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The Rubble Creek landslide Garibaldi, British Columbia 1976

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THE RUBBLE CREEK LANDSLIDE GARIBALDI, BRITISH COLUMBIA by DENNIS PATRICK MOORE B.A.Sc, U n i v e r s i t y of B r i t i s h Columbia, 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of GEOLOGICAL SCIENCES We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA April 1976 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced deg ree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r ee t h a t t he L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r ag ree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f GEOLOGICAL. &Q.ISA/CE S" The U n i v e r s i t y o f B r i t i s h Co l umb i a 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date X.4- ApfilL / ? 7 6 i i ABSTRACT During the l a t e w i n t e r of 1855-56 or e a r l y s p r i n g of 1856 about 33,000,000 cu b i c yards of v o l c a n i c rock s l i d from the h i g h c l i f f known as The B a r r i e r , near G a r i b a l d i , B.C. This d e b r i s t r a v e l l e d down a r a t h e r sinuous path along Rubble Creek v a l l e y to i t s confluence w i t h Cheakamus R i v e r about A m i l e s from the B a r r i e r and about 3400 f e e t lower. The i n i t i a l m a t e r i a l appears to have t r a v e l l e d as a h i g h v e l o c i t y tongue of d e b r i s which swept from one s i d e of the v a l l e y to the other as the d e b r i s stream rounded curves e v e n t u a l l y to be d e p o s i t e d on Rubble Creek fan. V e l o c i t i e s c a l c u l a t e d from the s u p e r e l e v a t i o n of the d e b r i s as i t rounded three d i f f e r e n t curves i n d i c a t e t h a t the d e b r i s was moving between 88 and 110 f e e t per second. A minimum v e l o c i t y of 80 f e e t per second was c a l c u l a t e d using the p r i n c i p l e of c o n s e r v a t i o n of energy where the d e b r i s overtopped a s m a l l h i l l at the apex of the f a n . A l l of the t r e e s i n the path of t h i s s l i d e were uprooted and c a r r i e d away. The t r e e s adjacent to the s l i d e were s c a r r e d and b r u i s e d by moving d e b r i s . The i n i t i a l high v e l o c i t y tongue was a p p a r e n t l y f o l l o w e d by mud flows which deposited l a r g e rounded boulders and p o o r l y s o r t e d , v o l c a n i c d e b r i s on an area of the fan which was not covered by the i n i t i a l s l i d e . This m a t e r i a l was apparently slow moving, as i t p i l e d up high on the u p h i l l s i d e of some tre e s which l a t e r died and f e l l across the top of the d e b r i s . Some x e n o l i t h o l o g i c d e b r i s cones s i m i l a r to those found at Sherman S l i d e i n Alaska and elsewhere a l s o occur i n the area of mudflow m a t e r i a l . i i i The s l i d e d e p o s i t i s formed of angular p o o r l y s o r t e d v o l c a n i c c l a s t s weighing up to about 250 tons. The s l i d e d e b r i s can be d i s t i n g u i s h e d from u n d e r l y i n g fan d e p o s i t s by the la c k of f i n e g r a v e l and s i l t s i z e d p a r t i c l e s i n the fan m a t e r i a l . Deposits of de b r i s s i m i l a r to the de b r i s of the 1856 s l i d e , beneath some of the fan d e p o s i t s , show th a t an e a r l i e r s l i d e may have occurred. The mechanism which t r i g g e r e d the l a n d s l i d e i s not known, but blockage of a subsurface drainage system, which d r a i n s the area behind The B a r r i e r and escapes as sp r i n g s at i t s toe, could have r a i s e d groundwater pressures enough to t r i g g e r the s l i d e . In a d d i t i o n , as the area i s one of recent v o l c a n i c a c t i v i t y a l o c a l earthquake may have been the immediate cause. In any event the u n d e r l y i n g cause f o r the l a n d s l i d e was th a t the e x c e s s i v e l y steep and high c l i f f face of l a v a was apparently deposited a g a i n s t g l a c i a l i c e , and subsequently, l o s t support when the i c e melted. Studies using a scale-model of the topography of the area and bento n i t e s l u r r i e s were c a r r i e d out to f i n d out i f the movement of the 1856 s l i d e c o u l d be modelled and i f so, could the movement of p o s s i b l e f u t u r e s l i d e s be p r e d i c t e d . Although no mathematical b a s i s was developed f o r the modelling i t i s thought that i f a m a t e r i a l c o u l d be found which modelled the complex movement of the 1856 s l i d e , f u t u r e s l i d e s c o u l d a l s o be modelled. Although modelling of the 1856 s l i d e was not e n t i r e l y s u c c e s s f u l s e v e r a l i n s i g h t s were given i n t o the movement and deformation of prototype s l i d e s of the same type as Rubble Creek S l i d e . There has been a t l e a s t one d e s t r u c t i v e s l i d e i n the area of Rubble Creek fan i n the recent p a s t and because i t cannot be demonstrated that c o n d i t i o n s have changed s u b s t a n t i a l l y s i n c e the 1856 s l i d e i t i s only prudent to accept the p o s s i b i l i t y of the occurrence of another s l i d e i n the near f u t u r e . TABLE OF CONTENTS Page ABSTRACT i i ACKNOWLEDGEMENTS v i i i INTRODUCTION 1 FIELD STUDIES 2 1. G e o l o g i c a l S e t t i n g 2 2. Geology of the Source Area 4 3. S l i d e Path 11 4. D e p o s i t i o n a l Area 15 5. Debris C h a r a c t e r i s t i c s 19 6. Age 21 7. Volume 22 8. Evidence of Previous S l i d e s 24 9. Hydrology 25 10. V e l o c i t y 26 11. F a i l u r e Mechanism 29 12. Transport Mechanism 31 13. S l i d e P o t e n t i a l 35 SCALE-MODEL STUDIES 38 1. General 38 2. Experimental Methods 39 3. R e s u l t s from Model Studies 42 CONCLUSIONS . 5 3 LITERATURE CITED 56 APPENDIX: ADDITIONAL FIELD DATA 58 V ILLUSTRATIONS Page Photographs Photograph 1. North Slope of the Source Area 5 Photograph 2. Northern L i m i t of T h i r d Lava Lobe 7 Photograph 3. The B a r r i e r 9 Photograph 4. Black Dacite Near the Toe of the B a r r i e r 10 Photograph 5. Bedding i n the Red Rubble 10 Photograph 6. Columnar J o i n t i n g i n the Fourth Lava Lobe 12 Photograph 7. Crushed Zones, Fourth Lava Lobe 12 Photograph 8. Cedar Tree w i t h Embedded Rock 14 Photograph 9. Ir o n Oxide Layer Near Mouth of Rubble Creek 14 Photograph 10. Buried Trees, Area I I I 18 Photograph 11. Debris Cones, Area I I I 18 Photograph 12. S t r i p i n g i n Model S l i d e 40 Photograph 13. S t r i p i n g , Head of Devastation G l a c i e r S l i d e 44 Photograph 14. S t r i p i n g , Toe of Devastation G l a c i e r S l i d e 45 Photograph 15. Path of. Devastation G l a c i e r S l i d e 45 Photograph 16. Model S l i d e From Fourth Lava Lobe 51 Figures Figure 1. L o c a t i o n Map of Rubble Creek S l i d e 3 Figure 2. Geology of the Source Area In Pocket Figure 3. G e o l o g i c a l Sections Through Source Area In Pocket Figure 4. S l i d e Path In Pocket Figure 5. Sections Along S l i d e Path In Pocket Figure 6. Flow of Model S l i d e In Pocket Figure 7. L o c a t i o n of Devastation G l a c i e r S l i d e 43 TABLE Page T a b l e 1. S l i d e V e l o c i t i e s from Model S t u d i e s 49 v i i ACKNOWLEDGMENTS This thesis was done under the patient supervision of Dr. W.H. Mathews, whose enthusiasm, observations and ideas.were a strong influence on me during the study. Mr. L.J. Cornish and Mr. B.J. Hutchison are thanked for their assistance during the f i e l d work and scale-modelling as are the numerous other friends who helped me during the preparation of this thesis. A grant from the National Research Council of Canada covered the cost of photogrammetry and of laboratory materials for the modelling. The B.C. Department of Highways provided support i n the f i e l d and the B.C. Hydro and Power Authority provided typing, drafting and reproduction of the manuscript. INTRODUCTION A major r o c k s l i d e which occurred i n e a r l y 1856 i n the G a r i b a l d i area, as shown on Figure 1, became of i n t e r e s t i n 1973 when a new housing development was proposed f o r an area on the toe of the s l i d e . The B r i t i s h Columbia Department of Highways refused to permit the development on the grounds that there was a danger of a d d i t i o n a l r o c k s l i d e s . During the s p r i n g of 1973, t h i s r e f u s a l was contested by the developer and subsequently upheld by the Supreme Court of B.C. The i n f o r m a t i o n contained i n t h i s t h e s i s i s mainly from a study of the r o c k s l i d e c a r r i e d out i n the summer of 1973 f o r the Department of Highways. The purpose of the study was to c o l l e c t i n f o r m a t i o n about the 19th Century s l i d e and to i n v e s t i g a t e the p o t e n t i a l f o r f u r t h e r s l i d e s . In a d d i t i o n , scale-model s t u d i e s were c a r r i e d out i n order to help assess the dangers to the development area from p o t e n t i a l s l i d e s of a s i m i l a r nature to the s l i d e of 1856. E a r l i e r g e o l o g i c a l i n v e s t i g a t i o n s i n the area have not d e a l t s p e c i f i c a l l y w i t h the r o c k s l i d e but r a t h e r w i t h the r e g i o n a l geology (Mathews, 1958) and the c o n s t r u c t i o n of a h y d r o e l e c t r i c dam at the toe of the r o c k s l i d e (Terzaghi, 1954 and 1960). 2. FIELD STUDIES 1. Geological Setting The source of the rockslide was the steep slope at the head of Rubble Creek known as "The Barrier". From The Barrier the rockslide travelled about 4 miles down Rubble Creek valley to i t s junction with Cheakamus River valley. Cheakamus River flows south through a channel cut in the toe of Rubble Creek fan, as shown on Figure 1. In 1957, a hydroelectric dam was completed across the Cheakamus River just upstream of i t s confluence with Rubble Creek. The reservoir has flooded the northern corner of the fan including the d i s t a l end of the slide debris to an elevation of about 1261 feet above sea level. Rubble Creek valley i s trapezoidal i n cross-section, with a floor that slopes 7 1/2 degrees downstream and walls that rise a few thousand feet at angles of about 30 degrees. The walls are formed by a thin mantle of s o i l underlain on the northeast side of the valley by conglomerate and greywacke of the Cretaceous Cheakamus Formation and on the southwest by the older, Cloudburst quartz diorite (Mathews, 1958). Near Rubble Creek, the structure and bedding i n the sedimentary rocks generally trend north and dip steeply east. During the late stages of glaciation, dacite lava flowed from Clinker Mountain and formed precipi- tous terminal faces where i t was ponded against ice remaining in the valleys below elevation 4000 feet (Mathews, 1952). Four lobes of lava flowed l a t e r a l l y to the north from the main flow (Figure 1). Water has been ponded behind the second and third lava lobes to form Garibaldi and Lesser Garibaldi Lakes respectively. The third lobe was the source of the 3. the r o c k s l i d e and the scarp which remains i s The B a r r i e r . West of The B a r r i e r , the f o u r t h l a v a lobe forms an impressive c l i f f about 1500 f e e t h i g h w i t h an average surface slope of about 64 degrees. 