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Groundwater hydrology and slope movement at Pavilion, B.C. Nadler, Denise Eileen 1984

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GROUNDWATER HYDROLOGY AND SLOPE MOVEMENT AT PAVILION, B.C.  by  DENISE EILEEN NADLER  B.Sc,  The U n i v e r s i t y of Washington,  1980  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  THE FACULTY OF GRADUATE STUDIES (The  Department of Geography)  We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA August  (c)  1984  Denise E i l e e n N a d l e r ,  3  1984  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  requirements f o r an advanced degree at the  the  University  of B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and  study.  I further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may  be granted by  department or by h i s or her  the head o f  representatives.  my  It is  understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l not be allowed without my  permission.  Department of  C\ejQQ^  f-?a^>/"vy  The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada  V6T 1Y3 Date  DE-6  (3/81)  written  ABSTRACT OF THESIS "GROUNDWATER HYDROLOGY AND SLOPE MOVEMENT AT PAVILION, B.C."  The. r a t e seasonally  of earthflow  with  maximum  therefore increased to  and minimum  Earthflow  high  groundwater r e c h a r g e  this  thesis  1982  annual  varies  early  during  winter  the period process;  i n t h e f a i l u r e zone as a r e s u l t o f s e a s o n a l l y  the causal  and s u b s u r f a c e  estimated  from  t r a n s p i r a t i o n values. the  from  movement o c c u r s  The o b j e c t i v e s of  r e l a t i o n s h i p between  hydrology,  the climate,  and t o c o r r e l a t e  cumulative  from s e v e r a l s i t e s on t h e e a r t h f l o w .  h y d r o l o g i c budget f o r the d r a i n a g e  was  Columbia  motion i s a moisture-dependent  movement w i t h p i e z o m e t r i c o b s e r v a t i o n s The  occurring  from snowmelt and r a i n f a l l .  a r e t o examine  regime  British  movement r a t e s i n s p r i n g and summer may be a t t r i b u t e d  h i g h pore water p r e s s u r e s  moisture  at P a v i l i o n ,  displacements  (December) t o m i d - J u l y , September t o December.  motion  precipitation  b a s i n from August 1981 t o June records  and  potential  evapo-  The c l i m a t e r e c o r d i n d i c a t e d t h a t more than 95% of  groundwater  recharge  occurred  from  snowmelt  and r a i n f a l l i n  A p r i l and May 1982. Two and 1981  notable  increases  of groundwater  levels  were observed  one r i s e of groundwater e l e v a t i o n was seen i n 1982. and t h e r i s e  correlated estimated  with  noted  i n 1982 o c c u r r e d  low-elevation  one-month  phase  snowmelt  l a g between  The f i r s t  in  1981,  rise i n  between May and J u l y and were  from  March  recharge  1 to April  and piezometer  1.  An  response  suggests  that  Tension  cracks  and  its  recharge and  flow  to  g r e a t e r than  Thus  recharge  accounted earthflow,  for,  in  to  the  groundwater  occurs  relatively  depths  (10-20m) of  provide  conduits  response.  the e a r l i e r  i n the b a s i n d u r i n g May  1981.  groundwater  probably  rapid piezometric  substantially  July  snowmelt  The  quickly.  the  earthflow  for  second  efficient groundwater  d i d not occur u n t i l the p e r i o d from October t o November  snowmelt h i g h e r  and  areas  and  l e v e l r i s e i n 1981 was  early  f r a c t u r e s at s h a l l o w  surrounding  groundwater  and  from  from  a  four-  and part,  and  response  by  time  basal  travel itself  and  failure  zone  T h i s was  June, and  five-month  piezometer  earthflow the  to  rise.  time is  rainfall in  lag  Mt.  by  slow  Cole,  south  upward  the  May  between r e g i o n a l  indicated.  from  into  attributed  This  is  of  the  movement  standpipes  in  of the  earthflow. E a r t h f l o w a c c e l e r a t i o n commenced i n December 1981 pore water p r e s s u r e s November 1981, until  J u l y 1982.  J u l y 1981, in  and  from Mt. Cole observed  the r a t e of movement remained r e l a t i v e l y The  r a t e of e a r t h f l o w motion was  h i g h at  sensitive  1981. to  These  changes  hydraulic  of  head  observations the  effective  fluctuations  earthflow.  iii  on  indicate normal the  in  least  a l s o h i g h from March to  wnich c o r r e l a t e s v e r y w e l l w i t h h i g h groundwater l e v e l s  spring  seasonal  from the impulse of recharge  as a r e s u l t of h i g h  that  stress  basal  the  earthflow  according  slip  observed  surface  is  to  the  of  the  TABLE OF CONTENTS  TITLE  PAGE  ABSTRACT OF THESIS  i i  TABLE OF CONTENTS  iv  LIST OF TABLES  v i i  LIST OF FIGURES  ix  ACKNOWLEDGEMENTS CHAPTER 1:  xvi  INTRODUCTION  1  1.1  Problem statement  1  1.2  Approach  2  1.3  P r e v i o u s work  3  1.4  Thesis organization  6  CHAPTER 2:  SETTING  7  2.1  Location  7  2.2  Bedrock geology  2.3  Pleistocene history  2.4  Climate  15  2.5  Vegetation  16  2.6  Hydrology  19  10  iv  '  13  TITLE  PAGE  CHAPTER 3:  EARTHFLOW CHARACTERISTICS  25  3.1  Morphology  3.2  Character  3.3  Debris character  32  3.4  E a r t h f l o w movement i n the Holocene p e r i o d  35  CHAPTER 4:  25 of movement  26  CLIMATE AND SUBSURFACE HYDROLOGY AT PAVILION  42  4.1  Introduction  42  4.2  Approach and data sources  44  4.3  Climate  47  4.4  B a s i c o p e r a t i o n of a standpipe  4.5  Groundwater flow and h y d r a u l i c c o n d u c t i v i t y  60  4.6  Piezometric observations  61  4.7  R e l a t i o n s h i p between c l i m a t e and groundwater l e v e l s at P a v i l i o n  71  Summary  75  4.8  CHAPTER 5:  record  SLOPE MOVEMENT AT PAVILION  piezometer  57  77  5.1  Introduction  77  5.2  Method of o b s e r v a t i o n  79  5.3  Movement i n the source  5.4  Movement of the main flow  88  5.5  Movement of the west lobe  90  5.6  Movement of the east lobe  94  v  area  82  TITLE  PAGE 5.7  C o r r e l a t i o n of movement w i t h groundwater hydrology  5.8  F l u c t u a t i o n s of e a r t h f l o w motion Holocene  5.9  95 i n the  period  104  Summary  CHAPTER 6:  110  CONCLUSION  112  6.1  Summary  112  6.2  E a r t h f l o w motion  6.3  Future work at P a v i l i o n  i n the I n t e r i o r P l a t e a u  116  BIBLIOGRAPHY APPENDIX I :  114  118 Atterberg l i m i t s :  T e s t procedure and  results  123  APPENDIX I I :  Reduction of s l o p e movement data  128  APPENDIX I I I :  P e r i o d i c and t o t a l d i s p l a c e m e n t s calculated f o r Pavilion  133  vi  LIST OF TABLES  TITLE  PAGE  TABLE 2.1.  A summary of the l i t h o l o g i e s and f o r m a t i o n s in the P a v i l i o n region (after Trettin, 1961).  12  TABLE 3.1.  Average c o n s i s t e n c y l i m i t s and n a t u r a l water contents of n e a r - s u r f a c e samples of the e a r t h f l o w d e b r i s and reworked t i l l .  34  TABLE 4.1.  Summary of the depth of piezometer below the l o c a l ground s u r f a c e .  tips  45  TABLE 4.2,  Details of the shallow i n s t a l l a t i o n s at P a v i l i o n .  nest  48  TABLE 4.3.  Mean monthly temperatures and potential e v a p o - t r a n s p i r a t i o n e s t i m a t e s computed from the P a v i l i o n Mountain temperature d a t a .  54  TABLE 4.4,  Estimated v a l u e s of groundwater recharge f o r the p e r i o d August 1, 1981 t o June 30, 1982. A l l v a l u e s a r e i n mm.  56  TABLE 4.5,  Hydraulic conductivity values earthflow debris obtained from measurements.  the situ  62  TABLE 4.6,  Summary of the measured v a l u e s head from the e a r t h f l o w .  of p r e s s u r e  63  TABLE 4.7,  The  basic  from  the s l u g  hydraulic  hydrostatic  time  t e s t data used  conductivity  d e b r i s at P a v i l i o n .  vii  piezometer  of  lags  of in  computed  t o e s t i m a t e the the  earthflow  74  PAGE  TITLE  TABLE 5.1.  Movement measured i n the source a r e a . Stake a r r a y l o c a t i o n s a r e g i v e n i n f i g u r e 5.2.  85  TABLE A I . l .  The results of A t t e r b e r g limit tests performed on several samples of the earthflow debris.  126  TABLE A I I I . l .  Movement  134  the  i n the x - d i r e c t i o n  stake  zones.  arrays  along  the  calculated lateral  for shear  A l l values are i n centimeters.  TABLE A I I I . 2 .  Movement i n the y - d i r e c t i o n c a l c u l a t e d from the s t a t e a r r a y measurements. A l l values are i n c e n t i m e t e r s .  135  TABLE A I I I . 3 .  Movement between the 1,5 and 4,5 stake p a i r at the f i v e - s t a k e a r r a y s . A l l v a l u e s a r e i n centimeters.  136  TABLE A I I I . 4 .  Measured displacement ( i n centimeters) between the 2,3 stake p a i r s i t u a t e d on the unstable earthflow d e b r i s .  137  viii  LIST OF FIGURES  PAGE  Map of the r e g i o n i n which Pavilion earthflow i s located. The e a r t h f l o w i s i n d i c a t e d by the s t r i p p l e d r e g i o n east of the v i l l a g e of P a v i l i o n . Base  map  of  the  delineation cross  of  section  earthflow the  which  earthflow  transects,  stake  array  locations.  includes divisions,  locations  s e i s m i c measurements, s u r f i c i a l  8  of  geology, and  _*  ( i n p^e4&e*--a fe--baek ^HP^'I^P*-• i  L o n g i t u d i n a l p r o f i l e of the e a r t h f l o w along the s e c t i o n A-B-C shown i n f i g u r e 2.2.  9  Vegetation map of the r e g i o n surrounding Pavilion. The map shows the d i v i s i o n s between the b i o g e o - c l i m a t i c zones d i s c u s s e d  17  by Mathewes (1978). The e a r t h f l o w i s the hatched r e g i o n near the c e n t e r of the map. ( a f t e r Mathewes, 1978) Base  map  vegetative  of  the  cover  the e a r t h f l o w .  earthflow  and s u r f i c i a l Included  showing hydrology  on the map  the of  are the  l o c a t i o n s of the piezometers and r a i n gauges at  the s i t e .  ( i n pocket at back of t h e s i s )  Photograph of the west lobe l o o k i n g south toward the c e n t r a l t e n s i o n zone. Note t h a t the l a r g e Douglas f i r stand i s t i l t e d from r e l a t i v e l y r a p i d motion of the west l o b e .  ix  20  FIGURE 2.7.  Photograph of a l a r g e Douglas f i r on the upslope s i d e of a l a r g e t e n s i o n c r a c k i n the source area. Expansion of the t e n s i o n c r a c k in the downslope d i r e c t i o n has caused removal o f e a r t h f l o w d e b r i s from the r o o t zone of the t r e e . The d i r e c t i o n of movement i s t o the l e f t i n the photograph.  20  FIGURE 2.8.  Photograph of a s p l i t Douglas f i r on the east l a t e r a l shear zone of the east l o b e .  21  FIGURE 2.9.  Photograph of the l a t e r a l d e p o s i t west of the east lobe showing the e x t e n s i o n of Douglas f i r r o o t s downslope. The d i r e c t i o n of motion i s t o the r i g h t .  21  FIGURE 2.10.  Photograph of Pond 3 taken i n J u l y 1981.  23  FIGURE 2.11.  Photograph of Pond 3 taken i n October 1981.  23  FIGURE 3.1.  A e r i a l view of P a v i l i o n e a r t h f l o w . The e a r t h f l o w boundaries a r e shown by the pen lines. ( a i r p h o t o number BC 7788-242, taken i n 1977)  27  FIGURE 3.2.  Cross s e c t i o n a l view of three of t h e earthflow d i v i s i o n s : (a) the source area; (b) the main flow; and ( c ) the east l o b e ,  29  flow b i f u r c a t i o n , and west l o b e . locations are given i n figure frorrket). FIGURE 3.3.  Transect 2.2 (in  Johnson's a n a l y s i s o f the development o f l a t e r a l r i d g e s u s i n g the concept of "dead" zones w i t h i n the flow channel. View (a) shows the concept of a r i g i d " p l u g " of d e b r i s f l o w i n g on a r a f t of v i s c o u s d e b r i s i n the flow c h a n n e l . View ( c ) shows the e v o l u t i o n of m u l t i p l e l a t e r a l d e p o s i t s which develop when s u c c e s s i v e l y s m a l l e r waves of d e b r i s move through the channel. (after Johnson, 1970)  x  ^  ^  C*MUJU*H«y<  30  FIGURE 3.4.  Photograph of the west l a t e r a l shear zone of the west lobe near the apex of the d e b r i s fan. Note the l a r g e conglomerate b o u l d e r a t the toe of the advancing west l o b e , near the l a t e r a l deposit.  FIGURE 3.5.  Photograph of a l a r g e conglomerate b o u l d e r on the west s i d e of the west l o b e . The exposed s u r f a c e appears t o have been sheared while i n transport within the e a r t h f l o w d e b r i s p r i o r t o e x t r u s i o n from the f l o w .  FIGURE 3.6.  G r a d i n g curves f o r the reworked and the red-brown d e b r i s .  FIGURE 3.7.  Generalized contour map of the south sideslope of P a v i l i o n Creek a p p r o x i m a t i n g the valley topography following deglaciation.  FIGURE 3.8.  Schematic profile of the main valley c o n s t r u c t e d from the g e n e r a l i z e d contour map depicting the configuration following d e g l a c i a t i o n , and the l o n g i t u d i n a l profile of the p r e s e n t e a r t h f l o w s u r f a c e . T r a n s e c t s are given i n figures 3.7 and 2.2, respectively.  FIGURE 4.1.  (a) Schematic diagram of the f l o a t and counterweight i n s i d e the piezometer. (b) Photograph of the continuous, floata c t i v a t e d r e c o r d e r mounted on BH-5.  FIGURE 4.2.  Precipitation Mountain, Hat earthflow.  FIGURE 4.3.  P l o t of B r i t i s h Columbia snow survey d a t a from P a v i l i o n Mountain (1,250 m), Harry Lake (1,350 m), and Cornwall H i l l s (2,000 m). The snowpack depth over Mr. Cole (1,725 m) was e s t i m a t e d from the p l o t s f o r each water year. The snow depths are a l l expressed as water e q u i v a l e n t v a l u e s .  xi  glacial  till  records from Pavilion Creek V a l l e y , and P a v i l i o n  FIGURE 4.4.  Estimated  change  equivalent) June 30,  of  f o r Mt.  1981  and  snowpack Cole  from  depth January  (water 1 to  1982.  FIGURE 4.5.  Schematic diagram demonstrating the use of a s t a n d p i p e piezometer f o r measuring h y d r a u l i c head h and i t s two components. The p r e s s u r e head i s the h e i g h t of the water column i n the s t a n d p i p e and the e l e v a t i o n head z i s the e l e v a t i o n of the piezometer t i p above the datum (z = 0 ) .  FIGURE 4.6.  Diagram  showing  the  use  of  a piezometer  to  measure h y d r a u l i c head i n a h i l l s l o p e where the groundwater t a b l e i s below the ground surface. The piezometer of length d measures the pore water p r e s s u r e at P. S i n c e P i s located on the e q u i p o t e n t i a l where h=2.8, the h e i g h t of the water in the piezometer i s equal to 2.8 on the v e r t i c a l s c a l e to the l e f t of the diagram. FIGURE 4.7.  P l o t of the piezometer level fluctuations a g a i n s t time. The d a t a from BH-2, BH-3, BH-5, and BH-6 are shown f o r the d u r a t i o n of the study. The data p l o t t e d f o r BH-4 are the only p o i n t s c o n s i d e r e d r e l i a b l e from the piezometer, w h i l e the data from the p e r i o d preceding October 1981 are considered anomalous p o s s i b l y due to a c r a c k i n the standpipe. The data f o r BH-1 are the o n l y two p o i n t s t h a t were measured at t h i s s i t e .  FIGURE 4.8.  The continuous records from the floata c t i v a t e d continuous water l e v e l r e c o r d e r s at BH-2, BH-4, and BH-5. No continuous r e c o r d i s a v a i l a b l e from the i n t e r v a l s when the c l o c k s stopped i n the w i n t e r , but the magnitude of the change that o c c u r r e d i n these i n t e r v a l s c o u l d be determined from the c h a r t s because an i n k t r a c e was made when a change o c c u r r e d , a l t h o u g h the c h a r t remained stationary.  xii  FIGURE 4.9.  Water l e v e l f l u c t u a t i o n s measured a t t h e shallow piezometer nest s i t e s from June 6, 1981 t o J u l y 7, 1982. The s i t e s a r e (a) N l , (b) N2, ( c ) N3, (d) N4, (e) N5, and ( f ) N6.  FIGURE 5.1,  Schematic diagram of the s t r a i n n e t s used a t P a v i l i o n f o r m o n i t o r i n g e a r t h f l o w movement.  FIGURE 5.2.  Enlargement o f t h e source area showing the arrangement o f t h e s t r a i n n e t s i n t h e upper t e n s i o n zone. The lower case l e t t e r s on the segments o f WUT-3, WR9, and WUT-4 i n d i c a t e the segment r e f e r r e d t o i n T a b l e 5.1. The individual s t a k e s a t WUT-3 and WUT-4 a r e shown by upper case l e t t e r s . The "x" n o r t h of ESR-1 i s t h e p e g a t t a c h e d to the recorder.  FIGURE 5.3.  Schematic diagram showing the i n s t a l l a t i o n of t h e continuous e a r t h s l i d e r e c o r d e r s .  FIGURE 5.4.  Continuous movement r e c o r d from ESR-1 i n t h e source area f o r the p e r i o d May 15 t o J u l y 9, 1982.  FIGURE 5.5.  Photograph l o o k i n g southeast a t WUT-4 and ESR-1. Note the g r e e n i s h - g r e y Pavilion Group r o c k s t h a t crop out from the red-brown e a r t h f l o w d e b r i s ( c o n t a c t i s shown by the dashed l i n e ) .  FIGURE 5.6.  Cumulative movement o f the main f l o w f o r t h e p e r i o d March 21, 1981 t o J u l y 9, 1982.  FIGURE 5.7,  The continuous movement r e c o r d from ESR-2 ( a d j a c e n t t o WR8) f o r t h e p e r i o d November 16, 1981 t o J u l y 9, 1982.  FIGURE 5.8.  Cumulative movement o f the west lobe f o r t h e p e r i o d March 21, 1981 t o J u l y 9, 1982.  xiii  FIGURE 5.9.  The continuous movement r e c o r d from ESR-3 (between WR2 and WR3 on the west l o b e ) f o r the p e r i o d November 16, 1981 t o J u l y 9, 1982. There a r e two diagrams because the r e c o r d e r was not i n the f i e l d from May 15 t o June 9, 1982, hence movement i n t h i s p e r i o d c o u l d not be accounted f o r i n the p l o t .  93  FIGURE 5.10.  Cumulative movement of the east lobe f o r the p e r i o d March 21, 1981 t o J u l y 9, 1982.  95  FIGURE 5.11.  A segment of an u n s t a b l e h i l l s l o p e w i t h a groundwater t a b l e a t h e i g h t h above the f a i l u r e p l a n e , and the depth t o the f a i l u r e s u r f a c e i s z. The pore water p r e s s u r e u above the f a i l u r e plane i s found by computing: u = h cos^9.  96  FIGURE 5.12.  Sketch of the l i n e a r r e l a t i o n s h i p between shear s t r e n g t h and e f f e c t i v e normal s t r e s s . The shear s t r e n g t h parameters c' and are defined by t h e d i a g r a m . The failure envelope i s the common tangent t o the Mohr c i r c l e s which r e p r e s e n t v a r i o u s s t a t e s o f stress at failure and are found by laboratory testing of soil samples f o r d e t e r m i n a t i o n of the shear s t r e n g t h of a soil (s).  98  FIGURE 5.13  P l o t of movement of the main flow measured at WR-8 and ESR-2, p i e z o m e t r i c data from BH-2, BH-3, and BH-4, and the e s t i m a t e d groundwater recharge f o r the second water year.  100  FIGURE 5.14.  P l o t of movement of the west lobe measured at WR-2 and ESR-3, p i e z o m e t r i c data from BH-5 and BH-6, and the e s t i m a t e d groundwater recharge f o r the second water y e a r .  101  xiv  FIGURE 5.15.  Cumulative movement measured earthflow from June 1978 t o (from B o v i s , 1980).  FIGURE 5.16.  (a) Photograph of the road cut through the west l a t e r a l shear zone of the e a s t lobe showing Mazama ash i n t e r s t r a t i f i e d with earthflow debris. (b) S c a l e drawing of the same photograph g i v i n g dimensions of the tephra l a y e r and l a t e r a l d e p o s i t s .  FIGURE 5.17.  Photograph of Mazama ash interstratified w i t h e a r t h f l o w d e b r i s d e r i v i n g from g l a c i a l t i l l i n the c e n t r a l t e n s i o n s c a r p .  FIGURE A I I . l .  Sketch of a f o u r - s t a k e a r r a y at P a v i l i o n showing the s i x p o s s i b l e d i s t a n c e s t h a t were measured at each stake a r r a y .  FIGURE A l l . 2 .  Diagram showing the v a r i a b l e s calculating earthflow movement stake a r r a y measurements.  FIGURE A I I I . l .  Diagram of stakes 1, 4, and 5 i n the f i v e stake a r r a y s which shows the p o s i t i v e and n e g a t i v e components of motion.  FIGURE A I I I . 2 .  Diagram showing the p o s i t i v e and n e g a t i v e components of movement between the 2,3 stake p a i r w i t h i n the stake a r r a y s .  xv  at Pavilion August 1980  used from  for the  ACKNOWLEDGEMENTS  Completion assistance to  Nadler,  thoughtful only  persons  grateful  and Penny  many  for their  me  Sandy  possible  without the  In p a r t i c u l a r , I am  indebted  Brown, N e i l Wanless, Gary  Barrett,  Dr. M.A.  the v a r i o u s  i n the f i e l d .  a t UBC f o r t h e i r  phases  Church  offered  of r e s e a r c h ,  To Dr. B o v i s Finally, continued  which have l e d t o the c o m p l e t i o n of my endeavors.  xvi  been  several  d r a f t s of the t h e s i s , and Dr. M.J. Bovis  time and p a t i e n c e .  to my c o l l e a g u e s  not have  and Don Jones.  through  hours  would  i n the f i e l d .  comments on p r e c e d i n g guided  contributed  and  of s e v e r a l  thesis  Anne Hanssen, James G a l l a g e r ,  Chris  not  of t h i s  but  also  and Dr. Church  I am  I am g r a t e f u l t o my support  family  and encouragement  "  . . . the  the  displaced  bedrock,  l a r i t i e s . . . . the  and  surface  seems to move p a i n f u l l y and  the  surface  landslips  in  is  this  broken area  look  into not  a  grindingly  thousand  unlike  an  irreguearthern  glacier." M.  B.  Begbie, 1871,  p.  ( r e f e r e n c e to P a v i l i o n xvii  over  141 earthflow)  CHAPTER 1  INTRODUCTION  1.1 PROBLEM STATEMENT Common among Columbia's that  Interior  present  made  to  of  analyses  movement  Plateau  these  1980).  the  Interior  systematically  investigated.  precipitation,  groundwater  causal  correlate  between  groundwater  The  are:  climate  level  reference  geologic  factors  Plateau,  In t h i s  features  Passing  i n regional  study,  such  remain  the r e l a t i o n s h i p  and s u b s u r f a c e  f l u c t u a t i o n s with  a description hydrology,  and  earthflow to  be  between  movement i s examined.  ( i ) t o develop  as  has been  reports  influencing  though,  l e v e l s , and s l o p e  of the p r o j e c t  linkages  earthflow-type  Columbia.  features  (Bovis,  within  objectives  a r e slow  at P a v i l i o n , B r i t i s h  several  terrain  l a r g e - s c a l e mass movements i n the t e r r a i n of B r i t i s h  The  of the  and ( i i ) to  the s e a s o n a l v a r i a t i o n of  movement r a t e . The Europe  r e s u l t s of s e v e r a l  (VanDine,  Swanston,  1977;  1974, and  1980; Kelsey,  availability  i s important  For  from  example,  these  mass movement s t u d i e s G i l and 1978)  i n determining studies  1  i t was  Kotarba,  have  1977;  indicated  the r a t e found  i n North America and  that  Swanson  that  of e a r t h f l o w  and  moisture motion.  