate r e l i e f , such as the Kamloops area and northeastern F i n l a n d , a l l o w the i c e sheet to become separated i n t o i s o l a t e d masses i n v a l l e y s . This r e s u l t s i n downwasting and stagnation w i t h damming of v a l l e y s by i c e i n t h e i r lower reaches. Low r e l i e f areas i n the i n t e r i o r of the i c e sheet are l i k e l y to experience widespread s t a g n a t i o n and hummocky a b l a t i o n t i l l i s l i k e l y to be common. 2.3 Combined Mountain and Ice Sheet Gla c i a t i o n Areas w i t h mountains high enough to support a l p i n e g l a c i e r s d u r i n g g l a c i a l c y c l e s , and which are l o c a t e d i n a p o s i t i o n which allows them to be overtopped by an advancing i c e sheet, may experience both a l p i n e and i c e sheet g l a c i a t i o n . These areas do not develop major accumulation zones w i t h r a d i a l l y outward flow because they do not rec e i v e enough snow or do not have s u f f i c i e n t area above snowline. E x i s t i n g s t u d i e s i n the B r i t i s h Columbia Cascades (Saunders et a l . 1987; Mathews 1968) suggest that t h i s s t y l e may have occurred here. Thus i t i s u s e f u l to examine s e v e r a l examples of t h i s s t y l e of g l a c i a t i o n . The l a s t g l a c i a t i o n i n the Washington Cascade Mountains, the I n s u l a r Mountains of Vancouver I s l a n d , and s e v e r a l areas i n the northeastern United States w i l l be des c r i b e d as examples of t h i s s t y l e of g l a c i a t i o n . 2.3.1 Washington Cascade Mountains During Fraser G l a c i a t i o n the g l a c i a t i o n t h r e s h o l d dropped below the l e v e l of most summits i n Washington (Porter 1977) . 22 I t was lowest where topographic lows, such as the Skagit R i v e r v a l l e y permitted moist maritime a i r to penetrate w e l l i n t o the mountains. Thus l a r g e r and lower g l a c i e r s could form near these v a l l e y s . Studies i n the Skagit V a l l e y and Washington Pass area i n the c e n t r a l Cascades by Waitt (1975, 1977), the Snowqulamie area by Mackin (1941) and Lake Tapps area by C r a n d e l l (1963) (Figure 2.3) show that a l p i n e g l a c i e r s advanced down v a l l e y s d u r i n g e a r l y Fraser G l a c i a t i o n , then receded before the C o r d i l l e r a n Ice Sheet extended i n t o the region, (Waitt Figure 2.3: Lo c a t i o n map of the southern B r i t i s h Columbia and northern Washington Cascades showing the l o c a t i o n of s t u d i e s mentioned i n the t e x t . 23 1977, 1975; C r a n d e l l 1963; Mackin 1941) l i k e l y p r i o r to 18,000 years BP (Armstrong et a l . 1965). The C o r d i l l e r a n Ice Sheet flowed southward i n t o Washington through d i v i d e s not covered by Fraser G l a c i a t i o n a l p i n e i c e (Waitt 1977). At the g l a c i a l maximum the i c e surface reached an a l t i t u d e of greater, than 2600 m at the I n t e r n a t i o n a l Boundary, higher than most summits i n the area (Waitt and Thorson 1983). Very l i t t l e e r o s i o n was accomplished by the i c e sheet so Waitt (1977) assumed i t overtopped summits only b r i e f l y . At i t s southern l i m i t the C o r d i l l e r a n Ice Sheet was l a r g e l y r e s t r i c t e d to the Puget Lowland. I t flowed i n t o v a l l e y s b u i l d i n g end moraines and impounding lakes behind i c e dams (Crandell 1963; Mackin 1941), but d i d not overtop summits. The t i m i n g of i c e r e t r e a t i n the Cascade Mountains i s not known i n d e t a i l . However, Mathews (1968) found evidence that the L i g h t n i n g Creek v a l l e y , i n southern B r i t i s h Columbia, c a r r i e d meltwater from the i n t e r i o r toward the coast, i m p l y i n g that the Cascade v a l l e y s were i c e fr e e before the I n t e r i o r . This i m p l i e s d e g l a c i a t i o n before 11,500 to 10,000 years BP (Clague 1981). The C h i l l i w a c k G l a c i e r had receded by 11,900 years BP (Saunders et a l . 1987). Kwoiek Creek i n the Coast Mountains was i c e fr e e before 11,115 years BP (Souch 1989). Because mountains i n the headwaters of Kwoiek Creek are higher and c l o s e r to i c e accumulation zones than nearby p a r t s of the Cascade Mountains i t i s probable that the Cascades became i c e fr e e f i r s t . Because the Washington Cascades are c l o s e r to the 24 p e r i p h e r y of the i c e sheet i t i s probable that they were i c e fr e e before areas f u r t h e r to the north. The Puget Lobe of the C o r d i l l e r a n Ice Sheet r e t r e a t e d r a p i d l y but i r r e g u l a r l y by downwasting and f r o n t a l r e t r e a t , s e v e r a l s t i l l s t a n d s are recorded by te r m i n a l moraines (Waitt and Thorson 1983) . Marginal lakes formed i n f r o n t of the i c e sheet dur i n g r e t r e a t , l e a v i n g s i l t d eposits and numerous drainage channels. A l p i n e g l a c i e r s do not appear to have advanced a f t e r the r e t r e a t of the C o r d i l l e r a n Ice Sheet as unweathered e r r a t i c s are w i d e l y d i s t r i b u t e d from v a l l e y f l o o r s to r i d g e c r e s t s , i n c l u d i n g on ci r q u e f l o o r s , and no Cascades d e r i v e d d r i f t o v e r l i e s Puget lobe d r i f t (Waitt and Thorenson 1983; Waitt 1975) . 2.3.2 Insular Mountains of Vancouver Island At the s t a r t of Fraser G l a c i a t i o n , g l a c i e r s formed around the high mountains of norbh c e n t r a l Vancouver I s l a n d and flowed down e x i s t i n g v a l l e y s (Howes 1981). A l p i n e g l a c i a t i o n was w e l l e s t a b l i s h e d by 25,000 years BP. Lower peaks t o the south remained i c e f r e e u n t i l overridden by the C o r d i l l e r a n Ice Sheet (Howes 1983; A l l e y and Chatwin 1979). During the Fraser maximum Coast Mountain i c e coalesced w i t h and overrode Vancouver I s l a n d i c e , reaching an a l t i t u d e of at l e a s t 1500 m (Howes 1981). During d e g l a c i a t i o n i c e downwasted, uplands emerged and the i c e sheet separated i n t o d i s c r e t e v a l l e y g l a c i e r s . Down 25 v a l l e y flow was maintained while there was s u f f i c i e n t t h i c k n e s s of i c e (Howes 1983, 1981). E v e n t u a l l y i c e thinned and stagnated d e p o s i t i n g t h i c k sequences of i c e contact and r e c e s s i o n a l g r a v e l s . Howes (1981) found no evidence that c i r q u e g l a c i e r s were a c t i v e at the end of d e g l a c i a t i o n on northern or c e n t r a l Vancouver I s l a n d , however i t i s l i k e l y t h at small i c e masses remained i n cir q u e s f o r some time. A l l e y and Chatwin (1979) found evidence, i n the form of r a d i a l flow away from the highest summits, f o r a resurgence of a l p i n e g l a c i a t i o n i n some upland areas on southern Vancouver I s l a n d . 2.3.3 The Presidential Range, New Hamphshire The P r e s i d e n t i a l Range i n New Hampshire (Figure 2.4) i s the highest p a r t of the White Mountains, w i t h peaks to 1900 m and ci r q u e f l o o r s between 1200 and 1350 m. Goldthwait (1970) has found evidence of l o c a l a l p i n e g l a c i e r s which formed at the s t a r t of Late Wisconsinan G l a c i a t i o n . At the peak of Late Wisconsinan G l a c i a t i o n a l l summits were overtopped by the Laurentide Ice Sheet which advanced i n t o the reg i o n from the north. This has r e s u l t e d i n considerable smoothing and rounding of a l p i n e forms. During d e g l a c i a t i o n the i c e sheet downwasted, and i c e i n v a l l e y s was cut of from i t s source. This r e s u l t e d i n st a g n a t i o n i n many of the l a r g e r v a l l e y s . Hummocky dead i c e de p o s i t s are common (Goldthwait 1970). There i s co n t i n u i n g debate about whether or not a l p i n e g l a c i e r s were a c t i v e i n the P r e s i d e n t i a l Range, at the end of 26 Legend West Central Maine Presidential Range N G een Mounra n Figure 2.4: Loca t i o n map of northeastern United States showing the l o c a t i o n of st u d i e s mentioned i n the t e x t . d e g l a c i a t i o n (Gerath and Fowler 1982; Bradley 1981; Goldthwait 1970). No t e r m i n a l moraines of a l p i n e g l a c i e r s have been found but f r e s h s t r i a t i o n s e x i s t i n c i r q u e s . Goldthwait (1970) a s s e r t e d that the s t r i a t i o n s were formed by post g l a c i a l processes such as avalanching and that the a l p i n e g l a c i e r s were not present at 'the end of the l a s t g l a c i a t i o n . Bradley (1981) p o s t u l a t e d that a l p i n e g l a c i e r s were a c t i v e during d e g l a c i a t i o n to form the s t r i a t i o n s and that they coalesced w i t h stagnant v a l l e y i c e , thus e l i m i n a t i n g a l l evidence of t e r m i n i . Gerath and Fowler (1982) concluded that i c e i n the P r e s i d e n t i a l Range downwasted r a p i d l y when the snowline rose 27 above the e l e v a t i o n of the summits, and thus no a l p i n e g l a c i e r s were present during d e g l a c i a t i o n . 2.3.4 Green Mountains, Vermont The Green Mountains of Vermont r i s e to an e l e v a t i o n of 1350 m. They were overtopped by i c e f l o w i n g from the north dur i n g the Wisconsinan maximum ( F l i n t 1951). During d e g l a c i a t i o n , i c e i n lowlands downwasted and r e t r e a t e d northward, toward the centre of the Laurentide Ice Sheet, damming a lake behind the i c e . Large d e l t a s occur at the mouths of v a l l e y s d r a i n i n g from the Green Mountains implying that sediment was su p p l i e d by a c t i v e i c e i n the mountains (Connally 1982). In a d d i t i o n , end and l a t e r a l moraines and outwash p l a i n s that e x i s t i n these v a l l e y s are thought to have been formed by a c t i v e c i r q u e g l a c i e r s during Laurentide Ice Sheet r e c e s s i o n (Wagner 1970). 2.3.5 West Central Maine The highest peak i n west C e n t r a l Maine i s Mt. Katahdin at 1600 m. Several c i r q u e s are present i n t h i s area between 900 and 1050 m. The cirq u e s are thought to have developed before the l a s t i c e sheet (Borns and C a l k i n 1977). A l l c i r q u e s have been modified by o v e r r i d i n g i c e . During d e g l a c i a t i o n the i c e sheet thinned and stagnated throughout the mountains without any r e o r g a n i z a t i o n of flow which would i n d i c a t e the presence of a c t i v e c i r q u e g l a c i e r s . 28 2.3.6 Summary of Combined Mountain and Ice Sheet G l a c i a t i o n In a l l the above areas cirque g l a c i e r s formed at the s t a r t of the g l a c i a l c y c l e when climate d e t e r i o r a t i o n caused l o c a l snowline to drop below summit e l e v a t i o n s . No ranges i n v e s t i g a t e d were high enough to generate extensive i c e caps but were overtopped by r e g i o n a l i c e at the g l a c i a l maximum. The r e g i o n a l i c e sheet e i t h e r coalesced w i t h l o c a l g l a c i e r s as on Vancouver I s l a n d (Howes 1983) or l o c a l g l a c i e r s r e t r e a t e d before the advance of the r e g i o n a l i c e sheet as i n Washington (Waitt 1975, 1977). Whether or not l o c a l g l a c i e r s r e t r e a t e d before the advance of an i c e sheet l i k e l y depended on the nearness of the area to the i c e margin. In areas such as Washington, which are near the i c e margin, c l i m a t e a m e l i o r a t i o n could have begun to e f f e c t l o c a l g l a c i e r s before i t a f f e c t e d the i c e sheet due to the d i f f e r i n g response times of the s m a l l e r and l a r g e r i c e masses. Thus a l p i n e g l a c i e r s c o uld recede before the i c e sheet a t t a i n e d i t s maximum extent. D e g l a c i a t i o n was c o n t r o l l e d by l o c a l topography, e l e v a t i o n of snowline and distance from the edge of the i c e sheet. As c l i m a t e warming began snowline rose, the i c e sheet thinned and upland areas became i c e f r e e . In a l l areas the i c e sheet r e t r e a t e d down-valley out of the mountain ranges. Stagnation of the i c e sheet i n l a r g e v a l l e y s was common but not u n i v e r s a l . I f cirques were below the l o c a l snowline at the time of d e g l a c i a t i o n , no a c t i v e g l a c i e r s were present, f o r example the Green Mountains (Wagner 19 70; Connally 1982) . In t h i s case, i c e i n l o c a l v a l l e y s may have been cut o f f from 29 source areas, l e a d i n g to downwasting and p o s s i b l y s t a g n a t i o n . I f c i r q u e s were above l o c a l snowline, g l a c i e r s occupied c i r q u e s during d e g l a c i a t i o n , as occurred i n w e s t - c e n t r a l Maine (Borns and C a l k i n 1977), and some v a l l e y s were d e g l a c i a t e d by f r o n t a l r e t r e a t of a c t i v e v a l l e y g l a c i e r s . 30 CHAPTER 3 METHODS OF DETERMINING STYLES AND PATTERNS OF GLACIATION In order t o determine which of the g l a c i a t i o n s t y l e s d e s c r i b e d i n Chapter 2 occurred i n a g l a c i a t e d area, i t i s necessary t o i d e n t i f y d i a g n o s t i c c r i t e r i a . Thus the landforms and sediments that are formed by g l a c i a t i o n and t h e i r i m p l i c a t i o n s f o r the st a t e of the i c e and i c e marginal p o s i t i o n s are des c r i b e d i n t h i s chapter. Techniques of r e c o g n i z i n g g l a c i a t i o n s t y l e from s u i t e s of landforms and deposits are a l s o described. Then the d e t a i l s of the techniques used i n t h i s research p r o j e c t , p a r t i c u l a r l y the f i e l d program, are discussed. 3.1 Landforms and Sediments Indicative of Glaciation Styles Landforms and s u r f i c i a l m a t e r i a l s provide evidence of the processes that have created the present landscape. In many p a r t s of B r i t i s h Columbia there has been only s l i g h t m o d i f i c a t i o n of the landscape since the l a s t g l a c i a t i o n . Thus most landforms and s u r f i c i a l deposits r e l a t e d i r e c t l y t o the processes that occurred during Fraser G l a c i a t i o n and can be used t o i n f e r s t y l e s of g l a c i a t i o n . 3.1.1 Erosional Landforms E r o s i o n a l landforms include a l l features carved by i c e or meltwater, such as ci r q u e s , aretes, troughs and meltwater channels. E r o s i o n a l forms may have been created during one or many g l a c i a l p e r i o d s . As e r o s i o n a l forms can not g e n e r a l l y be 31 dated, the e a s i e s t way of es t i m a t i n g the l e n g t h of time r e q u i r e d f o r e r o s i o n a l features to form i s by comparing the volume eroded w i t h e s t a b l i s h e d r a t e s of er o s i o n . Andrews (1975 p 113) estimated r a t e s of g l a c i a l e r o s i o n by two methods. The f i r s t y i e l d s data over time s c a l e s on the order of 1 m i l l i o n years by d i v i d i n g the amount of lowering r e q u i r e d t o create c i r q u e basins by the t o t a l age of the b a s i n . This y i e l d e d a r a t e of roughly 400 mm/1000 years i n Scotland, and 50 mm/1000 years f o r a p o l a r g l a c i e r . The second technique i s v a l i d f o r time s c a l e s on the order of 10 years and c a l c u l a t e s the volume of m a t e r i a l t r a n s p o r t e d by present streams d i s c h a r g i n g from the snout of g l a c i e r s . This y i e l d e d a higher r a t e of e r o s i o n of between 1000 and 5000 mm/lOOOyears f o r r i v e r s i n B a f f i n I s l a n d , Norway, Iceland and the Karakoram. These r a t e s are very approximate and i n v o l v e s e v e r a l assumptions. There i s no way of determining f o r how long out of the t o t a l of a l l g l a c i a l p e r i o d s a p a r t i c u l a r feature was being eroded. For example a cirqu e may be carved mainly during the a l p i n e phase of a g l a c i a l c y c l e . The short time s c a l e s a s s o c i a t e d w i t h the measurement of stream load means that these r a t e s may not be re p r e s e n t a t i v e of longer time s c a l e s . The measurements over long time s c a l e s a l s o i n c l u d e non g l a c i a l p e r i o d s , so the two ra t e s are c o n s i s t e n t . In a d d i t i o n stream measurements made i n f r o n t of v a l l e y g l a c i e r s that could be eroding s o f t sediments, may g i v e e r o s i o n r a t e s that are not r e p r e s e n t a t i v e of the er o s i o n of bedrock. These ra t e s should t h e r e f o r e be used o n l y as a rough guide to how much time was re q u i r e d to accomplish 32 the amount of e r o s i o n observed. They may however, be u s e f u l f o r i n d i c a t i n g the p r o b a b i l i t y that observed e r o s i o n was accomplished only by the l a s t g l a c i a t i o n . 3.1.1.1 Cirques, Aretes and Horns Cirques, aretes and horns are features of a l p i n e g l a c i a t i o n which formed during the a l p i n e , intense a l p i n e and mountain i c e sheet phases of Davis and Mathews. Cirques i n d i c a t e the general accumulation zones f o r v a l l e y g l a c i e r s and mountain i c e sheets. Past r e g i o n a l snowline can be approximated from the e l e v a t i o n of c i r q u e f l o o r s ( F l i n t 1971). Horns and a r e t e s are u s u a l l y sharp features which remain above a l p i n e g l a c i e r s . Cirques w i l l commonly be reoccupied by a l p i n e g l a c i e r s at the s t a r t of each g l a c i a l c y c l e , thus a l p i n e f eatures are g e n e r a l l y the product of s e v e r a l g l a c i a t i o n s . Where i c e l a t e r flows overtop of a l p i n e f e a t u r e s , they become rounded, smoothed and s t r i a t e d . Thus i t can be assumed that rounded a l p i n e features were formed by mountain g l a c i a t i o n p r i o r to o v e r r i d i n g by an i c e sheet. I f a l p i n e g l a c i a l landforms are rounded but s t i l l prominent, then the d u r a t i o n of the i c e sheet was l i k e l y short (Waitt 1975; F l i n t 1971). The p o i n t of t r a n s i t i o n from rounded to sharp r i d g e c r e s t s and summits i n d i c a t e s the approximate e l e v a t i o n of the surface of the i c e sheet. 33 3.1.1.2 Troughs G l a c i a l troughs were carved by a c t i v e i c e f l o w i n g i n channels any time from e a r l y advance u n t i l r e t r e a t or sta g n a t i o n . Three types of troughs have been recognized; each i s i n d i c a t i v e of a d i f f e r e n t s t y l e of g l a c i a t i o n (Sugden and .John 1976) . A l p i n e troughs were carved by v a l l e y g l a c i e r s d u r i n g the a l p i n e phase of Davis and Mathews. They head i n c i r q u e s and t h e i r e n t i r e l e n g t h i s overlooked by higher ground (Sugden and John 1976). Thus when these troughs are carved, adjacent peaks stand above the general i c e l e v e l . In some areas troughs change downstream to V shaped v a l l e y s c h a r a c t e r i s t i c of f l u v i a l e r o s i o n . This t r a n s i t i o n marks e i t h e r the t e r m i n a l p o s i t i o n of a v a l l e y g l a c i e r or the l o c a t i o n at which the v a l l e y g l a c i e r merged w i t h an i c e sheet (Ryder et a l . 