2. Geology of the Source Area The f a i l u r e of the t h i r d l a v a lobe (Figure 2) was l o c a l i z e d by the s i d e of the p r e - v o l c a n i c v a l l e y on the n o r t h , by steep j o i n t s on the east and by some unknown surface beneath the t a l u s on the south. These fe a t u r e s may be seen i n Photograph 1. P r i o r to the d e p o s i t i o n of the l a v a , the s i d e of the v a l l e y on the n o r t h had been worn smooth and covered by a discontinuous mantle of g l a c i a l and f l u v i a l d e b r i s a few f e e t t h i c k . This s u r f a c e trends east and s l o p e s about 37 degrees south. D e t a i l s of the s u r f a c e are l a r g e l y determined by a set of j o i n t s which d i p 40 degrees south and by bedding i n the greywacke. The j o i n t s form a s e r i e s of steps and the bedding forms low r i d g e s a n g l i n g downslope. A s m a l l r o c k s l i d e has occurred along a combination of the j o i n t s and the bedding, as shown on F i g u r e 2. The d a c i t e found on the north slope i s mainly l o o s e , a c t i v e t a l u s d e r i v e d ,from the rubble r i d g e which marks the northern d e p o s i t i o n a l l i m i t of the v o l c a n i c s i n t h i s area. However, s e v e r a l s m a l l b l o c k s of b l a c k d a c i t e a l s o occur high on t h i s s l o p e . These b l o c k s of d a c i t e are i n t a c t although h i g h l y j o i n t e d and the l a v a columns i n the d a c i t e g e n e r a l l y plunge a t a steep angle to the v a l l e y w a l l . I t i s thus apparent, t h a t the d a c i t e b l o c k s are s t i l l i n t h e i r o r i g i n a l d e p o s i t i o n a l p o s i t i o n . These b l a c k outcrops as w e l l as the northern l i m i t of v o l c a n i c d e b r i s can 5. Photograph 1 North wa l l of Rubble Creek Valley adjacent to the Barrier. 6. be seen on Photograph 2. The debris which forms the ridge i s bedded and contains large intact blocks of highly fractured dacite. This debris i s similar to that which forms the surface and edges of the lava flow elsewhere and is not thought to be normal talus. The main scarp of the slide, the Barrier, i s a 700 foot high lava c l i f f which reaches elevation 4800 feet. The c l i f f i s skirted by talus derived mainly from a layer of red, volcanic rubble which forms a steep, loose slope about 200 feet high at the top of the nearly v e r t i c a l c l i f f . Rockfalls from the red rubble layer are common and make close examination of the c l i f f - f a c e hazardous. Vertical columnar joints in the center of the flow are conspicuous from a distance and appear to form the strongest set of joints i n the c l i f f . Joints which dip very steeply out of the slope also occur as may be seen in the shadow near the centre of Photograph 3. These planar joints are usually found i n gray lava near the center of the flow and slabs of this material commonly occur i n the slide debris. Flat-lying discontinuities in the lava are also conspicuous particularly where they bend into parallelism with the volcanic-greywacke contact at the north end of the Barrier. Except i n a few small areas of bedrock which crop out through the talus, the rest of the failure surface i s buried. The outcrops are located close to the toe of the Barrier i n the upper part of the talus slope (Figure 2 and Photograph 3). The rock in these outcrops i s black dacite with columnar joints and cross joints which divide i t into about 4 inch blocks. These outcrops indicate that at least part of the failure 7. Photograph 2 Northern l i m i t of t h i r d l a v a l o b e , l o o k i n g towards B a r r i e r Lake. surface beneath the talus was through bedrock. The large bedrock spur toward the right side of Photograph 3 i s formed from black dacite which i s cut by closely spaced columnar j o i n t s with axes at a steep angle to the surface of the outcrop (Photograph 4). The upper part of t h i s outcrop i s formed from vaguely bedded, red dacite-rubble (Photograph 5). The trees growing on top of this rubble are s i m i l a r i n s i z e and species to trees found to the south which c l e a r l y pre-date the s l i d e . Thus showing that t h i s outcrop did not p a r t i c i p a t e i n the 1856 s l i d e . The c l o s e l y spaced columnar j o i n t s indicate that the present surface i s near the o r i g i n a l depositional surface. The scarp on the north side of t h i s spur marks the southern l i m i t of the s l i d e . A cross-section through t h i s area i s shown on Figure 3. According to l o c a l residents, the long talus slope south of the outcrop on the extreme r i g h t of Photograph 3 has been the source of several small talus s l i d e s during the l a s t 30 years which have cut into the adjacent vegetated slope. The fourth lava lobe i s s i m i l a r to the t h i r d except that i t s i n t e r i o r i s , for the most part, hidden by a surface layer. The surface layer i s characterized by remarkable, columnar j o i n t s which generally point outwards from the face of the lobe, as i l l u s t r a t e d on Photograph 6. Columns usually point i n the d i r e c t i o n of heat loss during cooling therefore i t i s probable that the present face i s e s s e n t i a l l y p a r a l l e l to the o r i g i n a l depositional face. Deeper within the flow, the columns are much thicker and more or less v e r t i c a l . The tendency for the columns to point downward near the toe of the fourth lobe indicates that the bottom Photograph 3 The Barrier 10. Photograph 5 Bedding i n the red rubble which o v e r l i e s the outcrop shown i n Photograph 4 . of the flow i s probably nearby. This lobe i s capped by a l a y e r of red d a c i t e rubble s i m i l a r to the t h i r d lobe. A cross s e c t i o n through the f o u r t h lobe i s shown on Figure 3. A s e r i e s of crushed zones near the toe of the f o u r t h l a v a lobe (Figure 2) can be seen i n Photograph 7. These zones are more than 100 f e e t long and c o n t a i n s e v e r a l f e e t of crushed and r o t a t e d l a v a columns. Although the a t t i t u d e s of these surfaces are d i f f i c u l t to measure, they s t r i k e roughly northeast and d i p s t e e p l y northwest. V e r t i c a l d i s c o n t i n u i t i e s which separate s l a b s from the face of the l a v a lobe are common. One such s l a b about 150 f e e t high can be seen on Photograph 4. S e v e r a l r u b b l e - f i l l e d troughs 10 t o 20 f e e t deep and a few hundred f e e t long p a r a l l e l the break i n slope along the top of the f o u r t h lobe. 3. S l i d e Path The passage of the s l i d e d e b r i s down Rubble Creek v a l l e y was recorded i n a number of ways. The s l i d e l e f t a t h i n but n e a r l y continuous c o a t i n g of v o l c a n i c d e b r i s which i s e a s i l y d i s t i n g u i s h a b l e from the l o c a l rock and the g l a c i a l d e p o s i t s . The upper l i m i t of t h i s continuous c o a t i n g can u s u a l l y be l o c a t e d w i t h i n a w i d t h of 20 f e e t and only w i d e l y s c a t t e r e d v o l c a n i c fragments are found above i t . I t i s the l o c a t i o n of t h i s l i m i t which has been marked on Figure 4. D ebris s c a t t e r e d above t h i s l i m i t i s not common but i s more o f t e n found downstream of t r a n s v e r s e r i d g e s which have o b s t r u c t e d the movement of the s l i d e . L a t e r a l r i d g e s occur l o c a l l y along the edge of the s l i d e path. They are v a r i e d i n shape from f l a t t e r r a c e s on the v a l l e y w a l l s , only a few f e e t a c r o s s , to steep-sided r i d g e s 20 f e e t h i g h . 12. Photograph 7 Crushed zones near the toe of the 4th l a v a l o b e . Many of the trees found above the debris limit have had. their bark torn off near the base. The scars which remain face upstream and sli g h t l y toward the valley axis. They commonly have deep bruises extending into the woody part of the trunk and in two instances, an angular piece of volcanic debris was found actually embedded i n the wood. Photograph 8 shows one of these rocks embedded in a tree. The tree has a scar typical of many trees found near the edge of the slide path. The trees l i v i n g within the slide area are more closely spaced, smaller and younger than those outside. The ages of about 150 of the largest trees on both sides of the slide limit were determined, by counting the annual rings. Those within the slide path were found to be younger than 113 years whereas many of those outside the path were more than 200 years old. The remains of some older trees were observed i n the depositional area of the slide (see following section) but, upstream of this, the slide path was swept clean. A line connecting the centroids of cross-sections of the slide as i t passed down the valley i s also shown on Figure 4. This line i s thought to approximate the path of the center of gravity. As such, i t has been connected to the center of gravity of the slide deposit and to the center of gravity of i t s reconstructed source position. Lines drawn perpendicular to the path of the center of gravity and joining debris limits on opposite valley walls slope as much as 10.5 degrees. A series of cross-sections.transverse to the direction of slide movement are shown on Figure 5. These cross-sections i l l u s t r a t e the path of the slide mass as i t banked from one side of the valley to the other. The longi- tudinal section of the slide path graphically i l l u s t r a t e s the remarkable efficiency and travel-distance of the slide. 14. Photograph 8 Cedar tree with volcanic rock embedded just above the k n i f e . Photograph 9 Iron oxide surface layer which marks the base of the most recent s l ide debris near the mouth of Rubble Creek. 15. The d e b r i s l i m i t s are broadly curved except downstream of tra n s v e r s e r i d g e s such as those at p o i n t A on Figure 4. I t can be seen th a t the height to which the s l i d e reached drops over 100 f e e t from the upstream s i d e of t h i s r i d g e to the downstream s i d e . This appears to be a "shadow e f f e c t " such as occurs downstream of an o b s t r u c t i o n i n f l o w i n g water. 4. D e p o s i t i o n a l Area A s m a l l p a r t of the s l i d e d e b r i s was deposited i n the v a l l e y of Rubble Creek but most of i t was deposited on i t s a l l u v i a l f a n . The f an can be d i v i d e d i n t o three s e c t o r s c o n t a i n i n g d i s s i m i l a r s urface d e p o s i t s . i The northernmost s e c t o r , Sector I (Figure 4 ) , c o n t a i n s the b u l k of the s l i d e d e b r i s . Logs of d r i l l h o l e s near the damsite, s e i s m i c surveys along s e v e r a l roads and surface observations i n d i c a t e the depth of s l i d e d e b r i s i n t h i s area to be about 32 f e e t . The surface i s hummocky w i t h many c l o s e d depressions and s m a l l mounds. The upper p a r t of t h i s s e c t i o n i s c h a r a c t e r i z e d by elongate mounds which trend downslope. Running water has cut g u l l i e s and g e n e r a l l y m o d i f i e d the s u r f a c e i n the area Three p a r a l l e l r i d g e s of d e b r i s occur on the edge of the g r a n i t i c knob a t the apex of the fan . These r i d g e s probably represent s u c c e s s i v e l y lower l e v e l s of moving d e b r i s which at one time, at l e a s t , overtopped the knob. I n a d d i t i o n , a mound of d e b r i s i s found j u s t upstream of the g r a n i t i c knob. This mound i s 40 f e e t h i g h e r than the surrounding l a n d and i s separated from the knob by a s a d d l e - l i k e depression. A c o n i f e r o u s f o r e s t has developed i n t h i s area s i n c e the s l i d e . The southwest boundary of t h i s s e c t i o n i s marked by a steep slope 6 to 25 f e e t h i g h which d i v i d e s 16. the elevated area of hummocky topography on the northeast from a lower section on the southwest. The d i s t a l end of the deposit i n Sector I i s beneath the surface of the reservoir and was not observed. The middle sector of the fan, Sector I I , i s the smallest and contains only a very small amount of s l i d e debris. Many of the tree stumps l e f t from the logging about 30 years ago have we l l over 200 annual rings. The roots of many of these stumps have been buried by a foot or two of dacite debris but they obviously l i v e d through the s l i d e . A layer of gravel cemented with iron oxides i s found j u s t under the surface i n t h i s area. The layer can be followed up Rubble Creek to a point about 1900 feet above the highway bridge. The oxidized deposit i s more sorted, rounded and bedded than t y p i c a l s l i d e debris. I t i s thought to be near the pre- s l i d e surface of the fan. Photograph 9 shows t h i s rusty surface layer near the present day surface at Rubble Creek. A terrace deposit of volcanic debris exists along the Cheakamus River. Many trees have been buried i n t h i s terrace deposit, some of which have been