maximum movement i s  observed  shortly  peak d i s c h a r g e Bovis  (1980),  Pavilion, early  summer,  been  that and  slope  This  investigation  displacement  suggested from  of the wet season or c o n c u r r e n t  that  established.  was  this  of e a r t h f l o w  highest  could  be  during  the s h e a r i n g However,  as the r o l e  s p r i n g and to  high  i n the s p r i n g  of h i g h  r e s i s t a n c e of s l i d e  sufficient  motion at  attributed  s p r i n g snowmelt and p r e c i p i t a t i o n  i s not unreasonable  i n reducing  with  depending on the l o c a t i o n of the r e s e a r c h .  i n the p r e l i m i n a r y  levels  summer.  pressures  from snowmelt  found  groundwater and  a f t e r commencement  pore  water  d e b r i s has long  groundwater  data  were  not  a v a i l a b l e from B o v i s ' r e s e a r c h t o a l l o w c o r r e l a t i o n w i t h movement. The thorough  desirable  earthflow.  to  have  and  the  a  snowmelt  at P a v i l i o n  relationship  effect good  penetration  on  i s t o conduct  between  understanding the  of  piezometric  a more  c l i m a t o l o g i c and  on e a r t h f l o w motion. the  Therefore, i t influence  conditions  of  of the  can be i n v e s t i g a t e d t o the depth  i n the e a r t h f l o w  i n the i n v e s t i g a t i o n  hydrology  study  The groundwater hydrology  piezometer  applied  of  f a c t o r s and t h e i r  precipitation  of  of the present  investigation  hydrologic is  goal  of the c a u s a l  debris.  This  can l a t e r  linkages  between  be  subsurface  and e a r t h f l o w movement.  ,2 APPROACH The include  data  r e q u i r e d t o achieve  the primary  o b j e c t i v e s of t h i s t h e s i s  s l o p e movement and p i e z o m e t r i c measurements c o l l e c t e d  intervals  during  the study,  and a  climate  record  at r e g u l a r  of s l i g h t l y  longer  duration.  Slope  around  earthflow  the  three  movement was  sites.  piezometers continuous  margins,  Groundwater installed  records  were  collected  with  continuous  to  of  in  depths  period  records  was the  measured  Hydro  and  stations and  1980-1981  Power and  Hills  Field hydrology  near  with  Snowpack  was  obtained  (the P a v i l i o n  from  movement  six  to  1981  to  16.55m,  with  The  early  Piezometer  at  standpipe  three boreholes.  data  July  1982,  nests  were  seeps on the e a r t h f l o w and the  boreholes.  five data  Pavilion  storage were  operated  from  the  gauges p l a c e d  for  British  on  from  British  information  the  Precipitation  obtained by  Snow Course, Harry  two  Columbia  the  winters  Columbia  Snow  Lake Snow Course,  and  Snow C o u r s e ) .  investigations were  also  to  carried  determine out.  d e t e r m i n a t i o n of the r e g i o n a l and  1.3  from  distributed  of  7.62m  1981.  climate  Authority.  1981-1982  Survey B u l l e t i n s , Cornwall  additional  from at  arrays  records  obtained  mid-March  to ponds and  obtained  located  were  November  f o r s i x months i n 1981  earthflow,  climate  levels  stake  continuous  levels  from  from  at 33  ranging  piezometric  the  groundwater  with  levels  p l a c e d at s i x s i t e s adjacent deeper  monitored  the  These  local  geology  factors  are  l o c a l groundwater f l o w  and  surface  important  for  regimes.  PREVIOUS WORK E a r t h f l o w motion has Kelsey  (1978) and  Kotarba  (1977).  been s t u d i e d i n the western U n i t e d  Swanson and In  British  3  Swanston  (1977),  Columbia,  and  VanDine  i n Poland (1974,  States  by  by G i l and  1980)  did  a  geotechnical described  survey  the  on  the  character  Drynoch  of  earthflow  t o p o g r a p h i c f e a t u r e s and v e l o c i t y Gil the  and  Polish  Kotarba  motion  c l i m a t e and  based  and at  Bovis  (1980)  Pavilion  from  on  an  a model  active  of  slope  Holocene  h y d r o l o g i c data w i t h  earthflow.  They  the dynamic f e a t u r e s of  T h e i r r e s u l t s showed t h a t the  rate  on  displacement  southwestern  Oregon,  was  motion  to p r e c i p i t a t i o n  rather  than  rate  rainfall  of movement.  precipitation and  Swanston  present  in  moisture to  a  Early  soil  in  late  found  rate i t s e l f ,  explained the  and  that at  the this  the  was  an  i n the wet  antecedent  important  season,  flow  resulted  low  the  wet  i n the wet  recharge.  season,  remained  the e a r t h f l o w had  the low.  season.  During  content,  affecting  antecedent  season  level  precipitation  volume  s i m i l a r o b s e r v a t i o n was Kelsey contribution  (1978) from  received  (Swanson  made by K e l s e y was  attributed  spring  4  Swanston,  low  snowmelt,  sufficiently  1977).  to A  (1978).  interested  e a r t h f l o w s undercut  and  of  moisture  s a t u r a t e d t o cause an i n c r e a s e of movement which became h i g h r e l a t i v e the  the  Swanson  The  was  become  In  earthflow  moisture  factor  from  of  related  the  total  regime.  f o r example,  velocity  beginning  groundwater  precipitation  (1977) a l s o  t h a t the  i n the e a r t h f l o w e a r l y the  the  Swanston  i n the wet  high while  content  delay  occurring  was  dependent  Swanson and  its  evolution for  e a r t h f l o w over a p e r i o d of 3 y e a r s . of  has  profiles.  (1977) developed  Carpathians,  correlated  earthflow,  in by  determining  rivers  the  i n the Van  sediment  Duzen R i v e r  Basin, C a l i f o r n i a .  He found  t h a t the sediment  r a t e of e a r t h f l o w motion was maximum, s h o r t l y of  the s l i d e  debris  had i n c r e a s e d  more r a p i d flow—probably Kelsey  further  acceleration  of the flow,  that  properties Spence's  while  heavy  the removal  of Drynoch e a r t h f l o w and  found  that  peak  maximum  remain  depending  rate.  slide  on the p o i n t  1980) concluded  important  Drynoch  movement  from  along  the base of the  Flow  i n determining  by  the  while  flow  failure  acceleration  pore  rate, also  of  surface  occurred  both  and up t o one month a f t e r  of o b s e r v a t i o n . that  south  snowmelt c o r r e l a t e d  the b a s a l  f o l l o w i n g a groundwater l e v e l r i s e  (1974,  initiated  response.  runoff  and  VanDine  pressures.  l o c a t e d on the Thompson R i v e r  i n c r e a s e d pore water p r e s s u r e  snowmelt,  t o promote  precipitation  of m a t e r i a l from  well with  immediately  enough  content  Columbia, VanDine (1974, 1980) s t u d i e d the g e o t e c h n i c a l  Bridge,  with  great  of i n c r e a s e d pore water  s l i d e by stream e r o s i o n enhanced e a r t h f l o w In B r i t i s h  a f t e r the moisture  to a value  as a r e s u l t  surmised  l o a d was h i g h e s t when the  Like water  Kelsey  (1978),  pressure  values  active undercutting  of the  Thompson  River  contributes  earthflow  has been d e s c r i b e d  to  earthflow  acceleration. Although (Begbie, and  type  1871; Dawson, 1896; D u f f e l l  Ryder,  features  Pavilion  1976),  Bovis  of the e a r t h f l o w .  movement  by  (1980) was Bovis  discussing  5  the  by s e v e r a l workers  and McTaggart, 1952; T r e t t i n , 1961; the f i r s t  explained spatial  t o examine  the dynamic  the c h a r a c t e r of e a r t h f l o w and  temporal  v a r i a t i o n s of  movement  rate,  similarities by  well  between  Johnson  noted.  as  as  details  of  the p r i n c i p l e s  of d e b r i s  (1970) and the apparent  From  this,  Bovis  the l o c a l  nature  suggested  that  topography.  flow  mechanics  of e a r t h f l o w certain  Many  described  movement  aspects  were  of Johnson's  a n a l y s i s might be a p p r o p r i a t e f o r the a n a l y s i s of e a r t h f l o w motion.  1.4 THESIS ORGANIZATION The  t h e s i s i s organized  description  and  includes  into  s i x chapters.  discussions  of  Quaternary h i s t o r y ,  c l i m a t e and v e g e t a t i o n ,  morphology  earthflow  includes  of an  Pavilion.  the  introduction The c l i m a t e  Chapter  Four.  between  these  record  These data time  series  measurements a r e presented the  spatial  description level  and  the  and s u r f a c e hydrology.  The  i n Chapter of  variations  of the r e l a t i o n s h i p  data  of  between  This  Chapter  and i n c l u d e s a b r i e f  motion  at  a r e presented  in  of s l o p e  movement  motion, and  and  a  piezometric  S i x i s a summary  of the  d i s c u s s i o n on the c h a r a c t e r  of e a r t h f l o w motion i n the I n t e r i o r P l a t e a u r e g i o n of B r i t i s h  6  movement  i n c l u d e s a n a l y s e s of  earthflow  slope  This  and the r e l a t i o n s h i p  The r e s u l t s  i n Chapter F i v e .  Three.  earthflow  temporally  i s analyzed.  temporal  of the r e s u l t s  the  and p i e z o m e t r i c  a r e compared  local  site  geology,  character  f l u c t u a t i o n s i n the e a r t h f l o w .  results  the  i s described  to  Chapter Two i s a  Columbia.  CHAPTER 2  SETTING  2.1  LOCATION Pavilion British 12,  earthflow  Columbia and  opposite  situated  on  the the  physiographic Plateau.  the flow and The  located  i s 30km n o r t h e a s t  Indian  village  southeastern  r e g i o n which  The  s i d e of Mt.  is  earthflow  Cole  (figure  a l l o w s easy  km  northeast  of L i l l o o e t  of P a v i l i o n  just  (figure  10.5°  south of Highway Pavilion  Holland  (1964) r e f e r r e d  issues  from  2.1).  An  the  to  watershed  unimproved  access to the study  as  the  flanking  t r a c k runs  the  is the  Interior the  north  l e n g t h of  area.  e a r t h f l o w ranges from an average of 720 m at the toe to 1080  from  80  (figure  Based  m  to 500  m.  The  I t is. 2.2  km  on  m  i n l e n g t h , and v a r i e s  average width  i s about  300  m.  The  the average  slope  2.3).  morphologic  i n t o seven u n i t s ( f i g u r e (i)  Vancouver,  2.1).  s l o p e of the e a r t h f l o w s u r f a c e ranges from 4° to 20 °; is  of  p o r t i o n of the F r a s e r P l a t e a u , p a r t of  at the upper headscarp ( f i g u r e 2.2). i n width  370  characteristics,  the  earthflow  is  2.2):  the source area r e f e r s to the r e g i o n of flow w i t h i n 200 m n o r t h of the  7  headwall;  extending  divisible  FIGURE The  2.1.  earthflow  Map  of  the  region  i s i n d i c a t e d by  Pavilion.  8  i n which  the  stippled  Pavilion region  earthflow east  of  the  is  located.  village  of  FIGURE 2.3.  Longitudinal  profile  of t h e e a r t h f l o w  the s e c t i o n A-B-C shown i n f i g u r e 2.2.  along  (ii)  t h e main f l o w i s t h e r e g i o n bounded t o t h e south by t h e source a r e a and by t h e c e n t r a l t e n s i o n zone to  the north;  ( i i i ) t h e c e n t r a l t e n s i o n zone r e f e r s t o t h e r e g i o n o f extending (iv)  f l o w w i t h i n 100m n o r t h o f t h e m a i n f l o w ;  t h e west lobe i s t h e l o b e which f l o w s around t h e west s i d e of t h e f l o w b i f u r c a t i o n and i s by f a r t h e l a r g e r o f t h e two l o b e s ;  (v)  t h e e a s t lobe i s t h e lobe which f l o w s t o t h e east of t h e f l o w b i f u r c a t i o n ;  (vi)  t h e f l o w b i f u r c a t i o n i s t h e lens-shaped  r e g i o n which  d i v i d e s t h e e a r t h f l o w i n t o t h e two l o b e s ; and ( v i i ) t h e d e b r i s f a n i s t h e l a r g e , hummocky f e a t u r e contiguous  w i t h t h e e a s t and west l o b e s .  2.2 BEDROCK GEOLOGY The largely  ensuing from  discussion  a regional  l e s s e r extent  compiled  study.  i n the f i e l d  the f o r m a t i o n s  study  of P a v i l i o n  by T r e t t i n  and McTaggart (1952),  and Shannon (1981).  made d u r i n g t h e p r e s e n t was  geologic  from D u f f e l l  Monger (1981),  on t h e geology  (1961),  Preto  Additional f i e l d  i s derived  et a l .  and t o a (1979),  observations  were  A g e o l o g i c map ( f i g u r e 2.2, i n p o c k e t )  w i t h r e f e r e n c e t o T r e t t i n ' s r e g i o n a l map, and  and l i t h o l o g i e s a r e summarized i n T a b l e 2.1.  10  The as  the  oldest  rocks found i n the  Pavilion  m and  1060  clastic  Group ( P e r m o - T r i a s s i c ) .  m elevation  lithology  consists  marine  t h i c k n e s s , and The  in  the  sediments.  of  metavolcanic  The  Pavilion  is  underlain  by  correlated  with  the  Mt.  earthflow  (Preto  et  al.,  the  most  Martley  Stock  1979).  Biotite  et  al.  1979), i n d i c a t i n g  caused  considerable  P a v i l i o n Group ( T r e t t i n , Continental  Pavilion  interbedded  with  from  Jurassic  the  rocks is  least  100  to the  east. portion which  2.1),  have  and  intrusive  deposits  rocks,  b a s a l member), conformably o v e r l a i n  of  alteration  of  and by  unconformably include  overlie  interstratified  lithic  conglomerate  sandstone  contain  of  and  set  i n a fine-grained  in  color.  probably  The  quartz, matrix  coarse,  floodplain  and  rounded  that  varies  well-sorted  deposits—their  11  fragments  clasts  chert  from b r i c k  sandstone  color  of  and  indicating  red  Pavilion and to  (the  sandstone,  ( f i g u r e 2.2).  angular  the  carbonaceous s h a l e  carbonaceous s h a l e s t r a t a  feldspar  near  intrusion  additional  rocks,  the  Present  conglomerate and and  been  of  m i l l i o n y e a r s Before  metamorphism  the  collected  The  in  of  south  samples  age.  m  1961).  sedimentary  Group and  contact  at  (figure  (BP)  rocks  The  intrusives,  141  these  study a r e a .  constricted  granodioritic  1010  the  Group  P a v i l i o n gave a potassium-argon date of (Preto  of  s t r i k e s northwest, d i p p i n g s t e e p l y overlooking  Trettin  These rocks occur between  southern p o r t i o n  primarily  topography  earthflow  P a v i l i o n area were mapped by  The Group  argillite  pale  yellow  conglomerate deposition  are in  a  TABLE 2.1. region  A summary of the l i t h o l o g i e s and f o r m a t i o n s i n the P a v i l i o n  ( a f t e r T r e t t i n , 1961 and Monger and M c M i l l a n 1984).  ERA  ;  PERIOD Quaternary  7  EPOCH  LITHOLOGY AND CONTACTS  Recent and  alluvium,  Pleistocene  glacial  till,  earthflow  Cenozoic  v o l c a n i c ash, mudflows, glacial  debris,  outwash,  colluvium  —unconformityLower Upper or  lithic  Upper M i d d l e  arenite,  carbonaceous  conglomerate,  shale  Cretaceous —unconformity—  Mesozoic  Lower  granodiorite,  Cretaceous  stocks  or  quartz-diorite  older —intrusive  contact—  Triassic GROUP:Pavilion  t u f f , v o l c a n i c a r e n i t e , greywacke,  FORMATION:  volcanic flows,  Division II  limestone  ASSEMBLAGE: Pavilion  12  argillite,  chert,  well-drained,  oxidizing  environment  (Trettin,  1961).  The  carbonaceous s h a l e shows that backswamp c o n d i t i o n s e x i s t e d Structural rocks  are  Trettin  Tertiary  and M c M i l l a n  Albian  (1984) have  near  relationships  (Duffell  therefore  R e c e n t l y , Monger  Lytton  and  sediments  conglomerate considered  (Bovis,  and  Upper  Middle  1952;  the  Hat  Creek  i s younger.  to Lower Upper  Trettin,  deposits  Valley,  remains from the  communication,  these  (1981), and  at P a v i l i o n i n d i c a t e  personal  that  the r o c k s w i t h s i m i l a r  Pollen  sandstone sequence  to be  McTaggart, that  of  locally.  suggest  (1981), Shannon  i n the Upper  of the u n i t  and  inferred  correlated  (Middle C r e t a c e o u s ) f l o r a .  s h a l e near the base the  i n age  (1961),  i n age.  out  stratigraphic  Pre-Miocene  1961).  crop  and  presence  were Monger  units  which  that  contain  carbonaceous  Cretaceous age f o r  1984). The  The  strata,  upper  then, are  Cretaceous i n age  (Table  2.1). The carried  depth to bedrock i s v a r i a b l e ,  out  crystalline Pavilion  at  several  rock  was  sites  detected  on  the  near  Group crop out i n s e v e r a l  of the e a r t h f l o w ,  as r e v e a l e d  earthflow. the  places  by In  a seismic the  surface,  and  (figure  2.2).  on the o t h e r hand, bedrock was  the maximum depth a t t a i n a b l e w i t h the S o i l t e s t MD-9  survey  source  rocks  area,  from  In the  not d e t e c t e d  the  center  at 12  m,  seismograph.  2.3 PLEISTOCENE HISTORY Fulton south-central  and  Smith  British  (1978) p r o v i d e a l a t e - Q u a t e r n a r y chronology f o r  Columbia.  13  Although t h e i r study i s c e n t e r e d i n the  Okanagan a r e a , e a s t of P a v i l i o n , t h e i r Pavilion  region  because  have had a s i m i l a r from  topographic  the e n t i r e  Interior  glacial history. and  chronology  stratigraphic  observations  Most of s o u t h - c e n t r a l B r i t i s h  the F r a s e r G l a c i a t i o n There  interstades  i s considered to  made  (1978) and Ryder  Columbia  at P a v i l i o n i n (1976).  was not c o m p l e t e l y  covered  19,000 years BP, and d e g l a c i a t i o n was p r o b a b l y complete  10,000 years BP ( F u l t o n  1978).  Plateau  to the  The f o l l o w i n g d i s c u s s i o n i s d e r i v e d  a d d i t i o n t o the work of F u l t o n and Smith  by i c e u n t i l  can be extended  and Smith,  1978).  i n the I n t e r i o r  i s no evidence  T h i s p e r i o d corresponds  Plateau region (Fulton  at present  of the F r a s e r G l a c i a t i o n  to i n d i c a t e  that  by  with  and Smith, stades and  can be r e c o g n i z e d i n the I n t e r i o r  Plateau. The height  i c e cap of the Kamloops  Lake  2,100 m t h i c k  than 900 m (Ryder, The  the  remained The  Mountains  (Duffell  over  the p l a t e a u were g e n e r a l l y l e s s  1976). moved  (Ryder,  earthflow  deglaciation,  a maximum  The major v a l l e y s were b u r i e d by i c e  and i c e depths  i c e sheet  the F r a s e r V a l l e y over  attained  of 2,400 m a l o n g the e a s t e r n edge of the Coast  and McTaggart, 1952; Ryder, 1976). over  Glaciation  upland  from  west  t o east  the C l e a r Range  1976) and d e p o s i t e d a t h i c k b a s a l t i l l  site  and  areas  the  became  surrounding  ice-free  o c c u p i e d by g l a c i e r lobes (Ryder, hillslopes  over  surrounding  14  Pavilion  blanket  uplands.  while  the major  from  During valleys  1976). earthflow  a r e mantled  by a  blanket  of g l a c i a l  ridges  appear  translocated elevation  to  till  and  on  The  consist  flow b i f u r c a t i o n ,  of  till  (figure  and  the h i g h e r  2.2),  and  are found on  the main flow between 940  most  east  of  the  lobe.  It  appears  movement of the e a r t h f l o w has  removed most of the t i l l  area, depositing  till  been  the reworked  o v e r r i d d e n by  sediments  2.4  till.  (Bovis,  flows  lateral  patches  m and that  from  1,000  primarily  of weathered  m  continued the  source  on the d e b r i s f a n where i t has  consisting  of  later  Cretaceous  1980).  CLIMATE The Plateau often  present climate region  from  300  November  to  frequent  from  below the  snowpack.  and  usually  likely  is  from  and  to March.  from  April  therefore to  g r e a t e s t annual v a l u e s .  15  southwestern potential  precipitation  during  June.  Interior  evaporation  i n the  precipitation  mean d a i l y  winter  for  the with  maximum  snowmelt,  available  May  annual  The  therefore  During s p r i n g  freezing;  The  mm,  i n winter,  of  sub-humid,  400  In the p e r i o d  above  evaporation  to  November  accumulation  recharge. remains  mm  valleys  to  precipitation.  February,  freezing  winter  the  i s semi-arid  exceeding  ranges  i n the  occurs  Snowfall  is  temperature  precipitation  region  most  remains  i s stored  then, the m o i s t u r e s u r p l u s spring  to October  runoff  from  and  the average  in from  groundwater temperature  some e v a p o r a t i o n o c c u r s w i t h maximum  September  when  the  temperatures  attain  The  mean  daily  temperature  in  January  averages  -7.7  C  in  the  r e g i o n and the mean d a i l y temperature i n J u l y averages 14°C. As 600  m  the  elevation  a.s.l.  of  the  the  trend  Interior  is  toward  temperatures (Mathewes, 1978). (figure  2.1)  from September  British  Columbia  no snowpack a f t e r  September  1, 1981  to J u l y  survey data show  q u a n t i t y was  Total  1, 1980  region  increased  to August  January 1,  10, 1982,  that  1981.  210 mm  at l e a s t  increases  moisture  31,  94  1981 was Mountain  cooler Mountain  329 mm.  The  indicate  that  In the second water y e a r ,  of p r e c i p i t a t i o n mm  above  and  p r e c i p i t a t i o n at P a v i l i o n  snow survey data from P a v i l i o n  t h e r e was  snow  Plateau  (water  fell  equivalent)  and the of  that  snow.  2.5 VEGETATION A figure  regional 2.4.  many p l a n t gradual  species  shows  on  the  delineation  biogeoclimatic of the zones  occur i n more than one  transition  (Agropyron  showing  Precise  the v e g e t a t i o n which  map  most  dominant generally  earthflow  sage  brush  dominate  (Artemisia the  debris  lower  875 in  m. the  part Sage  of  brush,  Ponderosa 16  the  i n figure  2.5  tridentata) fan.  in  because  i s usually  i s provided  the  occur  there  the  spicatum)  above  and  possible  to another (Mathewes, 1978).  that  of  i s not  i s provided  from one zone  (Pseudotsuga m e n z i e s i i ) and Ponderosa p i n e over  zone  zones  and  Interior  A map  a of  ( i n pocket) bunchgrass Douglas f i r  (Pinus ponderosa) are present  earthflow  fan, with  bunchgrass,  Pine-Bunchgrass  and Zone  Douglas f i r  Ponderosa (figure  pine 2.4),  FIGURE 2.4. shows  the  V e g e t a t i o n map of the r e g i o n s u r r o u n d i n g divisions  Mathewes (1978). the map.  between  the  biogeoclimatic  The e a r t h f l o w i s the hatched  ( a f t e r Mathewes, 1978)  17  Pavilion. zones  The map  discussed  by  r e g i o n near the c e n t e r of  which i s the d r i e s t , (Mathewes, 1978).  and i n summer the warmest, zone i n B r i t i s h I n t e r i o r Douglas f i r f a v o r s areas  a v a i l a b i l i t y i s s l i g h t l y higher bunchgrass. Ponderosa elevations  where  the  the moisture  Zone  of  the d e b r i s  of  supply.  At  f a n adjacent  probably  associated with  commonly  rises  willow  (Salix  discharge  along  (Mathewes,  influence  Douglas f i r i s h i g h on the lower  Pavilion,  and  occurs  the stand  p a r t of the east Creek  bottoms.  Aspen  along  are aquatic  sedge  (Carex  high  gradients of  lobe and along the toe  (figure  2.5).  (Populus  table,  which and  and groundwater  the margins  of  A l s o found  aquatilis)  This i s  tremuloides)  where s u r f a c e r u n o f f  f o r example  at  density  the e l e v a t i o n of the groundwater  l a s i a n d r a ) a r e found  the e a r t h f l o w  edges w i t h i n the  precipitation  streams and around p o o r l y - d r a i n e d d e p r e s s i o n s . on  stream  1978),  strong  to P a v i l i o n  valley  a r e abundant,  where the moisture  t h a t r e q u i r e d by Ponderosa pine and  Hence Douglas f i r o f t e n grows along  Pine-Bunchgrass  increases  than  Columbia  ephemeral  around  and other  ponds  wetland  vegetation. Wild map  area  moderately  rose  (Rosa nutkana, R. gymnocarpa) i s common  as i t can t o l e r a t e  a variety  of moisture  early  within shear  the  regimes r a n g i n g  from  wet t o v e r y wet.  Some l o g g i n g a c t i v i t y was conducted and  throughout  1960s.  the l a s t zones  displacements  As w e l l , fifty  and on (figure  forest  years.  18  have  i n the l a t e  swept  through  Many of the t r e e s a l o n g s i d e  the d e b r i s 2.6).  fires  at P a v i l i o n  lobes  are t i l t e d  from  1950s  the area  the l a t e r a l  large  Many of the t r e e s i n t h e source  downslope area  have  been uprooted  (figure  straddle  shear  several  the  as  zones  are  a  result  split  of  slumping,  (figure  a  2.8),  few  and  trees  the  that  roots  of  l a r g e Douglas f i r have been extended downslope ( f i g u r e 2.9).  contrast,  coniferous  appear to be of these  2.6  2.7)  trees  undisturbed.  growing This  landforms has not  on  the  implies  occurred  abandoned  lateral  that movement along  In  deposits  the  flanks  s i n c e the t r e e s became e s t a b l i s h e d .  HYDROLOGY Ephemeral phreatophytes drainage  that  routes  discharge them are (figure  streams  from  are  along  their  active  located flow  during  i s highest.  Pavilion but  easily  most  snowmelt  dry. 2.5),  grow  are  By  Creek runs along  does not  by  paths spring  late the  cause s i g n i f i c a n t  the  abundance  (figure and  2.5).  early  summer and base of  the  undercutting  of  These  summer  when  autumn most  of  earthflow  fan  of  the  debris  from  runoff  fan. Ponding accumulation  of and  depressions. portions  of  water  the  1981  in  the  was  on  the  earthflow  groundwater  These  basins  earthflow  major  than i t was  elevation  water  ponds  i n 1982.  observed  discharge are  appears in  commonly  underlain (numbered  by  located  reworked  19  the  on  topographic  low-lying  flat  till.  The  level  of  was  much  higher  in  i n f i g u r e 2.5)  3 during  result  poorly-drained  For example, a dramatic  i n Pond  to  change of water  study.  The  level  photograph  in  FIGURE  2.6.  central  Photograph  tension  from r e l a t i v e l y  FIGURE 2.7. large in  zone.  of  Note  the west that  the  lobe  looking  l a r g e Douglas  r a p i d motion of the west  south  toward  f i r stand  the  i s tilted  lobe.  Photograph of a l a r g e Douglas f i r on t h e u p s l o p e s i d e of a  t e n s i o n c r a c k i n the source a r e a .  the downslope  the  root  the  photograph.  direction  zone of the t r e e .  has caused  Expansion o f the t e n s i o n removal  The d i r e c t i o n  2U  of e a r t h f l o w  debris  crack from  of movement i s t o the l e f t i n  FIGURE 2.9. showing  Photograph  the e x t e n s i o n  of  the l a t e r a l  deposit  of Douglas f i r r o o t s  motion i s to the r i g h t .  21  west  downslope.  of the  east  The d i r e c t i o n  lobe of  f i g u r e 2.10 of  Pond  noted  3  was  taken  early  i n figure  snowmelt from May Seasonal ponds less  are than  varied 1981  and  m  once  was  several  winter  tended  1981,  any  to  began  June  1981  The  have  i n May  overview  can  recharge  at  is a July  photograph  1981  it  was  from the huge drawdown and  a h i g h volume of  much  than  bowl-shaped  location and  this  area  of  recent  main  flow  within  of they  the  the  small  basins  were completely  dry i n  i n the  i t continued on  1982  surface  the  where  on  the  been a s s o c i a t e d w i t h  rapidly.  from  basins.  In  earthflow  nor  station.  earthflow i n  groundwater  at  water  the P a v i l i o n Mountain snow survey on the  source  earthflow  storage  accumulated  observed  often  saturated  snowmelt May  numbered  depressions,  these  i n May,  during  snowpack had at  smaller  small snowpatches p e r s i s t e d  discharge  May and  1981. hydrology  of  but  i t is  probably  be  given.  It  Pavilion  2.11  early  recovered  grassy,  saturated depressions  must  and  intense r a i n f a l l  The  in  the  pool  subsurface  present,  in  evidence  snowpack measured the  not  basins  1982  however, no  a result,  figure  In May  to s p r i n g 1982,  In May  additional  heavy r a i n f a l l  at  storage  i n diameter.  melt  and  1982.  situated  l o c a t i o n s on  snowmelt  and  1.0  1981.  despite  from s p r i n g 1981  There  As  2.11,  surface  usually  1981,  of Pond 3 had  to J u l y  by m i d - J u l y .  area  was  i n October  t h a t the l e v e l  depicted  i n mid-July  occurs  by  22  the very  is  earthflow complex.  likely  that  infiltration  of  i s not  well-understood  Nonetheless, much  of  the  a  brief  groundwater  surface runoff  into  the  FIGURE 2.10.  Photograph  of Pond 3 taken i n J u l y  1981.  soil  and  rock d e b r i s capping  includes middle  slopes  toward  of  area.  from  the  close  over  the or  to  the  across  abundance  changes  to  most  earthflow  of  the  slumping area  steep ground  are  the  of  throughout  earthflow  If  in this  and  the  to  water  Groundwater  associated with  surface  upper  flow  recharge.  the  This  measured a d j a c e n t  headwall  of  of  indicate  gradient.  of  the width  of  phreatophytes  850 m e l e v a t i o n on the west lobe and (figure  and  Cole.  and  of  tension  extension  water  case,  most  table  discharge  of is  will  the f i s s u r e d d e b r i s .  Discharge  lobe  Cole  groundwater  base  source a  Mt.  b a s i n of Mt.  P i e z o m e t r i c data  of  table,  i n the  debris  occur through  the  ponds  Apparently,  development  sufficiently  from  major  i s evident  brittle  below  the e a r t h f l o w .  groundwater  source  crack the  the  the  discharge the  immediately  p o r t i o n of  several  the n o r t h drainage  2.5).  sage  and  Below  these  bunchgrass  the middle (aspen,  elevations, remain  where c o n i f e r o u s stands become abundant.  The  r i s e of the groundwater t a b l e at the v a l l e y  24  willow)  i s evident  extending  to  about  to about 830m e l e v a t i o n on the  which  flow system d i s c h a r g e s i n t o P a v i l i o n  t e n s i o n zone  Creek.  the  dominant  dominant  to  vegetation  about  l a t t e r i n d i c a t e s an  bottom where the  east  760  m,  abrupt  groundwater  CHAPTER 3  EARTHFLOW CHARACTERISTICS  3.1 MORPHOLOGY According Pavilion  is  features  as  there  is  moderate  a  t o Varnes' slow  "flows  the  (1978) c l a s s i f i c a t i o n of mass movement  earthflow. occurring  combination  slope,  Varnes  (pp.  i n relatively  of  clay  or  and adequate m o i s t u r e . "  19-20)  describes  dry, p l a s t i c  weathered Varnes  types, these  earth  clay-bearing  where rocks,  f u r t h e r d e s c r i b e s (p.  20) "a common e l o n g a t i o n of the flow w i t h c h a n n e l i z a t i o n and d e p r e s s i o n in  the  slope,  and  spreading  occurring  suggests  t h a t slow, v i s c o u s flow has taken p l a c e .  end  of  the  several  discharges area  (figure  and b a c k - r o t a t e d  i n tension.  bifurcation longitudinal  about  slump  earthflow  (figures  from a bowlr-shaped headwall 2.2).  poorly-drained topographic  i n width failed  study  Pavilion  debris  the  earthflow  of  the  Indeed,  The  topography  of  I t s surface  depressions.  at  the t o e . "  2.2  and  3.1)  i n the south  i s hummocky  with  Open c r a c k s up to 1.0 m  b l o c k s a r e present where the d e b r i s has  The e a r t h f l o w d i v i d e s i n t o two l o b e s around the flow 1,200 m upslope  gradient  at  this  from Highway 12.  location  bedrock " s t e p " i s c l o s e t o the s u r f a c e .  25  (figure Lateral  An abrupt 2.3)  change i n  suggests  that  a  d e p o s i t s run p a r a l l e l  to the e a r t h f l o w  margins  and c o n s i s t  d e b r i s and reworked g l a c i a l  till.  of mixed  material  character  deposited  suggests  600 m south  bowl-shaped  deposits,  The d e b r i s f a n which c o n s i s t s  by the e a r t h f l o w  once much g r e a t e r than  earthflow  ridges  i s very  large  and hummocky i n  ( f i g u r e s 2.2 and 3.1).  Topography  about  earthflow  These are analogous t o l a t e r a l  which o f t e n d e f i n e d e b r i s flow channels. of  unconsolidated  or  the a r e a l  i t i s at present.  o f the present  headwall  volume  that  i s derived  lateral  ridges  area  Further  from  the s i z e  (figure  of the e a r t h f l o w  F o r example, a l a r g e  source  ( f i g u r e 2.2).  extent  2.2)  appears  suggestion  landform  t o be an a n c i e n t of a o n c e - l a r g e r  of the abandoned located  was  well  lateral  outside  the  present e a r t h f l o w margins.  .2 CHARACTER OF MOVEMENT E a r t h f l o w movement at P a v i l i o n flow.  Tension  headwall  and  cracks middle  extension—perhaps surface. at  and b a c k - r o t a t e d tension  zone  slumps i n the area of the a c t i v e appear  s t r e s s e s probably  of the d e b r i s  to  be  related  to  flow  occur w i t h i n t h e main flow and  f a n where the s u r f a c e g r a d i e n t  r a t e a r e q u i t e small and the width of the source  to glacier  a r e s u l t o f a break i n s l o p e of the u n d e r l y i n g bedrock  Compressional  the apex  i s i n many ways s i m i l a r  of the flow i s l a r g e compared t o t h a t  area and the east and west lobes ( f i g u r e 2.2).  26  and movement  27  The  well-developed  boundaries 1970).  (figure  Lateral  3.2)  deposits  a r e analogous  d e p o s i t s develop  edges of the flow (1970),  lateral  which  to  define  lateral  from d i f f e r e n t i a l  and the c e n t e r of the c h a n n e l .  the m a t e r i a l tends  (figure  margins  of the flow  with  some  sandstone along  shear  movement between the t o Johnson  t o accumulate on the margins of the channel  The d e b r i s  or no movement i n the  t o be pushed  upward  so t h a t accumulation  of the s l i d e  d e b r i s may  of  debris  and conglomerate  ( f i g u r e 3.4).  (Johnson,  tends  "spilling"  the lower  (figure  3.3).  earthflow  moraines  According  where t h e r e a r e "dead" zones, or r e g i o n s of l i t t l e channel  the  out  boulders  of  the c h a n n e l .  Many of these  3.5), i n d i c a t i n g  blocks e x h i b i t  t h a t they  At  up t o 1.0 m i n diameter  p o r t i o n o f the west l a t e r a l  shear  along the occur  Pavilion, are common  zone of the west  one or more sheared  had been t r a n s p o r t e d along  lobe  surfaces the b a s a l  zone p r i o r t o e x t r u s i o n from the e a r t h f l o w . Johnson  (1970)  develop  when  smaller  (figure  margins. feature produced (Bovis, In profile.  further  successive  a l s o noted when  ridges  that  waves of m a t e r i a l  3.3), each  Linear  stated  wave  higher  by VanDine  the e a r t h f l o w  leaving than  moving  lateral  lateral  in a  much  larger  than  become  on i t s flow  earthflow  a r e undoubtedly  deposits  channel  deposits  the present  (1974), was  multiple  surface, a  lateral i t i s at  deposits present  1980). cross  section  The depressed  (figure center  28  3.2),  the  earthflow  i n d i c a t e s that  movement  has  a  occurs  concave at the  FIGURE 3.2. (a)  the source  bifurcation, (in  Cross  sectional  area;  and west  view of t h r e e  (b) the main lobe.  flow;  Transect  pocket).  29  of the e a r t h f l o w and  ( c ) the east  divisions: lobe,  l o c a t i o n s are g i v e n i n f i g u r e  flow 2.2  (c)  FIGURE  3.3.  Johnson's  analysis  using  the concept  o f "dead"  snows  the concept  of a  viscous multiple  debris lateral  deposits  zones  rigid  i n the flow  of the development within  "plug"  channel.  the flow  of d e b r i s View  of l a t e r a l channel.  flowing  ( c ) shows  on a  ridges  View (a) raft  the e v o l u t i o n of  which develop when s u c c e s s i v e l y s m a l l e r  of d e b r i s move through the c h a n n e l .  30  of  ( a f t e r Johnson, 1970)  waves  FIGURE 3.4.  Photograph of the west l a t e r a l  near the apex of the d e b r i s f a n .  shear zone of the west  Note the l a r g e conglomerate boulder at  the t o e of the advancing west lobe, near the l a t e r a l  deposit.  FIGURE 3.5.  Photograph of a l a r g e conglomerate boulder  of  lobe.  the west  while the  i n transport  The within  exposed  surface  the e a r t h f l o w  flow.  31  lobe  on the west s i d e  appears t o have debris  prior  been  sheared  to extrusion  from  highest  rate  boundary  in  the  center  of  r e s i s t a n c e i s minimum.  the r a t e of movement decreases up  the  The  debris  rapid to  movement  exhibit  pronounced where the  Bovis similar  (1980)  where  rapidly.  i n the  concave  T h i s causes  center  of  profile,  with  are  of  approached,  the d e b r i s to  build  channel, the  then,  effect  (e.g.,  the  causes  being  east  more  lobe  and  3.2).  has  shown  that  the  horizontal  From t h i s , he  velocity  substance  flow  channel  (figure  3.3),  is  semi-  " p l u g " flows  of the " p l u g " o c c u r r i n g above a c r i t i c a l and  profile  flowing i n a  speculated that a r i g i d  however, r e q u i r e s much f u r t h e r i n v e s t i g a t i o n , this  influence  (1970) theory of "dead"  the  i s most c o n s t r i c t e d  of v i s c o u s d e b r i s i n the  no d e f o r m a t i o n  the  the f l o w boundaries  to t h a t of a Bingham v i s c o - p l a s t i c  c i r c u l a r channel. raft  a  flow  tne west l o b e , f i g u r e  or  As  channel  a l o n g the f l o w margins a c c o r d i n g t o Johnson's  zones.  a  the  on  with  little  depth.  This,  i s beyond the scope of  thesis.  .3 DEBRIS CHARACTER The angular matrix  earthflow lithic  (figure  sheared presence  clasts 3.6).  Cretaceous of  vermiculite  d e b r i s i s a mixture variable  Apparently,  deposits.  illite (P.  of  with  Jones,  f e l d s p a r were r e c o g n i z e d  size  personal i n thin  32  poorly  within  and  silty-clay  the d e b r i s i s d e r i v e d from  weathered,  analysis expanding  a  s o r t e d , rounded red-brown  X-ray some  of  of the  layers,  communication, section.  shale indicated  I t was  1982), found  kaolinite, and  and  quartz  t h a t the  the  and  shale  COARSE  SAND MEDIUM  F/AIE  COARSE  SILT MEDIUM  FINE  COARSE  CLAY MEDIUM  FIHE i  too0 SIEVE X HYDROMETER  'RED-BROWN  REWORKED  "1  RED-BROWN DEBRIS 17% GRAVEL 2>r/* SAND zr/a SILT ZO'U CLAi (<O.OOZn,m)  DEBRIS  TILL-^  I—T  0.001  0.1  DIAMETER FIGURE 3 . 6 .  REWORKED TILL 30% GRAVEL 45% SAND IV/. SILT 6 7, CLAY  Grading curves  f o r the reworked g l a c i a l  (mm) till  and t h e red-brown  debris.  OOOOI  weathers  to  Evidently kaolinite  montmorillonite  the  smectite  comes from  Jones, p e r s o n a l sandstone and field  the  underlying  ( f i g u r e s 3.4  sorted  shale  reworked  liquid to  be  some  mica  abundant  in  and  3.5),  and  probably  1980).  The  the  of  was the  plasticity  low  (Table of  are  reworked  index  3.1).  kaolinite  of This  in  determine  the  the  of younger  consists Group  slide be  the  debris  consistency I.  Both  m a t e r i a l were  which  for  by  reduces  TABLE 3.1. Average c o n s i s t e n c y l i m i t s and n a t u r a l water c o n t e n t s n e a r - s u r f a c e samples of the e a r t h f l o w d e b r i s and g l a c i a l t i l l .  of  Material  Earthflow  L.L.(%)  debris  Translocated  till  41.5 30.2  34  P.L.(%)  26.2 20.3  P.I.(%)  15.3 9.9  the found  l i m i t s of m o n t m o r i l l o n i t i c d e p o s i t s .  type  of  clasts,  earthflow  accounted  debris  in  3.6).  i n Appendix  can  (P.  to f a i l u r e of  till  (figure  given  while  debris i s evident  o c c u r r e d due  to  (35%).  shale,  of b l o c k s  samples of the  conducted tests  the  granodiorite, Pavilion  of n e a r - s u r f a c e  till  kaolinite  f e l d s p a r fragments  Entrainment  set i n a s a n d y - s i l t matrix  details  abundance  consistency  and  testing  moderately  relative  of  1982).  fragments of  glacial  The limit  with  from  weathering  (Bovis,  angular  Laboratory  limits.  the  derived  communication,  and minor l i m e s t o n e  and  is  60%)  conglomerate s t r a t a w i t h i n the s l i d e  the  poorly  (about  w(%)  30.6 18.6  the the  Near-surface taken the  from  than  d e b r i s are s l i g h t l y  (1980),  Bovis  limit  the p l a s t i c  (1980),  debris  derived  limit.  by  t h a t the n a t u r a l water  over  the p l a s t i c  limit  the abundant  the a e r i a l  till  contents of ( T a b l e 3.1).  substantially  lower  slightly  Low n a t u r a l water c o n t e n t s , as d i s c u s s e d by the b r i t t l e b e h a v i o r tension  cracks  i s o c c u r r i n g — c o n t r a r y t o the i l l u s i o n  from  and reworked  t o depths of 8-10 m, below which v a l u e s  are consistent with  manifest  extension  debris  however, r e p o r t e d f i e l d water c o n t e n t s  the p l a s t i c  exceeded  of the e a r t h f l o w  s a t u r a t e d zones suggested  red-brown  Bovis  samples  of the e a r t h f l o w  present  of slow,  where  flow  viscous  flow  view of the e a r t h f l o w ( f i g u r e 3.1).  3.4 EARTHFLOW MOVEMENT IN THE HOLOCENE PERIOD A  sequence of events  e a r t h f l o w as i t appears topographic its  at present  and s t r a t i g r a p h i c  surrounding slopes.  supported  which may have  by  deep  has been c o n s t r u c t e d on the b a s i s of  relationships  The chronology  borehole  l e d t o the development of the  data  noted  on the e a r t h f l o w and  i s tentative  from  and u n t i l  the d e b r i s  i t can be  f a n , i t remains  conj e c t u r a l . From aerial  the t o p o g r a p h i c  photograph  (figure  map  of the e a r t h f l o w  3.1), i t appears  that  (figure  the s l o p e s  P a v i l i o n Creek s i t u a t e d on the east and west boundaries were  once  contiguous  with  a  steep  valley  earthflow.  In a d d i t i o n ,  i t i s evident  bifurcation  has a s i m i l a r  topographic  35  wall  2.2) and the  at  t h a t the n o r t h  south of  of the e a r t h f l o w the s i t e  of the  s i d e of the flow  c o n f i g u r a t i o n t o the steep  slopes  bounding figure  the e a r t h f l o w . 3.7  appeared  Based on these o b s e r v a t i o n s , the contour map  d e p i c t s the following  constructed  by  topography  be  linking  displaced  contours  the  deglaciation. the  c o n t o u r s on the n o r t h s i d e to  of  3.7  contours  of  valley  map  is  the  steep  from  were  i t s original  elevated  as  slopes The  accordingly.  figure  10,000 y e a r s caused  3.7  BP,  approximates  then  initiation  i t seems  The  of mass movement at  sidewall  on  i n d u r a t e d sediments  process i s that f a i l u r e r u n o f f through  the  main  from  through  the  glacial  scour and  and  valley  processes  First,  west  bifurcation, 3.7). about  may  have  oversteepening  i n c r e a s e d the h o r i z o n t a l  caused  clastic  the  and  deposits resulted  (figure valley  channels  slumping  of  3.8),  with  sidewall. the  east  accumulation  of the d e b r i s f a n , has  valley  prevailed  that  Pavilion.  two  appears  (figure  the  them t o f a i l .  of the Cretaceous d e p o s i t s was  post-glacial  valley  upslope  by  least  the  stress  The  initiated  second by h i g h  the steep channels at the s i t e of the e a r t h f l o w .  Continued clay-bearing  at  of  with  east  the f l o w  topography  that  of the v a l l e y the weakly  the  was  therefore i t s  t h e r e f o r e r u n o f f channels were i n c l u d e d i n these p o s i t i o n s If  have  and  latter  position,  l o b e s appear to occupy former water courses around  i t may  schematic  of the f l o w b i f u r c a t i o n .  downslope  i n figure  The  main  in  prior  to  36  d e b r i s flow  i n extension retrogressive Thus,  and  of of  the  of  lobes,  into  earthflow  accompanied  In  and  proceeding  the  c o n c e a l e d the topography  e a r t h f l o w movement.  shale slide  failure  movement  west  the  by  of the main  contrast,  the  FIGURE 3 7 Generalized contour map of the south sideslope of P a v i l i o n Creek approximating the valley topography following deglaciation.  4—~\ A  1  1  1  1  1  1  1  1  VERTICAL 1 1  I  EXAGGERATION-4X I 1 I Y" A  FIGURE 3.8.  Schematic profile o f t h e main valley c o n s t r u c t e d from t h e g e n e r a l i z e d contour map depicting the c o n f i g u r a t i o n following deglaciation, and t h e l o n g i t u d i n a l profile of t h e present e a r t h f l o w s u r f a c e . Transects are given i n figures 3.7 and 2.2, respectively.  valley  profile  undisturbed  east  and  apparently  west  because  rocks which dominate these The  flow  probably removal  shearing  be  slope of  between  relatively  and metamorphic  might  the t i l l  be  of  glacial  (figure  2.2)  till  and  shortly  after  o f the b i f u r c a t i o n  while  explained  by a d i f f e r e n c e i n  and the red-brown  debris.  The  of each m a t e r i a l was not determined, but the c o a r s e r  than  that  the angle of s h e a r i n g  of the red-brown  of the e a r t h f l o w  saturated  primarily  position  ( f i g u r e 3.6) suggests t h a t  greater  remains  plutonic  Stabilization  has continued  resistance  shear s t r e n g t h matrix  consists  t o i t s present  motion  earthflow  of the r i g i d  o f the i c e b u t t r e s s .  earthflow  the  slopes.  bifurcation  sheared  of  a t present  clay debris  earthflow  i s about  to p e r s i s t .  till  r e s i s t a n c e would  debris.  10°—sufficient  Some of the t i l l  The average f o r movement  i n the P a v i l i o n  r e g i o n , however, may have s i m i l a r mechanical p r o p e r t i e s t o the red-brown debris across  as Ryder the  (personal  main  communication,  valley  from  l i t h o l o g i e s as the e a r t h f l o w The the  large  depressed  i n d i c a t e that and  Pavilion  -earthflow  that  till  contain  deposits the  same  debris.  topographic  depression  configuration  of  surrounding  the main  flow  the source and  the  area  source  and area  a l a r g e q u a n t i t y of d e b r i s has been removed from the upper  central portions  of the b a s i n  d e b r i s removed was estimated from  1982) noted  the d e b r i s  fan.  by e a r t h f l o w  movement.  