1991). The l e n g t h of a l p i n e g l a c i e r s should be p r o p o r t i o n a l t o the area of t h e i r c irques ( F l i n t 1971; Goldthwait 1970). Thus i f the U - V t r a n s i t i o n represents the t e r m i n a l p o s i t i o n of the g l a c i e r s t h i s r e l a t i o n s h i p should be apparent from r e g i o n a l study of g l a c i a l morphometry. I c e l a n d i c s t y l e troughs head i n broad c o l s r a t h e r than c i r q u e s . There i s no w e l l defined area of accumulation w i t h i n the trough. They are thought to have been cut by i c e s p i l l i n g over the trough head, so formed when i c e was t h i c k enough to flow across low p o i n t s on d i v i d e s (Sugden and John 1976; Embleton and King 1975). These form during the intense a l p i n e and mountain i c e sheet phases of Davis and Mathews. 34 The f i n a l type of trough i s the through trough, which i s open at both ends, o f t e n forming low passes through mountain ranges. L i k e the I c e l a n d i c troughs there i s no l o c a l accumulation area. These troughs are thought to have been eroded under i c e sheets, when i c e streams i n t o and e x p l o i t s p r e - e x i s t i n g v a l l e y s which are then eroded headward and widened and deepened. (Clapperton and Sugden 1977; Sugden and John 1976) . They l i k e l y form during Davis and Mathews 1 intense a l p i n e and mountain i c e sheet phases. Troughs w i l l g e n e r a l l y be reoccupied by v a l l e y g l a c i e r s d u r i n g each g l a c i a t i o n . I t i s thus d i f f i c u l t to determine how many g l a c i a l c y c l e s these features represent. Repeated g l a c i a t i o n s of d i f f e r e n t magnitude can l i k e l y r e s u l t i n a b l u r r i n g of the U-V t r a n s i t i o n of a l p i n e troughs. L a t e r g l a c i a t i o n s which are smaller than e a r l i e r ones w i l l leave few e r o s i o n a l remnants as the e x i s t i n g troughs w i l l not be f i l l e d . 3.1.1.3 Meltwater Channels Meltwater channels are steep-sided, f l a t f l o o r e d channels carved by water from melting i c e . Several types have been de s c r i b e d by Derbyshire (1962). Three of these have been recognized i n the study areas: s u b g l a c i a l channels which formed under i c e , l a t e r a l meltwater channels which formed at the i c e margin, and d i r e c t overflow channels, which flowed away from the i c e . S u b g l a c i a l channels formed under warm based g l a c i e r s . Thus they may have formed at any time throughout the g l a c i a l 35 p e r i o d , although most l i k e l y during d e g l a c i a t i o n when abundant meltwater was generated. They have p o s s i b l y been carved by water under high h y d r o s t a t i c pressure. As a r e s u l t they tend to be deep rock canyons a l i g n e d d i r e c t l y downslope. They y i e l d i n f o r m a t i o n about i c e marginal p o s i t i o n s only i f the stream course changes a b r u p t l y from s u b a e r i a l to s u b g l a c i a l . L a t e r a l meltwater channels formed along the margin of i c e sheets and g l a c i e r s , between i c e and the adjacent h i l l s i d e (Derbyshire 1962). They tend to be p a r a l l e l or s l i g h t l y o b l i q u e to contours r a t h e r than running d i r e c t l y down slope. They may not c o n t a i n present-day streams. These are the most u s e f u l type of channel f o r r e c o n s t r u c t i n g g l a c i a l h i s t o r y because they mark the p o s i t i o n of the i c e margin at the time they formed. Where s e v e r a l contemporaneous channels are present, the shape of the r e t r e a t i n g i c e sheet margin can be recon s t r u c t e d . When successive channels occur the p a t t e r n of r e t r e a t can be determined. L a t e r a l meltwater channels a l s o i n d i c a t e the i c e surface gradient and thus i n d i c a t e the d i r e c t i o n of i c e flow and whether or not l o c a l flow was present d u r i n g d e g l a c i a t i o n (Fulton 1967). They formed during phase 3 or the stagnant i c e phase of Fulton's (1967) four phases of d e g l a c i a t i o n . D i r e c t overflow channels drained away from the i c e margin, e i t h e r d i r e c t l y down v a l l e y or over d i v i d e s i f water was ponded on the upstream side of i c e . Where flow over d i v i d e s occurred, channels were cut i n t o c o l s or rid g e tops. This was most common w i t h downwasting and stagnant i c e and as 36 the i c e mass thinned during the e a r l y stages of f r o n t a l r e t r e a t . Where meltwater flowed d i r e c t l y down v a l l e y , channels are o f t e n not apparent although outwash p l a i n s , fans, k e t t l e d outwash t e r r a c e s or other g l a c i o f l u v i a l deposits may be present, or the present stream may be u n d e r f i t to the v a l l e y (Fulton 1967). Flow d i r e c t l y down v a l l e y occurred d u r i n g f r o n t a l r e t r e a t , both normal and wit h s t a g n a t i o n of the snout. 3.1.1.4 Streamlined Forms Streamlined forms such as grooves, s t r i a t i o n s , and roches moutonnees were carved by a c t i v e l y f l o w i n g i c e under e i t h e r a l p i n e g l a c i e r s or i c e sheets. They are u s e f u l i n d i c a t o r s of the extent of a c t i v e i c e and they i n d i c a t e i c e flow d i r e c t i o n . Rounded r i d g e tops or summits wi t h streamlined forms i n d i c a t e overtopping by a c t i v e l y f l o w i n g i c e during the mountain i c e sheet stage of Davis and Mathews. 3.1.2 Landforms and Materials of Glacial Deposition G l a c i a l m a t e r i a l s were l a i d down by a c t i v e or stagnant i c e or by meltwater, during e i t h e r advance or r e c e s s i o n . They may have been draped over e x i s t i n g topography or s c u l p t e d i n t o c h a r a c t e r i s t i c landforms. 3.1.2.1 Till and Erratics Basal t i l l i s d e b r i s r e l e a s e d by melting at the base of a g l a c i e r . Two types are recognized: lodgement t i l l was deposited beneath a c t i v e l y f l o w i n g i c e and basa l meltout t i l l 37 was deposited by melting at the base of s t a t i o n a r y i c e (Dreimanis 1976). Both types of basal t i l l are massive, unsorted and c o n s o l i d a t e d . Lodgement t i l l i s more h i g h l y c o n s o l i d a t e d than meltout t i l l . C l a s t s are subrounded t o subangular and are o f t e n faceted and s t r i a t e d (Dreimanis 1976; F l i n t 1971). C l a s t l i t h o l o g y i s v a r i a b l e and r e f l e c t s the source areas. Thus i f c l a s t s of d i s t i n c t i v e l i t h o l o g i e s are present, i c e flow d i r e c t i o n can be determined. C l a s t l i t h o l o g y can be u s e f u l f o r d i s t i n g u i s h i n g between t i l l s of l o c a l a l p i n e g l a c i e r s and i c e sheets ( H e l l e r 1980). T i l l f a b r i c i s the o r i e n t a t i o n of the long axes of elongate p a r t i c l e s w i t h i n basal t i l l . O r i e n t a t i o n developed from s t r e s s e s due to g l a c i a l t r a n s p o r t and d e p o s i t i o n (Dreimanis 1976). T i l l f a b r i c i s used t o i n d i c a t e i c e flow d i r e c t i o n , and has been used to d i s t i n g u i s h meltout and lodgement t i l l (Boulton 1971). In meltout t i l l a/b planes are p a r a l l e l to the plane of d e p o s i t i o n . In lodgement t i l l the long axes has a tendancy to d i p upflow, but t h i s i s commonly masked by the e f f e c t of bedrock topography (Boulton 1971). A b l a t i o n t i l l accumulated on top of downwasting i c e . I t d i f f e r s from ba s a l t i l l by having a coarser t e x t u r e and more angular c l a s t s and by l a c k of c o n s o l i d a t i o n . Large amounts of hummocky a b l a t i o n t i l l i n d i c a t e widespread s t a g n a t i o n has occurred. The presence of e r r a t i c s on ridge tops and summits confirms that i c e overtopped an area. I f the source of the e r r a t i c s i s known i c e flow d i r e c t i o n can be determined. 38 3.1.2.2 Moraines and other landforms composed of t i l l End moraines are r i d g e s composed of t i l l that formed at the s i d e or terminus of g l a c i e r s when the snout of a c t i v e l y -f l o w i n g i c e remained s t a t i o n a r y , or i c e readvanced dur i n g d e g l a c i a t i o n . These can be ass o c i a t e d w i t h i c e sheets or v a l l e y g l a c i e r s . T i l l p l a i n s were deposited under i c e sheets. When f l u t e s , drumlins, crag and t a i l or other streamlined formations are present i c e flow d i r e c t i o n can be determined. The lower slopes of troughs g e n e r a l l y are mantled w i t h t i l l deposited by i c e f l o w i n g down the v a l l e y . 3.1.2.3 Glaciofluvial material G l a c i o f l u v i a l m a t e r i a l was deposited by meltwater at any time d u r i n g g l a c i e r advance, maximum, or r e t r e a t . I t c o n s i s t s of sands and g r a v e l s , and may i n c l u d e boulder g r a v e l s . Extreme ranges and abrupt changes i n g r a i n s i z e and s o r t i n g may occur. G l a c i o f l u v i a l d eposits are aggradational and as a r e s u l t are g e n e r a l l y t h i c k e r than more recent f l u v i a l d e p o s i t s . Often o n l y a t h i n cap of f l u v i a l m a t e r i a l was deposited on top of g l a c i o f l u v i a l g r a v e l s before the present stream began downcutting. Outwash was deposited by meltwater f l o w i n g away from the g l a c i e r terminus. M a t e r i a l deposited near the g l a c i e r snout tends to be coarse grained and have crude h o r i z o n t a l s t r a t i f i c a t i o n , while more d i s t a l d eposits are f i n e r g r a i n e d and may d i s p l a y planar cross bedding ( M i a l l 1983) . Outwash 39 p l a i n s that have been d i s s e c t e d by p o s t g l a c i a l streams leave t e r r a c e s w e l l above present day r i v e r s . Advance outwash was deposited i n f r o n t of advancing g l a c i e r s . As a r e s u l t i t has a coarsening upward sequence and was o f t e n overridden by the g l a c i e r , r e s u l t i n g i n a more co n s o l i d a t e d deposit than t y p i c a l r e c e s s i o n a l outwash. Kame t e r r a c e s and kames were deposited i n contact w i t h i c e . G e n e r a l l y bedding i s more d i s r u p t e d than that of outwash de p o s i t s due to melting of i c e blocks a f t e r d e p o s i t i o n , and the t e r r a c e may be p i t t e d w i t h k e t t l e holes ( F l i n t 1971). Eskers and moulin kames are s u b g l a c i a l f l u v i a l m a t e r i a l that were preserved only under stagnant i c e . Extensive kames, kame and k e t t l e topography and hummocky g l a c i o f l u v i a l d e p o s i t s i n d i c a t e d e p o s i t i o n i n contact w i t h stagnant i c e . Kame t e r r a c e s mark i c e marginal p o s i t i o n s and are most extensive i n a s s o c i a t i o n w i t h stagnant i c e . 3.1.2.4 Glaciolacustrine material G l a c i o l a c u s t r i n e m a t e r i a l i s composed of f i n e sand, s i l t and minor c l a y . Normally i t i s well-laminated or well-bedded. Where t h i c k sequences of t h i s m a t e r i a l have been d i s s e c t e d by p o s t g l a c i a l streams, t e r r a c e s are formed. The presence of g l a c i o l a c u s t r i n e deposits i n d i c a t e s damming of meltwater, by a c t i v e or stagnant i c e , during g l a c i e r advance or r e t r e a t . The extent of the deposits i s i n d i c a t i v e of the extent of the g l a c i a l l a k e . As these deposits commonly terminated against an i c e dam, t h e i r downstream l i m i t may mark a former i c e margin. 40 3.1.3 Suites Of Landforms And Materials Expected With Each Type Of G l a c i a t i o n Each s t y l e of g l a c i a t i o n i s c h a r a c t e r i z e d by a s u i t e of landforms and d e p o s i t s . Most i n d i v i d u a l features can form under more than one s t y l e of g l a c i a t i o n , so s e v e r a l are needed to determine s t y l e . Mountain g l a c i a t i o n i s c h a r a c t e r i z e d by e r o s i o n a l forms. Cirques, a r e t e s , horns and deep, steep sid e d troughs dominate: these w i l l be sharp and modified only s l i g h t l y by p o s t - g l a c i a l weathering. T i l l w i l l commonly be present on lower v a l l e y slopes and v a l l e y bottoms. D e g l a c i a t i o n by normal f r o n t a l r e t r e a t commonly r e s u l t s i n the d e p o s i t i o n of outwash over t i l l on v a l l e y f l o o r s . Occasional pockets of g l a c i o l a c u s t r i n e s i l t s may be present on v a l l e y s i d e s , l i k e l y due to d e p o s i t i o n i n small i c e marginal ponds. L a t e r a l and t e r m i n a l moraines may be present, however these are e a s i l y destroyed by l a t e r e r o s i o n . Because g l a c i e r s were t y p i c a l l y a c t i v e throughout d e g l a c i a t i o n , i c e stagnation deposits are r a r e . D e g l a c i a t i o n by f r o n t a l r e t r e a t w i t h stagnation of the snout, a l s o r e s u l t s i n g l a c i o f l u v i a l deposits o v e r l y i n g t i l l on v a l l e y f l o o r s . At the s t a g n a t i n g snout, kames, and i c e contact g l a c i o l a c u s t r i n e m a t e r i a l may have been deposited. K e t t l e holes may be present where i c e blocks became i s o l a t e d i n f r o n t of the r e t r e a t i n g margin. Ice sheet g l a c i a t i o n i s c h a r a c t e r i z e d by subdued topography and rounded, streamlined forms. Sharp summits and r i d g e c r e s t s are absent. T i l l may be deposited at any 41 e l e v a t i o n , i n c l u d i n g on summits and r i d g e c r e s t s . Drumlins, and f l u t e s are common, p a r t i c u l a r l y on upland areas. These were formed while the i c e was s t i l l a c t i v e . D e g l a c i a t i o n was commonly by downwasting and stagnation, r e s u l t i n g i n f e a t u r e s such as eskers, kames, kame te r r a c e s and hummocky a b l a t i o n t i l l i n v a l l e y s and lowlands. Drainage was o f t e n d i s r u p t e d and l a r g e i c e contact lakes formed, l e a v i n g extensive d e p o s i t s of g l a c i o l a c u s t r i n e sediments. In areas which have experienced both mountain and i c e sheet g l a c i a t i o n , a l p i n e forms may be rounded but s t i l l w e l l d e f i n e d . Streamlined forms are common on summits and r i d g e s . V a l l e y s may c o n t a i n deposits of e i t h e r f r o n t a l r e t r e a t , downvalley r e t r e a t of a c t i v e i c e , or stagnation and damming depending on whether or not l o c a l g l a c i e r s were a c t i v e near the end of g l a c i a t i o n . Thus landforms and deposits of both mountain and i c e sheet g l a c i a t i o n may be present and t h e i r d i s t r i b u t i o n w i l l depend on l o c a l c o n d i t i o n s . 3.2 F i e l d Techniques and Analysis Used To Determine Patterns and Styles of G l a c i a t i o n i n the Cascade Mountains R e c o n s t r u c t i o n of a complete h i s t o r y of g l a c i a t i o n r e q u i r e s the i d e n t i f i c a t i o n of features formed at s e v e r a l stages of the g l a c i a l c y c l e , from the s t a r t of g l a c i e r formation u n t i l the area i s once again i c e f r e e . This study r e l i e d h e a v i l y on the morphology of e r o s i o n a l forms such as c i r q u e s and troughs, d e p o s i t i o n a l sequences on v a l l e y f l o o r s , and i c e marginal f e a t u r e s such as moraines and meltwater channels. Data 42 c o l l e c t i o n began w i t h t e r r a i n mapping on a i r photographs and was f o l l o w e d by more d e t a i l e d study i n the f i e l d . 3.2.1 Air Photograph Interpretation The f i r s t step i n t h i s study i n v o l v e d t e r r a i n mapping on 1:15,000 a i r photographs of each study area, u s i n g the B r i t i s h Columbia system of t e r r a i n c l a s s i f i c a t i o n (Howes and Kenk 1988). Under t h i s system, the land surface i s d i v i d e d i n t o polygons on the b a s i s of s u r f i c i a l m a t e r i a l type and t e x t u r e , landforms, and a c t i v e g e o l o g i c a l processes. On-site symbols are used t o d e l i m i t the l o c a t i o n and s i z e of features such as c i r q u e s , meltwater channels and moraines. Many landforms, such as moraines, meltwater channels and drumlins, are more apparent on a i r photos than on the ground. Emphasis was placed on i d e n t i f y i n g d i a g n o s t i c landforms and m a t e r i a l s that could be used f o r the i n t e r p r e t a t i o n of s t y l e s of g l a c i a t i o n and, i n p a r t i c u l a r , i c e marginal f e a t u r e s such as moraines and meltwater channels. 3.2.2 Field Program A i r photo i n t e r p r e t a t i o n was followed by s i x weeks of f i e l d checking i n J u l y and August, 1993. The two goals of the f i e l d program were to v e r i f y the accuracy of t e r r a i n mapping and t o make a d d i t i o n a l observations and measurements. Rock weathering and v a l l e y f i l l s t r a t i g r a p h y were recorded, and sediment cores were obtained from a moraine-dammed la k e . 43 3.2.2.1 Surficial Materials S u r f i c i a l m a t e r i a l s were examined l a r g e l y i n road cuts and stream banks where exposures s e v e r a l metres high were found. This allowed two to three s t r a t i g r a p h i c u n i t s to be observed and, i n s e v e r a l l o c a t i o n s , complete s e c t i o n s to bedrock were obtained. Where n a t u r a l exposures were not present, s o i l p i t s were dug, however i t was not p o s s i b l e to o b t a i n a good exposure by t h i s method due to the thickness of o v e r l y i n g c o l l u v i u m (up to 2m) and the bouldery nature of many of the de p o s i t s . P a r t i c u l a r a t t e n t i o n was p a i d to the c h a r a c t e r i s t i c s of t i l l , g l a c i o l a c u s t r i n e and g l a c i o f l u v i a l m a t e r i a l s . At each exposure t e x t u r e , c o n s o l i d a t i o n , colour, c l a s t l i t h o l o g y , s o r t i n g , s t r a t i f i c a t i o n and s t r a t i g r a p h i c p o s i t i o n were de s c r i b e d f o r each m a t e r i a l present. Several t i l l f a b r i c measurements were taken i n both the Stoyoma and Outram study areas. However, i t was d i f f i c u l t to f i n d exposures of s u f f i c i e n t s i z e to o b t a i n the o r i e n t a t i o n of 50 elongate stones. Those l o c a t e d tended to be c l u s t e r e d along s e v e r a l l o g g i n g roads, so i t was not p o s s i b l e to o b t a i n samples throughout the study area. The samples c o l l e c t e d showed f a b r i c s d i p p i n g both up and down v a l l e y s , but not enough samples were obtained f o r a p a t t e r n to emerge. For these reasons i t was decided that f a b r i c measurement was not an e f f i c i e n t use of f i e l d time and i t was abandoned. 