subsequently exhumed. None of the l i v i n g trees on t h i s terrace was found to be older than the s l i d e even though many trees growing a few feet above the terrace were older. The terrace was probably formed during rapid aggradation of the Cheakamus riverbed immediately following the landslide. The southernmost sector of the depositional area, Sector I I I , covers the fan from Rubble Creek south. I t i s characterized by large f i e l d s of subrounded cobbles and boulders with very l i t t l e matrix at the surface. Many of these areas support l i t t l e vegetation other than moss and lichens. The boulders range up to 6 X 6 X 10 feet i n s i z e 17. (Photograph 10). The m a t e r i a l beneath the surface l a y e r of boulders i s very p o o r l y s o r t e d v o l c a n i c d e b r i s . This s e c t o r has a g e n e r a l l y v- uniform topography except f o r g u l l i e s marking former l o c a t i o n s of Rubble Creek which has apparently changed i t s channel s e v e r a l times s i n c e the s l i d e , and some shallow g u l l i e s which tend to s t a r t and d i e out a few hundred f e e t downslope. The boundaries of the area are very sharp and v o l c a n i c d e b r i s was not found much beyond the present extent of the f a n except on the West bank of the Cheakamus R i v e r where d e b r i s occurs about 15 f e e t above the r a i l w a y t r a c k . The boundary of v o l c a n i c d e b r i s was not e a s i l y t r a c e d near i t s western end because of the subsequent road and r a i l w a y c o n s t r u c t i o n i n the area, however, the d e b r i s appears to have reached an e l e v a t i o n on the west bank of the Cheakamus approximately equal to t h a t of the top of the east bank of the r i v e r . Many b u r i e d t r e e s occur along the boundaries of Sector I I I , these t r e e s were growing p r i o r t o the s l i d e and b u r i e d by i t without being t i l t e d , broken, or having t h e i r bark t o r n from the trunk. Only one area of b u r i e d t r e e s was found i n the i n t e r i o r of Sector I I I . The age of some of these t r e e s was determined by a count of t h e i r annual r i n g s to be g r e a t e r than 200 years. The trees were apparently b u r i e d by the s l i d e although s t i l l s t a n ding and then they d i e d and f e l l on top of the d e b r i s , as shown on Photograph 10. The d e b r i s p i l e d up 6 f e e t h i g h on the upstream s i d e of the t r e e s and a depression was formed on the downstream s i d e . Some of the boulders p i l e d a g a i n s t the trunk were 2 to 3 f e e t i n diameter. T h i s i s i n marked c o n t r a s t t o the other areas of the s l i d e where the p r e - s l i d e v e g e t a t i o n was c a r r i e d away and even t r e e s adjacent to the s l i d e path were s c a r r e d and broken. 18. P h o t o g r a p h 10 B u r i e d t r e e s n e a r the c e n t e r o f S e c t o r I I I on Rubble Creek f a n . P h o t o g r a p h 11 X e n o l i t h o l o g i c d e b r i s cone i n S e c t o r I I I Rubble Creek f a n . T r e e stump i s more t h a n 60 y e a r s o l d . 19. About 1000 f e e t d o w n h i l l of the b u r i e d t r e e s i n Photograph 10, two curious f e a t u r e s were observed. The p i l e of red rubble, shown on Photograph 11 and a s i m i l a r mound found AO f e e t away are d e b r i s cones s i m i l a r to those found on the s l i d e d e p o s i t s at Sherman Peak (Shreve, 1966) and elsewhere. The mound shown i n the photograph has a stump on i t which was over 60 years o l d , hence i t i s probable that the mound was not man-made. The adjacent mound r i s e s only a few f e e t above the surrounding boulder f i e l d and i t i s composed of the same p o o r l y s o r t e d , red rubble as the mound i n the photograph. The m a t e r i a l ranged from s i l t - s i z e to at l e a s t 1.5 f e e t i n diameter. There does not appear to be a l a r g e b l o c k of d e b r i s u n d e r l y i n g these mounds as observed at Sherman s l i d e f o r example (Shreve, 1966). 5. D e b r i s C h a r a c t e r i s t i c s The d e b r i s which forms the s l i d e deposit i s a l o o s e , unsorted mixture of angular v o l c a n i c fragments ranging i n s i z e from f i n e s i l t ( T e rzaghi, 1954) to more than 15 f e e t diameter. Gra i n s i z e d i s t r i b u t i o n s f o r 17 samples of the f r a c t i o n of the d e b r i s l e s s than 0.5 inches i n diameter, were measured u s i n g U.S. Standard Sieves ranging i n s i z e between #5 and #200 (Appendix). This f r a c t i o n was found to be very p o o r l y s o r t e d having an average c o e f f i c i e n t of u n i f o r m i t y (Cu) of 29 and a c o e f f i c i e n t of curvature (Cc) of l e s s than 1. Between 7 and 22 percent of each sample passed the #200 si e v e (Earth Manual, USBR, 1968). A sample of the m a t e r i a l u n d e r l y i n g the o x i d i z e d l a y e r at the mouth of Rubble Creek was a l s o analysed. This sample was a l s o w e l l graded but l e s s so than the other samples. I t was r e l a t i v e l y depleted of the f i n e g r a v e l and f i n e sand s i z e d m a t e r i a l . The c o e f f i c i e n t of u n i f o r m i t y was 8 and the c o e f f i c i e n t of curvature was 1.4. 20. The water contents of the samples at the time of analysis ranged from 3 to 9 percent. These values are probably lower than the in situ water content because of losses after the sample was taken. Natural water contents of the fraction less than 3 inches diameter were found to be between 12 and 16 percent during construction of the storage dam (Terzaghi, 1960). For these natural water contents and an assumed specific gravity of the solids of 2.7 the minimum porosity of the debris would have to be 25 to 30 percent. The relative density of the debris was indicated to be very low by the ease with which d r i l l hole casing could be driven into the ground, (Terzaghi, 1960). A total of 1234 pebbles, larger than about 0.08 inches, from 11 samples were classified as to size, lithology, roundness and sphericity (Krumbein, 1941). An attempt was made to find any regular variation i n the lithologic composition of the slide debris. Samples were taken from a l l three sections and up to elevation 2580 in the creek valley. No consistent variation in composition could be detected. The sample from beneath the oxidized layer showed a preponderance of black dacite over gray dacite unlike the other samples. This sample suggests that the supply of material to the fan prior to the slide was more from the black outer layer of lava rather than the gray core of the flow. The average content of green greywacke such as that found on the north side of the source area was 6.5 percent. The average content of granitic pebbles and pebbles of unknown lithology was 3.5 percent of the total number of pebbles. The granitic pebbles appeared to be mainly diorite. The bulk of the samples was a volcanic rock like that which forms 21. The B a r r i e r . An average of 42 percent of the fragments are gray, 30 percent are bl a c k and 18 percent are red. In many ins t a n c e s i t was r a t h e r a r b i t r a r y whether a sample would be c l a s s e d as b l a c k or gray. The fragments have a very broad range of s p h e r i c i t i e s w i t h a mean of about 0.68. Histograms were p l o t t e d of s p h e r i c i t i e s f o r each of the eleven samples using a c e l l width of 0.04. The d i s t r i b u t i o n i s very broad and the h i g h e s t peaks are only 20 to 25 percent of the sample. An exception t o t h i s i s the sample from beneath the o x i d i z e d l a y e r which shows a r e l a t i v e l y narrow peak and 30 percent of the sample i n a s i n g l e c e l l . Frequency histograms were a l s o p l o t t e d of the roundnesses measured f o r each of the eleven samples. These d i s t r i b u t i o n s are narrow and have an average mean of about 0.41. The range i n means i s from 0.3 to 0.5 and the range i n i n d i v i d u a l roundness i s from 0.1 to 0.7. The frequency d i s t r i b u t i o n of the l e n g t h of the b-axes of the pebbles f o r s i z e s greater than 0.16 inches i s s i m i l a r f o r a l l samples except the sample from below the o x i d i z e d l a y e r (Appendix). T h i s sample has a much higher content of pebbles having b-axes longer than 2.52 in c h e s . 6. Age The e a r l i e s t a v a i l a b l e r e f e r e n c e to the s l i d e i s the j o u r n a l of Major W i l l i a m Downie who t r a v e l l e d through the area i n 1858. He des c r i b e d the area as f o l l o w s : "...about noon we s t r u c k i n t o a lagoon, or a l a r g e t r a c t of overflowed l a n d , the Indians say t h i s was over flowed three years ago. We found the cause of i t as we came along, a Lake has broken away i n the Mountains, and swept away r i d g e , a f t e r r i d g e , c o v e r i n g a whole f o r e s t of timber, with rocks and sand for the space of 6 or 7 square miles changed the course of the r i v e r , and not l e f t a stump to be seen, where the t a l l timber stood three years ago, our t r a i l over t h i s was about two and a half miles..." The histo r y of the s l i d e i s also recorded i n the annual rings of the trees growing on the debris or adjacent to the s l i d e path. The rings of more than 150 trees were counted and without exception those trees growing on top of s l i d e debris were less than 113 years old whereas those outside the path of the s l i d e were commonly several hundred years old. The trees along the edge of the s l i d e path, which survived the s l i d e but were scarred by the debris, graphically i l l u s t r a t e the age of the s l i d e . Two of these trees were sawn down and a count of t h e i r rings indicated that the s l i d e occurred during the l a t e winter of 1855-56 or early spring of 1856. 7. Volume The volume of material between the reconstructed pre-slide surface (Figure 4), and the present surface i s estimated to be 33,000,000 cubic yards. The inferred pre-slide surface i s obtained by connecting the surface now found to the south of the source of the s l i d e with the l i m i t of volcanic debris north of the source. The volume compares w e l l with the volume of debris which i s estimated to be deposited i n the v a l l e y and on the fan of Rubble Creek. The volume of material i n the v a l l e y was estimated by calculating the amount of material required to form the present v a l l e y cross-section from a cross-section s i m i l a r to a nearby v a l l e y . C u l l i t o n Creek v a l l e y was selected f o r comparison because 23. i t i s a s i m i l a r s i z e , i t i s only a few mile s south, there has been no major s l i d e i n i t , i t has steep v o l c a n i c c l i f f s near i t s source and i t has a cross-section not u n l i k e most other creeks i n the area. The volume of s l i d e d e b r i s added to the v a l l e y bottom was thus estimated to be 12,100,000 cubic yards .incl u d i n g a s m a l l volume of d e b r i s which was subsequently removed. The depth of de b r i s d e p o s i t e d on the f a n can be estimated from borehole data near the damsite, the h e i g h t of the scarp at the southern edge of the d e b r i s , the thi c k n e s s of d e b r i s i n excavations and the topographic r e l i e f a s s o c i a t e d w i t h s l i d e r e l a t e d f e a t u r e s such as hummocks. The d e b r i s i n t h i s s e c t i o n has an average depth of 32 f e e t corresponding to a volume of 22,200,000 cubic yards. The t o t a l volume of d e b r i s i n the s l i d e deposit i s thus 34,300,000 c u b i c yards which compares w e l l w i t h the volume (33,000,000 cubic yards) c a l c u l a t e d through recon- s t r u c t i o n of the contours at the source. The i n c r e a s e i n volume from the source to the deposit accounts f o r some of the i n c r e a s e i n p o r o s i t y , which Undoubtedly occurred during motion. An estimated t h i c k n e s s of 6 f e e t f o r the s l i d e d e p osit south of Rubble Creek corresponds to a t o t a l volume i n t h i s a r e a of 3,200,000 cub i c yards. This thi c k n e s s i s c o n s i s t e n t w i t h the t h i c k n e s s of d e b r i s observed i n the banks of Rubble Creek, and the l o c a l r e l i e f i n t h i s p a r t of the f a n . The volume deposited i n s e c t i o n s I I and I I I i s s i m i l a r to the volume of an estimated 3,900,000 cu b i c yards which was removed from the upper p a r t of the v a l l e y subsequent t o the main s l i d e . I t i s thought that t h i s m a t e r i a l was t r a n s p o r t e d by mud flows and by Rubble Creek from the v a l l e y to the fan soon a f t e r the s l i d e occurred. in. Surface contours near the head of Rubble Creek were reconstructed for the time j u s t after the volcanics were deposited. These contours bound a lobe-shaped steep sided mass si m i l a r to the 4th lava lobe (Alternative 2 Figure 4). The volume contained between these contours and the present surface i s about 82,000,000 cubic yards. This volume i s not consistent with the volume of the s l i d e deposit and i s therefore not a very reasonable estimate of the volume of the 1856 s l i d e . However, i t i s an upper l i m i t to the possible s l i d e volume. 