f o r l a t e r comparison w i t h  Since  39  very  little  erosion  The volume of  a volume  of the d e b r i s  estimate fan i s  e v i d e n t , the d i f f e r e n c e between the two  volume e s t i m a t e s was  expected  to  be very s m a l l . The was  volume of d e b r i s removed from the south  estimated  removal. the  The  present  slope  by  first  approximating  maximum e l e v a t i o n of shear  zones  elevation prior  (figure  the h e a d w a l l - l i k e landform  was  considered,  to  displacement.  again,  to  The  2.2)  south  area  so t h a t a p l a t e a u - l i k e f e a t u r e was found  by  contour  and  selected  locations.  was  the  multiplied  computing  present  by  The  The estimated  volume by  generalized used  to f i n d  depth of and  later  5.4  the  The  the  debris  using  the  base map  contour  map  (figure  the volume  multiplied  and  west  the  boundary  used  top of which  the  slope  prior  e a r t h f l o w movement were tops of  the  The  a column  at  at  each  The  lateral  then  ridges  depth of the d e b r i s  d i f f e r e n c e between topography  of  the  extrapolated  several location  sum  randomly considered  of these v a l u e s i s  m . the  f a n and  debris  3  x 10 of  to  area  represent  the  e l e v a t i o n of  constructed.  of  to  of the e a r t h f l o w ,  earthflow area  r i d g e s east  southernmost  from the  the  prior  considered  the depth of t h a t column. 7  approximately  lateral  pre-dating  source  of the study  topography  was  approximate  contours  a c r o s s the  removed was  the  to d i s p l a c e m e n t .  was  extrapolated  the  end  the  estimate two  of  and the  3.7). i n the  the  east  earthflow The  to  source  obtain  and  the  west  (figure  method was area:  l o b e s were estimated  together 40  fan  at  volume  lobes  2.2)  similar the  area  was  and to  the that  and  the  several locations of  a  column  of  debris.  The  found  summation  by  volume of of  the  d e b r i s f a n and  the c o n t i g u o u s  lobes,  the volume e s t i m a t e s , i s a p p r o x i m a t e l y  then,  6.1  x  10^  m. 3  Although  the  two  values  ft difference  of  measurement  1.0  error  quantities. introduced  x  the  same  order  m  may  be  cause  source  a  of  extrapolation  accounted  arise  debris  fan  from  addition  that  should  source area volume. the  discrepancy  error  could  of contours  area-main density  flow  unit  of  actually  may  two  be  easily  the  to  further  the  ways. the  arise study  resulting from  the  estimate  of  the  in  estimate  of  the  the  t e n s i o n zone was  41  chosen  however, the  downslope.  Third,  sedimentary  would cause the volume e s t i m a t e f o r the d e b r i s f a n t o be volume e s t i m a t e of the source a r e a .  may  volume  In r e a l i t y ,  Cretaceous  bias  area i n the  earthflow m a t e r i a l i s probably l e s s  undisturbed  First,  Second, a d i s c r e p a n c y  included  regions.  extend  of the t r a n s l o c a t e d  bulk d e n s i t y of the  material  between  over  For example, the c e n t r a l  boundary between the  magnitude,  f o r several  c o n s t r u c t i o n of the p r e - e a r t h f l o w topography. also  of  3  could  This i n the  10  are  source  the than  deposits.  at  bulk the This  l a r g e r than the  CHAPTER 4  CLIMATE AND SUBSURFACE HYDROLOGY AT PAVILION  4.1 INTRODUCTION The  results  Pavilion July  from  suggested  was  during to  that  basin  to  high  period.  regime was c l o s e l y  the  rainy  (1978) found to  earthflow  movement season,  linked  of e a r t h f l o w  winter  study  of e a r t h f l o w  piezometric  that  (1978) found to earthflow  Kotarba  They  shortly  noted  after  and Swanson and Swanston  rate  commensurate w i t h  that  maximum displacement  month of peak d i s c h a r g e  present  snowmelt.  shortly  They after  and Swanston  Swanson  that  (1977),  Similarly,  of  evapotranspiration  42  figure  Kelsey  closely  linked  of  the  earthflow  winter  an i n c r e a s e  rainy  of the flow  VanDine (1974,  1980) found  l a n d s l i d e occurred  w i t h i n one  VanDine surmised  was  t h a t the  and  t h a t there was  no c o n t r i b u t i o n t o the groundwater flow system from r a i n f a l l estimated  and  commencement of  the v e l o c i t y  (1977) noted  of the Drynoch  noted  regime was  commencement  from snowmelt.  i n the  l e v e l s were not  (1977),  movement.  increased  and Swanson  at  t h a t the r e g i o n a l p r e c i p i t a t i o n  the r e g i o n a l p r e c i p i t a t i o n  movement.  increased  G i l and  movement  season,  levels  movement  from March mid-  However, the p i e z o m e t r i c  hydrology.  Swanston (1977), and K e l s e y  velocity  (1980)  t h a t the h i g h r a t e of motion observed  attributable  earthflow related  Bovis'  greater  than  because the  precipitation.  Hence,  only  groundwater dating  snowmelt recharge.  VanDine's  correlated suggest  was  an  with  indicated  peak  unmistakable  which accounts  by  VanDine  In a d d i t i o n , p e i z o m e t r i c  research  well  considered  that  discharge  data  increased  form  contribute  from Drynoch groundwater  snowmelt.  moisture-dependence  of  to pre-  levels  These  results  earthflow-type  motion,  f o r seasonal v a r i a t i o n i n the r a t e of movement.  Groundwater o b s e r v a t i o n s a r e important because of the r o l e of pore water stress  to  i n the s l i d e  pressure  i n any s l o p e movement i n determining  d e b r i s , and t h e r e f o r e the s h e a r i n g  study  the e f f e c t i v e  resistance.  If  the pore water p r e s s u r e w i t h i n the l a n d s l i d e d e b r i s i s below the maximum possible  value  but  is  sufficient  increase i n pressure w i l l  precipitation  groundwater  level.  movement.  Thus,  explicable seasonal The  from  allow  slope  displacement,  an  cause a c c e l e r a t i o n of the f l o w .  I n f i l t r a t i o n of a s u f f i c i e n t excess  to  volume of snowmelt, and r u n o f f due to  during p a r t i c u l a r Piezometric  the s e a s o n a l  seasons w i l l  data  can  variation  the groundwater  flow  then  cause an i n c r e a s e i n be  of e a r t h f l o w  regime  related  to  movement  and, i n d i r e c t l y ,  slope may  be  from the  climate v a r i a t i o n s . primary  relationship do  this,  be  estimated  objective  between  subsurface  the p o t e n t i a l from  of  this  hydrology  groundwater  precipitation,  is  and c l i m a t e  recharge  temperature,  the P a v i l i o n area r e l e v a n t t o the present  43  chapter  to  examine  the  at P a v i l i o n .  To  (or moisture  s u r p l u s ) must  and snowpack r e c o r d s f o r  study.  4.2  APPROACH AND  DATA SOURCES  Precipitation July  10,  1982  operated located  by on  earthflow Valley  from  British  Columbia  Hydro  Pavilion  Mountain  ( e l e v . 2115  Topography no  precipitation  m),  the  data  of  Hills  (2,000 m).  short  time  are  remaining  (May  (elev.  the  1,250  to  15,  1981  piezometers  the  first  km  northeast  mouth  of  Upper  the  on  British  represent  Harry  of  Hat  14,  Cole  sites  Lake  near  was  1981)  Hydro  over  the by  earthflow:  and  Cornwall  a l s o measured  in five  12.  estimated  the  (1,340 m),  the  systems  Columbia  was  is  Creek  Highway  precipitation  on Mt.  earthflow  to November  storage  for  a  gauges  2.5).  observations on the were  were  earthflow 1  10.47  are summarized i n Table  m  to  4.1.  44  made  16.55  in  six  open  diameter  PVC  tubing  inclinometer tubing. m.  standpipe  ( l o c a t i o n s i n f i g u r e 2.5).  1/12-inch  t h r e e were 1 1/2-inch ABS from  The  Pavilion  to  Pavilion,  14.5  of  from t h r e e  m),  on  1980  flow paths of v a r i o u s weather  data  Rainfall  installed  depths ranged  at  1,  s t a t i o n s near  m),  southeast  assumed  September  Power A u t h o r i t y .  nevertheless,  snow survey  Groundwater  the  km  region;  (locations i n figure  of  22  and  second  from  climate  c o n t r i b u t i o n from snowmelt  Mountain  piezometers  the  two  doubt i n f l u e n c e s the  The  interpolation  2.1);  864  through  Pavilion  records  obtained  (figure  earthflow.  temperature  were  (elev.  passing  and  The  details  of  The each  and  Three the  piezometer standpipe  TABLE  4.1.  ground  Summary  of  the  depth  of  Borehole  Water July  piezometer  tips  below  the  local  level.  9,  levels  1982  10.47  BH-2  15.75  BH-3  16.55  BH-4  13.95  BH-5  13.72  BH-6  9.05  were measured  witii  an  Borehole  the bottom  to prevent  the  Therefore,  cap  was  the  (m)  BH-1  standpipe.  when  Depth  electric  1 (BH-1),  r e c o r d from  water  located  intrusion  pierced,  regularly  between  level  March  sensor  lowered  i n the source a r e a , was  of muddy d e b r i s u n t i l  allowing BH-1  spans  22,  water only  1981 into  enter  the  latter  the  each  s e a l e d at  mid-November  to  and  1981  standpipe.  portion  of  the  study. Continuous-recording installed  i n BH-2,  mounted  on  (figure  4.1).  of  a fine  a  BH-4,  covered  float-activated  and  BH-5  i n November 1981.  p l a t f o r m and  A float  and  w i r e c a b l e draped  s e n s i t i v e t o water l e v e l  centered  counterweight over  changes.  water  a pulley  over  level  recorders  Each instrument the  top  of  each  were was pipe  were a t t a c h e d t o o p p o s i t e ends wheel.  The  floats  were v e r y  {P/ywtod hose for recorder housing 1.0mm wire  Cable  F/Oar  (b) FIGURE 4.1. the  (a) Schematic  piezometer.  diagram of the f l o a t  (b) Photograph  r e c o r d e r mounted on BH-5.  46  of  the  and counterweight  continuous,  inside  float-activated  The  record  mid-February the w i n t e r be  i s discontinuous  1982.  Apparently,  temperatures f e l l  r e s t a r t e d by  hand, o n l y  from  the  date  of  the b a t t e r y - o p e r a t e d  below -20°C, and the  p o r t i o n of  installation  until  c l o c k s stopped  when  s i n c e the c l o c k s needed  the  record  obtained  to  prior  to  on  the  clock f a i l u r e i s available. To  examine  earthflow  and  the  the  relationship  subsurface  flow  between regime,  these  installations  are  i n areas  summarized  i n Table  and  N6 were p l a c e d a d j a c e n t  to Pond 2, Pond 3, and  and  N3  piezometers  zone immediately  of  Two  t h a t were s a t u r a t e d d u r i n g  three  The  details  p a i r s (N4  summer 1981;  Nl,  and N2,  Pond 4, r e s p e c t i v e l y ;  t r a v e r s i n g the  n o r t h of Pond 3 ( f i g u r e  peizometers  2.5).  4.2.  were p l a c e d  seeps  shallow  (figure  N5)  consisted  and  thirteen  were p l a c e d at s i x l o c a t i o n s on the e a r t h f l o w of  ponds  central  tension  2.5).  4.3'CLIMATE RECORD Monthly are  summarized  included. near  precipitation  The  in  figure  data  from  4.2.  Rainfall  data show t h a t the  P a v i l i o n was  v a r i a b l e over  the  total  mm;  d u r i n g the same p e r i o d i n 1981 i n May  1981,  from  seasonal  the  rain f e l l  precipitation  22  September  Mountain  measured  on  distribution  months of  the of  record.  1 to November  o n l y 43 mm  w h i l e o n l y 3 mm  47  Pavilion  fell.  were recorded  30,  and  Hat  earthflow  is  precipitation For  example,  1980  was  Similarly, i n May  Creek  62 mm  1982.  166 of  TABLE 4.2. at  Details  of the s h a l l o w piezometer nest  installations  Pavilion. Piezometer nest  The slightly  data lower  show than  Depth  Nl-A  2.18  Nl-B  1.63  N2-A  1.93  N2-B  1.13  N3-A  2.02  N3-B  2.23  N3-C  1.57  N4-A  1.73  N4-B  1.42  N5-A  1.53  N5-B  1.13  N6-A  1.60  N6-B  1.62  that at  the  total  Pavilion  p r e c i p i t a t i o n a t Hat Creek t o t a l e d 10,  1982; i n the same p e r i o d  average r a i n f a l l Creek  twice  on the e a r t h f l o w  and i t exceeded  precipitation Mountain.  487 mm  554 mm  at Hat For  from September  fell  (figure  Pavilion  (m)  at P a v i l i o n  Creek  example,  rainfall  the  1, 1980 t o J u l y Mountain.  4.2) exceeded r a i n f a l l  Mountain  was  twice.  The at Hat Since  r u n o f f and groundwater r e c h a r g e over Mt. Cole and i t s f l a n k s undoubtedly contribute  t o groundwater f l o w i n the e a r t h f l o w , the c l i m a t e r e c o r d from  48  80-  70HAT  60-  I  WEEK  MOU/VTAlM  SO-i 44-  PA V/L/ON £APTHFL0IV  30ZO-  ll  10-  0 N 'WO FIGURE  4.2.  Valley,  D J  F M A  M J  Precipitation  I ll  J- A S mi  records  0 N  from  D  Mountain  i s considered  piezometric fluctuations The  Pavilion  British  from  F  M A  4*  M T T A I98Z  Mountain,  Hat Creek  appropriate  estimated  from  Hydro c l i m a t e data do n o t , however,  Therefore,  snowpack  Cornwall H i l l s . snowpack depth snow  data  the  from  The snow survey ( i n mm  depth  for correlation  with  i n the e a r t h f l o w .  Columbia  rain.  most  amount  of  c o n t r i b u t e d by snowmelt over Mt. C o l e i n s p r i n g  that  ?  and P a v i l i o n e a r t h f l o w .  Pavilion  snow  VALLE1  Pavilion  increases  49  1981 and s p r i n g  Mountain,  data were used  of water) w i t h linearly  elevation with  groundwater  separate recharge 1982 was  Hat Creek,  and  t o c o n s t r u c t a p l o t of (figure  elevation,  4.3).  Assuming  the  snowpack  t h i c k n e s s at the summit of Mt. 4.3.  In  1982,  1981,  snowpack depth  though,  less  spatial  accumulation  gradient  estimated 15,  1982  up  snow  at  of  the  ( f i g u r e 4.3)  the  depth  amount  by  month  in  the  15, 1981,  ablation  of  of snowmelt which  the  at l e a s t mm  from  period  falls  snowpack  is  November  to  until  26 mm of  snow.  not  equal  assumed to account  elevation. resulted  Pavilion  after  the  in  Mountain,  data p o i n t s t o survey  In  attain  station.  April  1,  1981  The and  May  the snow at  of  snowpack 4.4  shows  approximated had  by  decreased  that  about  1 and  May  computing  during  26 1,  mm  each (water  1981.  By  of net accumulation took p l a c e , f o l l o w e d by  the  snowpack  i n 1982  after  the  remains  the  of  and  snowpack  depths  for precipitation  below 0°C  the  Mt.  precipitation  50  15  during  June. 1, then  June.  majority  Although to  May  d i d not begin u n t i l a f t e r A p r i l  temperature  March,  as  March,  Cole  o c c u r r e d between March  the mean d a i l y  November  at  snow  Cole was  of melt o c c u r r e d by the end of Since  than  figure  had completely a b l a t e d by those d a t e s .  Figure  A p p a r e n t l y , net a b l a t i o n 168 mm  Hills  with  apparently  between these  from Mt.  depth  spring.  120  e s t i m a t e d from  are regarded as maximum v a l u e s because  e q u i v a l e n t ) of net melt May  Lake  f o r Mt.  Harry Lake and P a v i l i o n Mountain The  snowfall  Harry  Cornwall  snowpack  was  increased l i n e a r l y  to i n t e r p o l a t e  to  depths  (1,725 m)  v a r i a b i l i t y of  of  making i t n e c e s s a r y the  Cole  precipitation  Cole at  i n the  water  Pavilion  estimated  over  period  in  this  equivalent Mountain Mt.  from November u n t i l the  Cole  of  from are  ///  /?dl ZOOO 1  -i  90  1  1  100  ?  i  1  1  IZO 14-0 l(>0 180 200  W.E SNOW (mm)  i  i  i  i  r  ZZO 2-W 2(,0 ZSO 300  (a)  ZOOO  -i  ZO  40  60  80  ~WO ~lJo ~HC ~160 m>  ZOO Z20 240  Z60 ZSO  ~30O  hi- £ SNOW (mm) (b)  FIGURE  4.3.  Mountain  Plot  (1,250  The s n o w p a c k depth for  each  equivalent  water  of British  m) , H a r r y  Lake  Columbia (1,350  over Mt. C o l e  year.  (1.725  T h e snow  values.  51  snow  survey  data  from  m», a n d C o r n w a l l H i l l s m  ) was e s t i m a t e d f r o m  depths  are a l l expressed  Pavilion  (2,000  m)  the plots as water  (b)  FIGURE 4.4. Mt.  E s t i m a t e d change of snowpack depth  (water e q u i v a l e n t )  for  Cole from January 1 t o June 30, i n 1981 and 1982.  commencement Since  of snowmelt—after  the P a v i l i o n  Mountain  March  1,  1981 and a f t e r  precipitation  record  does  April  1, 1982.  not s e p a r a t e snow  from r a i n , p r e c i p i t a t i o n i n the p e r i o d s September 1 t o October 31, 1981, and  April  1  groundwater snowpack  to J u l y  recharge  figures  is  precipitation observations  from  found  P a v i l i o n Mountain w i l l It  10,  i s considered  snowmelt, f o r Mt.  then,  Cole  will  and  to be  be  to  influence  realize the  precipitation  spatial  transposition  and the B r i t i s h Columbia  52  that  rainfall.  estimated  be used t o e s t i m a t e recharge from  important may  1982  of  The  from the  measured  at  rainfall. variability  Pavilion  of  Mountain  snow survey data t o Mt. C o l e .  It  was  noted,  Pavilion  f o r example, Mountain  Nevertheless,  that  miss  many  Mt.  the B r i t i s h  summer  Cole  Columbia  storm  and  Hydro  cells  the climate  which  pass  over  earthflow  entirely.  record  the snow  and  survey d a t a are the most r e l i a b l e data sources at p r e s e n t . Daily calculate study to  temperature  data  the mean monthly  ( T a b l e 4.3).  estimate  Thornthwaite  the  from  Pavilion  were  used  to  temperatures f o r the d u r a t i o n of the p r e s e n t  The mean monthly potential  method  Mountain  temperature  evapotranspiration  (described  by  Dunne  v a l u e s were then  by  and  application Leopold,  used  of  1978,  the pp.  136-137):  E r r > — 1.6 !0  ^  (4.1a)  where E j i s the p o t e n t i a l e v a p o t r a n s p i r a t i o n  i n cm/month, T  monthly  I i s the annual heat  a i r temperature  i n degrees  Celsius,  a  i s the mean index  and i s a f u n c t i o n of the mean annual temperature, and  a = 0.49 + 0.01791 + 0.0000771I + 0.0000006I . 2  Evapotranspiration November  1980  mean monthly data  were  not  to A p r i l  estimates 1981  temperature available  e i g h t v a l u e s of p o t e n t i a l  was  were  and November less  than  f o r s i x months  (4.1b)  3  not  computed  1981  to A p r i l  0°C. In of  f o r the p e r i o d s 1982 when the  addition,  the s t u d y ,  temperature  therefore  only  e v a p o t r a n s p i r a t i o n were computed (Table 4.3).  53  TABLE 4.3.  Mean monthly  temperatures  and p o t e n t i a l  e s t i m a t e s computed from P a v i l i o n Mountain MEAN MONTHLY MONTH  TEMPERATURE  temperature  EVAPOTRANSPIRATION  64.0  10/80  4.7  20.7  11/80  -0.2  X * *  12/80  -1.1  X  1/81  2.1  2/81  -3.0  3/81  *  4/81  -0.1  5/81  — — —  6/81 7/81  0.9 X  — X  — — —  9.7  68.5  7.9  46.5  10/81  2.2  8.0  11/81  -3.1  X  12/61  -6.1  X  8/81 9/81  data.  POTENTIAL (°C)  10.2  9/80  evapotranspiration  1/82  -7.7  X  2/82  -7.7  X  3/82  -2.7  X  4/82  2.7  X  5/82  3.9  23.3  6/82  10.5  84.5  7/82  —  —  *No data **Erj,  was n e g l i g i b l e because the mean monthly  was below 0°C.  54  a i r temperature  (mm)  The p o t e n t i a l rainfall depths the  measured  at  from Mt. Cole  Pavilion  May  recharge  to July  June  30,  period over  1982.  The  Cole  was  Snowmelt i n A p r i l the  21 mm,  persists snow  in  with  15 mm  through the  June, upper  calculated  i n Table  of the t o t a l  April  and May  water y e a r .  of  snowmelt  A continuous  recharge  The t o t a l  f o r the  groundwater  f o r the p e r i o d August  and o c c u r r e d  and  from  of t h a t  1982.  i n April  record  1, 1981 to  values  recharge  The recharge  occurring i n April  therefore r a i n f a l l part  of  recharge  the  the P a v i l i o n  recharge  basin.  for this  from  snowmelt  and May  55  April  1982.  Furthermore,  rainfall  As  a  was  Mt. Cole snow  t o June  falls  result,  period  may  on the  not be  r e c o r d ; r a t h e r , the a c t u a l  g r e a t e r at Mt. C o l e .  1982 the p i e z o m e t r i c l e v e l s  should a l s o be h i g h l a t e i n s p r i n g .  from  1982.  for this  mountain  i n the second  t h i s p e r i o d or s h o r t l y a f t e r .  from  estimates  s p r i n g recharge would be s u b s t a n t i a l l y 76%  estimates  groundwater  97.7 mm  estimated  d a t a were a v a i l a b l e  reliable  4.4.  1981 t o June  evapotranspiration those  no  estimated  with  and May then, c o n t r i b u t e d 82% of the t o t a l recharge i n  p e r i o d August  about  temperature  f o r the f i r s t  about  and  t o g e t h e r w i t h the  the monthly groundwater recharge to  however, was a v a i l a b l e  a r e summarized  Mt.  No  1981, hence  c o u l d be found  temperature,  Mountain  t o approximate  e a r t h f l o w ( T a b l e 4.4).  period  of  e v a p o t r a n s p i r a t i o n v a l u e s a r e used  water  year  are expected  Since  occurred  about  between  t o be maximum i n  the r a t e of e a r t h f l o w  motion  TABLE August  4.4.  Estimated  values  1, 1981 to June 30, 1982.  Aug Recharge  Sept  of groundwater  recharge  f o r the  period  A l l v a l u e s a r e i n mm.  Oct  Nov  Dec  Jan  Feb  Mar  Apr  May  Jun  -  15.0  -  0  21.0  from  Total  0  0  6.0  -  -  -  -  snowmelt**  —  —  —  0  0  u  0  22.0 27.0 48.7  0  97.7  T o t a l recharge  0  0  6.0  0  0  0  0  22.0 42.0 48.7  0  118.7  0  0  5  0  0  0  0  19  0  100  rainfall* Recharge  from  Percentage of annual  total  35  41  (water y e a r )  *Estimated from P a v i l i o n Mountain p r e c i p i t a t i o n f o r the p e r i o d August to October 1981 and f o r the p e r i o d A p r i l  1 to June 30, 1982.  **Estimated from snowpack v a l u e s f o r Mt. Cole f o r the p e r i o d January to June  1982.  4.4 BASIC OPERATION OF A STANDPIPE PIEZOMETER A  standpipe  observation.  piezometer  length  table  because  ( f i g u r e 4.5).  its  entire  The  s t a n d p i p e should be open the atmosphere  the p o i n t  at the top  is  head  hydraulic  h  always i t is  elevation sea  lower  from  groundwater  and  column  in  regions  C h e r r y , 1979,  unit  weight)  h  has  Hydraulic  ( i ) the  elevation  of the piezometer above the p r e s s u r e head  the  along  i s at the base.  p.  open  23).  The  multiplied  standpipe  by  the  21):  (4.2)  where  4.5):  (ii)  tube must be s e a l e d  = gh  4.6).  of the base  and  per  (figure  (figure  level),  water  occurs  The  (Freeze and C h e r r y , 1979, p.  (J  components  for  p o t e n t i a l <J> (energy per u n i t mass) which  (energy  a c c e l e r a t i o n due to g r a v i t y  where  used  of measurement, P,  (Freeze  i s the f l u i d  Flow  device  t o water f l o w only at the bottom, and  parameter measured the  simple  The apparatus i s a tube p l a c e d i n the ground w i t h i t s t i p  below the groundwater  to  is a  above  f  higher head head  to  i s the  sum  z,  which  a specified  , which point  values  P.  regions of  two  is  the  datum (e.g.  i s the h e i g h t Hydraulic  of the  head  can  t h e r e f o r e be w r i t t e n as:  h = z +  57  4»  (4.3)  T Point of measurement  .0477///, FIGURE  4.5.  