44 3.2.2.2 Rock Weathering Rock weathering has been widely used as a method of r e l a t i v e d a t i n g , and a l s o f o r absolute d a t i n g where c a l i b r a t i o n curves have been e s t a b l i s h e d (Chinn 1981). I n ' B r i t i s h Columbia, most rock surfaces were eroded by i c e d u r i n g the l a s t g l a c i a t i o n so they tend to be r e l a t i v e l y smooth and unweathered. The exception i s peaks that remained above the i c e throughout the l a s t g l a c i a t i o n . Thus the upper l i m i t of g l a c i a t i o n can be i d e n t i f i e d as the highest l e v e l of g l a c i a l abrasion of bedrock. Peaks above t h i s l i m i t w i l l have much o l d e r surfaces than other areas and thus rock should be d i s t i n c t l y more weathered, except where f r o s t s h a t t e r i n g and r o c k f a l l have exposed f r e s h rock. On t h i s b a s i s rock weathering was examined to determine i f a l l summits were over topped by i c e sheets or i f nunataks e x i s t e d . Depth of weathering depends on rock mineralogy and g r a i n s i z e , as w e l l as time (Chinn 1981) so i t i s important to compare only s i m i l a r rock types. For t h i s reason measurements were confined to g r a n i t i c rocks. G r a n i t i c rocks do not always form c l e a r l y d e f i n e d weathering r i n d s . They are subject to g r a n u l a r d i s i n t e g r a t i o n : w i t h time surfaces become rougher, more r e s i s t a n t g r a i n s are exposed, weathering p i t s become deeper and grus accumulates (Benedict 1993). The degree of weathering was measured u s i n g a Schmidt hammer. This i s a device designed f o r measuring the hardness of concrete (Matthews and Shakesby 1984; Day 1980). I t i s a s p r i n g loaded hammer which s t r i k e s the rock surface and 45 measures the percent rebound. The harder the surface the gr e a t e r the rebound. The Schmidt hammer provides a numerical value f o r hardness which can e a s i l y be compared between s i t e s . As hardness i s c o r r e l a t e d w i t h weathering depth, t h i s i s a simple, o b j e c t i v e method of determining the r e l a t i v e amount of rock weathering. The most weathered surfaces w i l l be s o f t e s t and should produce the lowest Schmidt hammer readings. V a r i a b l e s such as moisture and d u r a t i o n of snowpack can a f f e c t weathering r a t e s s i g n i f i c a n t l y (Benedict 1993; H a l l 1993). These are hard to c o n t r o l when s e l e c t i n g sample s i t e s because amount of p r e c i p i t a t i o n and evaporation both vary l o c a l l y and w i t h a l t i t u d e . However, these v a r i a b l e s a c t i n g over the l a s t 10,000 years since d e g l a c i a t i o n should produce s m a l l e r d i f f e r e n c e s than those between g l a c i a t e d and non g l a c i a t e d s urfaces. I f nunataks were present there should be abrupt d i f f e r e n c e s i n Schmidt hammer readings. On g r a n i t i c rocks i n the Okanagan Range of the Cascade Mountains Ryder (1989, personal communication 1995) found s i g n i f i c a n t d i f f e r e n c e s i n hardness above and below the upper l i m i t of Fraser G l a c i a t i o n i c e . Measurements were taken at as many l e v e l s as p o s s i b l e from low i n v a l l e y s to summits and ridge c r e s t s . Where continuous outcrop was present measurements were taken roughly every 200 m e l e v a t i o n . At each s i t e 50 measurements were taken, e i t h e r 5 per boulder on 10 boulders i n moraines or e r r a t i c s , or along a g r i d p a t t e r n on rock outcrops. Readings on t r a n s p o r t e d boulders should give values r e p r e s e n t a t i v e of 46 g l a c i a t e d surfaces and u n g l a c i a t e d surfaces should have lower readings. 3.2.3 Reconstruction of Glacial History-After completion of f i e l d work the mapping on a i r photos was s t u d i e d and co r r e c t e d . The information was then t r a n s f e r r e d to 1:20,000 topographic maps and d i r e c t evidence of g l a c i a t i o n was h i g h l i g h t e d . E a r l y Fraser G l a c i a t i o n g l a c i e r s were re c o n s t r u c t e d by f i t t i n g g l a c i e r s i n t o cirques and troughs. G l a c i e r s were f i t i n t o these features by assuming the g l a c i e r s t a r t e d at the upper l i m i t of the steep c i r q u e headwall and that g l a c i e r s extended down v a l l e y s to the U - V t r a n s i t i o n . T o t a l c i r q u e area of each v a l l e y g l a c i e r was c a l c u l a t e d by measuring the area between the top of the headwall and the end of the f l o o r (taken as the po i n t where the v a l l e y narrows and steepens), and summing the areas of each cirque feeding a v a l l e y g l a c i e r . Cirque areas were measured from 1:50,000 topographic maps and so are approximate values. Trough length was taken as the longest p o s s i b l e length, that i s from the f u r t h e s t up-stream ci r q u e rim to the U-V t r a n s i t i o n . The t o t a l c i r q u e area was p l o t t e d against trough l e n g t h to determine i f a r e l a t i o n s h i p e x i s t e d . Goldthwait (1970) and F l i n t (1971) p r e d i c t a r e l a t i o n s h i p i f t h i s t r a n s i t i o n r e f l e c t s the l i m i t of v a l l e y g l a c i a t i o n . A l l i c e marginal features i n the study areas were assumed to have been formed during d e g l a c i a t i o n . In no study area i s 47 there s u f f i c i e n t marginal features to determine i c e surface slope. I t was a l s o assumed that marginal features l o c a t e d at s i m i l a r e l e v a t i o n s w i t h i n each study area were formed at roughly the same time. Marginal features at s i m i l a r e l e v a t i o n s were p l o t t e d on separate small s c a l e maps and connected. This created i c e form l i n e s s i m i l a r to those of F u l t o n (1967) which i n d i c a t e the shape of the receding i c e margin, but not i t s age. Due to the la c k of marginal features a l l form l i n e s are very approximate. Ice form l i n e s may mark a p o s i t i o n i n which the i c e f r o n t was s t a t i o n a r y f o r only a very b r i e f p e r i o d of time. These maps were then compared w i t h the d i s t r i b u t i o n of s u r f i c i a l d e p o s i t s to determine i f the i n d i c a t e d p a t t e r n of i c e r e t r e a t was c o n s i s t e n t w i t h other evidence, such as s t r a t i g r a p h y of v a l l e y f i l l d e p o s i t s . In t h i s manner s e v e r a l maps were produced f o r each area showing the i n f e r r e d p a t t e r n of mountain g l a c i a t i o n d u r i n g b u i l d up, and a s e r i e s of i n f e r r e d i c e l e v e l s during r e t r e a t . These were compared i n order to develop a model of g l a c i a t i o n a p p l i c a b l e to a l l three areas. The maps and d e t a i l s of t h e i r c o n s t r u c t i o n w i l l be discussed i n chapters 4, 5, and 6. 48 CHAPTER 4 MT. STOYOMA AREA 4.1 Introduction The Mount Stoyoma study area i s near the northern l i m i t of the Cascade Mountains (Figure 1.1). At t h i s p o i n t the Cascades begin to grade i n t o the Thompson Plateau. The area was s e l e c t e d t o encompass topographic v a r i a b i l i t y around moraines which were known to be l o c a t e d i n two cirques (Dr. J.M. Ryder personal communication 1992). A plateau area to the east of the ci r q u e s and troughs to the west were included i n an area bounded on the nort h by Miner's Creek and on the south by Spius Creek (Figure 4.2). The e n t i r e study area i s u n d e r l a i n by the Upper J u r a s s i c and Lower Cretaceous Eagle G r a n o d i o r i t e . ' T h i s i s a coarse grained grey rock of v a r i a b l e mineralogy and f o l i a t i o n (Monger 1989; Monger and McMillan 198 9). Outcrops may be competent and rounded or s t r o n g l y f r a c t u r e d . N o n f o l i a t e d white g r a n o d i o r i t e a l s o occurs i n some l o c a t i o n s . This rock i s o f t e n s l i g h t l y p i t t e d and i s g e n e r a l l y more competent than the f o l i a t e d g r a n o d i o r i t e . 4.2 Topography and Erosional Landforms The eastern p a r t of the study area i s a g e n t l y u n d u l a t i n g p l a t e a u , much l i k e the Thompson Plateau, w i t h rounded rocky h i l l s r i s i n g to 1700 m (Figure 4.3). R e l i e f i s l e s s than 500 m. L a t e r a l meltwater channels trend across slopes at e l e v a t i o n s between 1200 m and 1800 m (Figure 4.2). They are discontinuous depressions, 2 to 3 m deep, roughly 10 m wide and 100 to 500 m long. A l l 49 Legend for Stoyoma Area Maps Cirques Breached col / Moraine Meltwater Channel \ ~y Glacier - 3 - Drumlin © Location of Stratigraphic Sections Areas With Clay Rich-Till % Glaciofluvial Terraces Figure 4.1: Legend f o r Stoyoma area maps 50 Figure 4.2: L o c a t i o n map of the Mt. Stoyoma study area. 51 Figure 4.3: Plateau of the Mt. Stoyoma study area. Meltwater channels are v i s i b l e i n the c l e a r c u t . observed channels were cut i n t o t i l l . They are o f t e n c l u s t e r e d , but i s o l a t e d channels a l s o occur. The western h a l f of the study area i s higher and steeper w i t h rounded summits, which are remnants of the Miocene upland surfa c e , r i s i n g to 2300 m (Figure 4.4). R e l i e f i s roughly 900 m. Cirques occur around most summits, horns and aretes are l a c k i n g . Some cirq u e s are simple, s i n g l e basins, others are complex, c o n s i s t i n g of up to s i x cirque basins. Large complex c i r q u e s are present at the heads of Miner's and Spius Creeks; these face north and east, and t h e i r dimensions i n d i c a t e that they h e l d the l a r g e s t a l p i n e g l a c i e r s . In a d d i t i o n eleven simple c i r q u e s are present at the heads of smaller troughs. Of these f i v e face north, two face east, two face west, and two face south (Figure 52 Figure 4.4: Summits and cirques at the head of the south fork of Miner's Creek. 4.2). A l l c i r q u e s have w e l l developed c l i f f y headwalls, g e n t l y s l o p i n g f l o o r s and smooth rounded rims. Tarns are common. Upper v a l l e y s are broad U-shaped troughs which commonly are prominently stepped. Passes have a l l been widened, smoothed and deepened by i c e f l o w i n g through c o l s between v a l l e y s , but not to the extent that cirque headwalls have been l o s t . The exception i s the south f o r k of Spius Creek which heads i n a through trough, 7 k i l o m e t r e s south of the study area. Most v a l l e y s are V-shaped i n t h e i r lower reaches. The t r a n s i t i o n from U to V shaped occurs over a distance of roughly 1 km. Miners Creek flows i n a 5 to 10 m deep bedrock canyon f o r most of i t s length. The morphology suggests a s u b g l a c i a l meltwater channel. Benches on both sides of the creek appear to be cut i n t o bedrock, w i t h pockets of o x i d i z e d boulder g r a v e l on 53 the s u r f a c e , which could be a veneer of t i l l or g l a c i o f l u v i a l m a t e r i a l . 4.3 Depositional Landforms and S u r f i c i a l Materials In the steeper western h a l f of the study area s u r f i c i a l m a t e r i a l s are g e n e r a l l y r e s t r i c t e d to lower slopes and v a l l e y f l o o r s . Bedrock i s exposed on a l l summits and rid g e tops. C o l l u v i a l cones and t a l u s slopes are dominant on steep slopes below c l i f f s , e s p e c i a l l y i n upper v a l l e y s (Map 1). Rock outcrops are v i s i b l e on the f l o o r s of most cirques and upper v a l l e y s , i n d i c a t i n g that d e p o s i t s i n these.areas are patchy and t h i n . The p l a t e a u area to the east i s l a r g e l y covered by a blanket of b a s a l t i l l , w i t h rock outcrops at higher l e v e l s . Drumlins i n d i c a t e i c e flow to the southwest, transverse to l o c a l v a l l e y s . G l a c i o f l u v i a l t e r r a c e s occur above Prospect Creek and i n the v a l l e y of Spius Creek. 4.3.1 Till T i l l b l a nkets much of the g e n t l y undulating p l a t e a u i n the eastern h a l f of the study area and i s commonly exposed i n road c u t s . Thickness i s unknown, however exposures of 2 to 4 metres are common. T i l l a l s o l i k e l y blankets lower slopes i n the western p a r t of the area. Throughout the area t i l l i s h i g h l y c o n s o l i d a t e d and massive, w i t h subrounded to subangular c l a s t s of a mixture of l i t h o l o g i e s . On the pl a t e a u , matrix t e x t u r e i s s i l t y sand. In the lower p a r t of Miner's Creek v a l l e y , i n Spius Creek v a l l e y and s e v e r a l of i t s t r i b u t a r y v a l l e y s cohesive c l a y r i c h - t i l l occurs (Figure 4.5). 54 Figure 4.5: Map showing the extent of c l a y r i c h t i l l w i t h i n the study area. 55 This t i l l may o v e r l i e or u n d e r l i e g l a c i o l a c u s t r i n e or g l a c i o f l u v i a l deposits (see Figure 4.6 s e c t i o n s 2, 3, 4 and 7). Along Miner's Creek no g l a c i o f l u v i a l or g l a c i o l a c u s t r i n e m a t e r i a l s were observed near the c l a y - r i c h t i l l . In sandy t i l l s the dominant c l a s t l i t h o l o g y i s f o l i a t e d g r a n o d i o r i t e , w h i l e i n some c l a y r i c h t i l l s mafic v o l c a n i c s are more abundant. The nearest source area f o r the mafic v o l c a n i c s i s the Lower Cretaceous Spences Bridge Group which outcrops north of the study area (Monger and McMillan 1989), thus the d i f f e r e n t t i l l t e x t u r e s cannot be due s o l e l y to l o c a l v a r i a t i o n s i n l i t h o l o g y . The l o c a t i o n of c l a y r i c h t i l l s i n v a l l e y bottoms, above g l a c i o l a c u s t r i n e m a t e r i a l as i n s e c t i o n 7, suggests that t h i s t i l l was probably d e r i v e d from g l a c i o l a c u s t r i n e m a t e r i a l . G l a c i o l a c u s t r i n e m a t e r i a l could have formed as a r e s u l t of damming of these v a l l e y s by i c e advancing from the east. Fine grained sediment deposited i n lakes i n f r o n t of the advancing i c e would then be incorporated i n t o t i l l as the lake sediments were overridden. 4.3.2 Moraines Moraines dam cirque lakes at 1700 m on Mt. Hewitt Bostock at the head of Miner's Creek, and at 1860 m at Cabin Lake (Figure 4.2). The Miner's Creek moraine i s str o n g l y . a r c u a t e i n t o the c i r q u e , i t i s roughly 400 m long at the lake and extends a f u r t h e r 400 m along the north side of the v a l l e y i n s e v e r a l discontinuous, en echelon strands. These are roughly l e v e l or climb s l i g h t l y downvalley, suggesting that the g l a c i e r was a c t i v e l y f l o w i n g up v a l l e y at the time of d e p o s i t i o n . The Cabin 56 10m o o o . o O 6 o o ° • • A A " A - A A - " A 4 m Legend glaciolacustrine silts and clays 7 " o ° ° • ° ° ° o ; o ° • O o O glaciofluvial A . ° - A ' .O O o O ° sands and gravels - A A - A - A A A A — A 8m A - ^ > A A A ^ - A A " clay till — : stratified O o° o ° d o 'o glaciofluvial sands and gravels Figure 4.6: Sel e c t e d s t r a t i g r a p h i c s e c t i o n s . See f i g u r e 4.2 f o r the l o c a t i o n s of s e c t i o n s . 57 Lake moraine i s l i n e a r and s l i g h t l y longer than the c i r q u e width. I t i s roughly 500 m long, 15 m high and has a broad f l a t top (Figure 4.7). Both moraines have a p l a n form that i s more c o n s i s t e n t w i t h d e p o s i t i o n by C o r d i l l e r a n Ice f l o w i n g up v a l l e y , than by c i r q u e g l a c i e r s f l o w i n g downvalley. The Cabin Lake moraine has a f i n e sand matrix, and 40 to 60% c l a s t s dominantly of f o l i a t e d g r a n o d i o r i t e and l e s s e r mafic v o l c a n i c s . The c i r q u e headwall i s composed e n t i r e l y of f o l i a t e d g r a n o d i o r i t e . Thus the o r i e n t a t i o n , composition and l e n g t h of the Cabin Lake moraine are i n c o n s i s t e n t w i t h d e p o s i t i o n by a c i r q u e g l a c i e r . Figure 4.7: Cabin Lake w i t h moraine ri d g e to the l e f t of the l a k e . 58 4.3.3 Terraces, Glaciofluvial and Glaciolacustrine Deposits G l a c i o f l u v i a l d eposits comprise w e l l d e f i n e d t e r r a c e s which are present i n Spius Creek v a l l e y and on the south s i d e of Prospect Creek (Map 1). In the study area the Spius Creek t e r r a c e s begin near the j u n c t i o n of the north and south f o r k s . Along the south f o r k a t e r r a c e i s present 30 m above the creek. I t i s 800 m wide and extends f o r at l e a s t 3 km upstream of the study area (Figure 4.2). A t e r r a c e g e n e r a l l y l e s s than 100m wide extends 5 km downstream from the j u n c t i o n on both s i d e s of the creek, but i s broken by c o l l u v i a l fans i n s e v e r a l p l a c e s . At i t s downstream l i m i t the t e r r a c e i s 180 m above Spius Creek. Along Prospect Creek t e r r a c e s are smaller. At the j u n c t i o n of Miner's and Prospect creeks, a 200 m wide t e r r a c e extends 400 m downstream and a second t e r r a c e of s i m i l a r s i z e i s present 500 m downstream, both are at 925 m e l e v a t i o n or 90 m above Prospect Creek. A t h i r d t e r r a c e i s present s t r a d d l i n g a small t r i b u t a r y at 1150 m e l e v a t i o n or 480 m above Prospect Creek (Fig 4.2). Near the J u n c t i o n of Miner's and Prospect Creeks a blanket of g l a c i o f l u v i a l m a t e r i a l o v e r l i e s t i l l on a moderate slope. This m a t e r i a l could have been deposited adjacent to an i c e margin c o n t i n u o u s l y r e t r e a t i n g downslope towards Prospect Creek. G l a c i o f l u v i a l d eposits c o n s i s t of loose, s t r a t i f i e d sand and g r a v e l ; w e l l - s o r t e d , laminated sand i s interbedded w i t h more massive g r a v e l . L o c a l l y deposits are massive and coarse-textured w i t h c l a s t s i z e s to l a r g e cobbles. G l a c i o f l u v i a l d e p o s i t s are s e v e r a l metres t h i c k and commonly o v e r l i e t i l l (Figure 4.6 s e c t i o n s 2 and 7). In s e c t i o n 3, c l a y - r i c h t i l l appears t o o v e r l i e g l a c i o f l u v i a l g r a v e l s , although the contact was not w e l l 59 exposed. I f t h i s r e l a t i o n s h i p i s true t h i s could be advance outwash, or f l u v i a l g r a v e l s deposited by the creek before i c e advanced up the v a l l e y from the east. G l a c i o l a c u s t r i n e m a t e r i a l i s rare i n t h i s area. No extensive d e p o s i t s were observed although pockets up to 2 m t h i c k are present i n road cuts and stream banks along s e v e r a l creeks (Map 1). This m a t e r i a l i s cohesive, t h i n l y laminated, sand, s i l t , and c l a y w i t h o c c a s i o n a l stones. G l a c i o l a c u s t r i n e m a t e r i a l o v e r l i e s g l a c i o f l u v i a l g r a v e l s i n a t e r r a c e along Prospect Creek (Figure 4.6 s e c t i o n 1). Here the g l a c i o l a c u s t r i n e m a t e r i a l must have been deposited during d e g l a c i a t i o n . S e c tion 7 i s a road cut through a t e r r a c e i n Spius Creek. In t h i s s e c t i o n laminated s i l t s and c l a y s occur below t i l l and g l a c i o f l u v i a l g r a v e l s , i n d i c a t i n g that the g l a c i o l a c u s t r i n e m a t e r i a l was deposited before i c e advanced i n t o the v a l l e y . In an unnamed t r i b u t a r y of Spius Creek the t i m i n g of d e p o s i t i o n of the g l a c i o l a c u s t r i n e m a t e r i a l i s not c l e a r . Clay r i c h t i l l and g l a c i o l a c u s t r i n e s i l t s are exposed i n road cuts and stream banks (sections 4, 5, and 6), however t h e i r s t r a t i g r a p h i c r e l a t i o n i s not c l e a r , as no contacts are exposed. S e c t i o n 4 i s a composite, i n c l u d i n g a steam cut which exposed laminated s i l t s and c l a y s w i t h o c c a s i o n a l dropstones, and a road cut above t h i s s e c t i o n which exposed c l a y r i c h t i l l . Sections 5 and 6 are l o c a t e d across the creek from s e c t i o n 4 and at a s i m i l a r e l e v a t i o n . No t e r r a c e s are present i n t h i s area. The g l a c i o l a c u s t r i n e m a t e r i a l i n not c o n s o l i d a t e d , while the c l a y r i c h t i l l i s h i g h l y consolidated. L i k e l y these g l a c i o l a c u s t r i n e sediments were deposited i n lakes dammed by r e t r e a t i n g i c e , but there i s no f i r m evidence of t h i s . 