8. . Evidence of Additional Slides Although no s l i d e debris older than the 1856 s l i d e was seen on the v a l l e y walls an exposure of poorly sorted s o i l beneath fan deposits near the mouth of Rubble Creek suggests the p o s s i b i l i t y of an e a r l i e r s l i d e . Evidence f o r what may have been a s l i d e e a r l i e r than 1856 also exists i n the form of some wood recovered from a d r i l l hole, w e l l beneath the base of the 1856 s l i d e and two layers of wood i n another d r i l l hole. The basal layer of the 1856 s l i d e i s marked by wood therefore the addit i o n a l layers may mark e a r l i e r s l i d e s . The t h i r d lava lobe appears to have l o s t s i g n i f i c a n t l y more material since i t was deposited than has the fourth lobe. This may be in d i c a t i v e of i n s t a b i l i t y of the t h i r d lobe and perhaps additional s l i d e s . The low scarp above the trees on the ri g h t hand side of Photograph 3 may have been produced by s l i d i n g . 9. Hydrology Rubble Creek Slide occurred i n an area which receives about 68 inches of p r e c i p i t a t i o n per year. Near the toe of the deposit, about 25% of the p r e c i p i t a t i o n f a l l s as snow but the proportion i s much greater at the source of the s l i d e . Most of the p r e c i p i t a t i o n f a l l s during the winter months. The average temperature i s about 8°C. near the toe of the deposit. The Garibaldi Lake system has a watershed above the Barrie r of about 23 square miles. Except for occasional s p i l l a g e from B a r r i e r Lake during periods of high runoff, the lakes drain through the subsurface and emerge at the toe of The B a r r i e r . The springs at the toe are buried by talus but at least two seepage paths are indicated by the temperature difference between the water from the springs. During June and July of 1973 the water temperature i n the northern spring was 6.6°C. while the water i n the other two springs was at 5.7°C. Early investigations by the Water Resources Board indicated that the subsurface discharge beneath the Barrier was about 75-200 cubic feet/second consisting of 60-105 cubic feet/second from Garibaldi Lake and the rest from Lesser Garibaldi Lake. During t h i s i n v e s t i g a t i o n , an attempt was made to measure the v e l o c i t y of flow from Lesser Gari b a l d i Lake through use of a dye and a brine solution. The r e s u l t s were not conclusive however the conductivity of the spring water peaked about 5 hours a f t e r the brine was dumped i n the lake. 10. V e l o c i t y The hi g h v e l o c i t y of the l a n d s l i d e as i t came down the v a l l e y i s a t t e s t e d to by the removal of a l l the t r e e s i n i t s path as w e l l as by the damage i t d i d to the tre e s which bordered the path. In a d d i t i o n , where ri d g e s transverse to the d i r e c t i o n of s l i d e movement were passed by the s l i d e the upper l i m i t of de b r i s on the ground drops markedly from the c r e s t of the r i d g e to the downstream s i d e , such as near p o i n t A, Figure 4. This steep drop i n the s l i d e s u r f a c e i s s i m i l a r to the drop i n the surface of a stream of water as i t passes around an o b s t r u c t i o n . A t h i r d i n d i c a t i o n of the v e l o c i t y of the s l i d e i s the s u p e r e l e v a t i o n of the d e b r i s on one s i d e o f the v a l l e y where i t i s curved, as shown on Secti o n s 1 through 15, F i g u r e 5. S e v e r a l estimates can be made of the v e l o c i t y of a s l i d e . The f i r s t and most commonly used method i s to equate the k i n e t i c energy the moving d e b r i s possesses a t the base of a h i l l to the p o t e n t i a l energy gained i n c l i m b i n g up the h i l l . That i s : l/2mv^ = mgh where m i s a u n i t mass, v i s the v e l o c i t y at the base of the h i l l , g i s the a c c e l e r a t i o n due to g r a v i t y and h i s the h e i g h t to which the d e b r i s climbed. I t i s assumed that the d e b r i s does not have a r e s i d u a l v e l o c i t y at the top of the h i l l , t h at there i s no l o s s i n energy c l i m b i n g the h i l l and that the th i c k n e s s of d e b r i s does not change as i t passes over the h i l l . For Rubble Creek there i s some evidence f o r b u i l d - u p of d e b r i s upstream of the g r a n i t i c knob a t the apex o f the fan . However, the f i r s t two assumptions tend to counteract the e f f e c t of the change i n thickness of d e b r i s and th e r e f o r e the c a l c u l a t i o n may s t i l l be v a l i d . In any event the height of the knob before the s l i d e was about 100 f e e t and the c a l c u l a t e d v e l o c i t y i s thus about 80 f e e t per second. A second approximation of the v e l o c i t y can be made from the s u p e r e l e v a t i o n of the deb r i s on one si d e of the channel as i t rounds a curve. As the d i r e c t i o n of the v e l o c i t y i s changed a c e n t r i f u g a l f o r c e i s exerted on the p a r t i c l e s i n the flow. In order to balance t h i s f o r c e the surface of the mass i s t i l t e d towards the center of the curve so that the v e c t o r sum of the g r a v i t a t i o n a l and c e n t r i f u g a l f o r c e s i s pe r p e n d i c u l a r to the sur f a c e of the mass. The path of the center of g r a v i t y of the s l i d e d e b r i s was found by j o i n i n g the c e n t r o i d s of the c r o s s - s e c t i o n a l areas of the d e b r i s , as shown on Fi g u r e 5. The r a d i u s of curvature of the.path was found f o r three curves, l a b e l l e d X, Y and Z on Figure 4. The r a d i u s of curvature (R), maximum transverse surface slope w i t h i n the bend ( 9 ) , and the v e l o c i t y c a l c u l a t e d (V) usin g the formula: 2 V = Rg s i n 9 are shown below: R 9 V X 2083 f t . 10.5° 110 f t / s e c Y 3332 f t . 7.5° 118 f t / s e c Z 1874 f t . 7.5° 88 f t / s e c I t was' assumed f o r these c a l c u l a t i o n s that the d e b r i s f l o w reaches e q u i l i b r i u m w i t h the c e n t r i f u g a l f o r c e as i t rounds the bend; the flow 28. was uniform; the flow l i n e s were c o n c e n t r i c ; the flow was s u b c r i t i c a l ; the surface of the d e b r i s was c l o s e to the l i n e j o i n i n g the maximum height of deb r i s on the v a l l e y w a l l s and the deb r i s was able to deform r e a d i l y . The assumption of e q u i l i b r i u m would appear to be v a l i d p a r t - i c u l a r l y f o r curve X which has a rad i u s of curvature which i s constant f o r about 70 degrees of arc. Although there i s l e s s chance f o r e q u i l i - brium to have been reached through curves Y and Z, the general c o n s i s t e n c y of r e s u l t s i n d i c a t e s that i f e q u i l i b r i u m was not reached i t was not a major f a c t o r . I f the d e b r i s d i d not reach e q u i l i b r i u m w i t h the c e n t r i f u g a l f o r c e the c a l c u l a t e d v e l o c i t i e s would tend to be lower than the true v e l o c i t i e s . I f the flo w was non-uniform or the flow l i n e s non-concentric the e r r o r would not be l a r g e ( M o r r i s , 1963) and would give a lower c a l c u l a t e d v e l o c i t y i f taken i n t o account. For s u b c r i t i c a l flow of water the Froude number must be l e s s than 1, th a t i s ; the v e l o c i t y f o r a mean depth of 200 f e e t , such as shown on c r o s s - s e c t i o n 4, Fi g u r e 5, must be l e s s than 80 feet/second. For s u p e r c r i t i c a l or r a p i d flow the s u p e r e l e v a t i o n i s a f f e c t e d by d i s t u r b - ances generated through the curve ( M o r r i s , 1963). As these d i s t u r b a n c e s would tend to i n c r e a s e the s u p e r e l e v a t i o n the c a l c u l a t e d v e l o c i t y would be too hi g h . I f t h i s was the case, the true v e l o c i t y would l i e between the v e l o c i t y c a l c u l a t e d by assuming s u b c r i t i c a l flow and the c r i t i c a l v e l o c i t y . The e f f e c t of disturbances would be diminished by the s l o p i n g v a l l e y w a l l s on the outer s i d e of the curve. Although the tru e v e l o c i t y cannot be c a l c u l a t e d w i t h c e r t a i n t y u s i n g t h i s method unless the flow c o n d i t i o n s are known, the v e l o c i t y can be bracketed. The d e b r i s mass underwent many r a p i d changes i n shape as i t moved down the v a l l e y . The mass appears to have moved w i t h many of the q u a l i t a t i v e c h a r a c t e r i s t i c s , i f not the q u a n t i t a t i v e c h a r a c t e r i s t i c s , of a f l u i d . Thus i t seems reasonable to assume that the c r o s s - s e c t i o n s of the mass shown on Fi g u r e 5 are v a l i d and that the mass could deform r e a d i l y . I t seems reasonably c e r t a i n t h e r e f o r e , that the v e l o c i t y of the s l i d e d e b r i s as i t moved down Rubble Creek v a l l e y was between 80 and 118 feet/second. The best estimate i s probably t h a t d e r i v e d from the s u p e r e l e v a t i o n as i t rounded curve X, 110 feet/second. 11. F a i l u r e Mechanism In order to develop a reasonable e x p l a n a t i o n of the i n i t i a l f a i l u r e of the t h i r d l a v a lobe i t i s important to know the c o n d i t i o n s e x i s t i n g p r i o r t o the f a i l u r e . Although i t has been p o s t u l a t e d t h a t the s l i d e was caused by the l i q u e f a c t i o n of a t a l u s deposit (Brawner, 1975) the g e o l o g i c a l evidence does not favour t h i s h y p o t h e s i s . The e x i s t e n c e of the outcrops of l a v a on the n o r t h slope i n d i c a t e t h a t the m a t e r i a l removed from t h i s 'area was " i n s i t u " l a v a r a t h e r than t a l u s . The t a l u s which now covers p a r t of the n o r t h slope has been d e r i v e d mainly from these outcrops and from the r i d g e of v o l c a n i c rubble near the l i m i t of v o l c a n i c d e b r i s . The vague bedding and l a r g e i n t a c t b l o c k s i n t h i s r i d g e i n d i c a t e that the r i d g e i s formed by rubble s i m i l a r t o that on the s u r f a c e of the f l o w r a t h e r than formed by t a l u s . The r e s t of the f a i l u r e appears to have occurred mainly through bedrock as i n d i c a t e d by the outcrops along the f o o t of The B a r r i e r and the scarp along the south s i d e of the s l i d e as w e l l as the B a r r i e r i t s e l f . I t i s very u n l i k e l y that a s l i d e which was mainly t a l u s would remove a l a y e r of the u n d e r l y i n g bedrock. I n a d d i t i o n , i t i s u n l i k e l y that a t a l u s deposit could accumulate a g a i n s t a c l i f f which served as i t s source and f o r the c l i f f to remain near v e r t i c a l beneath the t a l u s . The s l i d i n g was probably l o c a l i z e d along the unconformity at the base of the l a v a on the north s i d e , and through d i s c o n t i n u i t i e s i n the l a v a elsewhere. The m a t e r i a l comprising the s l i d e was most l i k e l y l a v a bedrock w i t h an o v e r l y i n g l a y e r of rubble, and perhaps a toe of t a l u s . Floods or i n c r e a s e d water pressures beneath the B a r r i e r have been v a r i o u s l y c i t e d as p o s s i b l e t r i g g e r i n g mechanisms f o r the s l i d e . Floods or waves of water from G a r i b a l d i Lake are r u l e d out by the e x i s t e n c e of t r e e s which predate the s l i d e w i t h i n 10 f e e t of the bottom of the creek which d r a i n s G a r i b a l d i Lake ( P o i n t B, F i g u r e 4 ) . I t would not be p o s s i b l e f o r a l a r g e wave of water to pass t h i s p o i n t without u p r o o t i n g the t r e e s i n i t s path. High water pressures may have occurred along the f a i l u r e s u r f aces p r i o r to the s l i d e . Drainage of the G a r i b a l d i Lake system i s f o r the most p a r t by subsurface f l o w which springs out a t the toe of The B a r r i e r . This f l o w seems to be r e s t r i c t e d to zones near the base of the flow as no s p r i n g s i s s u e higher up the face of The B a r r i e r . I f the seepage path was blocked by an underground c o l l a p s e or by i c e forming at the e x i t d u r ing an extreme w i n t e r , very h i g h u p l i f t pressures c o u l d develop. 