piezometer  Schematic  diagram  f o r measuring h y d r a u l i c  p r e s s u r e head H* i s the h e i g h t the  d e m o n s t r a t i n g the  elevation  head  head h and  of the water  z i s the e l e v a t i o n  use  i t s two  column  of  a  standpipe  components.  The  i n the s t a n d p i p e  and  of the piezometer t i p above  the  datum (z = 0 ) .  5-1  FIGURE  4.6.  hydraulic ground  head  surface.  pressure the  Diagram  at P.  height  vertical  of  showing  i n a hillslope The Since the  the  where  use  water  s c a l e to the l e f t  in  the  on  length  piezometer  d  table  measures  the e q u i p o t e n t i a l  piezometer i s  of the diagram.  58  a  the groundwater  piezometer of P i s located  of  equal  to  measure  i s below the  the  pore  water  where h = to  2.8  on  2.8, the  The  dimension  expressed head  as  of  head  "centimeters  i s determined  piezometer  i s length  and  by  the  calculating  elevation  phreatic  water"  measuring  the h y d r a u l i c head i s the not  of  h  from  net  i s drawn  so  that  is a  are  dotted  and  the  groundwater  equation  surface  flow,  are  of  orthogonal  diagram shows t h a t flow o c c u r s from  which to  the  piezemeter  head).  (figure of water at  4.6),  If  a  piezometer  i s placed  t o the  elevation  P.  59  in  head  (figure  or 4.6)  groundwater  (lines  constant  of the  equipotential  The  flow head)  direction lines.  of The  hillslope  e l e v a t i o n s ( r e g i o n s of hillside  at p o i n t P w i l l  equal  is  pressure.  4.6.  the  then,  table,  the h i g h e l e v a t i o n s of the  the h y d r a u l i c p o t e n t i a l  to r i s e  groundwater  indicate  in a  t i p P and  in figure  ( r e g i o n s of h i g h h y d r a u l i c head) toward the lower low  level  definition,  f o r observing  lines  i t is  Hydraulic  the water  of v a r i a b l e  is illustrated  lines,  study  water."  By  The  piezometer  equipotential  flow  of  4.3.  table.  present  i s equal to atmospheric  hillslope the  "meters  p r e s s u r e at the  o p e r a t i o n of a s t a n d p i p e i n a simple  f o r the  elevation  of the groundwater  over which the p r e s s u r e head f  behavior  or  the  fluid  s u r f a c e , however,  The  [ L ] , and  to the v a l u e  to  a  cause the  depth  d  column  of h y d r a u l i c head  4.5 GROUNDWATER FLOW AND HYDRAULIC CONDUCTIVITY The  r a t e of groundwater f l o w can be found from Darcy's law:  v v = K  d  h  — dl  (4.4)  where v i s t h e flow r a t e , K i s t h e h y d r a u l i c defined two  as the h y d r a u l i c  points  of measurement  equipotential conductivity fluid  passing  by d i s t a n c e ,  through  K i s a velocity  term  the  that  i n head  (dh) between  1, measured  points.  expresses  normal to  The  the rate  through a porous medium; t h e r e f o r e  conductivity  injecting  a slug  then  used  completely that  divided  the d i f f e r e n c e  and dh/dl i s  hydraulic at which a  i t has dimensions of  ([L/T]).  The  were  lines  can t r a v e l  velocity  gradient,  conductivity,  of t h e e a r t h f l o w  of water i n t o each t o estimate  recover  piezometer.  the time  t h e head measured  the o r i g i n a l  rate  of  d e b r i s was e s t i m a t e d i n s i t u by  required prior  inflow  was  Two head measurements f o r the water  to slug  injection,  maintained.  The  l e v e l to assuming hydraulic  c o n d u c t i v i t y was then e s t i m a t e d from H v o r s l e v ' s (1951) e q u a t i o n :  K = r l n (L/R)  (4.5)  2  2LT o where L i s t h e l e n g t h intake, for  full  of t h e piezometer i n t a k e ,  r i s the r a d i u s water l e v e l  of the piezometer,  recovery.  60  In t h i s  R i s the radius  and T  q  i s t h e time  of  the  required  c a s e , the piezometer i n t a k e was  simply was  the base of the tube,  hence L was  equal to R whose v a l u e was The  i n Table  of  head  injection. slightly  4.6.  occurred  At less  concentration  boreholes  in  the  these  sites  than  the  of f i n e  i t is values  from  Pavilion  distribution  fissures  within  hydraulic  and  the  flow  material.  In that  the  period  that  listed,  perhaps  will  source  (figure also  hydraulic  and  provide  conductivity  the  greater The  range to  to  the  grain  presence  value  of  the  for  of bulk  efficient  c o n d u c t i v i t y of  tension of  a  Thus the measured  conduits bulk  no  slug  i s similar  The  the  are  where  debris.  according  affect  central  from  3.6).  i n c r e a s i n g the  area  r  conductivity i s  earthflow  reasonable  Fissures thus  f o r the  g r e a t e r than the measured v a l u e s summarized i n T a b l e  4.6  and  following  the  silty-sand deposits. seem  earthflow  to occur  the  plausible  material  conductivity.  groundwater  possible  mm,  shown were s i t e s  observation  found  earthflow  of  the  not  p a r t i c l e s w i t h i n the e a r t h f l o w  the range of v a l u e s f o r s i l t  size  1.0  cm.  The  of h y d r a u l i c c o n d u c t i v i t y v a l u e s  values  to be  r e s u l t i n g h y d r a u l i c c o n d u c t i v i t y v a l u e s from the e a r t h f l o w  summarized change  1.9  considered  zone,  then,  earthflow  the  i t is  debris  is  from  the  4.5.  PIEZOMETRIC OBSERVATIONS The  periodic  measurements  piezometers  on  pattern  groundwater  of  the e a r t h f l o w level  of  are used change  hydraulic  obtained  f o r determination at  Pavilion.  l e v e l measurements f o r the d u r a t i o n of the study  61  head  The  of  the  seasonal  absolute  water  are summarized i n Table  TABLE  4.5.  Hydraulic  c o n d u c t i v i t y values  of  the  o b t a i n e d from i n s i t u measurements.  Borehole  K (m/sec)  BH-3  1.5 x I O "  8  BH-4  1.6 x 1 0 "  8  BH-5  1.6 x 10~  7  Nl-A  1.5 x 10"  7  N2-A  2.9 x 10"°  N2-B  2.4 x 1 0 ~  8  N3-B  5.8 x 10"  8  N3-C  2.1 x  N4-A  1.1 x 10"  7  N4-B  4.1 x 1 0 "  8  N5-B  4.6 x 10  62  IO  - 8  -8  earthflow  debris  TABLE 4 . 6 .  Summary of t h e measured v a l u e s of p r e s s u r e head from the  earthflow. P r e s s u r e head Date  BH-1  (m)  BH-2  BH-3  BH-4  BH-5  BH-6  21/3/81  -  8.32  13.78  7.06  7.25  1.51  22/5/81  -  8 . 10  13.69  8.00  7.09  1.43  11/6/81  -  13.88  8.31  7.07  1.42  16/6/81  -  8 . 14  -  -  -  -  3/7/81  -  8 . 10  13.77  8.81  7.13  1.50  20/7/81  -  8 . 10  13.77  9 . 13  7.12  1.51  3/10/81  -  7.87  13.75  9.63  6.92  1.47  16/1 1/81  -  8.34  14.62  10.50  7.09  2.30  13/2/82  -  8.12  14.60  10.61  6.91  2.37  15/5/82  0.64  8.06  14.61  10.53  7.18  2.32  1/6/82  -  -  -  7.24  -  9/7/82  0.94  -  8.08  14.74  63  10.7 1  7.22  2.60  4.6.  The  piezometric fluctuations  early  October  1981  changes observed net  decrease  are  the  BH-3,  between  March  increased  steadily  by  21  3.34  d u r i n g the f i r s t  m.  and  levels  and  at  compared  BH-5,  piezometric  boreholes  BH-4  anomalous  at BH-2,  of  measured  with  BH-6.  3,  from the  For  occurred  October  The  BH-4  continuous  rise  hydraulic  the  the  latter head  this  was  piezometer  tip.  crack u n t i l the  top  case,  the  Instead,  the water l e v e l  of the  flaw.  point  water  of  would  measurement  seep  into  the  was  not  at  the  tube  through  the  i n the s t a n d p i p e became equal to the head at  Thus, the top  of the  f r a c t u r e would be  the p o i n t anomalous  likely  e x p l a n a t i o n f o r the  water  level  observed  prior  to  1981,  the b e h a v i o r  BH-5,  The  absolute  and  BH-6  figure 1981  to  4.7. July  measurements measurements  i n BH-4  of the water  of  October  l e v e l s i n BH-4  at the o t h e r changes  1981.  9,  data 1982  from from  from  h y d r a u l i c head  BH-1  BH-4  other are  are  with  measured  BH-3,  plotted  f o r the  at  BH-2,  a g a i n s t time i n  p e r i o d October  measurements were more s i m i l a r boreholes  plotted  on  f o r the  the  to  earthflow.  period  1982—the o n l y two measurements a v a i l a b l e from t h i s 64  October  sites.  when these  the  In  became more u n i f o r m  f o r the d u r a t i o n of the study are p l o t t e d The  BH-4  Assuming  T h i s i s the most  the l e v e l s observed  four  attributable  of measurement. rise  a  of h y d r a u l i c head at  seven months of the study i s probably  the  head  in  to a f r a c t u r e a l o n g a p o r t i o n of the l e n g t h of the piezometer. that  to  example, w h i l e  in  1981,  mid-March  May  site.  15  to  3, the The  July  9,  M A M J J - A S O N b 1181 FIGURE 4.7. The data the  Plot  reliable  o f the p i e z o m e t r i c  level  f l u c t u a t i o n s against  time.  from BH-2, BH-3, BH-5, and BH-6 a r e shown f o r the d u r a t i o n of  study.  October  J F M A M J T A MB2.  The data  from  p l o t t e d f o r BH-4 a r e the o n l y  the piezometer,  1981 a r e c o n s i d e r e d  standpipe.  The data  while  the data  anomalous  f o r BH-1 a r e the o n l y  site.  65  from  possibly  points  the p e r i o d  considered preceding  due t o a c r a c k  i n the  two p o i n t s measured  at t h i s  In  the  groundwater although the  period  from  fluctuations  they were out  mid-March was  similar  of phase  s m a l l peak observed at BH-2  2.5)  i n the middle  groundwater  f l o w o c c u r s through  Contrary the  level  the  which  appears  been  a  except  to be  similar  earthflow  i n the f a l l  BH-5,  and  to m i d - J u l y .  of  BH-6,  Apparently  the main f l o w , f i g u r e and BH-6  (on the west that  the e a r t h f l o w i n a w a v e - l i k e form.  An  site will  propagated  between  wave-like  trend  from t h i s  has  i n phase  the  I t can be i n f e r r e d  the marked  BH-5  1981,  BH-3,  (both on  at an upslope  "wave"  to t h i s p a t t e r n was  piezometers  BH-2,  mid-May  BH-3  ( f i g u r e 4.7).  i n groundwater until  at  of June d i d not occur at BH-5  early July  downslope  from and  lobe) u n t i l  increase  to mid-November  not be  through  the  i n c r e a s e of water  October  everywhere  3  and  (figure  propagation  of  registered earthflow.  levels i n a l l  Nobemver  4.7).  16,  There  groundwater  1981,  may  have  through  the  but the time r e s o l u t i o n of the data c o l l e c t i o n at  t h i s time d i d not permit o b s e r v a t i o n of the c h a r a c t e r of the water  level  rise. After was  November  variable  1981  the  the e a r t h f l o w .  1982  a net decrease of o n l y 4 cm was  level cm  fell  November 9 cm  16,  1981  and  February noted.  t o February  1982.  at BH-2  1982.  fluctuations  the water  after  At BH-3  and  level  February  13,  the head  decreased  At  the  BH-5  of December 1981  Between mid-February  66  groundwater  1982;  13,  from November 16 to the end  by mid-February  of  For example,  22  from  between mid-November  pattern  fell  2 cm  cm  over  16,  July  10,  water  and r o s e 5 1982,  then,  the  water  levels  The  continuous record  increased levels  12  cm  i n BH-3  also  to J u l y  10,  from BH-5  from May  13  drop  noted  1982.  cm  increased  At BH-4  on cm  15,  data  The  piezometric  and  in  surface  1981.  the  piezometric  N2-B  appears  and  October  1981  BH-6  however, the  A  and  i n the  15  and  38  30  section  and  The  The  to  the  water  are  till.  with  t i p of N2-A  67  was  level  level  entire in  head  BH-6  In  BH-6  a 5  cm  then  the  latter  in  figure  summarized  The  the  piezometer t i p by  shows t h a t  Thus, time  in  the  of  was  By  of  more water  of  the  sufficient  earthflow  summer ( f i g u r e 4.9b). a l s o r e s t i n g i n dry  lower  was  high  tip  was  drawdown  depth of N2-A  N2-A  the  t i p of N2-B  s u b s u r f a c e water l e v e l s i n the the  appears  f o r the  in  1981  cm.  ( f i g u r e 4.9b)  correlate  rise  by  lower than the  reworked  hydraulic  followed  1982.  red-brown d e b r i s , w h i l e the in  the  water  1982,  10,  of  level  November 16,  i s available  piezometers was  cm  4.7). July  increase  period  February  (figure  then  net  ( f i g u r e 4.8).  p r e v i o u s measurements made i n the 1981,  22, 10.  of Pond 3 l a t e i n summer 1981.  continue monitoring in  May  July  shallow  i t s t i p was  respectively.  1982,  1981  cross  cm,  and  continuous r e c o r d  May  41  water  l e v e l at N2-B  i n the  and  the  also increased  the  The  located  shallow level  from  cm  shows that  to  1982  between  The  was  and  no  the head i n BH-1  October 3,  to  May  14  the head i n c r e a s e d  between November  28  interval  N2-A  23  rose  ( f i g u r e 4.8)  to v e r i f y t h i s a s s e r t i o n  rose  4.9.  15  observed i n BH-4  to have been steady but period  BH-5  between May  r o s e 4 cm  head was  and  debris,  relative  to  November  16,  debris,  1  ^ 30.0-\ B H - S ^  ^  zo.o  5  m o -  No conHnuous record  %  „]  vj  o.0A  Mailable  I  -30.0,  //fl/ ///2 I5fl  //l/8Z  //2-  1/4  —r //5  -  i  FIGURE 4.8. The continuous r e c o r d s from the f l o a t - a c t i v a t e d c o n t i n u o u s water l e v e l r e c o r d e r s at BH-2, BH-4, and BH-5. No c o n t i n u o u s r e c o r d i s a v a i l a b l e from the i n t e r v a l s when the c l o c k s stopped i n the w i n t e r , but the magnitude o f the change that o c c u r r e d i n these i n t e r v a l s c o u l d be determined from the c h a r t s because an i n k t r a c e was made when a change o c c u r r e d , although the chart remained s t a t i o n a r y .  r  STRATIGRAPHY  1(0  NS-4  HI  115-6  FIGURE 4.9June 6. (f)  N6.  1981  Water l e v e l to J u l y  7,  N6-A  A/6-3  (f)  f l u c t u a t i o n s measured a t the s h a l l o w p i e z o m e t e r s i t e s  1982.  The s i t e s  are (a) N l ,  (b)  N2,  ( c ) N3,  (d),  N4,  N6-A  from  ( e ) N5,  and  N6-S  indicating  a  profound  decrease  of  the  near-surface  e l e v a t i o n between e a r l y October and mid-November During i n s t a l l a t i o n was  occurring  through  water at N3-B,  N3-C,  s i t e s was  dry  N3-A,  N3-B,  N3-C  The  and  increased  the  and  these  of N3  scarp  i n May  and  July  were g r e a t e r  water  face  downslope at N4  levels  at  than N3  groundwater  and  although  the  in  1981  1982  pond  surface.  the  grey  reworked  the  underlying  locally of  the  I t was till  noted  was  saturated  red d e b r i s was  perched surface  i n a poorly  turn,  of Pond 3 c o u l d  elevated partially  would  cause  groundwater account  two  were  located  lobe  (figure  discharge  was  water  the  be  till  t a b l e due  for  between October and The  the  (about  This  table  in  to recharge increase  of  the  f o r N3-A  that while  suggests t h a t Pond 3 i s The  red  of  rise  4.9c).  i n thickness)  lowered  elevation  drainage  through  red d e b r i s .  debris  from the  to  base of  head  in  This,  rise.  An  Pond 3  may  and  BH-4  BH-3  1981. were a l s o dry  at  of  north  m  a  at  levels in  (figure  hole  then, by  the  piezometers at N5 the  the  depression. explained,  surface  lower e l e v a t i o n of  i n t o the u n d e r l y i n g  marked  November  the  1.0  standing  the water  suggest  augering  unsaturated. drained  the base of the t r a n s l o c a t e d in  while  discharge  was The  values  groundwater t a b l e e l e v a t i o n around Pond 3 d e s p i t e the  there  ( f i g u r e 2.5).  1981,  level  1981.  i n l a t e June 1981,  central  groundwater  end  the  2.5).  In  June  1981,  abundant  at  this  site,  70  on October 3,  1981.  major d i s c h a r g e  zone  surface  from  but  i n May  runoff and  July  on  These  the  west  groundwater  1982  the  site  was  dry.  The water  indicate  l e v e l s measured i n June, October, and November 1981  groundwater  recharge.  Thus, d i s c h a r g e  on t h e west lobe were i n f i l t r a t i n g subsurface  flow regime.  and r u n o f f  the earthflow  upslope  s u r f a c e t o recharge the  T h i s , too, may p a r t i a l l y  groundwater l e v e l s observed  from  account f o r t h e r i s i n g  i n BH-5 and BH-6 l a t e i n 1981.  The i n c r e a s e  i n BH-5, however, d i d not become as marked as the water l e v e l r i s e at the o t h e r b o r e h o l e s  4.7  u n t i l February  1982 ( f i g u r e  noted  4.7).  RELATIONSHIP BETWEEN CLIMATE AND GROUNDWATER LEVELS AT PAVILION The occurred  between  4.7). BH-6  first  This  event  of  mid-May  are believed  early,  or low-elevation,  least  in  May was v e r y  snowmelt  was  recharge  probably  in  t o be  over  not f a r above  the earthflow  penetrate pulse  snowmelt  occurred  the flow  with  4.2).  Since  area.  and i t s s u r r o u n d i n g v i afissures  71  study  (figure  at BH-5 and  i n the piezometric  groundwater  the l e v e l  the e l e v a t i o n  t h e source  response.  the  recharge  from  Snowmelt up t o  1, 1981 ( f i g u r e 4.3) and r a i n f a l l  through  rapidly  peaks  and s p r i n g r a i n f a l l .  rapidly  of groundwater recharge  piezometric  These  associated  (figure  the d e b r i s s u r r o u n d i n g  during  by a peak of t h e h y d r a u l i c head  1350 m was complete by A p r i l high  rise  1981 at BH-2 and BH-3  and e a r l y J u l y .  record  at  level  and mid-June  was f o l l o w e d  between mid-June  groundwater  of the e a r l i e s t  of t h e e a r t h f l o w tension  cracks  itself,  and f i s s u r e s  In May 1981, heavy slopes  would  and enhance  rainfall  also  tend  the e f f e c t  from e a r l y snowmelt w i t h  little  to  of the  delay i n  The marked r i s e of groundwater BH-2,  BH-3,  recharge period  BH-4,  caused  May  parallel hydraulic  by  to  to  and BH-6  snowmelt  July  the  and  1981.  ground  gradient  (figure  If  be  4.7)  precipitation  from  taken  to  Mt.  till  and  range  that  groundwater  be  equal  to to  Cole  the the  of  the  Knowing  time when each  recharge  from Mt.  of  Cole,  Group r o c k s can be e s t i m a t e d by  K = v (dh/dl)"  1  =  4  ,  1  3  0  5  the  average  hydraulic  i n the  The  m  (0.136)"  4.6  element  i s that  plane.  the  Hence no  standpipes  until  of  = 2.3  1  increase  the  not  piezometers  of the h y d r a u l i c  sufficient  time  72  the  of  the  Pavilion  (4.6)  _3  transport  to  C o l e to the b o r e h o l e s i n 2.3  x 10  m/sec,  bedrock.  p i e z o m e t r i c response of  and  x 10 m/sec  resulting hydraulic conductivity,  tips  glacial  e a r t h f l o w respond  conductivity  d i s t a n c e from Mt.  i s r e a s o n a b l e f o r densely f r a c t u r e d An  Mt.  elevation  gradient  The d i s t a n c e used to e s t i m a t e the v e l o c i t y v of groundwater  the e a r t h f l o w .  the  backcalculation:  mo.  the s t a n d p i p e s i s the average  flows  surface  the o v e r l y i n g  hydraulic  the piezometers  the  the  Groundwater r e c h a r g e at  the P a v i l i o n Group r o c k s from  earthflow.  for  earthflow,  then be t r a n s p o r t e d through the P a v i l i o n Group t o the  approximate to  into  Mt.  Cole  at  groundwater  over  assumed  g r a d i e n t over the d i s t a n c e , which i s 0.136. Cole must pass  i n November 1981  probably represents  i t is  surface  can  l e v e l s observed  has  do  accounted not  head  f o r i n equation  p e n e t r a t e the can be  observed  e l a p s e d to a l l o w the  failure i n the  impulse  from  spring  snowmelt  earthflow time  and  debris  precipitation  from  below  and  l a g f o r each standpipe  in  early  equilibrate  has  summer  to  in  piezometers.  been estimated  the from  t h a t were used to e s t i m a t e  hydraulic conductivity.  lag  in  estimates  are  given  f o l l o w i n g equation  provided  Table  4.7,  by H v o r s l e v  these  flow  the The  were  into  the The  slug test  data  h y d r o s t a t i c time computed  by  the  (1951):  T = —ln(H /H)  (4.7)  D  where T i s equal  to T  equalization  a  of  pressure  surrounding  debris  variable  t  is  injection  at  injection.  time  variability  of  hydrostatic  time  rests  when  the  The  within  i n equation  Q  length and  time  lags  the  rate of  H  densely  of  the  over  i t i s the  between intake  remains  at  level  earthflow  represent debris.  data  groundwater relatively observed 1982  f o r the  level  rise  uniform.  period  mid-May  everywhere, except As  surmised  i n t h i s p e r i o d i n 1981,  are a t t r i b u t e d  to  for  the  early July BH-2  permit  1982  where the  elevated  t after  slug  to  the  shorter  piezometer more  rapid  pressure. show  level  another remained  piezometric  levels  the r i s i n g water l e v e l s e a r l y i n summer  to l o w - e l e v a t i o n snowmelt d u r i n g A p r i l  73  slug  the  p i e z o m e t r i c response to a change of the e x t e r n a l pore water The  the  The  where  would  the The  according  values.  sites This  for  time  vary  and  constant.  water  conductivity  fissured  standpipe  period  the  probably  the  time r e q u i r e d f o r  observation  i s the  hydraulic  lags  and  difference  the  t=0,  4.5  and May  1982.  TABLE  4.7  The b a s i c  hydrostatic  time  data used to e s t i m a t e the h y d r a u l i c at  lags  computed  Time l a g (days)  BH-3  92  BH-4  82  BH-5  8  Nl-A  9  Nl-B  22  N2-A  46  N2-B  57  N3-B  23  N3-C  65  N4-A  13  N4-B  33  N5-B  29  74  the s l u g  test  c o n d u c t i v i t y of the e a r t h f l o w d e b r i s  Pavilion.  Borehole  from  4.8  SUMMARY Analysis  of  the  the p e r i o d August  1981  May  1982  for  the  accounted second  from r a i n f a l l of  seasonal  to June 1982  f o r 64%  water  annual  of  year,  in April  the t o t a l  occurrence  total  while  13%  recharge  for  snowmelt i n A p r i l  and  groundwater  of  the  In the second  recharge  groundwater  i n d i c a t e d that  the  1982.  of  e s t i m a t e s was  net  recharge  recharge  estimated  was  derived  water y e a r , then, about contributed i n April  77%  and  May  1982. Correlation fluctuations were  two  of  showed  events  the  that  of  moisture  the  two  to c l i m a t e i n p u t .  July  was  1981,  attributed  over  a result  of t e n s i o n c r a c k s and  snowmelt  standpipes levels  from  spring  in  recharge  have e l a p s e d . from Mt. of  the  The  in  the  in  and  over  t r a n s p o r t e d from delay a r i s e s  from  bedrock  groundwater from the b a s a l f a i l u r e  Mt.  1981,  observed  There believed  from and  May  to  rainfall  do  As  the e a r t h f l o w s u r f a c e , the to  to  delay.  not  Cole  respond  show  until  the combination to  phase. each  snowmelt  little  apparently  of  piezometric  i t s surrounding slopes.  