60 4.4 Rock Weathering Rock weathering was d i f f i c u l t to assess due to the v a r i a b l e l i t h o l o g y and f r a c t u r e d nature of the rock. I t was d i f f i c u l t to be c e r t a i n that surfaces dated from the l a s t g l a c i a t i o n and were not the r e s u l t of more recent f r a c t u r i n g . An e f f o r t was made to sample only the more rounded surfaces on top of outcrops r a t h e r than f r a c t u r e planes. B u s t i n and Mathews (1979) found that r e l a t i v e l y small d i f f e r e n c e s i n b i o t i t e content had l a r g e e f f e c t s on weathering r a t e s i n g r a n o d i o r i t e i n t i l l . For t h i s reason i t i s important that l i t h o l o g y not vary between s i t e s . However l i t h o l o g y and degree of f o l i a t i o n are h i g h l y v a r i a b l e i n t h i s study area so i t was d i f f i c u l t to d i s t i n g u i s h the e f f e c t s of le n g t h of exposure and rock type on the v a r i a b i l i t y of Schmidt hammer readings. Rock weathering was measured at 11 s i t e s between 1840 and 2270 m. The lowest s i t e comprised boulders i n the Cabin Lake moraine. These boulders began to weather as soon as the i c e l e f t the moraine, thus any u n g l a c i a t e d areas should be c o n s i d e r a b l y more weathered. At a l l s i t e s there i s a wide spread i n the data (Appendix 1). There i s a decrease i n mean Schmidt hammer readings above 2100 m (Figure 4.8), but no sharp change as would be expected i f summits had remained above the i c e . The decrease i n readings w i t h e l e v a t i o n could be due to such f a c t o r s as increased freeze-thaw a c t i v i t y or l o c a l snowpatch e f f e c t s . There i s a l s o no grus formation or extensive p i t t i n g present at any e l e v a t i o n . 61 Mt. Stoyoma Area Schmidt Hammer Results Relation between means and elevation E E CO I +. T 3 E c o w c a » S 60 55 50 45 40 35 30 25 20 15 10 • 1400 f I I ...... T 1600 1800 2000 elevtion (m) 2200 2400 2600 Figure 4.8: R e l a t i o n between mean.Schmidt hammer readings and e l e v a t i o n . B a r s represent +/- 2 standard d e v i a t i o n s of the mean'. 4 .5 G l a c i a l History Ice form l i n e s have been reconstructed to show the extent of g l a c i e r s at va r i o u s stages of Fraser G l a c i a t i o n . No dates have been determined f o r any of these maps, thus they i n d i c a t e only the sequence of events and not absolute t i m i n g . The elapsed time between successive maps i s l i k e l y h i g h l y v a r i a b l e . 4.5.1 Valley Glacier Phase The presence of w e l l developed e r o s i o n a l landforms of a l p i n e g l a c i a t i o n around higher summits i n d i c a t e s that a l p i n e g l a c i e r s formed at the s t a r t of Fraser G l a c i a t i o n . The rounded nature of 62 a l l a l p i n e features suggests that they formed before an i c e sheet covered the area. This phase i s l i k e l y e quivalent to the prolonged a l p i n e g l a c i a t i o n that Clague (1981) described f o r the Coast Mountains. G l a c i e r s of t h i s phase were r e c o n s t r u c t e d by assuming that g l a c i e r s extended from the top of c i r q u e s headwalls downvalley to the p o i n t where v a l l e y s change from U to V shape cross p r o f i l e (Figure 4.9). The longest g l a c i e r s occurred i n troughs w i t h the l a r g e s t t o t a l c i r q u e area at t h e i r heads (Figure 4.10), as would be expected i f the U-V t r a n s i t i o n represents the t e r m i n i of a l p i n e g l a c i e r s (Goldthwait 1970) (see Chapter 3 f o r method used to c a l c u l a t e c i r q u e area). Snowline, as determined from the lowest n o r t h f a c i n g c i r q u e s , was roughly 1500 m during t h i s p e r i o d . 4.5.2 Ice Sheet Stage At the Fraser G l a c i a t i o n maximum a l l summits were overtopped. Evidence of t h i s c o n s i s t s of: w e l l rounded ri d g e tops, r e l a t i v e l y unweathered bedrock w i t h l i t t l e change i n weathering from moraines to summits, and the e r o s i o n of c o l s . Ice flow d i r e c t i o n appears to have changed from westward to southward as the C o r d i l l e r a n Ice Sheet thickened and advanced onto the p l a t e a u area. I f the c l a y - r i c h t i l l s i n east d r a i n i n g v a l l e y bottoms are due to o v e r r i d i n g of e a r l i e r g l a c i o l a c u s t r i n e m a t e r i a l , they must have been deposited by i c e advancing from the east, from, the Thompson Plateau r a t h e r than from the Coast Mountains. This westward i c e flow would have occurred e a r l y i n the i c e sheet stage. Drumlins on the Spius Plateau i n d i c a t e i c e flow to the southwest. As the drumlins are not at high e l e v a t i o n s 63 Figure 4.9: Map of e a r l y Fraser G l a c i a t i o n a l p i n e g l a c i e r s i n the Mt. Stoyoma area. 64 Mt. Stoyoma Area Cirque area trough length relation CM E u-8-7-6-• 5-3-2-• 1 -™ m - • 0-0 2 4 6 8 10 . 12 14 16 18 20 trough length (km) Figure 4.10: P l o t of cirqu e area versus trough l e n g t h showing a weak n o n - l i n e a r r e l a t i o n . they may have been formed before or a f t e r the g l a c i a l maximum. This i s transverse to most l o c a l v a l l e y s , which allowed the p r e s e r v a t i o n of the f i n e t e x t u r e d t i l l i n v a l l e y bottoms. This i c e flow d i r e c t i o n a l s o suggests that l o c a l g l a c i e r s were not a s i g n i f i c a n t i n f l u e n c e on i c e flow d i r e c t i o n , and may not have c o n t r i b u t e d t o the i c e sheet. North of the study area i c e flow, at the g l a c i a l maximum, was south to southeast (Ryder 1981), more c o n s i s t e n t w i t h a source i n the Coast Mountains. 65 4.5.3 Deglaciation Evidence of d e g l a c i a t i o n on the Spius Plateau i s r e l a t i v e l y -abundant . L a t e r a l meltwater channels give good c o n t r o l on the i c e •margins. The moraines at Cabin Lake and the head of Miner's Creek provide an i c e p o s i t i o n at the western margin of the p l a t e a u and i n t o the mountainous area. These features are c o n s i s t e n t w i t h r e t r e a t of an a c t i v e i c e margin away from the mountains. Ice form l i n e s were drawn by connecting i c e marginal f e a t u r e s of roughly equal e l e v a t i o n . The e a r l i e s t i c e marginal fe a t u r e s are the two moraines at 1700 and 1860 m (Figure 4.11). These mark the i c e f r o n t p o s i t i o n during a small readvance of a c t i v e i c e . A second form .line (Figure 4.12) i s based on two c l u s t e r s of meltwater channels at 1580 m. Below t h i s l e v e l meltwater channels become more sparse. S u c c e s s i v e l y lower i c e margins are approximately p a r a l l e l . There are no deposits i n the study area which i n d i c a t e stagnation, so i t i s l i k e l y that i c e remained a c t i v e and r e t r e a t e d continuously. The moraine i n Miner's Creek v a l l e y i s evidence that no c i r q u e g l a c i e r was present here during d e g l a c i a t i o n , and hence f r o n t a l r e t r e a t of l o c a l g l a c i e r s could not have occurred. This i s a r e l a t i v e l y high east f a c i n g cirque l o c a t e d below 2160 m Mt. Hewitt Bostock. This i s one of the higher peaks i n the northern Cascades, w i t h a r e l a t i v e l y extensive area above 1700 m. This i s the type of l o c a t i o n which seems most l i k e l y to have functioned as an accumulation zone. The f a c t that i t was i c e f r e e before C o r d i l l e r a n i c e disappeared from the area i s evidence that a l l c i r q u e s were below snowline by the time the i c e sheet had receded l o c a l l y . Thus snowline was above 1700 m throughout d e g l a c i a t i o n . 66 Figure 4.11: Ice form l i n e during d e g l a c i a t i o n , based on moraines at Cabin Lake and i n Miner's Creek. 67 Figure 4.12: Ice form l i n e during d e g l a c i a t i o n based on meltwater channels at 1580 m. 68 Both Spius and Miner's creeks should have been dammed or p a r t l y dammed throughout d e g l a c i a t i o n by i c e receding downvalley. However no deposits i n d i c a t i v e of damming were found i n any v a l l e y s , w i t h the p o s s i b l e exception of the unnamed creek at s e c t i o n 4 (Figure 4.2). This suggests that meltwater escaped s u b g l a c i a l l y or that g l a c i o l a c u s t r i n e deposits were e i t h e r too t h i n t o be found or mostly destroyed by l a t e r e r o s i o n . The bedrock canyon i n Miner's Creek'is p o s s i b l e support f o r s u b g l a c i a l drainage, but poses a problem that w i l l be discussed f u r t h e r i n chapter 7. Spius Creek contains extensive g l a c i o f l u v i a l outwash t e r r a c e s w i t h small pockets of g l a c i o l a c u s t r i n e s i l t . The former d e p o s i t s are more c o n s i s t e n t w i t h up v a l l e y f r o n t a l r e t r e a t than w i t h downvalley r e c e s s i o n . However i t i s u n l i k e l y that the ci r q u e s at the head of Spius Creek held g l a c i e r s because they are lower than those at the head of Miner's Creek and have roughly the same o r i e n t a t i o n . In a d d i t i o n the head of South Spius Creek i s a low pass, or through trough. A p o s s i b l e source of the g l a c i o f l u v i a l m a t e r i a l i s from a lobe of C o r d i l l e r a n i c e from the Coast Mountains pushing through the c o l at the head of Spius Creek. No landforms of d e g l a c i a t i o n were found i n the troughs i n the western p o r t i o n of the study area. A meltwater channel cuts across the d i v i d e i n t o Spius Creek, i n d i c a t i n g that these troughs may have h e l d i c e longer that those to the east. 69 4.5.3.1 Sediment Cores Two complete sediment cores were obtained from Cabin Lake. The f i r s t i s 1.85 m long and the second 0.90 m. The bulk of both cores i s composed of s o f t , brown g y t t j a , w i t h a l a y e r of Mazama tephra roughly h a l f way down. Both cores terminate i n a l a y e r of uniform grey c l a y . A wood fragment was found i n the second core i n s i l t y g y t j j a at a depth of 70 cm, 6 cm above the b a s a l c l a y . This fragment was dated at 9319 + 120 years BP (sample number TO-4325) . This i s a minimum age f o r the d e p o s i t i o n of the Cabin Lake moraine. I f uniform d e p o s i t i o n i s assumed, roughly 2500 years would have been r e q u i r e d to deposit the g y t j j a and c l a y below the wood sample. This gives a very t e n t a t i v e estimate of 11,800 years BP f o r the age of the lake, s l i g h t l y o l d e r that Souch's (1989) 11,100 years BP f o r d e g l a c i a t i o n of Kwoiek Creek v a l l e y . This i s c o n s i s t e n t because the Cascade Mountains are lower and d r i e r than the summits at the head of Kwoiek Creek so would l i k e l y have become i c e f r e e f i r s t . 4.6 Neoglaciation No d e p o s i t s or e r o s i o n a l features r e l a t e d to a N e o g l a c i a l advance were seen w i t h i n t h i s area. N i v a t i o n hollows i n t a l u s slopes below the headwalls of north and east f a c i n g c i r q u e s near Mt. Hewitt Bostock are evidence of l a t e l y i n g snowpatches. The undisturbed l a t e r a l moraines high i n Miner's Creek and at Cabin lake are evidence that cirque g l a c i e r s have not e x i s t e d s i n c e Fraser d e g l a c i a t i o n . 70 CHAPTER 5 ANDERSON RIVER AREA 5.1 Introduction The Anderson R i v e r study area i s centred around a c l u s t e r of prominent horns between the North and South Forks of Anderson R i v e r (Figure 5.2). Horns are uncommon i n other p a r t s of the Cascade Mountains so i t was thought that t h i s area may have undergone a d i f f e r e n t s t y l e of g l a c i a t i o n from other areas. The Anderson R i v e r flows to the northwest, i n t o the Fraser R i v e r , and thus towards the Coast Mountains. G r a n o d i o r i t e of the Eocene Needle Peak Pluton forms a l l higher summits. This i s a competent u n i t w i t h widely spaced j o i n t s . The Dewdney Creek Formation of the Lower J u r a s s i c Ladner Group u n d e r l i e s lower areas. This i s a mixed u n i t c o n t a i n i n g sandstone, a r g i l l i t e and l o c a l mafic to intermediate v o l c a n i c s . Generally rock of t h i s u n i t i s se v e r e l y f r a c t u r e d and weak (Monger 1989). At the j u n c t i o n of the North and South Forks of the Anderson R i v e r bedrock i s h i g h l y f r a c t u r e d , f i n e grained, black a r g i l l i t e . 5.2 Topography and Erosional Landforms Horns between the North and South Forks are between 1770 and 1980 m, and surrounding ridges reach e l e v a t i o n s of between 1520 and 1700 m. T o t a l r e l i e f i s 600 to 900 m. Horns are prominent but summits and ridges are w e l l rounded and smooth (Figure 5.3). Large subangular g r a n o d i o r i t e boulders, which 71 Legend for Anderson River Study Area Maps Cirques Breached Col Meltwater Channel: small, large Glacier, Position Known Glacier, Terminus Position Unknown © Location of Stratigraphic Sections Ice Dammed Lake Glaciofluvial Terrace Ice Flow Direction Figure 5.1: Legend f o r Anderson Ri v e r area maps 72 Figure 5.2: L o c a t i o n Map of the Anderson R i v e r study area. 73 do not appear to have weathered i n place, are common on many summits. F l u t i n g on top of Chamois Peak and on rid g e s 3 km to the west of the study area i n d i c a t e i c e flow toward the south to south-southwest, approximately p a r a l l e l to the Fraser R i v e r . The North and South Forks of Anderson R i v e r flow i n l a r g e I c e l a n d i c s t y l e troughs which are U-shaped throughout the study area. These head i n broad g l a c i a l l y carved c o l s which o f t e n p a r t i a l l y breach p r e - e x i s t i n g cirques (Figure 5.4). Small a l p i n e troughs occur only on the north side of lower e l e v a t i o n r i d g e s , p a r t i c u l a r l y the rid g e between the North Fork and East Anderson R i v e r . Cirques occur most commonly on the north side of r i d g e s , s e v e r a l face east or west and only one south f a c i n g c i r q u e was observed. Those at the head of the North and South Forks are complex shallow features composed of s e v e r a l c i r q u e basins. They are 1 km to 3 km wide w i t h rounded rims, low c l i f f y headwalls and commonly have no w e l l defined c i r q u e f l o o r s . Cirques at the head of small a l p i n e troughs are much sm a l l e r , simple f e a t u r e s , g e n e r a l l y l e s s than 1 km wide and a l s o w i t h rounded rims. A l l cirques are s t r o n g l y degraded and many headwalls and s i d e w a l l s are breached. Where present, c i r q u e f l o o r s are g e n t l y s l o p i n g , and commonly rocky. The ci r q u e f l o o r below Gemse Peak contains w e l l defined grooves, which are p a r a l l e l to the v a l l e y . In general north f a c i n g slopes are steep c l i f f s , while south f a c i n g slopes are moderately angled s l a b s . 74 Figure 5.3: Horns between the North and South f o r k s of the Anderson R i v e r . Several small meltwater channels cross the ridge on the west side of the South Fork (Figure 5.2). Their slope i n d i c a t e s flow to the west. These channels must have drained lakes ponded by i c e i n the South Fork. A l a r g e , steep sid e d bedrock canyon, that i s probably a s u b g l a c i a l meltwater channel, flows i n t o Boston Bar Creek from a c o l south of the head of South Fork. 5.3 Depositional Landforms and S u r f i c i a l Materials S u r f i c i a l m a t e r i a l s are present on lower slopes and v a l l e y f l o o r s throughout the study area. Summits and steep upper 75 slopes are rock. C o l l u v i a l cones and t a l u s slopes are common at the base of steep rock slopes (Map 2 ) . Figure 5 . 4 Head of the North Fork of the Anderson Ri v e r , ci r q u e headwall i s rounded and c l e a r l y overridden. 5.3.1 Till Well c o n s o l i d a t e d basal t i l l occurs on lower slopes and i n v a l l e y f i l l throughout the study area. Generally t i l l i s covered w i t h 1 to 2 m of colluvium on lower slopes or w i t h g l a c i o f l u v i a l and g l a c i o l a c u s t r i n e deposits i n v a l l e y f i l l . T i l l blanketed slopes tend to d i s p l a y a w e l l developed p a t t e r n of s u b p a r a l l e l g u l l i e s . Bedrock commonly outcrops i n stream beds of both Anderson Ri v e r and t r i b u t a r y creeks, i n d i c a t i n g 76 that t i l l on the lower slopes i s g e n e r a l l y l e s s than 5 m and commonly only 1 to 2 m t h i c k . In the upper p a r t s of the v a l l e y s the t i l l has a coarse sand matrix. The c l a s t s i n t h i s t i l l are dominantly g r a n i t i c , l o c a l l y w i t h minor amounts of v o l c a n i c and sedimentary rocks. At the j u n c t i o n of the North and South fo r k s the t i l l m a t r i x i s c l a y - r i c h and h i g h l y cohesive. This matrix t e x t u r e i s very s i m i l a r to that of g l a c i o l a c u s t r i n e deposits l o c a t e d f u r t h e r upstream i n both f o r k s . The c l a y - r i c h t i l l contains dominantly black a r g i l l i t e and v o l c a n i c c l a s t s . I t thus seems probable that the matrix t e x t u r e of the t i l l r e f l e c t s both l o c a l bedrock geology, and reworking of f i n e t e x t u r e d v a l l e y f i l l . The l o c a t i o n of the f i n e - t e x t u r e d t i l l i s c o n s i s t e n t w i t h i t s d e r i v a t i o n from lake sediments, the r e s u l t of damming of Anderson R i v e r by a lobe of i c e from the Coast Mountains durin g e a r l y Fraser G l a c i a t i o n . 