31. The G a r i b a l d i area i s near the boundary between s e i s m i c zones 1 and 2 (Milne, 1973) t h e r e f o r e the p o s s i b i l i t y of the s l i d e being t r i g g e r e d by an earthquake cannot be r u l e d out. Although s l i d e areas have been known to withstand l a r g e earthquakes before being t r i g g e r e d by earthquakes of s m a l l e r magnitude at a l a t e r date (Mathews and McTaggart, 1969), a major earthquake occurred i n the area only a few years p r i o r to the s l i d e and i t would seem that i f the slope was i n a c o n d i t i o n to . f a i l under earthquake a c c e l e r a t i o n s i n 1856 i t would have been i n a s i m i l a r s t a t e i n 1853 and would have f a i l e d during the 1853 earthquake. Records during these years are scanty, however, i f an earthquake l a r g e r than the 1853 earthquake had occurred i t i s very l i k e l y t h a t there would be some r e c o r d of i t . There i s the p o s s i b i l i t y of a s m a l l earthquake having occurred i n 1856 near the s l i d e which would not have been n o t i c e d i n the more populated areas but would have produced a c c e l e r a t i o n s at the B a r r i e r l a r g e r than the 1853 earthquake. I t can be concluded that an earthquake as the prime t r i g g e r i n g mechanism i s u n l i k e l y but cannot be r u l e d out completely. The development of h i g h u p l i f t pressures i s the most probable t r i g g e r i n g mechanism f o r the s l i d e . 12. Transport Mechanism Two of the most i n t e r e s t i n g f e a t u r e s of the Rubble Creek l a n d s l i d e are the extremely high e f f i c i e n c y and h i g h v e l o c i t y of the s l i d e as i t t r a v e l l e d down the v a l l e y . The r a t i o of the maximum h e i g h t dropped to the maximum d i s t a n c e t r a v e l l e d i s 0.15, as shown on F i g u r e 5. This i s a low value even compared to other high e f f i c i e n c y s l i d e s (Hsu, 1975, for example). This class of mass movement has been variously known as r o c k f a l l avalanche, debris stream (sturzstrom), debris avalanche, l a n d s l i p , catastrophic landslide, or catastrophic r o c k f a l l . The e f f i c i e n c y exhibited by the Rubble Creek s l i d e i s what could be expected of a somewhat larger s l i d e considering the general increase i n e f f i c i e n c y with volume that has been reported by numerous i n v e s t i - gators (Heim, 1932, Howard, 1974 and Hsu, 1975). The e f f i c i e n c y of these s l i d e s has been explained i n a number of ways, namely; f l u i d i z a t i o n (Kent, 1966), l u b r i c a t i o n by underlying weak layers, a i r launch (Shreve, 1968), dust cloud (Hsu, 1975) high vapour pressures (Habib, 1975), transfer of momentum to the leading part from behind (Eisbacher, 1976), or simply f l u i d flow (Heim, 1881). Any explanation of the transport mechanism must take i n t o account several features of these s l i d e s besides the high e f f i c i e n c y . These features include: "(1) a chaotic arrangement of blocks without gravity sorting; (2) a l i m i t e d amount, or absence of, abrasion of constituent blocks; (3) a high degree of f l u i d i t y at the time of emplacement; (4) r e l a t i v e thinness compared with great h o r i z o n t a l extent, eliminating the p o s s i b i l i t y of stress transmission through a s i g n i f i c a n t distance (5) very high speed of movement measured i n seconds or i n a very few minutes; and (6) association with a i r b l a s t s . . . " (Kent, 1966). In addition to those features l i s t e d by Kent the following should be added (7) parts of the debris maintain a semblance of t h e i r o r i g i n a l r e l a t i v e positions (Shreve, 1968); (8) the debris can pass over the ground surface i n some cases without disturbing i t very much (Shreve, 1966); (9) the a b i l i t y to flow around obstacles near t h e i r d i s t a l end without greatly disturbing them (Buss and Heim, 1881, p. 40); (10) the steep angle of repose of the material i n l a t e r a l ridges and d i s t a l scarps; and (11) the occurrence of s i m i l a r s l i d e s on the moon (Howard, 1973). In view of the fact that high e f f i c i e n c y rock s l i d e s have " occurred under a very wide range of c l i m a t i c , l i t h o l o g i c , topographic, g r a v i t a t i o n a l and atmospheric conditions i t seems imperative that the mechanism which enables these large masses to behave as they do should be inherent i n the mass i t s e l f rather than i n some outside conditions. In p a r t i c u l a r , the mechanisms of a i r launch, mud layer l u b r i c a t i o n and a i r f l u i d i z a t i o n can be ruled out by the occurrence of s i m i l a r s l i d e s on the Moon (Howard, 1974). In fa c t , the only conditions which appear to be necessary to generate a rockslide of th i s nature are a high i n i t i a l v e l o c i t y , disaggregation of the rock involved and a suitable path to follow. An available explanation i s that the rock debris i s carried i n a cloud of dust created by the i n i t i a l f a i l u r e and that the debris behaves as a f l u i d . There i s some experimental evidence supporting t h i s concept (Bagnold, 1954). He found that the resistance to shearing of grains suspended i n a Newtonian f l u i d decreased at high rates of shearing. He also found that there was a dispersive grain pressure created when these grains underwent shear (see Hsu, 1975 for a discussion). 34. I f i t i s accepted that the s l i d e d e b r i s behaves as a f l u i d a t high v e l o c i t i e s then some p r e d i c t i o n s can be made on i t s behaviour u s i n g c o n v e n t i o n a l f l u i d mechanics. For example, the v e l o c i t y of ths s l i d e would be p r o p o r t i o n a l t o , among other t h i n g s , the square root of the h e i g h t of the wave of d e b r i s . For s l i d e paths which are r e s t r i c t e d so that the d e b r i s cannot spread out, the high v e l o c i t y could be maintained f o r a longer d i s t a n c e . This could be an e x p l a n a t i o n f o r the anomalously lon g run out of the Huascaran and Rubble Creek s l i d e s . An a l t e r n a t i v e t r a n s p o r t mechanism f o r the Rubble Creek s l i d e i s t hat i t was a water satura t e d d e b r i s flow. There i s no reasonable source f o r the volume of water r e q u i r e d to s a t u r a t e the s l i d e mass a f t e r i t had gained p o r o s i t y i n the i n i t i a l f a i l u r e . There i s a p o s s i b i l i t y t hat the i n i t i a l s l i d e occurred and subsequently the d e b r i s became s a t u r a t e d and was r e m o b i l i z e d . I t appears that t h i s was the mechanism f o r t r a n s p o r t i n g the d e b r i s to Sector I I I of the fan but i t i s an unnecessary c o m p l i c a t i o n to invoke to e x p l a i n the main s l i d e . One would expect some of the d e b r i s from the dry s l i d e before i t was r e m o b i l i z e d as a wet s l i d e to be s t i l l v i s i b l e i n the upper p a r t of the v a l l e y but there i s no evidence of t h i s . The d e b r i s was deposited near the angle of repose f o r dry, c o h e s i o n l e s s s o i l at the d i s t a l r i m of the s l i d e mass and i n the l a t e r a l r i d g e s . The. s l i d e d e b r i s i n i t s present s t a t e has been observed to " f l o w l i k e wet concrete" (Terzaghi, 1960). This i s common behaviour f o r a l o o s e , s a t u r a t e d s o i l and i t need not be concluded t h a t i t i s a s p e c i a l c h a r a c t e r i s t i c of the d e b r i s of the o r i g i n a l s l i d e nor t h a t t h i s was s a t u r a t e d when the s l i d e occurred n e a r l y 100 years p r i o r to Terzaghi's o b s e r v a t i o n . 35. The debris covering Sector I I I of the fan must have been moving slowly i n order to move around the trees i n th i s area without toppling them. Immediately after the s l i d e the flow i n Rubble Creek Valley would have been greatly hindered by debris and i t i s reasonable to expect that water normally brought down by stream flow would b u i l d up and saturate the loose s l i d e debris i n the v a l l e y . This debris and water mixture would be expected to move as mud flows u n t i l unhindered drainage by the creek was re-established. A l a t e r a l ridge on the south side of the creek at the apex of the fan (Point C, Figure 4) indicates that the main s l i d e was moving i n a di r e c t i o n which would r e s t r i c t i t to the north half of the fan. The material covering Section I I I near the apex of the fan spread out nearly at righ t angles to the d i r e c t i o n of the l a t e r a l ridge. This i s addi t i o n a l evidence for secondary mudflows. Much of the debris i n the v a l l e y above the apex of the fan i s i n lobe-shaped mounds giving the appearance that the most recent movement was viscous flow. These lobes are not common i n Sector I of the fan. The debris cones may have been unsaturated debris rafted down on the surface of the mudflow. The s i m i l a r i t y of these cones to sand cones formed during l i q u e f a c t i o n by earthquakes and to the debris cones found on rapid, dry sl i d e s should not be overlooked. 13. P o t e n t i a l for Future Slides The main reason for concern i n t h i s area, indeed the reason t h i s investigation was begun i s that a large rapid s l i d e occurred recently. The r e p e t i t i o n of land s l i d i n g from the same or adjacent source areas i s a w e l l documented fact (Mathews and McTaggart, 1969; Shreve, 1968; Crandell and Fahnestock, 1965; McDowell, 1962;. and Browning, 1973; Patton, 1976). 