appear  with  the  out  event,  f i s s u r e s near  precipitation  Cole v i a fractured  rise  first  earthflow  earthflow  are  low-elevation  the e a r t h f l o w i t s e l f  levels  and  The  with  series  level  to  directly  groundwater  time  groundwater  attributable  budget  early  However, increased  about  five  the water  months  of t r a n s p o r t time  the e a r t h f l o w , slow  zone i n t o  the  upward  the p i e z o m e t e r s ,  flow  and  h y d r o s t a t i c time l a g f o r p r e s s u r e e q u a l i z a t i o n w i t h i n the s t a n d p i p e s .  75  the  levels have  from  recharge  elapsed.  from Mt.  Cole  The  transported delay  arises  from Mt.  Cole  from the  combination  v i a f r a c t u r e d bedrock to  of groundwater from the b a s a l f a i l u r e h y d r o s t a t i c time Since likely water to  that  the  corroborate  over  Mt.  through lag.  along the  the  is  of  earthflow,  a  failure  piezometer  time  slow upward  flow  from  the  i t s basal  delay  surface  the  of e a r t h f l o w movement at P a v i l i o n has  76  been d i s c u s s e d .  is  pore  be p o s s i b l e  groundwater  vertical  be examined i n the f o l l o w i n g chapter  it  increased  does r e f l e c t and  the  standpipes.  i t may  between  and  process  with  Therefore,  months  transport  moisture-dependent  plane.  response  five  zone i n t o the piezometers,  a c c e l e r a t e s synchronous  a s s e r t i o n that  earthflow  This w i l l  motion  earthflow  Cole and the  about  l a g f o r p r e s s u r e e q u a l i z a t i o n w i t h i n the  earthflow  pressures  the  until  input  travel  time  hydrostatic  time  a f t e r the c h a r a c t e r  CHAPTER 5  SLOPE MOVEMENT AT PAVILION  5.1 INTRODUCTION Bovis observed  (1980)  during  piezometric not  suggested  spring  and  that early  high summer  be  earthflow  movement  attributable  to high  l e v e l s r e s u l t i n g from snowmelt and s p r i n g r a i n f a l l .  This i s  1980;  Kelsey, amount  G i l and Kotarba,  1978) have shown t h a t of m o i s t u r e  hydrologic  data  1977;  to  the groundwater  to q u a l i f y  at that  time  Bovis'  during  the c u r r e n t  Swanston,  1977; and  flow  The  (1980) a s s e r t i o n , however,  fluctuations.  research,  on the  system.  t o i n v e s t i g a t e the r e l a t i o n s h i p  s l o p e movement and groundwater l e v e l obtained  Swanson and  (VanDine,  the r a t e of movement i s dependent  available  required  were i n s u f f i c i e n t  between  The p i e z o m e t r i c  data  on the o t h e r hand, a r e c o n s i d e r e d  be adequate f o r c o r r e l a t i o n w i t h movement. In  spatial the  may  of  unreasonable because s e v e r a l s t u d i e s o f e a r t h f l o w movement  1974,  to  rates  this  and s e a s o n a l  seasonal  data.  chapter,  displacement  movement  data  a r e examined  so that the  p a t t e r n of e a r t h f l o w motion can be a s c e r t a i n e d and  character  The l a t t e r  slope  will  of movement suggest  i s c o r r e l a t e d with  connections  between  and changes i n the e f f e c t i v e normal i  77  the p i e z o m e t r i c  the r a t e  stress.  of s l o p e  VanDine (1980, pp. data  from  These  the Drynoch e a r t h f l o w  records  concurrent and  motion then and  the  The  data  pore  maintainence  of  that  remained  sufficient  groundwater  of  month  the  pressure  flow  while  moisture  the  shear  until  the  the  basal  occurred  the groundwater l e v e l  delay  between  a  r e g i o n a l system  is  l o c a t e d upslope Swanson  and  underlying  the  acquired  to J u l y , of  debris  the  debris  with  rising  apparently  and  discharge  summer  rainfall.  earthflow acceleration  recharge  Drynoch  of  The  falling  earthflow  weight  as .a r e s u l t  be  levels  response  were  Thompson R i v e r ,  i n c r e a s e and  T h i s may  three  plane.  levels  clay-rich  from May  groundwater  e a r t h f l o w response.  June at  failure  t h a t was  i n the  August  Accelerated  to e a r t h f l o w d e c e l e r a t i o n .  increased unit stress  1960.  commenced  piezometric  r e l a t i v e to peak d i s c h a r g e i n summer suggests  five-month  regime and  high  rate u n t i l  groundwater  of  Peak d i s c h a r g e  relatively  t i m i n g of  an  Drynoch  accelerates i n direct the  the  contents  to m a i n t a i n  levels.  along  to June  u s u a l l y between December  although prior  and movement  measurement.  constant  site,  one  to snowmelt (VanDine, 1980)  i n winter to  water  therefore, retain  remained  location  at one  least  rapid  suggests  The  the  levels  show t h a t the Drynoch e a r t h f l o w  increased  due  on  1957  a c c e l e r a t i o n at  at a r e l a t i v e l y  at  p e r i o d June  of groundwater  September  fall  groundwater l e v e l  f o r the  earthflow  rise  depending  until  begun to  and,  that  continued  had  to  show  with  February,  sites  32-33) presented  to  accounted earthflow  at l e a s t a f o u r the  regional  flow  f o r by recharge whose recharge  to  area  a c o n s i d e r a b l e d i s t a n c e from Drynoch. Swanston  (1977)  78  and  Kelsey  (1978)  also  found  that  seasonally  large  displacements  of  earthflows  northern  California,  respectively,  were  moisture  contributed  seasonally  the  increased wet  flow  season.  groundwater moisture  r a t e d i d not occur  Rather, recharge  contents  resistance  to  of  i n western  caused  by  large  earthflow.  concurrent  with  sufficiently the  through  the flow  t o cause  earthflow  a  and  of  both  cases,  commencement  of the  of the wet  and r a i s e d  reduction  debris  and  amounts  In  a few days f o l l o w i n g the onset had o c c u r r e d  Oregon  of  season  the s o i l  the  shearing  subsequent  earthflow  acceleration. Crandell Lake  City,  movement  Colorado  was  variability  the f a i l u r e  regimes.  fluctations do v e r i f y  years  throughout  the moisture  neither dissipated  moisture  (1961) s t u d i e d the S l u m g u l l i o n e a r t h f l o w  f o r several  invariant  of  pressure along and  and Varnes  the  input.  plane  and  found  year,  They  the  regardless  suggested  that  rate of  the  of the  fluid  had a t t a i n e d i t s maximum p o s s i b l e v a l u e  nor i n c r e a s e d i n response Hence,  that  near  that  seasonal  i n the r a t e o f e a r t h f l o w motion a r e not u n i v e r s a l .  But they  t h a t the nature  Crandell  and  to seasonally v a r i a b l e  Varnes  of the groundwater flow  w i t h the d e b r i s c h a r a c t e r ) determines  earthflow  show  system ( i n c o n d u c t i o n  behavior.  5.2 METHOD OF OBSERVATION The through around  pattern periodic  of  earthflow  measurement  the e a r t h f l o w  perimeter  movement  at  of t h i r t y - t h r e e (locations  Pavilion stake  i n figure  was  arrays 2.2).  determined distributed This  allows  examination  of the s p a t i a l  and  temporal  variability  of movement.  Twenty-seven stake a r r a y s a l o n g the l a t e r a l to monitor  lateral  were arranged computing  as  displacements.  a strain  displacements  At  net, with (figure  pairs  of  the  gross  calculate  pegs  in  the  one  pair  strain  net.  the  y-direction  law  of  are  provided  respectively. i n Appendix  by  The  II.  a baseline for  six  dimensions  . These  data  were  (figure  5.1)  a p p l y i n g the details  of  U s u a l l y the  law  the  two  and of  data  two  values  of  without  of  an  accounted  average to  of  the  represent  were,  2.2),  direction judged  to  array.  f o r i n the two  the  net  the  displacement  situations  for  where  a  substantially  a  result  from  reasonable  i n the given  this  the c a l c u l a t e d  80  As  movement f i g u r e s .  displacement  most  (i.e.  the  that  deformation) there  could  the on be  stake p a i r s w i t h i n the s t r a i n net which  final  v a l u e s of  f o r example,  departed be  stake  of the two  however, a few  (figure  body  individual  movement between any i s not  a rigid  values i n  displacements  e a r t h f l o w does not scale  to  r e d u c t i o n method  which suggests  the  used  c o s i n e s and  computed f o r the x - d i r e c t i o n were not i d e n t i c a l move as  was  d u r i n g s u c c e s s i v e measurement p e r i o d s .  v a l u e s of movement i n the x - d i r e c t i o n  sines,  as  stakes  s u r v e y i n g tape between the s i x  Two  found  of  zones were used  f o u r wooden  serving  Each  a steel  displacement  c o u l d be  location  5.1).  measured r e p e a t e d l y by e x t e n d i n g possible  each  shear  one  with  In most cases  x - d i r e c t i o n was time  c o u l d not  taken  interval. be  done.  There At  v a l u e s of movement i n the another  so  that  respect  to  results  the  WL3 x-  the q u a n t i t y from  the  £  n_ !  >  \  . .  !  /'  ./  T  3  EARTHFLOW  j  X  SHEAR ZONE  I  /«& 3ASELINE  _^ \  / '  •  BS  0EP05IT  (STABLE)  FIGURE 5.1. Schematic diagram of the s t r a i n n e t s used at f o r m o n i t o r i n g e a r t h f l o w movement.  adjacent At  stake  some of  arrays  was  other  sites  the  believed (WR1,  to  represent  ELO,  and  ERO,  baseline stakes  became unusable f o r r e l i a b l e  of displacement  c o u l d not be  S i x of stake active  the stake  l o c a t e d on shear  the  zone  abandoned 5.1),  lateral  slump of  the  source  b l o c k s and  separation  area,  the  displacement.  2.2)  measurement  and  one  of  the  amount  four  flow  81  downslope movement had  the purpose  the  sets  from  being  flanking  a  fifth  the p r e s e n t l y  to check f o r movement  laterals. of  across tension cracks of  figure  deposits  of the b a s e l i n e r e l a t i v e to the a n c i e n t In  net  computed.  arrays monitoring  (figure  the  Pavilion  the  stakes  (figure source  were  5.2)  extended  to monitor  area.  In  between the r a t e  addition,  d i f f e r e n t i a l movement between b l o c k s o f d e b r i s was determined. Three  continuous  earthslide  network i n November 1981. figure  5.3.  recorders  were  added  t o the stake  The i n s t a l l a t i o n of the r e c o r d e r s i s shown i n  The r e c o r d e r s were  ( f i g u r e s 2.2 and 5.2), a d j a c e n t  l o c a t e d i n t h e source  area  o f WUT-4  t o WR8 on the e a s t l a t e r a l  shear zone of  the main f l o w , and between WR2 and WR3 on the east l a t e r a l  shear zone of  the west  lobe.  The r e c o r d e r s were  labelled  ESR-1,  ESR-2,  and ESR-3,  respectively.  The c l o c k s on t h e r e c o r d e r s were b a t t e r y - o p e r a t e d , and,  unfortunately,  they  temperatures  (less  stopped than  due t o exposure  -20°C).  Therefore  to the very  cold  the continuous  winter  record  from  these s i t e s i s l i m i t e d .  5.3  MOVEMENT IN THE SOURCE AREA From T a b l e blocks  of  5.1, i t can be seen  debris  a t WUT-3  (figure  displacement,  f o r example, ranged  of  Displacement  study.  stakes  B and C ( T a b l e  slump  block  extended.  WUT-4 ( f i g u r e This  suggests  5.2) was  direction  either  o f the t e n s i o n  the lower  observed  backward  crack  over  rotation which  between of  they  the  were  at the north side of  where -4.4 cm o f movement was measured. block  i s relatively  upslope b l o c k i s p r o g r e s s i n g s l o w l y downslope ( i . e .  82  Total  -0.8 cm t o 5.8 cm f o r t h e p e r i o d  i n the n e g a t i v e  5.1),  movement between  substantial.  d i s p l a c e m e n t s was a l s o observed  5.2, T a b l e that  from  5.1) r e p r e s e n t s  or c l o s u r e  Negative  that d i f f e r e n t i a l  stable  w h i l e the  retrogression).  /'1,250 Contour Interval-  5m  FIGURE 5.2. Enlargement o f t h e s o u r c e a r e a showing t h e arrangement o f the s t r a i n n e t s i n t h e upper t e n s i o n zone. The lower case l e t t e r s on the segments o f WUT-3, WR9, and WUT-4 i n d i c a t e the segment r e f e r r e d t o i n T a b l e 5.1. The i n d i v i d u a l s t a k e s a t WUT-3 and WUT-4 a r e shown by upper case l e t t e r s . The "x" n o r t h o f ESR-1 i s the peg a t t a c h e d t o t h e r e c o r d e r .  FIGURE  5.3.  Schematic  continuous e a r t h s l i d e  diagram  recorders.  84  showing  the  installation  of  the  TABLE 5.1. Movement measured i n the source a r e a . l o c a t i o n s a r e g i v e n i n f i g u r e 5.2. Displacement Array  15/5/81  *  WR9a  Not  3/7/81  3/10/81  —  —  Stake a r r a y  (cm)  16/5/82  9/7/82 12.3  Total 12.3  WR9b  —  —  —  2. 1  2. 1  WR9c  —  —  —  0.6  0.6  WR9d  —  —  —  8.2  8.2  WUT-1  -0.4  0.7  2.8  1.4  4.5  WUT-2  -0.3  0.3  8.4  0.9  9.3  WUT-3a  —  —  5.0  -0.2  4.8  WUT-3b  —  -1.0  -2.0  .0.6  -0.8  WUT-3c  —  —  6.0  -0.2  5.8  WUT-4a  —  —  -0.3  2.9  2.6  WUT-4b  —  —  -0.8  5.2  4.6  WUT-4c  —  —  -1.9  -2.5  -4.4  available.  85  1.6  —  '  The  continuous  installed  t o observe  b l o c k s a t WUT-4. was  earthslide  3.5 cm.  the r e l a t i v e  Total  From  movement  figure  ranging  (ESR-1) a d j a c e n t  displacement  between  5.4 i t can be seen After  from  this,  0.1 cm/day  T h i s d i s c r e p a n c y may be a t t r i b u t a b l e peg a t t a c h e d  (figure  5.2).  the upslope 9, 1982  t h a t no movement  occurred  t h e flow a c c e l e r a t e d w i t h  the r a t e  t o 0.5 cm/day.  During  i n t e r v a l , 5.2 cm of movement was recorded along t h e stake  the  t o WUT-4 was  movement f o r the p e r i o d May 15 t o J u l y  from May 17 t o June 4. of  recorder  the same  l i n e WUT-4A,B.  t o the l o c a t i o n s of peg WUT-4B and  t o the continuous  recorder  on t h e downslope  F o r example, the r e c o r d e r peg was l o c a t e d on the upslope  s i d e of t h e b l o c k , w h i l e stake WUT-4B was on t h e downslope s i d e . be,  then,  block  that  slumping  of the downslope  side  o f the d e b r i s  I t may slice i s  c a u s i n g a g r e a t e r r a t e of change o f d i s t a n c e between s t a k e s A and B than the r a t e of change on the upslope A (figure the  "stream"  earthflow  debris  Group r o c k s  i s slipping  over  a  Pavilion  t o the s u r f a c e  Group at t h i s  indicates location.  crops  out at WUT-4  the surface.  steep  b e l i e v e d to favor rapid displacement.  t h e exposed  springs  Pavilion  5.5), i n d i c a t i n g t h a t bedrock l i e s near  situation from  of fragmented  s i d e of the slump b l o c k .  that  bedrock  Apparently surface,  Seepage of groundwater the groundwater I f this  were  s i t u a t i o n , t h e d e b r i s probably would not be moving as r a p i d l y .  86  a  table  not the  FIGURE 5.5. greenish-grey earthflow  Photograph l o o k i n g southeast Pavilion  debris  Group  (contact  rocks  that  at WUT-4 and crop  shown by the dashed  87  out  line).  ESR-1.  from  the  Note  the  red-brown  5.4  MOVEMENT OF THE MAIN FLOW Lateral monitored 2.2).  movement of the main flow  at s i x stake  arrays  Differential  demonstrated (figure  2.2),  rates  where  on f i g u r e 2.2) was  (WR8, WR6, WL6, WL5, WL4, and ER5, f i g u r e of flow  by the r e s u l t s  (as d e f i n e d  within  this  segment  shown i n f i g u r e 5.6.  the s l o p e  angle  F o r example,  i s approximately  w i d t h i s about 225 m, the t o t a l measured displacement the study  period.  was  3.5 cm, and t h e c o r r e s p o n d i n g  only  On t h e other  width i s about 480 m. it  appears t h a t  angle  displacement The the  east  increases  recorded  continuous lateral  slope  periods the  (figure late  i s 4° and the flow  t h a t flow depth remains  constant,  the c o n t i n u i t y p r i n c i p l e .  Following  this,  to the middle t e n s i o n zone ( f i g u r e 2.2),  where  t o 12° and the flow  width  e a r t h s l i d e recorder  shear  of s t a g n a t i o n , This  ESR-2 was adjacent  zone of the main flow  periods  (figure  of very  little  i s consistent  although  with  of flow  88  The r e c o r d  or no flow.  Except f o r  uniform  the cumulative  record  d i d not i n c r e a s e  net displacement  1982.  2.2).  t o WR8 on  moved downslope i n a  t h e r a t e of motion was f a i r l y  5.6) where the v e l o c i t y  i n spring,  i s 310 m, t h e n e t  was 14.6 cm.  fashion after  record.  was 23.8 cm d u r i n g  angle  from ESR-2 ( f i g u r e 5.7) suggests t h a t the e a r t h f l o w surge-like  12° and the flow  the r a t e of motion i s a f u n c t i o n of s u r f a c e g r a d i e n t and  at WL4, which i s adjacent slope  at WR6  hand, the t o t a l movement measured at WL6  Assuming, then,  flow width i n accordance w i t h  the  are c l e a r l y  was g r e a t e r  throughout from  WR8  significantly  after  April  1,  M A  FIGURE 5.6.  M  J /90I  A  S  0  N  D  J  F  M  Cumulative movement of the main flow  A  M I1BZ  J  J  A  f o r the p e r i o d  March  21, 1981 t o J u l y 9, 1982.  3.0 -i  FIGURE 5.7.  The c o n t i n u o u s movement r e c o r d  from ESR-2 ( a d j a c e n t  f o r the p e r i o d November 16, 1981 t o J u l y 9, 1982.  89  to WR8)  The movement c a l c u l a t e d cm f o r t h e p e r i o d October continuous  record  array  are correct,  and  data  probably  1981  the stake a r r a y data from WR8 was 4.5  3, 1981 t o May 17, 1982.  accounts  occurred  from  f o r only  The t r a c e from the  2.1 cm of movement.  I f the stake  2.0 cm of movement were not r e c o r d e d  i n the i n t e r v a l  from  October  by ESR-2  3 t o November 16,  ( p r i o r t o i n s t a l l a t i o n of the continuous r e c o r d e r ) .  5.5 MOVEMENT OF THE WEST LOBE The from  highest  rate  the west l o b e .  shown i n f i g u r e  of e a r t h f l o w  The h i g h  5.8.  movement  flow v e l o c i t y  The net displacement  at P a v i l i o n  was r e c o r d e d  i s e v i d e n t from  the r e s u l t s  f o r t h e d u r a t i o n of the study  was h i g h e s t i n the most c o n s t r i c t e d p o r t i o n of t h e channel where 63.4 cm and  62.6 cm of movement were observed  5.8),  respectively.  slightly due  at WL2 and WL3  The r a t e of flow on the east l a t e r a l  lower—58.7 cm and 52.6 cm r e c o r d e d  to "dragging"  (figures  of the f l o w  around  2.2 and  shear zone was  from WR3 and WR2—apparently  the b i f u r c a t i o n  point.  The  c o n s i s t e n c y of t h e data i n f i g u r e 5.8 demonstrates t h a t a c c e l e r a t i o n and deceleration suggests  of t h e flow  (figures the flow  everywhere  t h a t the e a r t h f l o w moves as a r i g i d  Deceleration laterally  occurs  onto  of  the debris  2.2 and 5.8).  combined channel  the  effect  west  lobe  f a n i s shown  Again,  this  of t h e decreased  i f t h e depth  the same  time  which  body.  where  the  earthflow  by t h e low movement  spreads at WLO  i s b e l i e v e d t o be a t t r i b u t a b l e t o slope  i s considered 90  at  angle  and widening  to be c o n s t a n t .  of the  F o r example,  ?0-i  FIGURE 5.8.  Cummulative movement of the west  21, 1981 t o J u l y 9,  1982.  91  lobe f o r the p e r i o d  March  total  movement  displacement observation widening  recorded  a t WRO-A  a t WRO-B  (upslope  period.  channel  movement  array data  9, 1981 ( f i g u r e  accounts and  ( f i g u r e 5.9). functioning over  time.  chart  October yet  is  more  16.5 cm o f  r e c o r d from  ESR-3  from November 16, 1981 t o May 17, between  June  9 and J u l y  and  1982  9, 1982  o c c u r r e d w h i l e the r e c o r d e r c l o c k s were not  the t o t a l  displacement  was r e c o v e r e d  from t h e The  r e c o r d , o f c o u r s e , does not i n c l u d e d a t a f o r the p e r i o d  from  16, 1981 because  Data  a r e a l s o absent  p a t t e r n o f movement  consistent  with  5.9 t o complete  trace  the r e c o r d .  been i n s t a l l e d .  that  found  the continuous  shown by the c o n t i n u o u s from  around  r e c o r d from ESR-3  t h e stake a r r a y d a t a .  December 9, 1981 t o a r a t e  92  r e c o r d e r had not  from May 17 t o June 9, 1982.  the r a t e o f movement was low d u r i n g November and e a r l y increased  that  on the c h a r t , although not as a c o n t i n u o u s  Therefore  3 t o November  The  2.2) i s much  a t WR2 and WR3 between May 17  and has been i n c l u d e d i n f i g u r e  continuous  (figure  the e f f e c t of  3, 1981 and May 17, 1982 and t h a t 5.0  were r e c o r d e d  Movement t h a t  was noted  zone,  However, t h e c o n t i n u o u s  f o r 15.6 cm o f movement  2.3 cm o f movement  WL1  shear  WR2 and WR3 i n d i c a t e d  occurred  5.8).  while  1982.  o c c u r r e d between October  cm and 7.5 cm of movement July  from  27.7 cm,  f o r o n l y 4.6 cm o f movement measured a t  WLO from May 22, 1981 t o J u l y 9, stake  lateral  below  pronounced and p r o b a b l y accounts  2.2) was  o f WRO-B) was 47.0 cm f o r the e n t i r e  On the west  of t h e f l o w  The  (figure  (about  F o r example,  i n December,  and  0.05 cm/day) which  /6.0£0 MO 13.0 IZ.O  H  no  ~ 10.0  % ^  I  9.0  § 8.0  Ass—/V« continuous record  I  40 -  available  3.02.0 1.0  0.0  IIl/l ,  11/5 IZ/I  li/lS  I'/I 1/15  z}\  3/K ill  FIGURE 5.9. WR3 May  ill* 7/1 7/15 mi  t o June  from ESR-3 (between WR2 and  l o b e ) f o r the p e r i o d November 16, 1981 t o J u l y  a r e two diagrams  15  4/l 4/ff S/l $(s '  3/iS  The c o n t i n u o u s movement r e c o r d  on the west  There  Z/IS3/I  9,  because  1982, hence  accounted f o r i n the p l o t .  93  the r e c o r d e r movement  9, 1982.  was not i n t h e f i e l d  i n this  period  could  from  not be  was maintained  throughout  for  period  t h e 15-day  the s p r i n g .  i n March  There  1982.  was no movement  The next  period  recorded  of record  from  ESR-3 i n d i c a t e s t h a t the flow a c c e l e r a t e d t o 0.07 cm/day f o r one month. Arrays and  on the west  WRO-B. The c a l c u l a t e d  l i n e s are provided of  lobe h a v i n g  distance  indicates  displacement  i n Appendix I I I .  was recorded  that  five  from  the baseline  d e p o s i t s from e a r l i e r flows  stakes  figures  were WR2, WR1, WRO-A, along  t h e 1.5 and 4,5  I n each case, no s i g n i f i c a n t  the b a s e l i n e  stakes  to the f i f t h  are stable r e l a t i v e  change  peg which  to the l a t e r a l  ( f i g u r e 5.1).  5.6 MOVEMENT OF THE EAST LOBE Earthflow uniform  along  movement  on t h e west  the e n t i r e  length of the l a t e r a l  5.10 i t can be seen t h a t  the t o t a l  t o 27.8 cm a t EL2 ( f i g u r e 2.2).  the  east  (figure  branches  2.2) and movement  Maximum displacement lobe)  into  was  The shear  two segments  was monitored  along the i n t e r i o r  24.1 cm,  while  along  shear  displacement  ELI  lobe  side of the east  zone.  ranged  From  from  fairly figure  33.2 cm a t  zone on the east s i d e of  a t about  along shear  lobe was  both  882 m e l e v a t i o n  of these  segments.  