5.3.2 Terraces, Glaciofluvial and Glaciolacustrine deposits The t y p i c a l v a l l e y f i l l sequence i n the upper p a r t s of both f o r k s of Anderson R i v e r i s a g l a c i o f l u v i a l t e r r a c e cap 2 t o 5 m t h i c k , o v e r l y i n g 0.5 to 3 m of g l a c i o l a c u s t r i n e s i l t s and c l a y s , that i n t u r n o v e r l i e s e v e r a l metres of b a s a l t i l l (Figure 5.5 s e c t i o n s 1 and 9). These deposits are d i s s e c t e d by meltwater channels g i v i n g the v a l l e y f l o o r a hummocky appearance. Below s e c t i o n s 1 and 8 the North and South Forks are i n c i s e d i n t o t i l l , w i t h o c c a s i o n a l bedrock outcrops. 77 ° °° 6 ° °„° o o A A A A A A 2 2 m lOi 4 m A _A A A A A A — A A A ~ * _ A ^ A A A 1A± * i * A A A A A 7 A — * ^ A A 3 m 8 301 O °o o ° O o o o " ° \ o : 5 m 1 0 * A A 2 m 6 m O O u O o • ' * ~ A A A A i A » * A . Legend Fluvial or Glaciofluvial sands and gravels Glaciolacustrine sands Glaciolacustrine silts and clays Clay till Sandy till Figure 5.5: Selected s t r a t i g r a p h i c s e c t i o n s ; see f i g u r e 5.2 f o r l o c a t i o n s 78 G l a c i o l a c u s t r i n e sediments are g e n e r a l l y w e l l - l a m i n a t e d to massive s i l t s and c l a y s , w i t h 10 cm to 3 0 cm interbeds of f i n e t o coarse sand. They are very cohesive and p o o r l y drained. Deposits are most o f t e n found as part of the v a l l e y f i l l , u s u a l l y u n d e r l y i n g g l a c i o f l u v i a l m a t e r i a l , and vary from 0.5 m to g r e a t e r than 5 m i n t h i c k n e s s . O c c a s i o n a l l y pockets of laminated f i n e sands, or s i l t s and c l a y s are present on v a l l e y s i d e s above the l e v e l of t e r r a c e s (Map 2, Figure 5.5 s e c t i o n s 2 and 4). These are i n t e r p r e t e d as ice-marginal lake d e p o s i t s . G l a c i o f l u v i a l t e r r a c e s are present along the North Fork upstream of s e c t i o n 1," along the South Fork upstream of s e c t i o n 7, and along the Anderson R i v e r at and below the j u n c t i o n of the two f o r k s (Map 2, Figure 5.2). Road cuts and stream channels expose a complete v a l l e y f i l l sequence from t e r r a c e surface to bedrock i n s e v e r a l l o c a t i o n s . The highest t e r r a c e i s l o c a t e d downstream of the j u n c t i o n of the North and South Forks, t h i s t e r r a c e i s at 850 m, 180 m above r i v e r l e v e l and extends f o r 3 km downstream. Roughly 30 m of g l a c i o f l u v i a l g r a v e l s form a cap and below t h i s i s c l a y - r i c h t i l l . A short d i s t a n c e upstream at the j u n c t i o n the t e r r a c e l e v e l i s 790 m or 12 0 m above the r i v e r (Map 2). This t e r r a c e i s composed dominantly of c l a y - r i c h t i l l w i t h a t h i n cap (< 2 m) of g l a c i o f l u v i a l g r a v e l s . G l a c i o f l u v i a l deposits are loose, w e l l s o r t e d sand and sandy g r a v e l , ranging i n thickness from 2 m to g r e a t e r than 10 m. Sand beds are massive to laminated, while g r a v e l beds are 79 g e n e r a l l y massive to weakly s t r a t i f i e d . Bedding i s h o r i z o n t a l . Well developed f l u v i a l s t r u c t u r e s are l a c k i n g . These depos i t s are l i k e l y outwash deposited i n f r o n t of a v a l l e y g l a c i e r receding by normal f r o n t a l r e t r e a t . 5.4 Rock Weathering The Anderson R i v e r study area contains s e v e r a l N e o g l a c i a l moraines which enclose h i g h l y p o l i s h e d slabs of g r a n o d i o r i t e . Slabs are a l s o present on the f l o o r s of o l d e r Fraser G l a c i a t i o n c i r q u e s outside of the N e o g l a c i a l moraines, and on horns. This allowed more d i r e c t observation of g r a n o d i o r i t e weathering than the other areas. N e o g l a c i a l slabs have very smooth s l i p p e r y s u r f a c e s . The Schmidt hammer readings f o r these surfaces were very t i g h t l y c l u s t e r e d , w i t h a mean of 66 and standard d e v i a t i o n of 1.8 Appendix 2). A l l surfaces outside of the N e o g l a c i a l moraines, i n c l u d i n g c i r q u e f l o o r s , summits, and boulders on summits d i s p l a y e d a s i m i l a r degree of weathering. These surfaces are rougher and more v a r i a b l e than N e o g l a c i a l s l a b s , i n d i v i d u a l g r a i n s have weathered out and shallow p i t s , g e n e r a l l y l e s s than 1 cm deep and 15 cm across are common. Small f l a k e s 1 to 2 g r a i n s t h i c k and s e v e r a l centimetres long can be e a s i l y p u l l e d o f f . Scattered g l a c i a l l y p o l i s h e d surfaces, s i m i l a r to the N e o g l a c i a l s l a b s , are a l s o present. Means of 11 Schmidt hammer samples are between 40 and 50 wit h standard d e v i a t i o n s of 8 t o 12 (Appendix 2). V a r i a b i l i t y w i t h i n i n d i v i d u a l samples 80 depends on l o c a l c o n d i t i o n s , w i t h lowest values o c c u r r i n g on or near f l a k e s and higher values o c c u r r i n g on remnant p o l i s h e d s u r f a c e s . There i s a weak trend of decreasing mean Schmidt hammer readings w i t h e l e v a t i o n (Figure 5.6). However, i f summits were u n g l a c i a t e d they should have s i g n i f i c a n t l y lower mean readings and p o s s i b l y higher standard d e v i a t i o n s than sla b s i n c i r q u e s . The d i f f e r e n c e between g l a c i a t e d and u n g l a c i a t e d should be of a s i m i l a r order to the d i f f e r e n c e between N e o g l a c i a l and Fraser G l a c i a t i o n (see Figure 5.6). Ryder (Personal 70 65 ID 60 3 i-l id > 55 M | 50 A •P •o •H 1 45 X. ow 40 c id v 6 35 30 25 Anderson River Schmidt Hammer Data mean values versus elevation L 1 \ H i i T J X t 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 e l e v a t i o n (m) ol d slabs n e o g l a c i a l slabs Figure 5.6 P l o t of mean Schmidt hammer values versus e l e v a t i o n . B a r s represent +/- 2 standard d e v i a t i o n s of the mean. 81 communication 1995) found that i n the Okanagan Range of the Cascade Mountains surfaces which were above the e l e v a t i o n reached by the C o r d i l l e r a n Ice Sheet had much lower Schmidt hammer readings. The observed v a r i a b i l i t y must t h e r e f o r e be due to f a c t o r s other than g l a c i a t i o n , such as l o c a l moisture c o n d i t i o n s , d u r a t i o n of snow patches, or s l i g h t d i f f e r e n c e s i n mineralogy of the g r a n o d i o r i t e . 5.5 G l a c i a l History 5.5.1 Valley Glacier Phase Prominent horns, cir q u e remnants, and a l p i n e troughs i n d i c a t e t h a t , as i n the Mt. Stoyoma Area, g l a c i e r s formed around higher peaks and on north sides of ridges during the e a r l y stages of g l a c i a t i o n . The Anderson R i v e r v a l l e y narrows downstream. However no c l e a r t r a n s i t i o n from trough to V shaped v a l l e y occurs above i t s confluence w i t h the Fraser R i v e r . I t i s thus probable that v a l l e y g l a c i e r s flowed towards the Fraser R i v e r and were confluent w i t h a lobe of Coast Mountain i c e advancing up Anderson R i v e r r e l a t i v e l y e a r l y i n the g l a c i a l c y c l e ( l i k e l y during the intense a l p i n e phase of Davis and Mathews). A lake may have been t e m p o r a r i l y ponded i n the Anderson R i v e r before l o c a l and Coast Mountain i c e coalesced. The e l e v a t i o n of the lowest north f a c i n g c i r q u e s i n d i c a t e s snowline was roughly 1500 m during t h i s stage. Two small troughs on the north side of Anderson R i v e r Mountain become V-shaped a short distance above the North 82 Figure 5 .7 : E a r l y Fraser G l a c i a t i o n a l p i n e g l a c i e r s . Fork, suggesting that these g l a c i e r s were not confluent w i t h the main v a l l e y g l a c i e r (Figure 5.7). A small trough on the east s i d e of the South Fork, between Chamois and Ibex a l s o becomes V-shaped before j o i n i n g the South Fork. E a r l y Fraser G l a c i a t i o n a l p i n e g l a c i e r s were re c o n s t r u c t e d on the b a s i s of cirq u e remnants, and the U-V t r a n s i t i o n , where present. V a l l e y g l a c i e r s i n the main r i v e r v a l l e y s are drawn w i t h dotted l i n e s as t h e i r t e r m i n a l p o s i t i o n s are unknown (Figure 5.7). 5.5.2 Ice sheet Stage Evidence that an i c e sheet covered a l l peaks i n the Anderson R i v e r Area i s extensive. Cirque rims and horns are rounded and smooth, the summit of Chamois Peak i s f l u t e d , and s t r i a t i o n s occur near the summit of 2040 m Yak Peak, 3 km east of the study area, and 6 0 m higher than any peaks i n the study area. Large I c e l a n d i c s t y l e troughs are common. Schmidt hammer data i n d i c a t e s no s i g n i f i c a n t increase i n weathering from low on rid g e s t o summits. Subrounded g r a n o d i o r i t e e r r a t i c s which are too f r e s h to have weathered i n place are common on summits. Ice flow at the Fraser maximum as i n d i c a t e d by f l u t i n g was to the south. 5.5.3 Deglaciation L i t t l e evidence e x i s t s to i n d i c a t e the p a t t e r n of d e g l a c i a t i o n , as no unequivocal i c e marginal features were found i n t h i s study area. Small pockets of g l a c i o l a c u s t r i n e 84 d e p o s i t s on h i l l s l o p e s are thought to have been deposited i n small lakes ponded by t h i n n i n g i c e . The degraded nature of the cir q u e s and the l a c k of Fraser r e c e s s i o n a l moraines suggests that c i r q u e g l a c i e r s were not very a c t i v e at the end of g l a c i a t i o n . However, there were l i k e l y small remnant a l p i n e g l a c i e r s , which s u p p l i e d d e b r i s and meltwater to form the g l a c i o f l u v i a l t e r r a c e s . G l a c i o l a c u s t r i n e deposits occur throughout both f o r k s of the Anderson r i v e r , up to an e l e v a t i o n of 1370 m. These are t h i n d e p o s i t s which may have been l a i d down i n small lakes ponded between i c e and v a l l e y w a l l s , or more l i k e l y , on the upstream side of i c e receding down v a l l e y s toward the Coast Mountains. These lakes p o s s i b l y followed the receding i c e down v a l l e y , so never became very l a r g e . Drainage of these lakes i s p r o b l e m a t i c a l as no l a t e r a l or s u b g l a c i a l meltwater channels were found. Upstream of the lakes , creeks deposited f l u v i a l and g l a c i o f l u v i a l m a t e r i a l on top of t h e . g l a c i o l a c u s t r i n e s i l t s . At the s t a r t of d e g l a c i a t i o n the i c e sheet thinned and highest horns, were exposed as nunataks. Ice was s t i l l t h i c k enough to flow and erosio n of the c o l s continued. I t i s probable that the larg e s u b g l a c i a l meltwater channel which d r a i n s i n t o Boston Bar Creek (Figure 5.2) was l a r g e l y formed at t h i s time, before i c e receded below the c o l at the head of the channel. The Fraser R i v e r v a l l e y l i k e l y s t i l l h e l d a l a r g e volume of Coast Mountain i c e , b l o c k i n g drainage i n t h i s d i r e c t i o n . Thus l a r g e amounts of meltwater from r a p i d l y 85 receding g l a c i e r s could have been f u n n e l l e d through t h i s channel. The c o l at the head of the meltwater channel i s one of the lowest passes between the Fraser River/Anderson R i v e r system, and the Boston Bar Creek/Coquihalla R i v e r system, above t h e i r j u n c t i o n . Boston Bar Creek and C o q u i h a l l a R i v e r may have been an a l t e r n a t e route to the Fraser R i v e r f o r meltwater from a larg e part of the northern Cascades. The i c e form l i n e i n f i g u r e 5.8 i s based on the upper l i m i t of g l a c i o l a c u s t r i n e deposits at 1370 m. G l a c i o l a c u s t r i n e m a t e r i a l occurs up to t h i s l e v e l i n both the North and South Forks and a l s o a t r i b u t a r y of the North Fork (Figure 5.2 s e c t i o n s 2, 5, and 11). The form l i n e was drawn to show the highest lake l e v e l s . This f i t s w i t h the v a l l e y f i l l sequence, but i s not based on any i c e marginal f e a t u r e s , so i t i s only a very approximate and l i k e l y t r a n s i e n t i c e p o s i t i o n . Siwash Pass i s a broad pass north of Siwash Creek and 2 ki l o m e t r e s west of the study area. I t i s f i l l e d w i t h hummocky de p o s i t s , which are probably i c e contact g l a c i o f l u v i a l d e p o s i t s , or a b l a t i o n t i l l . The north fork of Siwash Creek, makes a sharp bend at t h i s p o i n t . I t s most d i r e c t route to the Fraser i s to the northwest through the pass, i n s t e a d the creek turns to the southwest and flows i n t o Siwash Creek. This pass i s at a s i m i l a r e l e v a t i o n to the high t e r r a c e below the j u n c t i o n of the fo r k s of the Anderson R i v e r . I t i s thus l i k e l y t h at they formed at roughly the same time, l i k e l y adjacent t o a lobe of i c e from the Coast Mountains which was g e n e r a l l y a c t i v e , w i t h some stagnation at the snout, and r e t r e a t i n g down 86 87 Figure 5 . 9 : An i c e l e v e l near the end of d e g l a c i a t i o n , based on the t e r r a c e below the j u n c t i o n of the North and South Forks and hummocky deposits i n a pass to the south. 88 v a l l e y towards the Coast Mountains (Figure 5.9). The i c e would have blocked drainage to the northwest f o r c i n g Siwash Creek i n t o i t s present channel. I t i s probable that both d e g l a c i a t i o n maps show very short l i v e d i c e margins. The l a c k of i c e marginal and s t a g n a t i o n features suggests that d e g l a c i a t i o n was r a p i d and continuous. 5.6 Neoglaciation N e o g l a c i a l a c t i v i t y i n the Anderson R i v e r area was r e s t r i c t e d to north f a c i n g bowls at the base of c l i f f s , where avalanches, fed the accumulation zones. Fresh moraines, found w i t h i n a few hundred metres of headwalls, tend to be small f e a t u r e s , l e s s than 10 m high. N e o g l a c i a l cirques are very steep w i t h l i t t l e f l o o r area. Head w a l l s are f r e s h and g r a n o d i o r i t e f l o o r s are h i g h l y p o l i s h e d . 89 CHAPTER 6 MT. OUTRAM AREA 6.1 Introduction The Outram area (Figure 1.1) i s l o c a t e d i n the Hozameen Range of the Cascade Mountains. This range, along w i t h the S k a g i t Range to the south, contains the highest and most rugged mountains i n the B r i t i s h Columbia Cascade Mountains. L a t e r a l moraines of the C o r d i l l e r a n Ice Sheet were known to be present i n two c i r q u e s on the south side of Mt. Outram (J.M. Ryder personal communication 1992). The study area was s e l e c t e d t o encompass topographic v a r i a t i o n i n an area around these c i r q u e s . The area i n c l u d e s Nicolum and Sumallo v a l l e y s which form a l a r g e through trough, craggy summits and a l p i n e troughs around Mt. Outram, and the Podunk Plateau area between Montigny and Sowaqua Creeks (Figure 6.2). The area i s u n d e r l a i n by mixed sedimentary and mafic v o l c a n i c rocks of the Permian to J u r a s s i c Hozameen Complex. This i s i n t r u d e d by g r a n o d i o r i t e of the Eocene Mt. Outram P l u t o n (Monger 1989). G r a n o d i o r i t e u n d e r l i e s much of the area south of Sowaqua Creek w i t h the exception of the highest summits, which are v o l c a n i c , and a bench along the south s i d e of Sowaqua Creek, which i s u n d e r l a i n by f i n e grained sediments and v o l c a n i c s . Ridges to the north are l a r g e l y u n d e r l a i n by sandstones and conglomerates. 90 Legend for Mt. Outram Area Maps Cirques >L. Breached Col / Moraine Meltwater Channel Glacier, postion roughly known Glacier, position unknown 0) Location of Stratigraphic Sections Kame Terraces Hope Slide Glaciofluvial Terrace ice flow indicator, direction unknown gure 6.1: Legend f o r Mt. Outram area maps. 92 6.2 Topography and Erosional Landforms The area between Nicolum-Sumallo trough and Sowaqua Creek contains the best developed a l p i n e g l a c i a l f e atures and the highest peaks i n the study area, i n c l u d i n g 2440 m Mt. Outram (Figure 6.3). T o t a l r e l i e f i s 1370 m. The highest summits are r e l a t i v e l y sharp. There are w e l l defined c i r q u e s , many w i t h sharp rims, around most summits (Figure 6.2). Figure 6.3: Mt. Outram and surrounding south f a c i n g c i r q u e s , from Johnson Peak. Podunk Plateau i n the northeastern part of the study area c o n s i s t s of remnants of a Miocene e r o s i o n surface (see Mathews, 1968). This area i s c h a r a c t e r i z e d by low rounded summits, the highest being 1980 m Mt. Davis, and broad g e n t l y 93 s l o p i n g upland areas. The t o t a l r e l i e f i s 300 m. The few ci r q u e s present are a l l i n c i s e d below the plat e a u surface and are s t r o n g l y degraded, w i t h rounded rims and low headwalls. The p l a t e a u surface i s i r r e g u l a r and boggy. Hummocky rock outcrops are common. A t o t a l of 19 cirques i s present i n the study area. Of these e i g h t face north, four west, four south and 3 east. Most ci r q u e s have prominent, steep, c l i f f y headwalls and w e l l d e f i n e d f l a t to g e n t l y s l o p i n g f l o o r s . Tarns and lakes dammed by t a l u s are common. Headwalls of north f a c i n g c i r q u e s are c l i f f s some of which are 200 m high. South f a c i n g headwalls are l e s s steep, and broken by benches and short c l i f f bands. In general the l a r g e s t cirques and the longest troughs occur on the north side of r i d g e s . Aretes and most summits are rounded (Figure 6.4) . A l p i n e troughs are the most common trough type i n the study area. Trough lengths vary from 0.5 km f o r troughs heading i n s i n g l e south f a c i n g cirques on the Podunk Plateau, to 19 km f o r Sowaqua trough which i s fed by s e v e r a l higher north f a c i n g c i r q u e s . Troughs which run i n t o Sowaqua Trough from Mt Outram are truncated by the Sowaqua Trough, c r e a t i n g hanging v a l l e y s . This suggests these g l a c i e r s were confluent w i t h Sowaqua g l a c i e r . A l l a l p i n e troughs change to V-shaped, f l u v i a l forms w i t h i n s e v e r a l kilometres of t h e i r head. The c o l s between the heads of Eleven M i l e Creek and Eight M i l e Creek and between Eleven M i l e Creek and the unnamed v a l l e y to the east have been breached, e i t h e r under an i c e 94 Figure 6.4: Johnson Peak showing rounded summit and steep north s i d e . Note p r o t a l u s ramparts to r i g h t of Johnson Peak sheet or by d i f f l u e n c e . One cirque at the head of Sowaqua Creek has been breached and replaced by a pass which drops a b r u p t l y i n t o Snass Creek (Figure 6.2). I t i s l i k e l y t h a t much of the o r i g i n a l c i r q u e was eroded under o v e r r i d d i n g i c e . Ghost Pass i s a broad (1 km) trough which could not have been carved by a l p i n e g l a c i e r s because no peaks above the pass supported g l a c i e r s on the sides f a c i n g the pass. Shallow, l i n e a r troughs cross the slope below Johnson Peak at an e l e v a t i o n of between 1770 and 1850 m (Figure 6.1). These fea t u r e s are 2-3 m wide w i t h f l a t f l o o r s and small r i d g e s (2-4 m high) on t h e i r downslope s i d e . These have been i n t e r p r e t e d as sackung by Dr. Wayne Savigny (personal 95 communication 1993). P i t s dug i n the centre of two of these r e v e a l a 60 cm t h i c k organic l a y e r o v e r l y i n g w e l l s o r t e d sand, whereas s o i l p i t s i n slopes above the troughs c o n t a i n coarser t e x t u r e d m a t e r i a l w i t h abundant cobbles. This suggests that these troughs may have c a r r i e d g l a c i a l meltwater. I t i s l i k e l y t h at meltwater e x p l o i t e d p r e - e x i s t i n g troughs created by bedrock sagging near the margin of the g l a c i e r . Snass Creek flows i n a s t r i k i n g V-shaped v a l l e y , which begins a b r u p t l y at the edge of Podunk Plateau. This has been i n t e r p r e t e d as a larg e s u b g l a c i a l meltwater channel (Figure 6.2). In the middle reaches of Sowaqua Creek many t r i b u t a r i e s have a d i s t i n c t down v a l l e y d e f l e c t i o n (Figure 6.2), r a t h e r than f l o w i n g d i r e c t l y downslope i n t o the creek. The d e f l e c t i o n could be a r e s u l t of r e d i r e c t i o n around a r e t r e a t i n g i c e tongue. Montigny Creek o r i g i n a t e s i n a cirqu e i n c i s e d below Podunk Plateau. The cirque has been breached and two steep w a l l e d g u l l i e s cut through the headwall. The creek i s i n c i s e d i n t o a bedrock canyon, which resembles a s u b g l a c i a l meltwater channel f o r part of i t s length. 