36. The p r o b a b i l i t y of another s l i d e o c c u r r i n g should not be s u b s t a n t i a l l y d i f f e r e n t from the p r o b a b i l i t y of a f i r s t s l i d e o c c u r r i n g unless i t ,can be c l e a r l y demonstrated that the c o n d i t i o n s which l e d to the f i r s t s l i d e have been s u b s t a n t i a l l y changed s i n c e i t occurred. As t h i s cannot be done at t h i s time f o r the Rubble Creek s l i d e i t i s only prudent to accept the p o s s i b i l i t y of a s i m i l a r s l i d e i n the f u t u r e . The c o n d i t i o n s which l e d to the 1856 s l i d e began w i t h the d e p o s i t i o n of l a v a a g a i n s t i c e i n the v a l l e y s and the subsequent removal of the i c e some 10,000 years ago (Mathews, 1952). This l e f t steep slopes u n d e r l a i n by l a r g e volumes of m a t e r i a l which have had t h e i r f a c t o r of s a f e t y a g a i n s t f a i l u r e s i g n i f i c a n t l y reduced by removal of the i c e i n recent g e o l o g i c a l times. G e n e r a l l y , rock such as t h a t i n v o l v e d i n the Rubble Creek s l i d e i s strong enough to support i t s e l f ; a c c o r d i n g l y p r e e x i s t i n g d i s c o n t i n u i t i e s are r e q u i r e d f o r a slope to f a i l . The f o u r t h l a v a lobe and north s i d e of the t h i r d lobe are probably u n d e r l a i n by the s i d e s of the p r e - v o l c a n i c v a l l e y . Under the t h i r d l o b e , the n o r t h s i d e of the v a l l e y i n c o n j u n c t i o n w i t h a d i s c o n t i n u i t y through the l a v a formed a s u r f a c e o r i e n t e d i n such a way as t o be conducive t o s l i d i n g . The south s i d e of the p r e - v o l c a n i c v a l l e y i s thought to be o r i e n t e d i n such a way as to be conducive to s l i d i n g of the f o u r t h l o b e . I n the t h i r d l a v a lobe f u t u r e r o c k s l i d e s could occur along the i n t e r s e c t i o n of the p r e - l a v a v a l l e y w a l l and steep j o i n t s i n the l a v a f l o w . Depending upon the o r i e n t a t i o n of the steep j o i n t s the plunge of t h i s i n t e r s e c t i o n i s v a r i a b l e . J o i n t s u r f a c e s which have s t e e p l y p l u n g i n g i n t e r s e c t i o n s are a s s o c i a t e d w i t h s m a l l e r s l i d e volumes i n 37. comparison w i t h j o i n t surfaces which have a s h a l l o w l y plunging i n t e r s e c t i o n . For example, a j o i n t s u rface which i n t e r s e c t s the o l d v a l l e y w a l l a t a plunge of 15° would i n v o l v e a p o t e n t i a l s l i d e volume of about 25,000,000 cu b i c yards. In the f o u r t h lobe as i n the t h i r d , f u t u r e r o c k s l i d e s could occur along the i n t e r s e c t i o n of the p r e - l a v a v a l l e y w a l l and steep j o i n t s i n the l a v a f l o w . The s i d e of the p r e - l a v a v a l l e y appears to slope about 28° (Figure 4) towards Rubble Creek and s l i d e movement could occur down t h i s s u r f a c e . The toe of t h i s p o t e n t i a l s l i d e i s b u r l e d by i n c r e a s i n g l y t h i c k e r d e p o s i t s of m a t e r i a l i n Rubble Creek V a l l e y from the western end of the lobe towards the east. This i n c r e a s e i n toe support towards the east l i m i t s the t o t a l volume of rock which could s l i d e from the f o u r t h lobe a t one time. The area, from the western l i m i t of the f o u r t h lobe to an e a s t e r n l i m i t ' where the toe support becomes l a r g e (Figure 5 ) , i n c l u d e s a p o t e n t i a l s l i d e volume of 76,000,000 cubic yards r e s t i n g on the p r e - l a v a s u r f a c e . Various mechanisms may t r i g g e r movement of these l a r g e masses. Increased groundwater pressures appears to be a l i k e l y mechanism e s p e c i a l l y f o r the t h i r d lobe because of the subsurface drainage which occurs beneath the lobe. S l i d e movement could be i n i t i a t e d i n e i t h e r lobe by an earthquake. Once s l i d e movement begins the a c c e l e r a t i o n and t r a n s p o r t of the mass i s not f u l l y understood and i t s behavior i s best estimated by comparison w i t h s i m i l a r s l i d e s . Because the 1856 s l i d e t r a v e l l e d down the f u l l l e n g t h of Rubble Creek V a l l e y at a high v e l o c i t y i t should be considered that any f u t u r e l a r g e s l i d e s could reach the populated areas of the f a n at a high v e l o c i t y . SCALE - MODEL STUDIES 1. General The mechanism by which s l i d e masses, such as Rubble Creek s l i d e , are transported to the d e p o s i t i o n a l area i s not f u l l y understood and depends on a number of f a c t o r s . Complex p h y s i c a l behaviour i s o f t e n i n v e s t i g a t e d through use of scale-models p a r t i c u l a r l y i n the study of f l u i d flow. The motion of Rubble Creek s l i d e appears to have been f l u i d - l i k e and many of the v a r i a b l e s such as g r a v i t y , s l o p e , d e n s i t y , s i d e f r i c t i o n and i n t e r n a l s t r e n g t h which c o n t r o l f l u i d flow a l s o appear to c o n t r o l s l i d e movement. For the case of Rubble Creek s l i d e , i t was thought that i f a f l u i d c ould be found which would model the complex path of the 1856 s l i d e then t h i s f l u i d c ould be used to p r e d i c t the behaviour of p o t e n t i a l s l i d e s of a s i m i l a r nature from the same area. S i m i l a r s t u d i e s , based on a t r i a l and e r r o r method, have been c a r r i e d out f o r the Elm s l i d e (Hsu, 1975). Comparable model s t u d i e s have been c a r r i e d out f o r t u r b i d i t y c u r r e n t s (Middleton, 1966). For a s c a l e f a c t o r of 1:2500 a u n i t l e n g t h on the model (fm) i s e q u i v a l e n t to 2500 times t h i s l e n g t h on the prototype ( i p ) (Hubbert, 1937). For t h i s case the v e l o c i t y i n the prototype (Vp) i s r e l a t e d to the v e l o c i t y i n the model (Vm), by the f o l l o w i n g r e l a t i o n s h i p : Vp = Vm /j?p/J?m = 50Vm s i m i l a r l y f o r time: = 50 tm 2. Experimental Methods 0> A topographic model of the area i n v o l v e d i n the s l i d e was c o n s t r u c t e d , as shown on Photograph 12. The model was made from corrugated cardboard cut i n the shape of each 100 f o o t contour and spaced by wooden b l o c k s . The cardboard was subsequently covered by p l a s t e r , sanded and p a i n t e d . The f i n a l o u t s i d e dimensions o f the model were about 6 f e e t by 10 f e e t by 3 f e e t h i g h . C o n s t r u c t i o n i s l a b o r i o u s f o r a model b u i l t i n t h i s way, but more important, i t was very d i f f i c u l t to modify topography or s l i d e c o n f i g u r a t i o n s as d e s i r e d . P l e x i g l a s s sheets were f i t t e d i n t o s l o t s i n the p l a s t e r so tha t the sheets could be removed q u i c k l y to r e l e a s e a model s l i d e . The path of the prototype s l i d e was marked on the model so that the movement of a model s l i d e c o u l d be compared to that of the prototype. S e v e r a l volumes were t e s t e d t o i n v e s t i g a t e the i n f l u e n c e of volume on v e l o c i t y and path. Three volumes (20, 30 and 81 m i l l i o n cubic yards) were r e l e a s e d from near the source of the 1856 s l i d e and a volume e q u i v a l e n t to 91 m i l l i o n c u b i c yards was r e l e a s e d from the f o u r t h l a v a l o b e . Due to l i m i t a t i o n s on the shape of the p l e x i g l a s s sheets the t e s t volume r e l e a s e d from the f o u r t h lobe was about 20% l a r g e r than the volume e q u i v a l e n t to the p o t e n t i a l s l i d e d e s c r i b e d i n the previous s e c t i o n . Because of the l a r g e e r r o r i n h e r e n t i n e s t i m a t i n g p o t e n t i a l s l i d e volumes the 20% excess volume was not thought to be s i g n i f i c a n t . Most of approximately 100 t e s t s l i d e s c a r r i e d out f a l l i n t o one of f o u r d i f f e r e n t s e r i e s of t e s t s . The f i r s t s e r i e s of t e s t s ( S e r i e s A) was designed to t r y out d i f f e r e n t p o s s i b l e m o d e l l i n g m a t e r i a l s 40. Photograph 12 T y p i c a l model s l i d e showing coloured s t r i p e s . The s l i d e m a t e r i a l was h o r i z o n t a l l y l a y e r e d at the s t a r t w i t h red at the t o e , bl u e a t the top and brown between the two. 41. In a l l , about twenty d i f f e r e n t m a t e r i a l s or combinations of m a t e r i a l s were t r i e d , i n c l u d i n g : water, sand, water and sand, p l a s t i c beads, beads and water, f i n e mica, f i n e mica and water, b a r i t e , b a r i t e and water, b e n t o n i t e and b e n t o n i t e - b a r i t e - w a t e r combinations. The b e n t o n i t e s l u r r i e s were made from tap water and commercial b e n t o n i t e (Quik G e l , B a r o i d I n d u s t r i e s Ltd.) w i t h commercial b a r i t e ( B a r o i d , Baroid I n d u s t r i e s Ltd.) o f t e n as an a d d i t i v e . From S e r i e s A i t became obvious t h a t the onl y m a t e r i a l t e s t e d which had any chance of m o d e l l i n g the prototype s l i d e i n d e t a i l was the b e n t o n i t e - b a r i t e - w a t e r s l u r r y . A c c o r d i n g l y , a second s e r i e s of t e s t s ( S e r i e s B), was c a r r i e d out i n order to determine the best combination of these m a t e r i a l s to model the prototype s l i d e . From S e r i e s B the p a r t i c u l a r mix which best modelled the s l i d e path was chosen and t h i s mix was used f o r a subsequent s e r i e s of t e s t s ( S e r i e s C), i n which d i f f e r e n t s l i d e volumes and p o s i t i o n s were t r i e d . A f o u r t h s e r i e s of t e s t s ( S e r i e s D), was c a r r i e d out w i t h the model t i l t e d a t 1, 2 and 3 degrees u s i n g f o u r mixtures having a range i n v i s c o s i t i e s from too t h i c k to too t h i n . As p a r t of S e r i e s B four t r i a l runs were made u s i n g b e n t o n i t e - b a r i t e s l u r r i e s made w i t h the same measured weight of each i n g r e d i e n t . These t e s t s were done i n order to check the r e p e a t a b i l i t y of the t r i a l runs. I n a d d i t i o n , the flow of a l l mixes through a f u n n e l was timed i n order to have a crude measure of t h e i r r e l a t i v e v i s c o s i t i e s . Food c o l o u r i n g was used to mark v a r i o u s l a y e r s i n many of the s l i d e s i n order to f o l l o w the movement of d i f f e r e n t p a r t s . P l a s t i c e n e b l o c k s about a tenth of an i n c h i n diameter suspended i n the s l u r r y were a l s o used f o r t h i s purpose. 42. Twenty-four of the model s l i d e s were recorded on 8 mm movie f i l m and l a t e r analysed frame by frame f o r v e l o c i t y and p a t t e r n of movement (Figure 6). Notes and sketches were made of most of the other model s l i d e s . 3. R e s u l t s of Model Studies i ) General Although an attempt was made to o b t a i n q u a n t i t a t i v e r e s u l t s through t i m e - p o s i t i o n measurements, the q u a l t i t a t i v e r e s u l t s appear to be the most i n t e r e s t i n g . Some of the most remarkable o b s e r v a t i o n s were made when coloured l a y e r s of b e n t o n i t e s l u r r y were used f o r the s l i d e m a t e r i a l . In these t e s t s the l a y e r which was o r i g i n a l l y a t the toe of s l i d e remained along the l e a d i n g edge of the s l i d e when i n motion and was deposited along the outer edge of the s l i d e path and a t the extreme d i s t a l end, as shown on Photograph 12. The l a y e r which was o r i g i n a l l y placed i n the middle of the s l i d e at the source was deposited between the l a y e r o r i g i n a l l y at the toe and the l a y e r o r i g i n a l l y at the top. The top l a y e r was deposited along the center of the f l o w . The coloured l a y e r s a l s o showed a s t r i p e d p a t t e r n which i s produced by d i f f e r e n t i a l movement between p a r t s of the s l i d e d e b r i s . This s t r i p i n g has been -observed on many s l i d e d e p o s i t s and i t i s i n t e r e s t i n g to compare Photograph 12 w i t h Photographs 13 and 14. The l a t t e r two photographs were taken of the Deva s t a t i o n G l a c i e r s l i d e which occurred during J u l y 1975 near Pemberton, B.C. (Figure 7). This s l i d e was composed of very weak recent v o l c a n i c s which s l i d o f f a steep mountain s i d e (Photograph 13) and thence down a v a l l e y f o r s e v e r a l m i l e s before 43. Photograph 13 Dev a s t a t i o n G l a c i e r S l i d e . Source a r e a , s t r i p i n g i n the d e b r i s and mud fl o w s along f a r s i d e of g l a c i e r . The mass s l i d toward the viewer, swept up on the near s i d e of the v a l l e y , a b r u p t l y changed d i r e c t i o n and moved to the r i g h t . 