zone (proximal t o the east  the e x t e r i o r  branch  movement  was  g e n e r a l l y l e s s than 4.8 cm. The  only  Unfortunately, measurements believed,  five  stake  the f i f t h from  however,  this that  stake  array became  location very  pegs. 94  on  the  loose  during  a r e probably  little  movement  east  lobe  was EL4.  t h e study  unreliable. occurred  between  so  the  Iti s these  M  A  M J  A S  J  0  N  D  7  F  M  A  M 7  7  A  I18Z  FIGURE 5.10.  Cumulative movement of t h e east  21, 1981 t o J u l y 9,  lobe f o r t h e p e r i o d  March  1982.  .7 CORRELATION OF MOVEMENT WITH GROUNDWATER HYDROLOGY The function  development o f pore  relationship pressure known.  of  water  between  groundwater  the groundwater  items  data  explanation  of  pressure f l u c t u a t i o n s  be u n d e r s t o o d , These  an  and t h a t  will  from  table  earthflow first  therefore  water  stress i s  briefly  are correlated  as a  t h a t the  and pore  of e f f e c t i v e  be reviewed  the earthflow  requires  elevation  the p r i n c i p l e  motion  b e f o r e the  with  seasonal  movement. Figure hillslope  5.11  is a  with a f a i l u r e  longitudinal plane at depth  the  groundwater  the  l o c a t i o n of the f a i l u r e  section z below  through  a  t h e ground  t a b l e i s a t h e i g h t h above the f a i l u r e  hypothetical s u r f a c e and  plane.  Hence, i f  s u r f a c e i s known, the pore water p r e s s u r e u  can be found from the e q u a t i o n :  95  FIGURE table  5.11.  A  segment  at h e i g h t h above  surface  i s z.  The  found by computing:  u =  w  surface to  an  pore water  u = T h  where T w  of  unstable  the f a i l u r e  pressure  the ground Now,  a  groundwater  the  failure  failure  plane i s  (5.1)  the h o r i z o n t a l  and 9 i s the angle of the  direction  (which i s assumed  to be  failure parallel  surface).  consider  a saturated  soil  column c o n s i s t s of two phases:  the  soil  two  above  cos26  the  At  u  with  the depth to the  h cos 8.  i s the u n i t weight of water from  hillslope  p l a n e , and  skeleton,  and  the t o t a l  ( i ) the e f f e c t i v e  96  Because  i t i s saturated,  ( i ) the s o l i d p a r t i c l e s which make up  ( i i ) the water  the base of the column, components:  column.  filling normal  normal  the i n t e r p a r t i c l e stress  stress  cT  0"  voids.  on the s o i l  has  i s the component  derived  from the  only  component  (ii)  the  i n t e r p a r t i c l e contacts  that  contributes  pore water p r e s s u r e  i n t e r p a r t i c l e voids.  to  of the  the  u i s the  shear  soil  skeleton  is  the  soil,  and  to water w i t h i n  the  strength  component  due  of  and  the  T o t a l normal s t r e s s , then, can be expressed  as:  a = c7 + u  (5.2a)  o'=  (5.2b)  /  or  If  the  total  raising  the  occurring  normal  stress  elevation  in  laterally),  the the  of  of  increase  increase i n t o t a l  in  is  clear  effective the  an  pore  s t r e s s to be  increase  water  increased, table,  with  (i.e.  the  pressure  will  In o t h e r words, the  the pore water. of  the  pore  example  no  deformation  soil  is  be  equal  by  confined to  the  i n c r e a s e i n normal  From e q u a t i o n water  reduced, thus r e d u c i n g  for  pressure  the s h e a r i n g  5.2b,  then,  causes  the  r e s i s t a n c e of  soil. The  shear s t r e n g t h  originally stress  expressed  by  of a s o i l Coulomb  at a p o i n t as  a  on  linear  a p a r t i c u l a r plane function  of  the  was  normal  tT at the same p o i n t :  s = c + cT tan  where s i s the c  is  groundwater  normal s t r e s s .  that  soil  direction  s t r e s s i s c a r r i e d e n t i r e l y by it  - u  the  the  horizontal  6  and d> are  the  shear s t r e n g t h apparent  <j>  (or s h e a r i n g  cohesion  and  the  (5.3)  r e s i s t a n c e ) of angle  of  the  shearing  soil,  and  resistance  of the soil  soil  ( C r a i g , 1978).  skeleton,  the  shear  Since  shear s t r e s s i s o n l y  strength  is  usually  resisted  expressed  in  by  terms  the of  effective stress:  a'  s = c'+  s = c'  where c' stress  and  <(>' are  (figure  5.12).  r e s i s t a n c e of a s o i l and,  the  +  tan 4'  (5.4a)  ( c T - u ) t a n (/>'  (5.4b)  shear s t r e n g t h parameters i n terms of Equations  5.4a  i s c o n t r o l l e d by  and  5.4b  show how  effective  the  the pore water p r e s s u r e  shearing  conditions  t h e r e f o r e , by the e f f e c t i v e normal s t r e s s .  O ' (kN/m ) a  FIGURE 5.12.  Sketch of  and  normal  effective  are d e f i n e d to and  by  the  stress.  the diagram.  linear The The  failure  the Mohr c i r c l e s which r e p r e s e n t are found by  laboratory testing  the shear s t r e n g t h of a s o i l ( s ) .  98  r e l a t i o n s h i p between shear shear  strength  parameters  envelope i s the  various of s o i l  s t a t e s of  strength c'  and  common tangent  s t r e s s at  failure  samples f o r d e t e r m i n a t i o n  of  The  relationship  fluctuations piezometric the  at  between  Pavilion  level  i s most  fluctuations  p i e z o m e t r i c data  earthflow easily  with  from October  motion examined  movement  data.  1981 t o May  alone  are  displacement ESR-3  insufficient  i n winter.  can be used  to  show  The continuous  to f i l l  the v o i d  groundwater  by  plotting  the  The r e s o l u t i o n of  1982 i s g r e a t e r than the  r e s o l u t i o n of the stake a r r a y data i n t h i s p e r i o d . data  and  the  Thus the stake  pattern  movement r e c o r d s  i n the p e r i o d  of  array  earthflow  from ESR-2 and  October  1981 t o May  1982.  To demonstrate movement of the main flow f o r the d u r a t i o n of the  study,  the data from WR8  curve site  (figure  5.13).  as WR8.  and ESR-2 have been merged t o form one movement  This i s v a l i d  Similarly,  movement  s i n c e ESR-2 i s l o c a t e d a t the same of the west  f i g u r e 5.14 by the merged data s e t s from WR2 Figure  5.13  shows  that  the r a t e 3,  lobe  i s represented i n  and ESR-3.  of movement  high  21, 1981 and J u l y  from  J u l y to  e a r l y October  1981, d e c e l e r a t i o n of the e a r t h f l o w i s i n d i c a t e d .  Between  flow of  occurred,  March  displacement  1982, s l i g h t  f o l l o w e d by a l e s s e r  1982.  In  was  the  period  relatively  I n the p e r i o d  was  between March  mid-November 1981 and l a t e January  1981.  at WR8  a c c e l e r a t i o n of the main  r a t e of displacement from  high,  April  however,  to  July  phases  of  until 1982 rapid  the end the net motion  o c c u r r e d a f t e r p e r i o d s of s t a g n a t i o n . At WR2, May from  displacement  15 and J u l y July  3 (figure  3 t o October  i n s p r i n g and summer 1981 was maximum between 5.14).  3,  1981. 99  The west  lobe a l s o shows d e c e l e r a t i o n  At ESR-3  (figure  5.14) the r a t e of  FIGURE 5.13. ESR-2,  Plots  piezometric  groundwater r e c h a r g e  of movement data  from  of the main f l o w  BH-2,  f o r the second  100  BH-3,  measured  and BH-4,  water y e a r .  a t WR8  and  and the estimated  100  m\ FIGURE 5.14. ESR-3,  Plot  iiez of movement  p i e z o m e t r i c data  s u r p l u s f o r the second  from  of  BH-5  water y e a r .  101  the west and  BH-6,  lobe and  measured  at WR-2  the e s t i m a t e d  and  moisture  movement  was  January  1982,  lobe  substantially followed  accelerated  u n t i l J u l y 9, The rise and  of  earthflow  the  end  levels  month  1981  1981,  and  movement  5.14),  a month.  prior  observations,  it  the  rise  is  believed the  of  the  level  recharge  piezometers the in  failure  a  1981  rate  plane  can  into  be the  rise  that  1981, of  to  late  The  west  maintained  the  in  the  72-74).  at  e l e v a t i o n by  a c c e l e r a t e d about From  these  earthflow  piezometric does  in  levels,  not  permit  r e l a t i o n s h i p between e a r t h f l o w motion that e a r t h f l o w  directly  by  flow  on  and  by  of  a c c e l e r a t i o n occurs  failure  the  a c c e l e r a t i o n and  standpipes  continuous  prominent  the  period  summer p r e c i p i t a t i o n .  pressure  102  most  levels.  of  this  The  5.13  f l u c t u a t i o n s show  earthflow  rise  the  (figures  groundwater  i s maximum i n the  explained  d i s c u s s e d i n Chapter 4 (pp.  level  a c c e l e r a t i o n of  observed  The  1981  June 1982.  groundwater  data  and  measured water  earthflow  the  of  phase l a g between e a r t h f l o w the  to  June  groundwater  change suggests  from snowmelt  and  and  In s p r i n g 1982  when the pore water p r e s s u r e of  1982  December  followed  a l s o preceded  piezometric  i n May  in  to  resolution  i n May  and  o b s e r v a t i o n of the phase l a g . and  December  l a t e March 1982.  of A p r i l  observed  acceleration  (figure  about o n e - h a l f  the  deceleration until  at  i n November  WR2/ESR-3  but  early  1982.  earthflow  spring  from  phases of a c c e l e r a t e d e a r t h f l o w motion c o r r e l a t e w e l l w i t h  5.14),  that  one  again  of p i e z o m e t r i c  records  by  greater  Since basal  result  none of slip  piezometric  the the  zone as a  hydrostatic  surface,  level  groundwater  the  from time  rise the lag  F i g u r e s 5.13 and 5.14 a l s o show t h a t the e a r t h f l o w spring and  1982 a s h o r t  snowmelt.  recharge  from  time  This areas  f o l l o w i n g groundwater  indicates  surrounding  accelerated i n  recharge  efficient  transport  the e a r t h f l o w  itself.  w i n t e r i n d i c a t e s t r a n s p o r t from Mt. Cole through  from of  rainfall  groundwater  Acceleration i n  the u n d e r l y i n g  Pavilion  Group rocks and i n t o the b a s a l f a i l u r e zone o f the e a r t h f l o w . Although (figure  the e a r t h f l o w a c c e l e r a t e d s l i g h t l y  5.13), the movement r e c o r d s  the  l a r g e groundwater  not  as g r e a t  explained recharge  by  level  as e a r t h f l o w the  to spring  between  i n the s p r i n g from snowmelt  rainfall  wets  the  the e a r t h f l o w  from  of  winter  the  effective  the e a r t h f l o w .  causes w e t t i n g  This of  normal  Delayed  and  of e f f e c t i v e  low-conductivity unchanged. in  normal  stress,  of  the  while  stress  discharge  and from  the e f f e c t i v e  earthflow  of  the e a r t h f l o w , c a u s i n g an significant Mt.  of the e a r t h f l o w from the bottom up.  portions  be  recharge  the r i s e  will  Cole i n  As a r e s u l t ,  only the h i g h e s t c o n d u c t i v i t y zones w i t h i n the e a r t h f l o w w i l l increase  may  groundwater  and delayed  the top down  overall  of  to  F o r example, p e r c o l a t i o n of s p r i n g snowmelt  o c c u r s u n i f o r m l y throughout  acceleration  recharge.  and r a i n f a l l ,  response  and December 1981 was  mechanism  groundwater l e v e l s increase  1981 t o 1982  that earthflow  between October  response  difference  from Mt. Cole i n the f a l l . and  rise  indicate  i n winter  undergo an  stress  remain  i n the  relatively  S i n c e the i n c r e a s e of e f f e c t i v e normal s t r e s s i s not uniform  the e a r t h f l o w ,  does i n response  the r a t e o f movement does not i n c r e a s e as much as i t to s p r i n g recharge.  103  The  movement  presented be  by Bovis  recognized  data  presented  in  this  (1980) ( f i g u r e 5.15).  from August  t o December  chapter  and i n the p e r i o d  therefore,  also  show  December  earthflow  with  data  The s m a l l e s t displacements can  1979 and from March t o June 1980.  Displacement was maximum between March and August 1980,  agree  1979, June and August  1979 t o March  1980.  Bovis'  a c c e l e r a t i o n i n winter  and  data,  earthflow  d e c e l e r a t i o n from l a t e summer t o the end of autumn.  5.8 FLUCTUATIONS OF EARTHFLOW MOTION IN THE HOLOCENE PERIOD There that  suggest  times  west  movement  began  at  Pavilion.  ash up t o 3.0cm i n t h i c k n e s s  side  of the east  identified  lobe  separates  earthflow  debris  events.  The d e b r i s  thickness  (figure  earthflow  volume  implication  evidence  on the e a r t h f l o w  (figure  (figure  lateral  5.16).  5.16). has  From  not  ( f i g u r e 5.17).  104  c o n s i s t i n g of  i t can  constant  from be  3.5  till  over  c u t on the (1969)  unconsolidated different t o 4.0  inferred  through  of  In the road  that  time.  by the s u p e r p o s i t i o n of a  of d e b r i s d e r i v i n g from g l a c i a l  tension scarp  BP.  three  layer  and Westgate  are associated with  this  remained  i s f u r t h e r supported  Smith  the ash ranges  a  i n a road  6,600 years  deposits  5.16) that  overlying  F o r example,  i s exposed  the ash as Mazama, which f e l l  the t e p h r a  layer  and morphologic  that the volume of moving d e b r i s has changed a t l e a s t  since  volcanic  cut  i s stratigraphic  1.0m  flow m in the This thick  the ash i n the c e n t r a l  o  im  FIGURE 5.15.  Cumulative  movement  earthflow from June (from B o v i s , 1980).  mo  measured 1978  to  at  Pavilion  August  1980  (a)  FIGURE 5.16. shear  zone  e a r t h f 1 ow  (a) Photograph of the east  debris.  of the road  lobe  (b) S c a l e  dimensions of the tephra  showing drawing  Mazama of  l a y e r and l a t e r a l  106  cut through  the west  lateral  ash i n t e r s t r a t i f i e d  the same  deposits.  photograph  with giving  FIGURE  5.17.  Photograph  of Mazama  d e b r i s d e r i v i n g from g l a c i a l  Judging (figure  the  It  BP.  lateral  Holocene  period  deposit  that  deposit  over  until  be  explained  major i c e sheet  107  Subsequent  the present  of the e a r t h f l o w by  the  small  several  10,000 y e a r s  BP.  of the  a c c u m u l a t i o n of decrease  level  was  volume  climate  tephra  p r i o r to  of t h e a s h , the volume  the a s h .  occurred  earthflow  scarp.  beneath  substantially, permitting  fluctuations  may  of the l a s t  deposition  increased  of moving d e b r i s  i s believed  retreat  of the l a t e r a l  Following  i n transport  larger  volume  the s i z e  i n the c e n t r a l t e n s i o n  with  5.16), the volume of the e a r t h f l o w was r e l a t i v e l y  6,600 years debris  from  till  ash i n t e r s t r a t i f i e d  of the  attained.  during  changes  the since  Ryder (1978), f o r  example,  suggested  material  continued  debris  that  slow  movement  at a r a t e  and the p r e v a i l i n g  of  commensurate  moisture  saturated, with  regime.  weathered  the r a t e  rock  of supply of  The i n f l u e n c e of c l i m a t e  f l u c t u a t i o n s upon landform development, however, has not been s t u d i e d i n great d e t a i l If be  i n British  Columbia.  the v a r i a t i o n of e a r t h f l o w r a t e d u r i n g the Holocene p e r i o d can  attributed  t o c l i m a t e change, the w e t t e r  p e r i o d s would  w i t h growth of the e a r t h f l o w w h i l e d r y phases would flow.  The r e a s o n i n g  periods  of h i g h  earthflow  here  i s that  piezometric  acceleration.  levels  Dry  Holocene  environment  summarized  by  environment  were conducted  to  Clague  areas period of  (1981),  of B r i t i s h  sediments  showed  that  6,200 y e a r s until of  BP.  (1981),  of southern and  local  renewed  show  early  from warm,  British  After  6,200 y e a r s  of  the  (1980).  post-glacial  vegetation.  Since  108  (Clague  analyzed  prevailed  until  BP, the m o i s t u r e  The l a t t e r  corresponds  6,000 years  piezometric  Columbia  studies  area were  dry c o n d i t i o n s  and  activity.  t o as the ' h y p s i t h e r m a l ' the L i l l o o e t  with  slumping  falling  (1976) and K i n g  during  correspond  Columbia was as warm as or warmer than  about 4,000 y e a r s BP.  modern  would  correspond w i t h low  would  favor  earthflow  by A l l e y  the c l i m a t e  i s often referred  lake  and  Clague  phases  which  phases  l e v e l s and, by i n f e r e n c e , decreased The  wet  be a s s o c i a t e d  BP,  has been Holocene According  time  i n most  present.  This  1981).  Cores  by King  (1980)  about  6,100 t o  levels  increased  t o the c o l o n i z a t i o n  s e v e r a l f l u c t u a t i o n s of  temperature expansion cooler  and p r e c i p i t a t i o n of  alpine  and w e t t e r  Neoglacial  5,800-4,900 y e a r s BP t o p r e s e n t .  glaciers,  until  intervals  have  although  present.  have  BP;  occurred,  been  In  the l a t t e r  identified  a v e r y moist  lateral  low  hypsithermal that  earthflow  deposit  volume  underlying  interval.  At t h i s  i n transport  accumulation after  BP f o r the L i l l o o e t  during  From t h i s  i t can be i n f e r r e d  date  at l e a s t  the  elevation  probably BP,  which  relatively refers  I t can be  small t o the  and d r y so  argued  the ash commenced  King  Neoglacial interval t h a t the l a r g e ,  t o a decreased  the b a s i n ( i . e . a reduced  i n the Kelowna  that  shortly  (1980) e s t i m a t e d  a r e a , and c o n t i n u e d  of the e a r t h f l o w s u r f a c e  as w e l l as a decrease  the  probably  small.  as f a r as 6,000 y e a r s  attributable  years  t o be  t o accumulate  A l a r g e p o r t i o n of the d e b r i s may have been  deposited  back  67): ( i ) 1,000  the c l i m a t e was warm  been  the end of the h y p s i t h e r m a l ,  the f i r s t  from  deposit overlying  about 4,000 y e a r s BP.  1978, p.  main  water t o the e a r t h f l o w and the volume of  have  of the l a t e r a l  about 6,100 y e a r s until  would  three  BP; and ( i i i )  a s h , then,  time,  period,  became  1976).  inferred  Mazama  the net i n p u t of m e t e o r i c  debris  (Ryder,  t o cause  gradually  phase p r e v a i l e d  area from 3,200 t o 2,000 y e a r s BP ( A l l e y , The  sufficient  the c l i m a t e  ( i i ) 3,300-2,300 years  Apparently  some  (5,800-4,900 y e a r s BP).  abandoned l a t e r a l  BP.  (i.e.  moisture  of the d e b r i s supply  Subsequent a reduced  109  r e d u c t i o n of flow  supply  after  from  upslope  r a t e of r e t r o g r e s s i v e s l u m p i n g ) .  deposits  rate) i s  4,000  years  sources i n  10 SUMMARY The  results  of the s l o p e  amount of e a r t h f l o w  displacement  From the s p a t i a l v a r i a b i l i t y of  the flow  channel  determining constant, slope of  movement  the r a t e  and  of movement i t was suggested t h a t the width  the s u r f a c e  of motion.  was s m a l l .  the flow  relatively  that  high.  i n d i c a t e t h a t the  depends on the l o c a t i o n o f measurement.  That  the v e l o c i t y was lowest  angle  observations  gradient  a r e important  i s , i f the depth  factors  i s considered  where the flow width was l a r g e and the  Higher r a t e s of movement were observed i n areas  were  most  constricted  The h i g h e s t  velocity  and  was  where  the g r a d i e n t  observed  was  i n t h e narrowest  l e n g t h of the west lobe where the s l o p e was about 10°. Comparison 5.4) w i t h  of the continuous  area  lack  of c o r r e l a t i o n  and movement region  lobes.  F o r example,  causes  area  between  i s unimportant several  of the h e a d w a l l , accelerated  loading.  area  i s more s p o r a d i c movement  at the downslope  headwall  loading  record  from  ESR-1  (figure  the r e c o r d s from ESR-2 and ESR-3 ( f i g u r e s 5.7 and 5.8) r e v e a l s  that movement i n the source The  movement  o f the d e b r i s suggests  i n determining slope  perhaps  downslope  sites  movement  from  movement  than i t i s downslope.  that  movement studies  i n the loading  have  with  At P a v i l i o n , however, the volume of d e b r i s i n p u t  i s very  small  compared  t o the amount of d e b r i s  downslope.  110  i n the  of the e a r t h f l o w  l a r g e - s c a l e slumping commensurate  source  shown  that  of d e b r i s ,  the r a t e  of  i n the source  already  i n motion  Correlation the  earthflow  the  failure  to the  of the p i e z o m e t r i c  data  with  movement  i s s e n s i t i v e t o the p r e v a i l i n g h y d r o s t a t i c  zone.  The r e s u l t s , then, show that  changes of the e f f e c t i v e s t r e s s i n the f a i l u r e amount  has shown  of s u r p l u s  moisture  system.  Ill  that  that  conditions i n  the e a r t h f l o w  responds  zone as determined by  i s recharged  to  the  groundwater  CHAPTER 6  CONCLUSION  6.1 SUMMARY A n a l y s i s of the c l i m a t e input  record  i n d i c a t e d t h a t most of the c l i m a t i c  t o the groundwater system a t P a v i l i o n i s d e r i v e d from snowmelt and  rainfall  i n the s p r i n g and e a r l y summer.  In the p e r i o d  from August 1981  to June 1982 64% of the groundwater recharge was c o n t r i b u t e d in  April  and May  by snowmelt  1982, and 13% of the recharge was due t o r a i n f a l l i n  April. The  piezometric  record  groundwater l e v e l r i s e apparent  climate  was  input.  surrounding by  caused  by  The f i r s t  surrounding  July.  early,  the source a r e a .  abundant r a i n f a l l slopes.  the e a r t h f l o w  showed  two phases of  i n 1981, both of which were out of phase w i t h the  between mid-May and e a r l y head  from  or  of these was a s m a l l It i s believed  that  low-elevation,  snowmelt  The e f f e c t  i n May d i r e c t l y Recharge  pulse  was probably  on the e a r t h f l o w  from  these  sources  this  increase i n from  slopes  enhanced  i n 1981  itself  f r a c t u r e d d e b r i s i n the source area  surrounding  are believed  which  112  t o have  and on the  can occur  because of the d i s t u r b e d , slopes  observed  undergone  quickly  and on the  retrogressive  failure.  The presence  increase permit  o f f r a c t u r e s i n the e a r t h f l o w d e b r i s can g r e a t l y  the h y d r a u l i c  c o n d u c t i v i t y of  r a p i d groundwater recharge The  October  second  phase  of  through  expected  recharge  derived  from  precipitation  gradient.  This  precipitation  d u r i n g May  and J u l y  travel the  response  time  range  groundwater i n t o  by  snowmelt  of  pulse,  recharge The  pore  the  the s t a n d p i p e s  water  1981.  earthflow  i n spring,  which i s  snowmelt because of a probably  The f i v e  input  enhanced  month d e l a y  and  a t Mt. C o l e to  from the b a s a l s l i p  upward  i n the f a i l u r e  zone  between t o the  passage  plane.  