6.3 Depositional Landforms and S u r f i c i a l Materials A l l upper v a l l e y slopes are steep and dominated by bedrock, l o c a l l y w i t h a t h i n c o l l u v i a l cover. Lower slopes are l e s s steep and are mantled w i t h t i l l and colluvium. V a l l e y f l o o r s and lower slopes of smaller creeks are f i l l e d w i t h c o l l u v i a l 96 cone and fan deposits which obscure any e a r l i e r g l a c i a l d e p o s i t s . Sowaqua Creek v a l l e y contains extensive t e r r a c e d e p o s i t s of g l a c i o f l u v i a l g r a v e l s o v e r l y i n g t i l l (Map 3, Figure 6.2). 6.3.1 Till Basal t i l l i s exposed i n road cuts on moderately steep lower slopes throughout the study area. I t f i l l s hollows i n bedrock and t h i c k n e s s v a r i e s from l e s s than 1 m to over 10 m. Commonly a c o l l u v i a l veneer or blanket d e r i v e d from rock ouctrops up slope o v e r l i e s the t i l l . T i l l i s i n v a r i a b l y h i g h l y c o n s o l i d a t e d . G e n e r a l l y i t i s po o r l y drained and seepage i s common over the surface. The matrix t e x t u r e i s sandy wi t h o c c a s i o n a l f i n e r t e x t u r e d pockets. The t e x t u r e may r e f l e c t the bedrock geology, w i t h g r a n i t i c areas having more sandy t i l l than areas u n d e r l a i n by f i n e r t e x t u r e d rocks. C l a s t s are subrounded to subangular, and l a r g e l y pebbles w i t h o c c a s i o n a l cobbles. Throughout the study area g r a n i t i c rocks are the most common c l a s t type; mafic and f e l s i c v o l c a n i c s and sediments are minor components. A mound of unsorted, moderately c o n s o l i d a t e d sandy rubble i n Sowaqua Creek v a l l e y could be e i t h e r a b l a t i o n t i l l or col l u v i u m . The deposit resembles colluvium, but occurs on a t e r r a c e . A l t e r n a t i v e l y , i t could be l a n d s l i d e d e b r i s t r a n s p o r t e d by i c e , then deposited as the i c e melted. A f t e r d e p o s i t i o n , t h i s m a t e r i a l was then p a r t i a l l y covered by g l a c i o f l u v i a l outwash. 97 6.3.2 Moraines Two w e l l d e f i n e d moraine ridges loop i n t o adjacent southwest f a c i n g c i r q u e s at an e l e v a t i o n of 1600 m between Mt. Outram and Johnson Peak (Figure 6.2). The northernmost of these moraines was v i s i t e d . This i s the l a r g e s t moraine at 500 m long and 5 to 10 m high (Figure 6.5). The second moraine i s roughly 2 00 m long. Rounded to subrounded g r a n o d i o r i t e Figure 6.5: Moraine damming lake on the south side of Mt. Outram. Note breached c o l behind the lake. boulders are common on the surface of the northern moraine. However a s o i l p i t revealed that pebbles and cobbles are dominantly mafic v o l c a n i c s w i t h g r a n o d i o r i t e and f e l s i c v o l c a n i c rocks as l e s s e r c o n s t i t u e n t s . The cirque headwall i s composed of g r a n o d i o r i t e , so a cirque g l a c i e r should leave d e p o s i t s w i t h only t h i s rock type. I t i s thus concluded from both t h e i r plan-form and composition that these are moraines which were deposited by a c t i v e i c e i n the Nicolum-Sumallo trough r a t h e r than by cirque g l a c i e r s . A broad low rid g e i n a t r i b u t a r y v a l l e y on the south s i d e of Sowaqua Creek at 1200 m i s i n t e r p r e t e d as a l a t e r a l moraine deposited by the Sowaqua G l a c i e r . The ridge has an i r r e g u l a r hummocky surface w i t h s c a t t e r e d g r a n o d i o r i t e boulders. A s o i l p i t r e v e a l s i t i s composed of s i l t y sand w i t h subrounded v o l c a n i c and g r a n o d i o r i t e c l a s t s . 6.3.3 Terraces, Glaciofluvial and Glaciolacustrine Deposits Extensive v a l l e y f i l l d eposits are present i n Sowaqua v a l l e y , where t e r r a c e s of g l a c i o f l u v i a l outwash g r a v e l s o v e r l i e t i l l . The t h i c k e s t of these deposits occurs at the mouth of Montigny Creek where 3 0 m of g l a c i o f l u v i a l g r a v e l s o v e r l y i n g over 5 m of t i l l are exposed along the path of a s l i d e i n t o the creek (Figure 6.6 s e c t i o n 1). The surface of t h i s t e r r a c e i s at an e l e v a t i o n of 850 m, 60 m higher than adjacent t e r r a c e s . Upstream of Montigny Creek the t e r r a c e s are continuous f o r 5.5 km on both sid e s of Sowaqua Creek, and have a surface gradient of 6% (Map 3). Terrace deposits along Sowaqua Creek are cr u d e l y s t r a t i f i e d sandy g r a v e l s , t y p i c a l of i c e proximal outwash de p o s i t s (Brodzikowski and van Loon 1991; M i a l l 1983). Near the upstream l i m i t of the t e r r a c e s deposits become more 99 o O . 0 0 . o O o 0 o ° 0 0 o o o o o 0 ° o o 0 O 0 o 0 0 40 m 2m 2m 11 m o o o o o 00 o o o o 0 0 o 0 o °o°°°o° o o o o o 0 u OO o 0 0 o o o o o OOO o. oo 0 0 40 m Legend 9. o° • O o 0 o o 0 • o _2_ glaciofluvial sands and gravels glaciofluvial stratified sands glaciolacustrine silts Figure 6.6: Selected s t r a t i g r a p h i c s e c t i o n s , see f i g u r e 6.2 f o r l o c a t i o n s . 100 i r r e g u l a r (Figure 6.7); bedding i s d i s r u p t e d and lenses of t i l l and g l a c i o l a c u s t r i n e sediments are present (Figure 6.6 s e c t i o n 2). G l a c i o l a c u s t r i n e m a t e r i a l i s up to 5 m t h i c k and composed of massive to laminated s i l t . These deposits are i n t e r p r e t e d as i c e contact. Further upstream the v a l l e y of Sowaqua creek contains only basal t i l l . F igure 6.7: Road cut through upper end of g l a c i o f l u v i a l t e r r a c e i n Sowaqua Creek v a l l e y , near s e c t i o n 2, exposing i r r e g u l a r bedding. T i l l and g l a c i o l a c u s t r i n e s i l t s are exposed 5 0 m downstream. Debris from the Hope S l i d e , a lar g e rock avalanche which occurred i n 1965, f i l l s much of the Nicolum-Sumallo trough (Map 3, Figure 6.2). Between Eight M i l e Creek and the Hope S l i d e i s a l a r g e k e t t l e d t e r r a c e (Figure 6.2). A road cut 101 through t h i s t e r r a c e reveals a 40 m t h i c k s e c t i o n of g l a c i o f l u v i a l g r a v e l s and sands (Figure 6.6 s e c t i o n 3 and 4, Figure 6.8). The deposit i s planar bedded, and c l a s t s i z e v a r i e s from f i n e sand to boulders 30 cm i n diameter. Well s o r t e d beds are from 10 cm to 2 m t h i c k . No s t r u c t u r e s i n d i c a t i v e of flow d i r e c t i o n were found. A pocket of laminated s i l t s , 1 m t h i c k a l s o occurs i n t h i s s e c t i o n . This t e r r a c e i s l i k e l y a kame t e r r a c e deposited adjacent to i c e i n the Nicolum V a l l e y . Figure 6.8: Road cut through kame t e r r a c e above Nicolum Creek at s e c t i o n 3, exposing over 3 0 m of planar bedded sands and g r a v e l s . Two to three kilometres upstream from i t s j u n c t i o n w i t h Skagit R i v e r , a wider s e c t i o n of Snass Creek v a l l e y contains a 102 hummocky g l a c i o f l u v i a l t e r r a c e , s i m i l a r i n appearance to the kame t e r r a c e near Eight M i l e Creek. This was l i k e l y deposited adjacent to i c e i n the lower Snass v a l l e y . 6 . 4 Rock Weathering I t i s impossible to compare weathering of rock i n v a l l e y s w i t h that on the highest summits because they e x h i b i t d i f f e r e n t l i t h o l o g i e s and s t y l e s of weathering. The highest summits i n the study area, 2440 m Mt Outram and 2160 m Macleod Peak, are composed of f r a c t u r e d v o l c a n i c rocks. On Mt. Outram v o l c a n i c rocks outcrop above 2000 m. Here rock i s s e v e r e l y f r a c t u r e d and n i v a t i o n hollows i n t a l u s are pronounced. Outcrops of v o l c a n i c rocks are rare i n v a l l e y bottoms and, where present are a l s o s e v e r e l y f r a c t u r e d . G r a n o d i o r i t e weathering i n the Mt. Outram study area showed more v a r i a b i l i t y than the other areas. Most rock outcrops are r e l a t i v e l y smooth w i t h minor d i f f e r e n t i a l weathering of i n d i v i d u a l g r a i n s . Round to subrounded boulders, d i s p l a y i n g a s i m i l a r degree of weathering are common on r i d g e tops. S i x s i t e s on these smooth outcrops and boulders, ranging i n e l e v a t i o n from 1400 m to 1900 m, were sampled u s i n g the Schmidt hammer. A range i n mean Schmidt hammer readings of 4 0 to 45 w i t h a standard d e v i a t i o n of 6 to 10 was obtained (Figure 6.9, Appendix 3). Above 1800 m on Johnson Peak g r a n o d i o r i t e outcrops are rounded w i t h crumbly f l a k y surfaces coated w i t h s e v e r a l m i l l i m e t r e s of g r i t s i z e d fragments of weathered g r a n o d i o r i t e 103 (grus). Grus forms t h i c k aprons at the base of outcrops. Schmidt hammer readings were lower here than elsewhere w i t h means of f i v e samples ranging from 23 to 3 0 and standard d e v i a t i o n of 5 to 6 (Figure 6.9). No larg e boulders are present i n t h i s area. Between 1750 m and 2085 m on ridges between Mt. Outram and Macleod Peak g r a n o d i o r i t e i s knobby and p i t t e d . Weathering p i t s are c i r c u l a r , g e n e r a l l y l e s s than 10 cm wide and may be e i t h e r shallow (1- 2 cm) w i t h s l o p i n g sides or up to 10 cm deep w i t h v e r t i c a l w a l l s . Knobs are up to 10 cm high. One small 3 0cm diameter boulder i s attached to the u n d e r l y i n g s l a b Outram Area, Schmidt Hammer Results Mean rebound vs elevation 70-60-50-TJ C 3 o •g 40-c CD o CD CL 30-c a 11 E 20-i ! fx f r i i i i 4 i i f i * i 1000 1400 1600 1800 elevation (m) 2000 2400 flakey slabs normal weathering • pitted weathering Figure 6.9: P l o t of mean Schmidt Hammer readings w i t h e l e v a t i o n . Bars represent +/- 2 standard d e v i a t i o n s of the mean. 104 at i t s base, so i t appears to have weathered i n p l a c e . No f l a k i n g or grus formation i s present i n t h i s area. Schmidt hammer readings were s i m i l a r to u n p i t t e d g r a n o d i o r i t e i n other l o c a l i t i e s w i t h the means of s i x samples ranging from 40 t o 45 and standard d e v i a t i o n of 7 to 11 (Figure 6.9 Appendix 3). The type of knobby, p i t t e d weathering i n the Outram area i s very s i m i l a r i n appearance to that observed by the w r i t e r i n the L i z z i e Lake area of the Coast Mountains. ( L i z z i e Lake i s l o c a t e d i n a l a r g e a l p i n e area to the east of L i l l o o e t Lake, near the head of the S t e i n River.) Several summits around L i z z i e Lake have slabs w i t h knobs and p i t s which are the same s i z e as those near Mt. Outram. Many of the L i z z i e Lake s l a b s a l s o have f r e s h s t r i a t i o n s on the same outcrop, so the knobs and p i t s must have formed a f t e r Fraser G l a c i a t i o n . Twidale and Corbin (1963) have found weathering p i t s of 10 cm i n diameter on surfaces i n A u s t r a l i a known to be at most a few thousand years o l d . Sorensen (1988) has observed t h i n veneers of grus, s i m i l a r to that on Mt. Johnson, on surfaces i n southeastern Norway which emerged from the sea onl y one thousand years ago. Sugden and Watts (1977) argue that l a r g e weathering p i t s , g r eater than 75 cm wide and 2 0 cm deep, on B a f f i n I s l a n d l i k e l y formed p r i o r to the l a s t g l a c i a t i o n and were preserved under c o l d based i c e . Ryder (personal communication 1995) observed that weathering p i t s i n the Okanagan Range of the Cascade Mountains were more than 1 m i n diameter on surfaces above e l e v a t i o n s reached by the C o r d i l l e r a n Ice Sheet during Fraser G l a c i a t i o n . Although these 105 s t u d i e s are from a v a r i e t y of environments, they do suggest that the depth of grus and the s i z e of p i t s observed i n the Mt. Outram study area could have formed since the l a s t g l a c i a t i o n . The p l o t of mean Schmidt hammer readings versus e l e v a t i o n (Figure 6.9) re v e a l s there i s no trend between mean values and e l e v a t i o n . Means of samples on normal and p i t t e d weathered surfaces are somewhat c l u s t e r e d . An exception i s a sample at 1600 m w i t h normal weathering which has an anomalously low value. This surface was somewhat rougher than other s i t e s , w i t h more i n d i v i d u a l g r a i n s p r o t r u d i n g . The la c k of a sharp drop i n mean values w i t h e l e v a t i o n suggests that f a c t o r s other than l e v e l of g l a c i a t i o n are res p o n s i b l e f o r the v a r i a b i l i t y i n the readings. Some of the v a r i a b i l i t y i n weathering could be a f u n c t i o n of v a r i a t i o n s i n snow pack .duration and moisture. Benedict (1993) found that weathering of g r a n i t i c rocks i s f a s t e s t where snow cover i s t h i n to moderate and meltout occurs e a r l y , so there are more freeze thaw c y c l e s . H a l l (1993) found the opposite, that the maximum chemical weathering occurred under l a t e l y i n g snow packs. A second p o s s i b i l i t y could be minor l i t h o l o g i c v a r i a t i o n s w i t h i n the g r a n o d i o r i t e , p a r t i c u l a r l y the percentage of b i o t i t e (see B u s t i n and Mathews 1978) • S o i l development v a r i e s w i t h rock weathering. On Johnson Peak i n the v i c i n i t y of the f l a k y g r a n o d i o r i t e , s o i l i s composed of grus, w i t h very l i t t l e f i n e grained matrix; LFH and A horizons are up to 2 0 cm t h i c k . This i s very d i f f e r e n t 106 from s o i l developed on the moraines and i n areas w i t h e i t h e r smooth or p i t t e d g r a n o d i o r i t e . In these areas s o i l has a s i l t y sand matrix and g r a n o d i o r i t e c l a s t s to cobble s i z e , t y p i c a l of s o i l formed on t i l l . LFH and A horizons are g e n e r a l l y 5 to 10 cm t h i c k . This and a general lack of boulders suggests that there i s l i t t l e or no t i l l d e p o s i t i o n i n the area- of f l a k y s l a b s near Johnson Peak, or t h i c k grus was deposited over t i l l a f t e r d e g l a c i a t i o n . The f l a k y surfaces of Johnson Peak have lower Schmidt hammer readings than any other s i t e s i n the study areas. These values are s i m i l a r to those i n areas not a f f e c t e d by Fraser G l a c i a t i o n i n the Okanagan Range (J.M. Ryder 1989, personal communication 1995). However, s t r i a t i o n s occur at a s i m i l a r e l e v a t i o n roughly 3 km to the east. Ridges 2 km northeast have e r r a t i c s at the same e l e v a t i o n as the f l a k y s l a b s . The l o c a t i o n of Johnson Peak and i t s r e l a t i v e l y low e l e v a t i o n (1950 m) makes i t u n l i k e l y that i t was not overtopped by C o r d i l l e r a n Ice, thus the anomalously low values are d i f f i c u l t to account f o r . They may i n d i c a t e that l i t t l e e r o s i o n was accomplished by the C o r d i l l e r a n Ice Sheet due to short d u r a t i o n , t h i n i c e , or l i t t l e basal movement. 6.5 G l a c i a l History 6.5.1 Valley Glacier Phase The presence of w e l l defined e r o s i o n a l landforms of a l p i n e g l a c i a t i o n again i n d i c a t e s that a l p i n e and v a l l e y g l a c i e r s 107 formed around higher summits during the e a r l y stages of g l a c i a t i o n (Figure 6.10). The extent of these g l a c i e r s i s r e c o n s t r u c t e d e n t i r e l y from e r o s i o n a l topography. Figure 6.10: E a r l y Fraser G l a c i a t i o n a l p i n e g l a c i e r s . 108 I t i s assumed that g l a c i e r s extended down v a l l e y s to U -V t r a n s i t i o n s , which are w e l l defined i n t h i s area. There i s a weak r e l a t i o n between cirque area and trough l e n g t h (Figure 6.11) (See Chapter 3 f o r a d e s c r i p t i o n of the method used to measure c i r q u e area and g l a c i e r length) and north f a c i n g c i r q u e s are l a r g e r and t h e i r troughs longer than those f a c i n g south. These f a c t s lend support f o r the U-V t r a n s i t i o n marking the terminus of v a l l e y g l a c i e r s ( F l i n t 1971; Goldthwait 1970) . This phase i s res p o n s i b l e f o r dominant topographic forms such as ci r q u e s and a l p i n e troughs. Outram Area Cirque Area Trough Length Relation 24-0 22-20-€m\t 18-• 16-. . i \j CM E * 1/1 e Area •A 0 4 1 • cr 5 10 1 V 8-6-A . 2-• m • 0-c • • : m • ) 2 > A \ e \ 1 Trough Le 0 1 ngth (km) 2 1 4 1 6 1 8 2 Figure 6.11: P l o t of cirque area versus trough length. 