45. Photograph 14 D e v a s t a t i o n G l a c i e r S l i d e d e p o s i t , s t r i p i n g i n the d e b r i s and i m p r i n t of subsequent mudflow. Ph o t o g r a p h 15 D e v a s t a t i o n G l a c i e r S l i d e P a t h , showing b a n k i n g of the h i g h v e l o c i t y tongue as i t rounded a c o r n e r (1, 2) and the n e a r l y h o r i z o n t a l l i n e o f the subsequent mudflow ( 3 ) . to. coming to r e s t . I t can be seen that the s t r i p i n g i s almost p a r a l l e l to the edges of the s l i d e path and the dep o s i t , s i m i l a r to the model s l i d e s . The Devastation G l a c i e r s l i d e i s s i m i l a r to the Rubble Creek s l i d e i n t h a t ; i t f o l l o w e d a long path down a gentle slope (Photograph 15) apparently at a high v e l o c i t y a f t e r i n i t i a l l y s t a r t i n g on a steep s l o p e ; i t was composed of recent v o l c a n i c d e b r i s ; i t was f o l l o w e d by mud fl o w s ; the l e a d i n g tongue swept up from one s i d e of the v a l l e y to the ot h e r ; the d e b r i s was p o o r l y s o r t e d and very broken up; and the d e b r i s appears to have been very f l u i d . I t should be noted t h a t the s t r i p i n g at Deva s t a t i o n G l a c i e r s l i d e wasoobviously only i n the h i g h v e l o c i t y tongue which preceded the mudflows. This comparison between the model s l i d e s , D e v a s t a t i o n G l a c i e r s l i d e and Rubble Creek s l i d e i s important i n that i t shows that the models e x h i b i t some of the fe a t u r e s of t h i s type of n a t u r a l s l i d e . Therefore, more credence may be plac e d on other f e a t u r e s which the models showed. Two other secondary f e a t u r e s shown by the model s l i d e which were s i m i l a r to the prototype s l i d e were (1) r e l a t i v e l y t h i c k , s t e e p - s i d e d d e p o s i t s along the edge of the s l i d e path and (2) a t r i a n g u l a r mound of d e b r i s deposited on the upstream s i d e o f the knob near the apex of the f a n . These model f e a t u r e s could be compared to the l a t e r a l r i d g e s and the mound of d e b r i s a t the apex of the fan which were observed at Rubble Creek. The movement of the model s l i d e i s s i m i l a r to the prototype i n t hat they both show an i n i t i a l r a p i d movement and a quick stop f o l l o w e d by secondary mudflows. ( i i ) Test S e r i e s A This s e r i e s of t e s t s was p r i m a r i l y c a r r i e d out to determine what type of m a t e r i a l would be most s u i t a b l e f o r use i n t r y i n g to model the s l i d e . Dry m a t e r i a l s such as uniform sand, p l a s t i c beads, f i n e mica, powdered b a r i t e and powdered b e n t o n i t e were t r i e d ; however, none of these m a t e r i a l s t r a v e l l e d f a r enough and they were thus u n s u i t a b l e f o r modelling the s l i d e . Tests were a l s o c a r r i e d out w i t h mixtures of the above m a t e r i a l s and water as w e l l as water alone. I t was found t h a t most of these mixtures were u n s u i t a b l e . In the cases of sand and beads the water ran out of the mixture l e a v i n g the p a r t i c l e s behind as a d e p o s i t near the top of the v a l l e y . The most p r o m i s i n g mixture was found to be b e n t o n i t e and water. This mixture was s e l e c t e d because a wide range of v i s c o s i t i e s was a v a i l a b l e and the s l u r r y was t h i x o t r o p i c . Because i t i s t h i x o t r o p i c there was some p o s s i b i l i t y of m o d e l l i n g the very f l u i d behaviour i n motion, the r a p i d stop and the steep d e p o s i t i o n a l slopes at the edges of the d e p o s i t . ( i i i ) Test S e r i e s B B a s i c a l l y t e s t s e r i e s B was c a r r i e d out to f i n d which combination of b e n t o n i t e , b a r i t e and water would b e s t f o l l o w the s c a l e d path of the s l i d e . I t was found t h a t a l l combinations tended to flow too high on the f i r s t curve on the south s i d e of the creek. I t i s considered that i n t h i s area the estimated e l e v a t i o n of the p r e - s l i d e v a l l e y f l o o r was too h i g h . Because of the way the model was c o n s t r u c t e d , however, the contours i n the upper p a r t of the v a l l e y were not changed. For s e v e r a l t e s t s l i d e s , 48. d e f l e c t o r s were put along t h i s f i r s t curve i n order to f o r c e the mud to f o l l o w . t h e curve more c l o s e l y . Thus d e f l e c t e d , the mud was found to f o l l o w the successive curves more c l o s e l y . The heights reached on curves below the f i r s t and above the apex of the fan were s i m i l a r to the prototype; however, the maximum r i s e s were o f f s e t downstream, perhaps because the f i r s t curve was too long and h i g h . The l a s t curve along the edge of the f a n below the apex was never modelled p r o p e r l y . I t i s considered t h a t the curves were a l l developed too f a r downstream and t h a t the second from l a s t curve, which would have d i r e c t e d the d e b r i s up the v a l l e y w a l l on the north s i d e of the f a n , d i d not have a chance t o f u l l y develop. A l l model s l i d e s showed a r a p i d l y d e creasing v e l o c i t y from the upper p a r t of the v a l l e y to the lower p a r t . The record of the prototype however, i n d i c a t e s t h a t a r e l a t i v e l y constant v e l o c i t y was maintained along the path of the s l i d e (pp 26 - 29) except below the apex of the fan where i t spread out and stopped. A t y p i c a l p l o t of the p o s i t i o n of the l e a d i n g edge of the b e n t o n i t e s l u r r y versus time i s shown on Figure 6 and the v e l o c i t i e s c a l c u l a t e d from the t r i a l t e s t s are given i n Table I . I f the mud was thickened enough so t h a t i t d i d not r i d e very h i g h on the f i r s t curve, i t a l s o stopped i t s r a p i d movement near the apex of the f a n . This was the main shortcoming of the b e n t o n i t e - b a r i t e - w a t e r s l u r r y f o r mo d e l l i n g the Rubble Creek S l i d e . In a d d i t i o n , the v e l o c i t i e s given on Table I are much hi g h e r than TABLE I Slide V e l o c i t i e s From Model Studies T r i a l No. Volume Equivalent Velocity (fps) (cc) Upper Half Lower Half Average 15-1 2000 246 207 226 24-1 2000 246 149 190 24-2 4000 266 255 261 24-3 4000 290 298 294 24-4 2000 220 199 210 24-6 2000 291 168 219 23-2 1300* 200 168 184 23-3 2000* 273 300 281 23-4 2000 ** 256 153 197 23-5 2000** 239 199 219 23-6 2000** 183? 215 197 23-7 2000 290 244 279 23-8 2000 237 224 234 Same mixture of bentonite and water Same mixture of bentonite and water 50 the v e l o c i t i e s calculated for the s l i d e (Section 10). I t was found that mud with model v e l o c i t i e s s i m i l a r to those given i n Section 10 did not t r a v e l the f u l l distance down the va l l e y . T r i a l 24-4. was t y p i c a l of the models which best followed the path of the prototype. This mixture was composed of 80 grams of QuikGel, 1000 grams of Baroid, and 800 cubic centimeters of Ottawa sand i n 2000 cubic centimeters of water. A l l of the model s l i d e s slowed markedly when they spread out on the fan. This slowing i s an expression of the control the height of a wave has on i t s velo c i t y (compare t u r b i d i t y currents, avalanches, dam bursts, et c . ) . Repeated model s l i d e s using the same mixture of bentonite, b a r i t e and water produced e s s e n t i a l l y s i m i l a r model s l i d e paths and deposits. (iv) Test Series C Although most tests were carried out using a volume of mud si m i l a r to the estimated volume of the 1856 s l i d e , several tests were carried out using smaller or larger volumes. I t was found that the larger the volume for a given mixture, the farther and fast e r i t tra v e l l e d . The paths of s l i d e s from the same source area were e s s e n t i a l l y the same f o r a l l volumes although the larger volumes rode higher on the curves and were deposited farther down the fan and the smaller volumes rode lower on the curves and were deposited near the apex of the fan or i n the va l l e y . The model s l i d e s released from the fourth lobe moved d i r e c t l y across the va l l e y and swept high up on the opposite side. A f t e r t h i s f i r s t curve the s l i d e followed a s i m i l a r path to the s l i d e s from the t h i r d lobe. The f i n a l deposit covered a larger area of the fan. (Photograph 16). Photograph 16 Model s l i d e e q u i v a l e n t to 91,000,000 cubic yards from the Fourth Lava Lobe. Cheakamus Dam i s on the lower l e f t s i d e of the photograph, source of s l i d e on the upper r i g h t . 52. (v) Test S e r i e s D In order to f i n d out whether a s l i g h t t i l t i n g of the model i n the d i r e c t i o n of flow and a t h i c k e r mixture would more c l o s e l y model the prototype path, s e v e r a l t e s t s were c a r r i e d out w i t h the model t i l t e d at 1°, 2° and 3°. I t was found that the mixtures which t r a v e l l e d the f u l l l e ngth of the s l i d e path were s t i l l too f a s t to model the curves i n the upper p a r t of the path. I t i s thought that l a r g e r t i l t s would i n c r e a s e the slope of the v a l l e y f l o o r by too l a r g e an amount f o r any c r e d i b i l i t y to be placed on the r e s u l t s without some t h e o r e t i c a l b a s i s . CONCLUSIONS The f o l l o w i n g c o n c l u s i o n s can be drawn from the f i e l d and l a b o r a t o r y study of the Rubble Creek S l i d e : 1) The i n i t i a l f a i l u r e of the s l i d e occurred along the contact of the v o l c a n i c s w i t h the g l a c i a l d e b r i s o v e r l y i n g the Cheakamus Formation on the nor t h s i d e , steep j o i n t s i n the head scarp and through c l o s e l y j o i n t e d v o l c a n i c rock below the head scarp; 2) The s l i d e was dominantly composed of v o l c a n i c bedrock, rub b l e and t a l u s ; 3) The i n t e r n a l s t r u c t u r e of the f o u r t h l a v a lobe appears to be e s s e n t i a l l y the same as the t h i r d lobe and i t - a l s o r e s t s on p r e - v o l c a n i c v a l l e y w a l l ; 4) A tongue of d e b r i s t r a v e l l e d down the v a l l e y a t a h i g h v e l o c i t y , sweeping from s i d e to s i d e and uprooting a l l v e g e t a t i o n i n i t s path; ) This tongue of d e b r i s was deposited on the n o r t h s i d e of the f a n and was f o l l o w e d by mudflows which modified the d e b r i s i n the upper p a r t of the v a l l e y and which were deposited on the south s i d e of the f a n , k i l l i n g and bu r y i n g the v e g e t a t i o n i n t h i s area; The v e g e t a t i o n on a s e c t i o n of the fan i n the shadow of the g r a n i t i c knob a t the apex of the fan was not destroyed at the time of the s l i d e ; - The d e b r i s i n the s l i d e d e p o s i t s i s v e r y p o o r l y s o r t e d angular d e b r i s p r i m a r i l y v o l c a n i c i n composition; The d e b r i s can be d i s t i n g u i s h e d from the u n d e r l y i n g a l l u v i a l f a n d e p o s i t s by the absence of s o r t i n g i n the 2 to 4 mm range and i n the s i l t s i z e s ; 54. 9) The s l i d e occurred during the l a t e w i n t e r of 1855-56 or e a r l y s p r i n g of 1856; 10) The volume of the s l i d e i s estimated to be about 33,000,000 cubic yards; 11) There i s some evidence of e a r l i e r s l i d e s i n the form of deposits of wood and dep o s i t s of coarse unsorted d e b r i s beneath the fan d e p o s i t s ; 12) There i s some evidence of l a t e r s l i d e s i n the form of younger v e g e t a t i o n and lobe-shaped deposits along the v a l l e y adjacent to the base of the f o u r t h lobe; 13) The s l i d e maintained a v e l o c i t y between about 80 and 118 f e e t per second down the low slope of the v a l l e y f l o o r and through s e v e r a l changes i n d i r e c t i o n ; 14) The s l i d e may have been t r i g g e r e d by a bui l d - u p of ground water pressures although l o c a l earthquakes may a l s o have been the cause; 15) The s l i d e d e b r i s was probably t r a n s p o r t e d as a s e l f - s u s p e n d i n g mixture of r a p i d l y moving p a r t i c l e s which behaved i n a f l u i d - l i k e manner; 16) Both the f o u r t h l a v a lobe and the t h i r d l a v a lobe were deposited under c o n d i t i o n s which make them much more s u s c e p t i b l e to s l i d i n g than most other slopes i n the area; 17) S c a l e models are a u s e f u l means by which to study the motion and some of the c h a r a c t e r i s t i c s of s l i d e s such as Rubble Creek S l i d e ; 18) The model s l i d e s as w e l l as Rubble Creek and De v a s t a t i o n G l a c i e r s l i d e s move as a high v e l o c i t y tongue of d e b r i s f o l l o w e d by slower mudflows; 55. 