by  t o flow t o of  The movement  i n w i n t e r which undoubtedly  pressure  s l o p e movement  groundwater  failure  between  from  was  caused  the delayed  from Mt. C o l e .  i n 1981.  the f i r s t  late  t o o , was  record  f o r the p e r i o d October  7, 1982 showed t h a t the r a t e of displacement found  occurred  groundwater recharge i s a t t r i b u t e d  show e a r t h f l o w a c c e l e r a t i o n  the h i g h  rise  the e a r l i e r  r e q u i r e d f o r the groundwater  elevation  data  and a c t u a l  level  T h i s event was a t t r i b u t e d , i n p a r t , t o  t o be g r e a t e r i n volume than  piezometer  and, t h e r e f o r e ,  the d e b r i s .  piezometric  3 and November 15, 1981.  groundwater  the m a t e r i a l  This  recharge  observation  i n the second  water y e a r , which would zone  t o be  less  than  may  decreased  indicate  water year  was  cause the pore  i n the p r e v i o u s  that lower  from  the v a l u e s  the volume than  of  i t was i n  water p r e s s u r e s i n the year.  c o r r e l a t i o n of the movement data w i t h p i e z o m e t r i c l e v e l  113  3, 1981 t o J u l y  In  addition,  change  indicated  that  the  stress that  on  earthflow  is  the b a s a l  slip  temporal  sensitive  to  plane.  variability  of  changes  From these  earthflow  of  the  results,  movement  i t can  rate  the p r e v a i l i n g h y d r a u l i c c o n d i t i o n s w i t h i n the b a s a l are a f f e c t e d by the c l i m a t e regime and The  observed  spatial on  were  obtained  most  east  and  constant,  from  west  lobes.  an  increase  unchanged w i l l of  the  and  flow  result  width  depth  are  the  input  that  the  the  If of  depth  the  the  constant.  of  surficial  earthflow  i n the  gradient  data  source  area  EARTHFLOW MOTION IN THE Observations the  Thompson  character British 1980) from  of  INTERIOR PLATEAU  from P a v i l i o n  River  may  allow  earthflow-type  Columbia.  A  motion  the  four-year  does not  December  December.  to  This  August, trend  and  i s nearly  114  values of  the  considered  the  width  is  an  increase  i f the  gradient  area  affect  indicated  the  pattern  from Drynoch e a r t h f l o w  record  was  identical  about  Interior  occurred  movement  the  shear zones.  and  the  movement  shows t h a t maximum displacement  source  generalizations in  on  •  earthflow  some  is  Similarly,  decelerate,  from  recharge.  portions  while  by  zone, which  depends  earthflow  of motion observed downslope along the l a t e r a l  6.2  failure  steepest  the  to  surmised  g r e a t e s t movement  acceleration.  Movement  of d e b r i s  The  normal  i s determined  displacement  c o n s t r i c t e d and  i n earthflow  causes  of  earthflow.  the  be  r e s u l t i n g groundwater  variability  l o c a t i o n of measurement  effective  Plateau  from  at  the  from  pattern  seasonal region  Drynoch  a fairly  minimum to  the  of  (VanDine,  uniform  rate  September of  on  to  movement  observed  at P a v i l i o n  i n 1981  and  1982.  Since  e a r t h f l o w a c c e l e r a t i o n o c c u r s from i n c r e a s e d basal  failure  zone,  the  earthflows  at  i t has  been  shown  pore water p r e s s u r e s i n the  Pavilion  and  Drynoch  adequate m o i s t u r e i n December to cause e a r t h f l o w a c c e l e r a t i o n and the m o i s t u r e s u r p l u s remains adequate at l e a s t u n t i l The groundwater usually  rose  remained rise  that  data from Drynoch show t h a t  receive  i n winter,  July.  the p i e z o m e t r i c  levels  from December t o F e b r u a r y to a peak where the water  unchanged  until  of groundwater  to d i s c h a r g e  about  levels  from snowmelt  April.  This  between May  was  followed  and June, a p p a r e n t l y  as i n d i c a t e d  by  level  a second  i n response  by hydrographs f o r the Thompson  R i v e r over the same time p e r i o d  as the groundwater and movement r e c o r d s .  The  June,  period  from  e l e v a t i o n was acceleration  December  maximum and  to this  then,  correlates  of the Drynoch e a r t h f l o w .  was  when  very w e l l  the  with  This i s s i m i l a r  groundwater  the t i m i n g  of  to o b s e r v a t i o n s  made at P a v i l i o n d u r i n g the present s t u d y . Transposing Pavilion occur  conclusions  i n w i n t e r at Drynoch may the  levels  in  impulse  drawn  t o Drynoch, i t appears t h a t  during  preceding winter,  from  spring  therefore,  spring  system u n d e r l y i n g beyond  the  and  from  the r i s i n g  be the r e s u l t and  the  summer.  probably  observations  groundwater  made at  levels  of maximum annual r e c h a r g e The  increased  represent  the  groundwater  passage  summer r e c h a r g e through a r e g i o n a l  of  of the e a r t h f l o w  115  itself.  The  the  groundwater  the Drynoch s l i d e , whose r e c h a r g e area i s l o c a t e d  the maximum e x t e n t  that  well  secondary peak  of  groundwater  initial the  e l e v a t i o n recorded  response  earthflow,  t o recharge  which would  show up as a p i e z o m e t r i c From  the  fluctuations, River,  trends  from  that  same as the behavior is  expected  that  pass  other  and June  snowmelt  quickly  over  at Drynoch  the s l o p e s  t o the b a s a l  i s the  surrounding  failure  zone and  level r i s e shortly following input. of  the  movement  and from  the b e h a v i o r  observed  a l s o behave s i m i l a r l y  .3  from  Drynoch,  i t appears  i n May  data  to P a v i l i o n  groundwater  the hydrographs of Drynoch  at P a v i l i o n .  earthflows  and  f o r the Thompson  earthflow  If this  level  i s much the  i s the c a s e , then i t  i n the I n t e r i o r  Plateau  r e g i o n would  earthflow.  FUTURE WORK AT PAVILION As be the  a result  useful  t o monitor  regional  present  of annual  climate  study.  A  groundwater  recharge  investigate  annual  addition,  the groundwater  f o r a longer record  of  of f i v e changes  i t might  groundwater l e v e l  both  climate v a r i a b i l i t y  be  duration  groundwater  i n the r e g i o n , i t would  levels than  i n t h e e a r t h f l o w and was  f l u c t u a t i o n s and  or t e n y e a r s . d u r a t i o n i n the b e h a v i o r  possible  to  possible  would  of these  determine  f o r the estimated  allow  one t o  parameters.  the v e r t i c a l  range  In of  f l u c t u a t i o n s i n the e a r t h f l o w .  An i n v e s t i g a t i o n of the c h a r a c t e r i s t i c s of the b a s a l r e g i o n of the earthflow answers research,  at s e v e r a l l o c a t i o n s on the e a r t h f l o w to  many  questions  remain u n s o l v e d .  which, First,  116  within  the  would scope  certainly  provide  of  the  present  the depth t o the b a s a l  slip  surface  could  be found,  thickness.  I t would a l s o  the d e b r i s w i t h allow  the pore  earthflow  together  their  changes  t h e s i s suggest  the degree  of v a r i a b i l i t y  of e a r t h f l o w  be d e s i r a b l e to p l a c e s e v e r a l piezometers i n l o c a t e d along the f a i l u r e  water p r e s s u r e  movement;  groundwater  tips  with  t o be monitored  perhaps  one  and e a r t h f l o w  t h a t the pore  would  find  response.  water p r e s s u r e  zone c o r r e l a t e r e a s o n a b l y w e l l w i t h movement.  117  plane.  and l a t e r less  T h i s would  correlated  delay  between  The c o n c l u s i o n s fluctuations  of  with the this  i n the f a i l u r e  BIBLIOGRAPHY  Alley,  N.F.,  dated  1976,  core  Columbia: Armstrong,  The p a l y n o l o g y and p a l e o c l i m a t i c  of  Holocene  76:  Valley,  J.E., C r a n d e l l , Columbia  D.R.,  southern  British  1131-1144.  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P r e t o , V.A.,  Osatenko,  Isotopic  dates  volcanic  and  J.M.,  1976,  J.M.,  Terrain  area. of  inventory  Geomorphology  and  and  ratios  for  Nicola  Belt,  1979,  plutonic  and  southcentral  1658-1672.  Quaternary  and  the  Reports of the L i l l o o e t  1, I n t r o d u c t i o n and Mus.  isotopic Trough  R.L.,  geology,  Ashcroft,  G e o l . Survey of Canada, Paper 74-49, 17 p.  1978,  Lillooet Nat.  strontium  and Armstrong,  Can. J o u r . E a r t h S c i . , 16:  B r i t i s h Columbia: Ryder,  M c M i l l a n , W.J.,  r o c k s i n the Quesnel  B r i t i s h Columbia: Ryder,  M.J.,  Man  Setting: Mercury  Quaternary  Archaelogical  i n S t r y d , A.H.  Ser.  history  of  Project.  and Lawhead, S.  A r c h a e o l . Surv.  Canada,  the No.  (eds.),  Paper  73:  56-67. Shannon,  K.R.,  Ashcroft,  1981, British  The  Cache  Columbia:  of Canada, Paper 81-lA: Smith,  D.G.W. and  L e t t e r s , 5:  the  and  J.A.,  pyroclastic  1969,  Electron  deposits:  Swanston, D.N.,  western  T r e t t i n , H.P.,  Cascade  Creek:  1977,  Range,  British  Resources, B u l l . 44, 109  and 176:  1978,  Krizek,  Academy  geology,  G e o l . Survey  and  technique f o r Planetary  Complex mass-movement  Sci.  Oregon:  Geol.  Soc.  Am.,  terrains Boulder,  113-124.  1961, Geology of the F r a s e r R i v e r V a l l e y between  B i g Bar  Varnes, D.J.,  A,  probe  Earth  C o l o r a d o , Reviews i n E n g i n e e r i n g Geology, 3:  and  contiguous  313-319.  Swanson, F . J . and in  Group  217-221.  Westgate,  characterizing  Creek  C u r r e n t Research, P a r t  R.J.  Columbia  Dept.  of Mines  and  Lillooet Petroleum  p.  Slope movement types and p r o c e s s e s : (eds.), Landslides,  of S c i e n c e s , T r a n s p o r t a t i o n  11-33.  121  analysis Research  and  Schuster,  control,  Board,  R.L.  National  Special  Report  VanDine,  D.F.,  Drynoch  1974,  Geotechnical  Landslide,  B.C.:  and  geological  [Unpublished  engineering  M.Sc.  study  thesis],  of  Queens  U n i v e r s i t y , K i n g s t o n , O n t a r i o , 123 p. VanDine,  D.F.,  1980,  Engineering  Drynoch L a n d s l i d e , B r i t i s h  geology  Columbia:  and  Geol.  geotechnical  study  Survey of Canada,  of  Paper  79-31, 34 p. W i l l i a m s , R.E.  and F a r v o l d e n , R.N.,  movement of groundwater  1967, The i n f l u e n c e of j o i n t s  through g l a c i a l  till:  Jour,  on the  of H y d r o l . ,  5:  163-170. Yatsu,  E.,  A, 49:  1967,  Some problems on mass movements:  396-401.  122  Geog. A n n a l e r ,  Ser.  APPENDIX I ATTERBERG LIMITS:  TEST PROCEDURE AND RESULTS  123  TEST PROCEDURE  The  Atterberg  consistency  c o n j u n c t i o n w i t h the mechanical for  identification  tests  fraction  of the s o i l  The  test  results  at  varying  p a s s i n g through  are  index.  used,  in  general,  soil.  a no.  the  The  liquid  A l l of these  consistency  limit,  soil  limit on the  40 s i e v e ( l e s s than 0.42  the e n g i n e e r i n g b e h a v i o r  the  limits  that  plastic  characteristics  limit,  in  curves  The A t t e r b e r g  by Lambe, 1951, pp. 22-28) a r e performed  contents.  used  plasticity  of a  a l l o w one t o e s t i m a t e  water  are  a n a l y s i s or g r a i n - s i z e d i s t r i b u t i o n  and c l a s s i f i c a t i o n  (described i n d e t a i l  frequently  limits  mm).  of a  soil  are  most  and  are affected  the  by the  amount of c l a y p r e s e n t i n the s o i l , as w e l l as the type of c l a y . The becomes  liquid liquid  limit when  i s the m o i s t u r e  agitated,  thus,  content the wetter  (%) above which the m i x t u r e ,  a g i t a t i o n r e q u i r e d t o cause i t t o flow as a v i s c o u s m a t e r i a l . limit,  on the other  soil-water  mixture  the n u m e r i c a l the s o i l .  the c l a y  behaves  difference  i s the minimum water content as a p l a s t i c  solid.  between the l i q u i d  limit  behaves as a p l a s t i c  content  the c l a y c o n t e n t  of a s o i l  solid.  the  The  less  plastic  (%) at which the  The p l a s t i c i t y  index i s  and the p l a s t i c  l i m i t of  I t , t h e r e f o r e , r e p r e s e n t s the range of m o i s t u r e  which the s o i l as  hand,  the s o i l  The p l a s t i c i t y  contents w i t h i n index i n c r e a s e s  i n c r e a s e d , and, c o n v e r s e l y , i t decreases  decreases.  124  as  The  results  samples of the  of  the  earthflow  are  c o n s i s t e n t and  the  laboratory  are  Atterberg  d e b r i s are  therefore  procedure.  125  limit  tests  summarized  considered  performed  i n Table  on  AI.l.  r e l i a b l e within  the  several  The  values  limits  of  TABLE A I . l .  The  results  of A t t e r b e r g  limit  tests  performed  on s e v e r a l  samples of the e a r t h f l o w d e b r i s .  Sample No.  Depth  (cm)  Description  LL(%)  PL(%)  PI(%)  DEM-81-5a  70  fine-grained, redbrown  34.2  24.5  9.7  -5b  80  fine-grained, redbrown  43.4  25.7  17.7  -5c  120  fine-grained, redbrown  38.2  25.4  12.8  -5d  140  fine-grained, redbrown  39. 1  22.6  16.5  -5f  65  fine-grained, redbrown  55. 1  -5g  110  fine-grained, redbrown  50.6  28.3  26.2  -6a  70  reworked t i l l , grey, coarse-grained  23.9  15.4  8.5  -6b  120  reworked t i l l , grey coarse-grained  27.7  19.6  8. 1  -6c  160  reworked t i l l , grey, coarse-grained  25.3  15.9  9.4  -6d  8  reworked t i l l , grey, coarse-grained  28.5  19. 1  9.4  -6e  140  reworked t i l l , grey, coarse-grained  21.2  16.2  5.0  -7b  100  reworked t i l l , grey, coarse-grained  23.7  19.3  4.4  -7c  145  reworked t i l l mixed 24.6 w i t h red-brown, fine-grained debris, near c o n t a c t  19.9  4.7  -7d  160  f i n e , red-brown mixed 31.6 w i t h reworked t i l l  2 1.6  10.0  -8a  65  organic-rich till  26.3  8.6  -8b  85  reworked t i l l , sandy m a t r i x  -8c  130  * No data a v a i l a b l e . 126  reworked 34.9  —  grey,  33.8  25.4  8.4  reworked t i l l , grey, somewhat c l a y e y  36.3  24.3  12.0  TABLE A I . l .  (continued)  Sample no.  Depth  (cm)  Description  Li.m  PL(%)  PI(%)  34.6  30.4  4.2  DEM-8l-8d  165  -8e  90  very s t i f f f i n e g r a i n e d , red-brown  45.0  24.6  10.4  -8f  145  very s t i f f f i n e g r a i n e d , red-brown  43.8  24.6  19.2  -8g  240  very s t i f f f i n e g r a i n e d , red-brown  46.0  25.9  20. 1  -10a  65  reworked t i l l w i t h o r g a n i c s mixed i n  29.4  20.4  9.0  -10b  130  reworked t i l l mixed with' red-brown d e b r i s  25.9  18. 1  7.8  -10c  65  reworked t i l l , stoney  28.9  19.4  9.5  -lOd  155  sandy red-brown d e b r i s  32.2  18.8  13.4  -1 l a  65  stony grey, c l a y - r i c h  30.6  26.3  13.4  -lib  65  c o a r s e , grey, has c l a y - r i c h matrix  44.5  28.2  16.3  -13b  100  c o a r s e , grey mixed w i t h 34.2 f i n e , red-brown d e b r i s  20.0  14.2  -13c  140  c o a r s e , grey mixed w i t h 20.6 f i n e , red-brown d e b r i s  16.5  4. 1  -14a  65  sandy, o r g a n i c - r i c h reworked t i l l  23.2  17.0  6.2  -14b  150  sandy, o r g a n i c - r i c h reworked t i l l  20.2  17.3  8.9  -16a  65  red-brown, f i n e g r a i n e d mixed w i t h organic debris  54.3  32.2  22. 1  -16b  105  red-brown, grained  45.4  27.4  18.0  -16c  130  red-brown grained  47.6  28.7  18.9  reworked t i l l , gravelly  127  grey,  grey,  finefine-  APPENDIX I I REDUCTION OF SLOPE MOVEMENT DATA  128  REDUCTION OF SLOPE MOVEMENT DATA  Each AII.l.  At  (figure  each  AII.l)  triangles of  four-stake  was  array  site,  s e t up  the d i s t a n c e  measured  using  i n the manner  between  a steel  r e s u l t whose l e n g t h on a l l s i d e s  the c o s i n e  law, each t r i a n g l e was used  movement i n the x - d i r e c t i o n i n the y - d i r e c t i o n As  was  and the s i n e  shown  s i x possible  surveying i s known.  tape.  in  stake Two  figure pairs oblique  With t h e a p p l i c a t i o n  to c a l c u l a t e  the net downslope  law was used t o f i n d displacement  f o r a g i v e n time i n t e r v a l .  an example, the procedure f o r c a l c u l a t i n g  Ax  will  the  d i s t a n c e x, i s c a l c u l a t e d  be shown f o r the t r i a n g l e  1-2-4  the change i n d i s t a n c e ,  shown i n f i g u r e  i n the f o l l o w i n g  All.2.  First,  manner:  (All.1) 2  and  S i m i l a r l y , x~ i s c a l c u l a t e d  a  l  c  l  x^= a^ cos  .  (All.2)  by:  (All.3)  and  X 2 = a 2 cos /2>z  129  (All.4)  \  EARTHFLOW  I  v  i 'WFWI  20A/£  4 FIGURE A I I . l . Sketch of a f o u r - s t a k e a r r a y at P a v i l i o n showing the s i x p o s s i b l e d i s t a n c e s that were measured at each stake a r r a y .  FIGURE A l l . 2 . displacement  Diagram showing the v a r i a b l e s used to c a l c u l a t e e a r t h f l o w from the stake a r r a y measurements.  130  From  equations  All. 2  and  All. 4  the  change  in  distance,  Ax  can  be  computed:  A: A  similar  process  x^ - X2  to f i n d Ax'  i s used  (All.5)  f o r the 1-3-4  triangle  shown i n  f i g u r e A l l . 2 w i t h l e n g t h s on a l l s i d e s b e i n g l a b e l l e d a', b', and c'. Ideally, A a  certain  manual is  time  field  likely  expansion from  equal,  and  the  displacement Once ^  duration,  however  this  was  rarely  the case.  measurements were assumed to be w i t h i n 1.0 mm  that  season  x and Z A X ' f o r a g i v e n stake a r r a y would be i d e n t i c a l f o r  the e r r o r  was  contraction  of  greater, the s t e e l  perhaps tape  due  S i n c e the v a l u e of Ax  to season. arithmetic  mean  was  as  considered  a  Although  of accuracy i t  result  of  t o temperature  and  Ax'  thermal changes  were not always  to  represent  of  the  the  net  f o r a g i v e n time i n t e r v a l . and  were  known,  computation  y-componenf  of  movement was done by u s i n g :  y^ = a^ s i n  (All.6)  y2 = a2 s i n  (All.7)  Hence,  Ay  = Iy  131  x  - y  2  (All.8)  In was  general,  the  l e s s than 5.0  value mm,  of  /\y  was  indicating  very  small.  For  t h a t the m a j o r i t y  the x - d i r e c t i o n .  132  most of  the  sites i t  of movement o c c u r r e d  in  APPENDIX I I I PERIODIC AND TOTAL  DISPLACEMENTS  CALCULATED FOR PAVILION  133  TABLE A I I I . l .  Movement i n the x - d i r e c t i o n  along the l a t e r a l  shear  ARRAY  zones.  15/5/81  calculated  f o r the stake  arrays  A l l values are i n centimeters.  3/7/81  3/10/81  16/5/82  9/7/82  Total  WR$  4.4  4.8  5.1  8.2  1.3  23.8  WR8  5.2  4.5  3.5  4.5  1.0  18.7  WL6  0.5  0.2  0.4  0.6  1.8  3.5  WL5  1. 1  1.3  1.0  2.5  0.8  6.7  WL4  3.1  1.2  1.9  7.3  1. 1  14.6  ER5  0.9  1.7  4.2  2.3  0.8  15.5  WL3  1 1.9  13.9  13.2  8.7  14.9  62.6  WL2  11.2  12.3  15. 1  18.8  6.0  63.4  —  9.5  11.3  2.2  23.0  —  —  —  —  4.6  4.6  WRO-B  3.4  3.1  4.7  9.0  2.5  22.7  WRO-A  7.1  9.6  1 1.0  14.7  4.6  47.0  WR1  8.0  11.7  —  19.7  WR2  9.3  12.0  11.3  18.4  5.2  56.2  WR3  12.3  10.5  12.6  16.0  7.3  58.7  EL4  8.8  14.6  —  4.8  2.3  30.5  EL3  9.8  8.2  4.2  6.3  2.4  30.9  EL2  8.8  7.8  3.5  5.6  2. 1  27.8  ELI  8.6  9.0  6.4  5.8  3.4  33.2  ELO  9.5  8.4  5.0  —  —  22.9  ER4  6.0  3.6  0.2  4.9  0.8  15.5  ER3  7.5  5.5  3.3  5.2  1.5  23.6  ER2a  1.8  1.4  0.4  1. 1  0. 1  4.8  ER2b  5.0  4.7  3.1  3.5  1.4  17.7  ER1  7.3  5.5  4.1  5.2  2.0  24. 1  ER20  0.4  0.4  0.3  —  2.0  3.1  ER21  0.7  1.0  0.5  1.7  0.2  4.1  ER22  —  0.6  1.4  1.4  0.6  4.0  *  WL1 WLO  No d a t a  available. 134  —  —  TABLE A I I I . 2 .  Movement i n the y - d i r e c t i o n c a l c u l a t e d  measurements.  A l l values are i n centimeters.  ARRAY WR9a WR9b WR9c WR9d  15/5/81  3/7/81  3/10/81  16/5/82  —  —  —  —  —  —  —  —  —  —  —  —  from the stake  9/7/82  array  Total  1.7 1.0 0.5 2.5  1.7 1.0 0.5 2.5  WR8  1.3  1.2  0.3  1.3  0.2  4.3  WR6  1.0  1.8  2.3  1.8  0.8  7.7  WL6  0. 1  0.3  1.6  0.5  0.3  2.8  WL5  1.5  0.4  0.1  0.8  1.2  4.0  WL4  0.2  0.3  0.8  0.4  0. 1  1.8  ER5  1.1  0.4  2.3  1.2  3.3  8.3  WL3  0.4  1.0  0.3  0.2  1.5  3.4  WL2  0.8  1.2  2.5  1.6  0.5  6.1  WL1  —  —  0.8  0.4  0.8  2.0  WLO  —  —  —  —  3.6  3.6  WRO-B  0.2  0.2  1.1  0.3  0. 1  1.9  WRO-A  0.4  0.8  0.8  0.1  0.0  2.1  WR1  0.9  0.7  —  —  —  WR2  0.7  0.7  0.8  1.7  0.2  3.1  WR3  2.0  0.8  1. 1  3.2  1. 1  8.2  EL4  0.8  0.7  —  0.5  0.3  2.3  EL3  0.4  0. 1  0.9  0.4  0.3  2. 1  EL2  0.3  0.3  0.5  0.7  0.3  2.1  EL 1  3.4  3.4  1. 1  0.4  0.4  8.7  ELO  0.6  0.4  1.9  —  —  2.9  ER4  0.9  0.9  0.3  0.9  0. 1  2.8  ER3  1.3  0.3  1.0  1.0  0. 1  3.7  ER2a  0.7  0.9  1.0  0.3  0.1  3.0  ER2b  0. 1  0.3  0.1  0.4  0.3  1.2  ER1  0.4  0.7  0.9  0.6  0. 1  2.7  ER20  0.3  0.2  0.4  —  0.9  1.8  ER21  0.2  0.2  0.4  0. 1  0.2  1. 1  ER22  —  0. 1  0.6  0.4  0.2  1.3  135  1.6  TABLE A I I I . 3 . stake a r r a y s .  Movement  between the 1,5  and 4,5  stake p a i r  at the  five-  Values are i n c e n t i m e t e r s .  ARRAY  15/5/81  3/7/81  WRO-B 1,5 4,5  -0.1 0. 1  0.0 -0.4  WRO-A 1,5 4,5  -0.9 -0.5  -0.3 -0.9  16/5/82  9/7/82  Total  0.4 0.5  -0.7 -0.5  -0.2 0.2  -0.6 -0. 1  0.7 1.1  -0.1 -0.6  0.7 0.2  0.0 -0.7  3/10/81  WR1 1,5 4,5  0.0 0. 1  1,5 4,5  -0.1 0.2  1,5 4,5  1.3 0.5  1,5 4,5  -0.4 -0.8  0.0 0.0  -0.5  —  —  -0.5 0. 1  WR2 -0.4 -0.6  0.9 0.2  -0. 1 -0.4  0. 1 -0.5  0.9 -0. 1  2.0 -0.4  0.2 0.0  4.5 -0.5  0. 1 0.3  -0.4 1.5  1.0 1 .6  0.3 2.6  —  -0.6 -0.6  WL6  EL4 —  OLD  LATERAL 0EPOS/T  STABLE UNSTABLE  FIGURE A I I I . l . The  Diagram of s t a k e s  1, 4, and 5 i n the f i v e - s t a k e  diagram shows the n e g a t i v e components of motion.  136  arrays.  TABLE  AIII.4.  Measured  stake p a i r s i t u a t e d ARRAY  displacement  ( i n centimeters)  on the u n s t a b l e e a r t h f l o w  15/5/81  WR8  0.2  WR6  -0.3  3/7/81 -0.5 0. 1  3/10/81  between  the 2,3  debris.  16/5/82  9/7/82  Total  0.6  0.0  0.0  0.3  -0.7  -4.8  -0.2  -4.1  WL6  0. 1  -0.3  0.7  -0.6  -0. 1  -0.2  WL5  0.0  -0. 1  0. 1  -0.5  0. 1  -0.4  WL4  0. 1  -0. 1  -0.5  0.3  -0. 1  0. 1  ER5  -0.5  0.2  -2.8  -0.9  0.6  -3.4  WL3  0.0  0.2  0.6  -1.8  0.2  -0.8  WL2  0.0  -0.7  1.6  -1.2  0. 1  -0.2  WL1  -1.5  0.3  -0.5  -2.5  WLO  —  —  —  WRO-B  0.2  WRO-A  -0.5  0. 1  WR1  -0. 1  WR2  —  -0. 1  -4.3  -0.8  -0.8  0.4  -0.6  0. 1  -0.2  -0.2  -0.4  0.1  -1.0  0.0  0.4  -0.5  —  -0.2  0.3  -0.6  -0.4  -0.1  0.0  -0.8  WR3  -0.6  0.3  0.5  -0.9  -0.3  -1.0  EL4  -0.9  —  0. 1  -0.7  EL3  0.4  -0.2  0.5  EL2  -0.2  -0. 1  ELI  0.5  ELO ER4 ER3  -0.3  0. 1  -1.4  0.0  -0. 1  0.6  0. 1  -0.4  -0. 1  -0.7  0.4  1. 1  0.1  0.0  2.1  0.3  0. 1  0.9  -0. 1  1.2  -0.5  0.0  0.3  —  —  —  —  -0.1 —  0.4  0.1  —  —  ER2a  -0.2  0.2  0.2  -0.3  -0.1  -0.2  ER2b  0.0  0.0  0.3  -1.2  0.0  -0.9  ER1  -0.3  0.0  0.6  -0.5  ER20  -0. 1  0.0  0.4  ER21  0. 1  -0.2  -0. 1  ER22  0.0  -0.1  2.4  137  -0.3  -0.2  —  -0.6  -0.3  0.0  -0.1  -0.3  -1.0  0.2  2.4  . 4  UNSTABLE STABLE  FIGURE A I I I . 2 . Diagram showing the p o s i t i v e and n e g a t i v e movement between the 2,3 stake p a i r w i t h i n the stake a r r a y s .  138  components  

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