109 6.5.2 Ice Sheet Stage At the Fraser G l a c i a t i o n maximum a l l summits were l i k e l y -overtopped by i c e . Ridge c r e s t s are g e n e r a l l y broad and rounded and e r r a t i c s are common on ridges below Mt. Outram and MacLeod Peak. The presence of breached c o l s , such as at the head of E i g h t , Eleven M i l e , and Sowaqua Creeks, and broad passes such as Ghost Pass i s f u r t h e r evidence f o r o v e r r i d i n g C o r d i l l e r a n i c e . Nicolum-Sumallo pass i s a deep steep-walled through-trough fed almost e n t i r e l y by v a l l e y s that become V-shaped before e n t e r i n g i t . I t must the r e f o r e have been carved l a r g e l y by C o r d i l l e r a n Ice. Rock weathering i s v a r i a b l e i n the Mt. Outram Study area, but no g r a n o d i o r i t e outcrops are weathered s t r o n g l y enough t o i n d i c a t e they could not have been g l a c i a t e d . The enhanced weathering on Johnson Peak and the ridge between Mt. Outram and Macleod Peak may i n d i c a t e that the i c e sheet covered these r i d g e s f o r only a short p e r i o d of time. Both Mt. Outram and MacLeod Peak are craggy summits composed of h i g h l y f r a c t u r e d rock. There i s no strong evidence that they were overtopped by C o r d i l l e r a n Ice. However at the I n t e r n a t i o n a l Border 32 km south of the study area the i c e surface was higher than 2600 m (Waitt and Thorson 1983), 200 m higher than Mt. Outram. As Mt. Outram i s f u r t h e r from the per i p h e r y of the i c e sheet i t i s l i k e l y that i t was overtopped, at l e a s t b r i e f l y . Few i c e flow i n d i c a t o r s are present i n t h i s area. Grooves i n meadows below Mt. Outram have an o r i e n t a t i o n of between 78° 110 and 83°. A s i n g l e p o o r l y preserved groove west of Mt. Davis has an o r i e n t a t i o n of 140°. In both cases the grooves are roughly p a r a l l e l to adjacent v a l l e y s suggesting that when they formed flow was c o n t r o l l e d by l o c a l topography. I t i s l i k e l y t h at at the Fraser Maximum i c e from the Fraser R i v e r flowed eastward through Nicolum-Sumallo Trough (Evans 1990) . 6.5.3 Deglaciation Evidence of d e g l a c i a t i o n i s patchy. In the Nicolum-Sumallo trough two moraines and one kame t e r r a c e provide two i c e l e v e l s . In Sowaqua Creek one l a t e r a l moraine and one kame t e r r a c e are the only i c e marginal features observed. As a r e s u l t , maps of d e g l a c i a t i o n are not p r e c i s e , each map i s based on only one or two features . They have been drawn to demonstrate a p o s s i b l e sequence of d e g l a c i a t i o n which i s c o n s i s t e n t w i t h the a v a i l a b l e evidence. The highest i c e l e v e l recorded i s 1680 m at the e l e v a t i o n of the l a t e r a l moraines west of Mt. Outram (Figure 6.12). The moraines were l i k e l y deposited during a b r i e f resurgence of i c e i n t h i s v a l l e y . At t h i s time i c e i n the pass was over 1000 m t h i c k and l i k e l y was' s t i l l a c t i v e and fl o w i n g east. A l p i n e g l a c i e r s were present i n higher north f a c i n g c i r q u e s . The deposits i n Sowaqua Creek are most c o n s i s t e n t w i t h u p - v a l l e y r e t r e a t , p o s s i b l y w i t h minor stagnation of the g l a c i e r snout; g l a c i o f l u v i a l t e r r a c e s grade upstream i n t o i c e contact d e p o s i t s and f i n a l l y t i l l . This g l a c i e r was fed almost e n t i r e l y from high n o r t h - f a c i n g c i r q u e s , many of which appear 111 Figure 6.12: An i c e l e v e l near the s t a r t of d e g l a c i a t i o n , based on moraines below Mt. Outram. 112 r e l a t i v e l y f r e s h . I t i s t h e r e f o r e p o s s i b l e that g l a c i e r s remained a c t i v e i n t h i s v a l l e y throughout d e g l a c i a t i o n and r e t r e a t e d by a combination of t h i n n i n g of a c t i v e i c e and f r o n t a l r e t r e a t , w i t h l o c a l stagnation of the g l a c i e r snout. The i c e l e v e l shown i n f i g u r e 6.13 i s based on a s i n g l e l a t e r a l moraine found at 122 0 m on the south side of Sowaqua Creek. The map was drawn assuming s i m i l a r r a t e s of t h i n n i n g throughout the study area. This may not be a v a l i d assumption; i c e i n Nicolum-Summallo trough may have e i t h e r been l a r g e l y cut o f f from i t s source areas or i t may have s t i l l been fed by a lobe of a c t i v e i c e from the Fraser V a l l e y . In e i t h e r case i t i s u n l i k e l y that i t r e t r e a t e d at the same rat e as Sowaqua G l a c i e r , which was fed by l o c a l cirque g l a c i e r s . As the Sowaqua G l a c i e r continued to recede i t would have thinned and separated i n t o d i s c r e t e v a l l e y g l a c i e r s , which continued to r e t r e a t up v a l l e y . Figure 6.14 i s drawn at the time of kame t e r r a c e formation i n Sowaqua and Nicolum Creeks. No evidence of t e r m i n a l p o s i t i o n s of other v a l l e y g l a c i e r s was found, so the g l a c i e r s were drawn assuming a s i m i l a r r e l a t i o n of c i r q u e s i z e to g l a c i e r length as was found f o r the a l p i n e g l a c i e r phase (Figure 6.11). During the f i n a l stages of r e t r e a t , i c e i n the Nicolum-Sumallo trough may have stagnated, while meltwater deposited kame t e r r a c e s at the mouth of Eleven M i l e Creek and i n Snass Creek (Figure 6.14). The kame t e r r a c e at Eleven M i l e Creek i s approximately the same e l e v a t i o n as the pass between Nicolum and Sumallo creeks. I t i s t h e r e f o r e p o s s i b l e that meltwater 113 Figure 6.13: A l a t e r i c e l e v e l , based on a l a t e r a l moraine at 1220 m i n Sowaqua Creek. 114 Figure 6.14: An i c e l e v e l near the end of d e g l a c i a t i o n , based on the kame t e r r a c e s i n Nicolum and Sowaqua Creeks. 1 drained eastward i n t o the Skagit b a s i n r a t h e r than to the Fraser R i v e r at t h i s time. Eight M i l e Creek heads i n a north f a c i n g c i r q u e which i s lower and l e s s f r e s h l o o k i n g than n o r t h f a c i n g c i r q u e s to the east. I t does not appear to have h e l d a la r g e a c t i v e g l a c i e r throughout d e g l a c i a t i o n , but small g l a c i e r s may have e x i s t e d on surrounding peaks and c o n t r i b u t e d m a t e r i a l t o the kame t e r r a c e i n Nicolum v a l l e y v i a a meltwater channel which ran along the margin of the i c e i n Nicolum v a l l e y (Figure 6.14). This channel may a l s o have c a r r i e d m a t e r i a l to the t e r r a c e from a c t i v e i c e behind the stagnant snout i n Nicolum Creek. Much of Podunk Plateau, which i s r e l a t i v e l y high, l i k e l y remained i c e covered u n t i l r e l a t i v e l y l a t e during d e g l a c i a t i o n . Ice here downwasted and stagnated, d e p o s i t i n g hummocky t i l l . The heads of both Montigny and Snass Creeks are at the pl a t e a u edge so i t i s l i k e l y they c a r r i e d meltwater from the pla t e a u . The larg e g l a c i o f l u v i a l t e r r a c e at the mouth of Montigny Creek, which i s 60 m higher than adjacent t e r r a c e s i n Sowaqua Creek may have been formed by meltwater from the pl a t e a u . S i m i l a r l y plateau meltwater may have c o n t r i b u t e d m a t e r i a l to the g l a c i o f l u v i a l t e r r a c e i n Snass Creek. Extensive downwasting or downvalley r e t r e a t should produce considerable damming of upper v a l l e y s and t r i b u t a r i e s , as these would become i c e f r e e f i r s t . However l a c u s t r i n e d e p o s i t s are rare throughout the study area. This suggests that s u b g l a c i a l drainage was common, or g l a c i o l a c u s t r i n e 116 d e p o s i t s have been eroded or b u r i e d by c o l l u v i u m s i n c e d e g l a c i a t i o n . 6.6 Neoglaciation N e o g l a c i a l ( L i t t l e Ice Age) a c t i v i t y was r e s t r i c t e d to n o r t h f a c i n g c i r q u e s . The dominant a c t i v i t y appears to have been the formation of p r o t a l u s ramparts. In a d d i t i o n small g l a c i e r s may have e x i s t e d at the base of steep slopes where avalanches fed the accumulation zones. A remnant of one such g l a c i e r s t i l l e x i s t s on the north side of Mt. Outram. 117 CHAPTER 7 DISCUSSION 7.1 G l a c i a t i o n of the Northern Cascade Mountains A c o n s i s t e n t p a t t e r n of g l a c i a t i o n has been observed i n a l l three study areas. At the s t a r t of Fraser G l a c i a t i o n a l p i n e g l a c i e r s formed around higher summits, dominantly on t h e i r n o r t h s i d e s (Figure 7.1). They l i k e l y advanced to a roughly s t a b l e p o s i t i o n marked by a t r a n s i t i o n from trough to V shaped v a l l e y s . A p l o t of cirque area versus trough l e n g t h f o r both the Outram and Stoyoma areas r e v e a l s a c o n s i s t e n t r e l a t i o n i n both areas (Figure 7.2). The U-shaped p o r t i o n s of v a l l e y s are between 100 and 300 m wider than the V-shaped p o r t i o n s . (As measured across v a l l e y f l a t s , roughly 1 km above and below the t r a n s i t i o n zone). Cirque f l o o r s are 100 to 500 m lower than adjacent r i d g e tops, and c o l s have been lowered by up to 400 m assuming that a continuous, roughly f l a t r idge p r e v i o u s l y e x i s t e d . Using Andrews (1975) r a t e s of ero s i o n (see chapter 3) as a rough guide the leng t h of time r e q u i r e d to accomplish t h i s much e r o s i o n can be c a l c u l a t e d . At the slowest quoted r a t e of 400mm/l000 years, up to 1 m i l l i o n years would be r e q u i r e d to accomplish the observed lowering of c o l s and the e r o s i o n of the l a r g e s t c i r q u e s . Even the f a s t e s t quoted r a t e of 5,000 mm/1000 years would r e q u i r e 80,000 years. Between 40,000 and 125,000 years would be req u i r e d f o r the observed widening of the troughs. As the t o t a l d u r a t i o n of Fraser G l a c i a t i o n was roughly 20,000 years, i t i s c l e a r , even from very rough 118 Figure 7.1: G l a c i a t i o n model f o r the northern Cascade Mountains, a ) . E a r l y Eraser G l a c i a t i o n a l p i n e g l a c i e r s , b ) . E a r l y advance of the C o r d i l l e r a n Ice Sheet up north t r e n d i n g v a l l e y s , c ) . At the Fraser Maximum a l l summits are overtopped by an e x t e r n a l i c e sheet, d). During d e g l a c i a t i o n i c e r e t r e a t s down v a l l e y s without a l o c a l i c e source or.those of lower and south f a c i n g cirques which are below the l o c a l snowline. Higher north f a c i n g cirques may remain above snowline g l a c i e r s w i l l remain a c t i v e and r e t r e a t up v a l l e y . 119 Cirque Area Trough Length Relation 24-22-20-18-~ 16-Oi E < u § 12-E" 0 in 10-8- D 6- • 4-2 • • • • i : • n B 0-0 2 4 6 8 1 Trough L 0 1 ength (km) 2 1 4 1 6 1 8 2 >0 Figure 7.2: P l o t of Outram and Stoyoma cirq u e areas versus trough l e n g t h . c a l c u l a t i o n s , that much of the ero s i o n i n a l l study areas, i n c l u d i n g the formation of the larg e troughs and c i r q u e s , pre-dates Fraser G l a c i a t i o n . The shortest time of 80,000 years f o r the e r o s i o n of the la r g e cirques i s s i m i l a r to the 100,000 year c y c l e f o r the l a s t major g l a c i a t i o n (Sugden and John 1976). However i t i s u n l i k e l y that t h i s e r o s i o n r a t e would have been sustained f o r the e n t i r e g l a c i a t i o n because f o r part of t h i s time cir q u e g l a c i e r s would l i k e l y have been very s m a l l . Thus most a l p i n e forms must be a r e s u l t of e r o s i o n 120 d u r i n g the a l p i n e stage of s e v e r a l major g l a c i a l c y c l e s . Therefore the a l p i n e and intense a l p i n e phases must have been repeated during each g l a c i a t i o n . In Washington near the periphery of the i c e sheet, a l p i n e g l a c i e r s r e t r e a t e d before the i c e sheet moved i n t o the area. In the study areas there i s no evidence to suggest that a l p i n e g l a c i e r s r e t r e a t e d before the advance of the C o r d i l l e r a n Ice Sheet. No more than one t i l l was found at any l o c a t i o n . I t i s l i k e l y that a l p i n e g l a c i e r s coalesced w i t h or were overridden by the C o r d i l l e r a n Ice Sheet. Toward the end of the intense a l p i n e phase (Davis and Mathews 1944), g l a c i e r s from the Coast Mountains began to advance i n t o surrounding lowlands. The Cascade Mountains would have posed a s i g n i f i c a n t b a r r i e r to t h i s i c e . South of L y t t o n , Coast Mountain i c e l i k e l y would have been d i v e r t e d south, down the Fraser R i v e r . Lobes would then have advanced up major Cascade v a l l e y s which drained i n t o the Fraser, p a r t i c u l a r l y those which drained to the northwest such as the Anderson R i v e r , Nicolum Creek and Silverhope Creek (Figure 7.3). North of L y t t o n , Coast Mountain i c e would have moved eastward and southeastward up the N i c o l a v a l l e y . A major depression on the east s i d e of the Cascade Mountains, extends from the Thompson R i v e r to the Similkameen R i v e r (Figure 7.3), and l i k e l y served as a conduit f o r Coast Mountain i c e . While advancing down t h i s depression, lobes of i c e l i k e l y would have blocked and flowed up Cascade v a l l e y s that drained to the northeast, such as 121 Figure 7.3: Map of the Cascade Mountains and surrounding areas d e p i c t i n g probable routes f o r the e a r l y advance of i c e from the Coast Mountains i n t o the Cascade Mountains. 122 Spius Creek, Coldwater Ri v e r , C o q u i h a l l a R i v e r and the uppermost Similkameen Ri v e r . Thus northward d r a i n i n g v a l l e y s near both the east and west margins of the Cascade Mountains were l i k e l y dammed by lobes of C o r d i l l e r a n i c e r e l a t i v e l y e a r l y i n Fraser G l a c i a t i o n , while Cascade a l p i n e g l a c i e r s were s t i l l c o n fined to upper v a l l e y s . Continued advance of both a l p i n e g l a c i e r s and the i c e sheet would have caused them to coalesce and ov e r r i d e the f i n e t e x t u r e d g l a c i o l a c u s t r i n e sediments deposited i n f r o n t of the advancing i c e sheet. These sediments would have been incorporated i n t o t i l l , r e s u l t i n g i n the f i n e t e x t u r e d t i l l of these v a l l e y s . In the Stoyoma area drumlins i n d i c a t e flow to the southwest on the plateau. As these are not at high l e v e l s , they may represent i c e flow during e a r l y Fraser G l a c i a t i o n . Flow to the southwest on the Spius Plateau i s c o n s i s t e n t w i t h a lobe of C o r d i l l e r a n Ice advancing up Spius Creek from the northeast, and expanding over the plateau area. F o l l o w i n g mountain g l a c i a t i o n , an i c e sheet covered a l l areas i n c l u d i n g the highest summits ( f i g u r e 7.1c). Ice flow n o r t h of the Stoyoma area at the Fraser maximum was g e n e r a l l y to the south (Ryder 1981). In the Anderson R i v e r area f l u t i n g on summits and rid g e tops i n d i c a t e s flow at the Fraser maximum was a l s o to the south, oblique to l o c a l v a l l e y s . This suggests that i n t h i s area i c e thickness was con s i d e r a b l y more than r e l i e f , that i s much greater than 2000 m. Grooves near r i d g e tops i n the Outram Area are roughly p a r a l l e l to l o c a l v a l l e y s 123 suggesting that i n t h i s area i c e flow was c o n t r o l l e d by l o c a l topography, and i c e may not have been much t h i c k e r than r e l i e f . Thus the i c e surface may not have been much higher than 2400 m Mt. Outram. Where the i c e sheet was f l o w i n g roughly p a r a l l e l to l o c a l v a l l e y s , these would have continued to be widened and deepened. In the northern two areas where the i c e sheet was f l o w i n g oblique to v a l l e y s at the Fraser maximum, e r o s i o n of v a l l e y s would have ceased while the i c e was at i t s maximum th i c k n e s s . At the s t a r t of d e g l a c i a t i o n the i c e sheet remained a c t i v e and thinned u n t i l higher peaks became i c e f r e e . Snowline had r i s e n above lower e l e v a t i o n and south f a c i n g c i r q u e s before they emerged from under the i c e sheet, thus they were no longer able to support a l p i n e g l a c i e r s . However some higher north f a c i n g cirques i n the Mt. Outram area, and l i k e l y a l s o i n the Anderson R i v e r area, remained above the snowline and were able to support g l a c i e r s throughout d e g l a c i a t i o n . As a r e s u l t , i c e g e n e r a l l y remained a c t i v e and thinned while r e t r e a t i n g back up these v a l l e y s . Some sta g n a t i o n of g l a c i e r snouts l i k e l y occurred during f r o n t a l r e t r e a t , a l l o w i n g t h e ' d e p o s i t i o n of kame t e r r a c e s i n v a l l e y s such as Sowaqua Creek. Down-valley r e t r e a t of a c t i v e lobes of C o r d i l l e r a n i c e appears to have been the dominant mode of r e t r e a t throughout the study areas. The main evidence f o r t h i s i s the moraines l o c a t e d i n the Stoyoma and Outram areas and the general l a c k 124 of f r e s h features i n most c i r q u e s . Once the higher summits became i c e f r e e the C o r d i l l e r a n Ice Sheet r e t r e a t e d away from the mountains, i n roughly the reverse d i r e c t i o n of advance. E a r l y during d e g l a c i a t i o n , there was a b r i e f resurgence when the i c e sheet deposited the moraines i n s e v e r a l south f a c i n g and low e l e v a t i o n c i r q u e s . There are few deposits i n d i c a t i v e of s t a g n a t i o n so i t i s l i k e l y that subsequent r e t r e a t was continuous. L a t e r a l meltwater channels most o f t e n form when i c e i s a c t i v e (Fulton 1967), thus the channels i n the Stoyoma area are f u r t h e r evidence of a c t i v e i c e . There i s l i t t l e evidence i n any study area to suggest how meltwater escaped from v a l l e y s i n which a c t i v e i c e r e t r e a t e d down-valley. I f i c e i s a c t i v e , the i c e surface slope should c o n t r o l s u b g l a c i a l flow of meltwater (Shreve 1972). This would prevent down-valley flow, and r e s u l t i n lakes being ponded up-v a l l e y from the r e t r e a t i n g i c e margin. Only the Anderson R i v e r study area contains s i g n i f i c a n t g l a c i o l a c u s t r i n e d e p o s i t s i n v a l l e y s that should have been dammed by downwasting i c e (see D e g l a c i a t i o n maps). There i s no i n d i c a t i o n of how these lakes drained. There are s e v e r a l p o s s i b l e explanations f o r the problem of drainage i n v a l l e y s which underwent down-valley r e t r e a t . 1. The i c e surface slope could have been very c l o s e to 0° a l l o w i n g bedrock topography to dominate s u b g l a c i a l flow. This may have permitted these v a l l e y s to d r a i n s u b g l a c i a l l y . Bedrock canyons i n Miner's and Montigny Creeks could have o r i g i n a t e d as s u b g l a c i a l tunnel v a l l e y s , and are p o s s i b l e 125 evidence of s u b g l a c i a l drainage. 2. There could have been damming i n many v a l l e y s but no evidence of lake sediments was found due to e r o s i o n , or mixing of t h i n g l a c i o l a c u s t r i n e d e p o s i t s w i t h t i l l by p e r i g l a c i a l processes, or i n s u f f i c i e n t f i e l d checking. 3. The lobes of C o r d i l l e r a n i c e were stagnant r a t h e r than a c t i v e , but c a r r i e d l i t t l e d e b r i s so few d e p o s i t s remain. In t h i s case meltwater could escape down-valley e i t h e r s u b g l a c i a l l y or s u p r a g l a c i a l l y . 4. L a t e r a l drainage was present and no channels were observed. This would r e q u i r e lakes to be ponded to a s u f f i c i e n t depth to a l l o w flow around the u p - v a l l e y s l o p i n g i c e tongues. More d e t a i l e d f i e l d work i s r e q u i r e d i n v a l l e y s which should have been d e g l a c i a t e d by down v a l l e y r e t r e a t i n order to determine the best e x p l a n a t i o n . N e o g l a c i a l a c t i v i t y throughout the Cascades was r e s t r i c t e d to north f a c i n g slopes that were fed by avalanches (and to l a r g e volcanoes i n Washington). No extensive g l a c i e r s , as were present i n the Coast Mountains e x i s t e d i n the Cascades. This may be due to a d r i e r c l i m a t e without enough p r e c i p i t a t i o n , and a l a c k of s u f f i c i e n t l y high l a r g e a l p i n e areas f o r i c e accumulation. 7.2 Pattern of Glaciation i n areas with Mountain and Ice Sheet g l a c i a t i o n The broad d e t a i l s of the Cascades g l a c i a t i o n appear to be i n common w i t h other areas that had both l o c a l and e x t e r n a l i c e sources, such as the Washington Cascades (Waitt 1977, 1975; Waitt and Thorson 1983), the P r e s i d e n t i a l Range i n New 126 Hampshire (Goldthwait 1970; Bradley 1981), the Green Mountains i n Vermont (Wagner 1970; Connally 1982), mountains of west-c e n t r a l Maine (Borns and C a l k i n 1977) and the I n s u l a r Mountains on northern Vancouver I s l a n d (Howes 1981, 1983) . The e a r l y g l a c i a l stages of l o c a l a l p i n e g l a c i a t i o n f o l l o w e d by overtopping by a r e g i o n a l i c e sheet occurred i n a l l areas. In a l l areas, d e g l a c i a t i o n was c o n t r o l l e d by l o c a l topography, e l e v a t i o n of snowline and distance from the edge of the i c e sheet. Thus d e g l a c i a t i o n of areas that experienced mixed mountain and i c e sheet g l a c i a t i o n followed a complex p a t t e r n that depended s t r o n g l y on l o c a l c o n d i t i o n s . I t i s thus more d i f f i c u l t to p r e d i c t the p a t t e r n of d e g l a c i a t i o n i n these areas than i n those where only one s t y l e of g l a c i a t i o n , e i t h e r mountain or i c e sheet, occurred. 7.3 A pplication of G l aciation Models to Terrain Mapping The manner i n which g l a c i e r s move i n t o and out of an area l a r g e l y determines the r e s u l t i n g types of landforms and s u r f i c i a l m a t e r i a l s . Knowledge of g l a c i a l h i s t o r y can a l l o w the p r e d i c t i o n of deposits, p a r t i c u l a r l y those on lower slopes and v a l l e y bottom. Commonly, v a l l e y s contain s e v e r a l l a y e r s of m a t e r i a l , which have been deposited throughout the g l a c i a l and post g l a c i a l p e r i o d . The uppermost u n i t i s l i k e l y to determine the surface expression and lower u n i t s may be d i f f i c u l t to recognize. I f v a l l e y s have been dammed at any time i n the g l a c i a l c y c l e f i n e t e x t u r e d sediments may be present. T y p i c a l l y these 127 w i l l be o v e r l a i n by coarser m a t e r i a l and w i l l have no surface expression. Because f i n e textured sediments have a strong i n f l u e n c e on s t a b i l i t y , i t i s important to be able to p r e d i c t t h e i r occurrence. Each of the three s t y l e s of g l a c i a t i o n , that i s mountain, i c e sheet or mixed, produces a d i f f e r e n t s u i t e of landforms and d e p o s i t s , and so knowledge of the g l a c i a t i o n s t y l e should be h e l p f u l i n p r e d i c t i n g the expected m a t e r i a l s i n v a l l e y f i l l . 7.3.1 Examples from the northern Cascade Mountains In the Cascade Mountains the s t y l e of g l a c i a t i o n was mixed mountain and i c e sheet. Under t h i s model, at the s t a r t of g l a c i a t i o n , a l p i n e g l a c i e r s began to expand down v a l l e y s , p a r t i c u l a r l y those which face north. L a t e r during the advance phase, lobes of the C o r d i l l e r a n Ice Sheet began to advance up many v a l l e y s that drained out of the Cascades. These lobes e v e n t u a l l y coalesced w i t h the a l p i n e g l a c i e r s , and i c e e v e n t u a l l y overtopped a l l summits. Lower and south f a c i n g v a l l e y s were d e g l a c i a t e d by down-valley r e t r e a t of a c t i v e lobes of C o r d i l l e r a n i c e while higher, north f a c i n g v a l l e y s underwent f r o n t a l r e t r e a t of l o c a l v a l l e y g l a c i e r s . As a consequence of t h i s sequence of events, v a l l e y s that d r a i n toward The d i r e c t i o n from which the C o r d i l l e r a n Ice Sheet was advancing, may have had a p e r i o d during advance when i c e was moving up v a l l e y s at the same time as a l p i n e g l a c i e r s were advancing down v a l l e y s . While the middle p o r t i o n of the 128 v a l l e y was i c e fre e i t would have been dammed by the i c e sheet and the r e s u l t i n g g l a c i o l a c u s t r i n e deposits overridden as i c e continued to advance. The Mt. Stoyoma area contains c l a y - r i c h t i l l i n the lower p a r t s of s e v e r a l east and northeast f a c i n g v a l l e y s (see f i g u r e 4.4), c o n s i s t e n t w i t h damming by o v e r r i d i n g C o r d i l l e r a n i c e . The presence of t h i s t i l l would not have been p r e d i c t e d on the b a s i s of l i t h o l o g y as the l o c a l rock i s g r a n i t i c . I f the area had been g l a c i a t e d p r i m a r i l y by l o c a l a l p i n e g l a c i e r s , v a l l e y s would not have been dammed and t i l l would l i k e l y be much coarser t e x t u r e d . C l a y - r i c h t i l l near the j u n c t i o n of the North and South Forks of the Anderson R i v e r i s a l s o l i k e l y r e l a t e d to reworking of f i n e - t e x t u r e d v a l l e y f i l l by i c e advancing u p - v a l l e y . The l o c a l bedrock i s f i n e grained, but the t i l l m a trix tex t u r e i s very s i m i l a r to that of g l a c i o l a c u s t r i n e sediments up v a l l e y . In the Cascades, v a l l e y s which d i d not support s i g n i f i c a n t l a t e stage a l p i n e g l a c i e r s g e n e r a l l y head i n broad c o l s , h i g h l y eroded breached c i r q u e s , or have no l o c a l source area, and a few contain i c e sheet moraines. These v a l l e y s were d e g l a c i a t e d by down-valley r e t r e a t of a c t i v e i c e . Meltwater f l o w i n g down these v a l l e y s should have been blocked by the a c t i v e i c e , unless the i c e surface slope was very low. The Anderson R i v e r study area i s the only one which contains r e l a t i v e l y extensive g l a c i o l a c u s t r i n e m a t e r i a l i n v a l l e y s which should have been dammed by down-valley r e t r e a t . These are not t h i c k d e p o s i t s , but occur throughout a l l v a l l e y 129 bottoms. Damming of the Anderson R i v e r l i k e l y was caused by a lobe of a c t i v e i c e from the Coast Mountains i n the lower part of the Anderson R i v e r v a l l e y . In the other two areas no f i n e t e x t u r e d sediments were observed i n v a l l e y s which should have been dammed during d e g l a c i a t i o n . Nicolum v a l l e y contains a l a r g e kame t e r r a c e that was deposited next to stagnant i c e . I t i s d i f f i c u l t to d i s t i n g u i s h on airphotos v a l l e y s that c o n t a i n g l a c i o l a c u s t r i n e sediments from those that do not. Thin but extensive g l a c i o l a c u s t r i n e deposits i n Anderson R i v e r are not v i s i b l e on a i r photos. In some cases, such as Miner's Creek, an i n c i s e d meltwater channel i s present i n v a l l e y s without g l a c i o l a c u s t r i n e sediments suggesting that s u b g l a c i a l drainage may have occurred ( e i t h e r due to stagnant i c e or a low i c e surface s l o p e ) . Other v a l l e y s , such as Eleven M i l e Creek i n the Outram area, have n e i t h e r an i n c i s e d stream nor g l a c i o l a c u s t r i n e d e p o s i t s . Thus i n the study areas, the model does not al l o w the accurate p r e d i c t i o n of the l o c a t i o n of g l a c i o l a c u s t r i n e d e p o s i t s . However i t does suggest that v a l l e y s which head i n truncated c i r q u e s , c o n t a i n i c e sheet moraines and la c k obvious s u b g l a c i a l meltwater channels, should be suspected of c o n t a i n i n g g l a c i o l a c u s t r i n e sediment and t a r g e t e d f o r more d e t a i l e d f i e l d work, p a r t i c u l a r l y i f i d e n t i f i c a t i o n of t h i s m a t e r i a l i s a p r i o r i t y of t e r r a i n mapping. V a l l e y s i n which f r o n t a l r e t r e a t of l o c a l g l a c i e r s was dominant g e n e r a l l y have g l a c i o f l u v i a l outwash o v e r l y i n g t i l l i n the v a l l e y f i l l , and few f i n e - t e x t u r e d sediments are 130 present. These v a l l e y s can be recognized because they head i n fr e s h e r l o o k i n g cirques than other v a l l e y s and by the presence of g l a c i o f l u v i a l t e r r a c e s . Through troughs which o r i g i n a t e on the west side of the Cascade Mountains, such as South Spius Creek may have been conduits f o r meltwater from the Coast Mountains. These v a l l e y s c o n t a i n t h i c k deposits of g l a c i o f l u v i a l m a t e r i a l which cannot be e x p l a i n e d by l o c a l f e a t u r e s . Some v a l l e y s , where i c e r e t r e a t e d down-valley to the east, may a l s o have been dammed. In t h i s case g l a c i o l a c u s t r i n e s i l t s may u n d e r l i e the g l a c i o f l u v i a l m a t e r i a l i n the lower reaches of the v a l l e y . T i l l t h i c k n e s s i s not w e l l p r e d i c t e d by the model. There i s some i n d i c a t i o n that t h i c k deposits of t i l l may be common i n northeast and northwest tre n d i n g v a l l e y s , i n which t i l l was deposited by i c e advancing up v a l l e y e a r l y during g l a c i a t i o n . These v a l l e y s are g e n e r a l l y transverse to i c e flow at the maximum, a l l o w i n g the p r e s e r v a t i o n of t h i s t i l l . 7.3.2 Conclusions A l l areas which have been g l a c i a t e d by mixed mountain and i c e sheet g l a c i a t i o n have rounded and subdued a l p i n e features such as c i r q u e s and horns. V a l l e y f i l l s t r a t i g r a p h y v a r i e s , and depends l a r g e l y on the s t y l e and p a t t e r n of d e g l a c i a t i o n . The s t y l e of d e g l a c i a t i o n may be i n f e r r e d from a i r photo a n a l y s i s , combined w i t h an understanding of r e g i o n a l i c e flow d i r e c t i o n s . This allows some broad g e n e r a l i z a t i o n s to be made about probable v a l l e y f i l l s t r a t i g r a p h y . 131 The model of g l a c i a t i o n developed f o r the Cascade Mountains cannot a c c u r a t e l y p r e d i c t v a l l e y bottom depos i t s i n a l l study areas. The model does however p r e d i c t which v a l l e y s are most l i k e l y to have been dammed during advance and r e t r e a t , and thus where f i n e - t e x t u r e d t i l l and g l a c i o l a c u s t r i n e sediments are most l i k e l y to be l o c a t e d . Not a l l of these v a l l e y w i l l c o n t ain f i n e - t e x t u r e d sediment, but the model does i d e n t i f y where more d e t a i l e d f i e l d checking may be worthwhile to determine the extent of f i n e - t e x t u r e d sediment, p a r t i c u l a r l y i f s t a b i l i t y i s sues are important. The model a l s o i n d i c a t e s which v a l l e y s are l i k e l y to have undergone f r o n t a l r e t r e a t and w i l l thus c o n t a i n g l a c i o f l u v i a l m a t e r i a l o v e r l y i n g t i l l . 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(1975) Late P l e i s t o c e n e a l p i n e g l a c i e r s and the C o r d i l l e r a n Ice Sheet at Washington Pass, North Cascade Range, Washington. A r c t i c and Alpine Research, 7: 25-32. Waitt, R.B. (1977) E v o l u t i o n of g l a c i a t e d topography of upper Skagit drainage basin, Washington. A r c t i c and Alpine Research, 9: 183-192. Waitt, R.B., and Thorson, R.M. (1983) The C o r d i l l e r a n Ice Sheet i n Washington, Idaho, and Montana. In Late -Quaternary environments of the United States. Vol. 1. The late Pleistocene. E d i t e d by S.C. P o r t e r . U n i v e r s i t y of Minnesota Press, Minneapolis, MN, pp. 53-70. 139 APPENDIX 1 This appendix contains histograms of Schmidt hammer data f o r the Mt. Stoyoma study area. See Map 1 f o r the l o c a t i o n of s i t e s . mean 45.7 std 7.7 •10 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A l . 1 : Schmidt hammer r e s u l t s S i t e 1, at 192 0m. 140 20-c CD 13 U~ CD 10 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A l . 2 : Schmidt hammer r e s u l t s S i t e 2, at 2050m. >. o c CD cr cu 10 15 20 25 30 35 40 45 50 55 Schmidt Hammer Reading (% rebound) Figure A l . 3 : Schmidt hammer r e s u l t s S i t e 3, at 214 0m. 141 20-O c a> cr 10 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A1.4: Schmidt hammer r e s u l t s S i t e 4, at 2270m. o c (1) cr 10 15 20 - 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A l . 5 : Schmidt hammer r e s u l t s S i t e 6, at 1850m. 142 20-O c CD cr a> 10 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A l . 6 : Schmidt hammer r e s u l t s S i t e 7, at 193 0m. 10 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A l . 7 : Schmidt hammer r e s u l t s S i t e 9, at 1980m. 20-mean 40.8 std 7.9 Schmidt Hammer Reading (% Rebound) Figure A l . 8 : Schmidt hammer r e s u l t s S i t e 10, at 2040m. I6H 144 20 18 12H O c cu => 10 a> mean 33.0 std 6.8 - i r 1 0 1 5 2° 25 ' 30 • 35 1 40 ' 45 ' 50 ' 55 ' 60 ' 65 ' 70 Schmidt Hammer Reading (% rebound) Figure A1.10: Schmidt hammer r e s u l t s S i t e 12, at 223 0m. Mt. Stoyoma Area Site 13 1840 m 45 50 55 BO 65 70 Schmidt Hammer Reading (% rebound) Figure A l . l l : Schmidt hammer r e s u l t s S i t e 13, at 184 0m. 145 A P P E N D I X 2 This appendix contains histograms of Schmidt hammer data f o r the Anderson R i v e r study area. See Map 2 f o r the l o c a t i o n of s i t e s . mean 47.6 std 10.3 10 ' 15 ' 20 ' 25 ' 30 ' 35 ' 40 ' 45 ' 50 ' 55 ' 60 ' 65 ' 70 ' Schmidt Hammer reading (% rebound) Figure A2.1: Schmidt hammer r e s u l t s S i t e 1, at 1210m. 146 Figure A2.3: Schmidt hammer r e s u l t s S i t e 3, at 1640m. Figure A2.5: Schmidt hammer r e s u l t s S i t e 5, at 193 0m. 148 Schmidt Hammer reading (% rebound) Figure A2.6: Schmidt hammer r e s u l t s S i t e 6, at 1980m. Schmidt Hammer reading (% rebound) Figure A2.7: Schmidt hammer r e s u l t s S i t e 7, at 1770m. 149 16 Schmidt Hammer reading (% rebound) Figure A2.8: Schmidt hammer r e s u l t s S i t e 8, at 1710m. is-, ~~ — . . . : Schmidt Hammer reading (% rebound) Figure A2.9: Schmidt hammer r e s u l t s S i t e 9, at 1850m. 150 12-10H § 6-D-mean 42.9 std 11.2 Schmidt Hammer reading (% rebound) Figure A2.10: Schmidt hammer r e s u l t s S i t e 10, at 193 0m. Schmidt Hammer reading (% rebound) Figure A2.11: Schmidt hammer r e s u l t s S i t e 11, at 2060m 151 APPENDIX 3 This appendix contains histograms of Schmidt hammer data f o r the Mt. Outram study area. See Map 3 f o r the l o c a t i o n of s i t e s . 2 0 Schmidt Hammer Reading (% rebound) Figure A3.1: Schmidt hammer r e s u l t s S i t e 1, at 1750m, on normally weathered s l a b s . 152 20 Schmidt Hammer reading (% rebound) Figure A3.2: Schmidt hammer r e s u l t s S i t e 2, at 1940m, on normally weathered s l a b s . 40i 1 Schmidt Hammer Reading (% rebound) Figure A3.3: Schmidt hammer r e s u l t s S i t e 4, at 1940m, on g r u s s i f i e d s l a b s . 2 6 -mean 41.5 std 10.8 Schmidt Hammer Reading (% Rebound) Figure A3.4: Schmidt hammer r e s u l t s S i t e 5, at 1820m, on normally weathered s l a b s . 2 0 - , — 1 Schmidt Hammer Reading (% rebound) Figure A3.5: Schmidt hammer r e s u l t s S i t e 7, at 1770m, on normally weathered s l a b s . 154 40-47 37 47 44 50 50 46 46 46 42 40 50 Schmidt Hammer Reading (% rebound) Figure A3.6: Schmidt hammer r e s u l t s S i t e 8, at 1600m, on normally weathered boulders i n moraine at Outram Lake. Schmidt Hammer Reading (% rebound) Figure A3.7: Schmidt hammer r e s u l t s S i t e 40, at 1425m, on normally weathered s l a b s . 20 18H 16-14H 12-3 10-8H mean 44.4 std 8.8 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A3.8: Schmidt hammer r e s u l t s S i t e 45, at 1843m, on normally weathered s l a b s . mean 24.0 std 5.7 £ 12H 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A3.9: Schmidt hammer;'results S i t e 46, at 1863m, on g r u s s i f i e d s l a b s . Schmidt Hammer Reading (% rebound) Figure A3.10: Schmidt hammer results Site 47, at 1848m, on g r u s s i f i e d slabs. Schmidt Hammer Reading (% rebound) Figure A3.11: Schmidt hammer results Site 48, at 1813m, on g r u s s i f i e d slabs m e a n 30.6 std 7.0 10 15 20 25 30 35 40 45 50 55 60 65 70 75 Schmidt Hammer Reading (%rebound) Figure A3.12: Schmidt hammer r e s u l t s S i t e 49, at 1933m, on g r u s s i f i e d s l a b s c <u D Schmidt Hammer Reading (% rebound) Figure A3.13: Schmidt hammer r e s u l t s S i t e 50, at 3513m, on p i t t e d s l a b s 158 1 4 Schmidt Hammer Reading (% rebound) Figure A3.14: Schmidt hammer r e s u l t s S i t e 51, at 2085m, on p i t t e d s l a b s 1 4 Schmidt Hammer Reading (% rebound) Figure A3.15: Schmidt hammer r e s u l t s S i t e 52, at 1935m, on p i t t e d s l a b s 20-18-16H 14H 12H " 10-mean 43.5 std 11.3 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A3.16: Schmidt hammer r e s u l t s S i t e 53, at 1935m, on p i t t e d s l a b s 16-14-12-10-mean 40.3 std 8.8 i 1 1 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A3.17: Schmidt hammer r e s u l t s S i t e 54, at 1855m, on p i t t e d s l a b s 160 20 18H 16 14 12 I 10 mean 34.5 std 6.3 15 20 25 30 35 40 45 50 55 60 65 70 Schmidt Hammer Reading (% rebound) Figure A3.18: Schmidt hammer r e s u l t s S i t e 58, at 1813m, on normally weathered s l a b s . Schmidt Hammer Reading (% rebound) Figure A3.19: Schmidt hammer r e s u l t s S i t e 59, at 1495m, on normally weathered s l a b s . 161 

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