19) The s t r i p i n g observed i n many s l i d e s can be e x p l a i n e d by d i f f e r e n t i a l movement as the d e b r i s s t r e t c h e s out i n the d i r e c t i o n of motion; 20) The model t e s t s suggest that the prototype s l i d e v e l o c i t y was l e s s than about 200 f e e t per second; 21) The model s l i d e s i n d i c a t e t h a t l a r g e r s l i d e s t r a v e l f a r t h e r and f a s t e r than s m a l l e r s l i d e s ; 22) The model s t u d i e s i n d i c a t e that the v e l o c i t y i s a l s o p r o p o r t i o n a l to the t h i c k n e s s of the moving d e b r i s ; 23) The model s l i d e s i n d i c a t e t h a t the path f o l l o w e d by a s l i d e i s l a r g e l y determined by the topography and that l a r g e changes i n d i r e c t i o n without l a r g e l o s s e s i n v e l o c i t y are p o s s i b l e ; 24) The model i n d i c a t e d that m a t e r i a l s i n v o l v e d i n flows such as the ones t e s t e d tend t o maintain t h e i r r e l a t i v e p o s i t i o n s , and t h i s c h a r a c t e r i s t i c of l a n d s l i d e deposits i s not n e c e s s a r i l y an i n d i c a t i o n of s l i d i n g r a t h e r than flo w ; 25) I t i s only prudent to accept the p o s s i b i l i t y of the occurrence of another s l i d e s i m i l a r to the 1856 s l i d e because i t cannot be demonstrated that c o n d i t i o n s have s u b s t a n t i a l l y changed s i n c e 1856. 56. LITERATURE CITED R.A., 1954, Experiments on a gravity free dispersion of large solid spheres i n a Newtonian f l u i d under shear: Royal Soc. London P r o c , ser. A, V. 225, pp. 49 - 63. CO., 1975, Case examples of i n s t a b i l i t y of rock slopes: B.C. Professional Engineer, V. 26, No. 2, pp. 12 - 13. J.M., 1973, Catastrophic rock slide, Mount Huascaran, north- central Peru, May 31, 1970: Am. Assoc. Petroleum Geologists Bull., V. 57, pp. 1335 - 1341. and Heim, A., 1881, Der Bergstruz von Elm den 11. September 1881: Zurich, Wurster, 163 pp. D.R., and Fahnestock, R.K., 1965, Rockfalls and Avalanches from L i t t l e Tahoma Peak on Mount Rainier Washington: U.S. Geol. Survey Bull. 1221-A, pp. A l - A30. ijor W., 1858, Report to Governor Douglas on a Proposed Route Dated 2nd October 1858. lal, 1968, United States Department of the Interior, Bureau of Reclamation, F i r s t Edition - Revised, Chapter 1 Properties of soi l s pp. 1 - 69. 1976, Very large rockslides in the Canadian Cordillera: in Abstracts for Symposium on Geomorphology of the Canadian Cordillera and Its Bearing on Mineral Deposits, Seol. Assn. Canada, Cordilleran Sect. p. 17 - 18. 1975, Production of Gaseous Pore Pressure During Rock Slides: lock Mechanics, V. 7, pp. 193 - 197. L882, Der Bergsturz von Elm: Zeitschrift der deutschen ;eologischen Gesellschaft, V. 34, pp. 74 - 115. L . , 1973, Avalanche mode of motion: Implications from unar examples,: Science, V. 180, pp. 1051 - 1055. 1975, Catastrophic debris streams (sturzstroms) generated y rockfalls: Geol. Soc. America Bu l l . , V. 86, pp. 129 - 140, fi g s . , January 1975, Doc. no. 50117. £., 1937, Theory of Scale Models as Applied to the Study of aologic Structures: Geol. Soc. Amer. Bul l . , V. 48, p. 1459 - 1519. 1966, The transport mechanism in catastrophic rockfalls: >ur. Geol., V. 74 pp. 79 - 83. 5/. Krumbein, W.C., 1941, Measurement and geological significance of shape and roundness of sedimentary p a r t i c l e s : Jour. Sediment. P e t r o l . , 11:68 Soc. of Economic Paleontologists and Mineralogists. McDowell, B., 1962, Avalanche: Natl. Geog. Mag., V. 121, no. 6 pp. 854 - 880. Mathews, W.H., 1952, Ice-dammed lavas from Clinker Mountain, southwestern B r i t i s h Columbia, Amer. Jour, of Science, V. 250, pp. 553 - 565. 1958, Geology of Mount Garibaldi map-area, southwestern B r i t i s h Columbia, Canada: B u l l . Geol. Soc. America, V. 69, pp. 161 - 179, 179 - 198. Mathews, W.H., and McTaggart, K.C., 1969, The Hope lan d s l i d e , B r i t i s h Columbia: Geol. Assoc. Canada, Proc. V. 20, pp. 65 - 75. Middleton, G.V., Small-scale models of t u r b i d i t y currents and the c r i t e r i a of auto-suspension: Jour. Sedimentary Petrology, V. 36, No. 1, pp. 202 - 208, March 1966. Milne, W.G., Pers. Comm. Canada, Department of Energy, Mines and Resources, D i v i s i o n of Seismology, V i c t o r i a Geophysical Observatory, January 25, 1973. Morris, H.M., 1963, Applied Hydraulics i n Engineering: The Ronald Press Company, New York, p. 132, p. 148. Patton, F.D., 1976, The Devastation Glacier S l i d e , Pemberton, B.C. . In Abstracts for Symposium on Geomorphology of the Canadian C o r d i l l e r a and i t s bearing on mineral deposits; Geol. Assn. Can., Cordilleran Sect., p. 26. Scheidegger, A.E., 1973, On the prediction of the reach and v e l o c i t y of catastrophic landslides: Rock Mechanics, V. 5, pp. 231 - 236. Shreve, R.L., 1966, Sherman landslide, Alaska: Science, V. 154, pp. 1639 - 1643. 1968, Leakage and f l u i d i z a t i o n i n a i r - l a y e r lubricated avalanches: Geol. Soc. Amer. B u l l . , V. 79, pp. 653 - 658. Terzaghi, K., 1954, Report on the proposed storage dam south of Lower S t i l l w a t e r Lake on the Cheakamus River, B.C.: Earth Dams Selected Professional Reports pp. 394 - 403. 1960, Storage dam founded on s l i d e debris: Jour. Boston Society of C i v i l Engineers, pp. 64 - 94. APPENDIX ADDITIONAL FIELD DATA TABLE OF CONTENTS Tree Ages, Sample Locations and L i t h o l o g y of C l a s t s G r a i n S i z e D i s t r i b u t i o n s - Sheet 1 G r a i n S i z e D i s t r i b u t i o n s - Sheet 2 G r a i n S i z e D i s t r i b u t i o n s - Sheet 3 G r a i n S i z e D i s t r i b u t i o n s - Sheet 4 G r a i n S i z e D i s t r i b u t i o n s - Sheet 5 G r a i n S i z e D i s t r i b u t i o n s - Sheet 6 G r a i n S i z e D i s t r i b u t i o n s - Sheet 7 G r a i n S i z e D i s t r i b u t i o n s - Sheet 8 Pebble Size,. S p h e r i c i t y and Roundness - Sheet 1 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 2 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 3 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 4 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 5 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 6 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 7 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 8 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 9 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 10 Pebble S i z e , S p h e r i c i t y and Roundness - Sheet 11 Rubble Creek Survey Traverse Seismic Survey - Sheet 1 Seismic Survey - Sheet 2 Seismic Survey - Sheet 3 Seismic Survey - Sheet 4 Seismic Survey - Sheet 5 59. too 90 t so X O UJ 5 70 CO 2 X 60 5£> 40 or UJ 2 :JO z LU o a: io UJ 0- #10 RUBBLE CREEK VALLEY EL. 2300 N #9 RUBBLE CREEK VALLEY EL. 1900 150 FEET ABOVE CREEK N 6 0 3 0 U L D E R S COSiJLES 20 C O A R S E r GRAIN i .J ' o1 M E D I U M D I A M E T E R T ! N F M I L L I M E T R E ? ( D ) . I I 0 FIME C O A R S E M E D I U M 2 I L 0 - 0 6 0 0 FINE C O A R S E #J0 GRAVEL # 2 2 #30 044 * 6 0 tlOO- #200BRITISH STANDARD SIEVE — I — i 1 1 > . , SAND S ILT GRAIN SIZE DISTRIBUTION MASSACHUSETTS INSTITUTE OF TECHNOLOGY CLASSIFICATION ( 1931 and 1949 ) SHEET I CTl BOULDERS C033LES COARSE • MEDIUM FINE | COARSE MEDIUM *9 * ' lO # 2 2 f 30 044 « 6 0 » 1 . 1,11 , < T , 1 In, 1 • „ , FINE COARSE #200 BRITISH STANOARO S1TVE GRAVEL SAND SILT GRAIN SI2E DISTRIBUTION MASSACHUSETTS INSTITUTE OF TECHNOLOGY CLASSIFICATION ( 1931 end 1949 ) SHEET 2 30ULDERS |C033l£S COARSE - MEDIUM FINE J COARSE MEDIUM *!* * » © #22 *30 0«4 #60 FINE COARSE #100 #200 BRITISH STANDARD SIEVE GRAVEL .AND SILT GRAIN SIZE DISTRIBUTION MASSACHUSETTS INSTITUTE OF TECHNOLOGY CLASSIFICATION ( 1931 and 1949 ) SHEET 3 X tii >- CQ Q Z <I X U i z z LU o UJ a. 1 1— 1— \ I • - -1- .. — >> \ ' — \ x v #16 x _ TOP THE SEP OF GRANITIC APEX OF THE u? I F/ OB A 1 >> <• • #1 BORROW PIT FOR CHEAKAMUS DAM SECTOR T > N <k x <> *> >» - 1 - DOULDERS IC033LES COARSE GRAIN 01 AM ETER • MEDIUM FINE IN. M ILL IMETRES (D), COARSE MEDIUM G R A V E L « 1 .—i i— #30 044 #60 1 » t J- FINE C O A R S E #100 #200 BRITISH STANDARD SIEVE SAND SILT GRAIN SIZE DISTRIBUTION MASSACHUSETTS INSTITUTE OF TECHNOLOGY CLASSIFICATION ( 1931 and 1949 ) SHEET 4 CTl co IOC1 901 J 8 0 1 U l £ 701 I CD Z < I 601 5D4 401 or LU Z 3 0 - l HO- z LU o CC 10-j LU 6 0 30ULDERS C033LES 20 COARSE r GRAIN N S N S N #6 BLACK TUSK ACCESS ROA|) TOP OF SECTOR I " N N N ~V <C \ #17 EASTERN EDGE OF V SECTOR I 1 s T FT EASTERN EDGE OF SECTOR I MEDIUM D IAMETER j IN, MILL I METRES (D). I I 0 ^ X V s FINE 0 0 6 COARSE MEDIUM o o FINE COARSE * I 0 GRAVEL <*?2 #30 #44 #60 #00 - #200 BRITISH STANDARD SIEVE SAND SILT GRAIN SIZE DISTRIBUTION MASSACHUSETTS INSTITUTE OF TECHNOLOGY CLASSIFICATION ( 1931 and 1949 ) SHEET 5 lOOl 90 i 5 ^ ijj 5 70j CD z 60 i 504- eoJ cr LU LU o LT )0-| Ixl O. #7 WATER SUPPLY TO EVERGREEN VILLAGE SFXTCR I I I #18 POWERLINE IN EVERGREEN VILLAGE SECTOR I I I IT 60 30ULDERS C03i)LES 20 COARSE GRAIN M E O I U K DIAMETER f IN, M ILL IMETRES (0). I 2 I t 0 0 6 FINE COARSE MEDIUM 0 0 FINE COARSE #10 GRAVEL #22 #30 #44 « 6 0 #KX) #200 BRITISH STAN0AHO SIEVE i I , i . t i i » - • SAND SILT GRAIN SIZE DISTRIBUTION MASSACHUSETTS INSTITUTE OF TECHNOLOGY CLASSIFICATION ( 1931 and 1949 ) SHEET 6  too 90 eo 70 Is X l U >- CO a z <i X V- 01 LU z u . z LU SO 5 0 40 :so \ A T \ #20 WEST BANK OF CHEAKAMUS RIVER NEAR MOUTH OF RUBBLE CRE #*4 MOUTH OF RUBBLE CREEK BENEATH OXIDIZED LAYER K T K O CC 50 UJ 0- 60 30ULDERS C03i!LES 20 COARSE GRAIN O IAMETER f IN, MEDIUM FINE I 0-6 1 I I 0 ! 2 I M ILL IMETRES (D), I 0 0 6 0 0 COARSE MEDIUM FINE COARSE **6 ±2. * I 0 GRAVEL « 2 2 #50 044 #60 **>1 #200 BRITISH STANDARO SIEVE —I—— 1 1 1 > 1 i >A ND S'LT GRAIN SIZE DISTRIBUTION MASSACHUSETTS INSTITUTE OF TECHNOLOGY CLASSIFICATION ( I93I and I949 ) SHEET 8' 68. - 4 - i - 4 -4 -4 -4 T T " 1 i i i r SqmpleNo.- I- r Bare i A ^ n » i A n . ; - - Ctrebkqrrnjs--9t3m!-BofrQw 5 - 1 9 7 5 - -Pftr ^of-Fines-XOT^O" No. of Pebbles Counted- 50.0% 4 4 T T T + •t-H- T t a _ i - 4 4 - 40 Hi 0 1 30 it 20 T T T TJX t t t I I ' i > 1 llllrt r r 69. +-M--T-t- -H-t- 5 +-H- r r - t - i j 1 i i . : : ;: T-Scmpte-No^T'jg- -t—1-« Jx 1 -1—I—>—i— \. 111 rvi rt~H~ - 4 - 4 - r i f T t P - r r- June 5;i9-7-3—; -~ -k-eft-Bank :o£'j - --Location- ! i - i -U- Chcakomu3 Rivier %-of_FJnes_<Q.530^ ! M ! i i I i I I I T T T Counted T T T I i i M r • ' t - r - f - T T T T + -t—i- I I i i t -H - •f-M-4- 4 - 4 - T T -H-+- 40 - M 4 - H - r -r-+ T T - H30 30 36 su. -20 T T T T T T T T T T T T T 3o: 1 ! I HM T T T T 6-50-5rt:58^-66-7D-74-78-32-86-90- SPHERtOTY •H-f ^H2r\3~^H$ f^0Nf)N£SS "7 -L I ... - l . 70. 71. 14 ScjmpleiN or] j4j :Dqte Dojcdfloru ^ttn6g-l-1973; TT1 { "} t -n- r No. of Pebbles Counted 4 4 4 4 - -H- T T rrr - H - 4-4- i-frt H-40 -i—'—i—t—t F30 30 ft -20 •i 1 1 1 1 4-0- I • i i i , 1 1 0 4 . T T -46-50-S4-58-62 x t r 0-L J P H E R I C I T T 66-70-7$-78-82 r86-Sc> -a r2 I O i.4 .?:.€- 71.8-9- R O U N D N E S S ! I I I ! II T~. i T rt-r i i i. - r r r -4-0- T - t " B H E E I 4- • ?   ..LJ 4 J - i ! i m Sample No-.- -7 i - H - 5 %- No. of Pebbles,' S3 - t — r T T -ft 40 t-r 1-T T-rr -An- "Sqrrple:No. 14 •June! 2 9 4 9 7 3 - ; p t f-EVergrefgrr- ?. <X6fIFi nesT<6.530* No. of P̂ bfe+gg "3" rcj: :si2Eit»r>m) «3L I i. 40 T T T 40 - H - T30 30 2£t -20 T T i n +++ " T T -I—!—I— ^5054-58-62'66-70-7A-7S-32r86-SO- SPHERICITY SOUNDNESS — r T 1 I ! T - T T - r "i i i xn: SHEET] a  77 4+4- j|M 14-4-' i i 1 ! i- 4 _ I 1 1 I i i ! i i | 1 II I 1 1 | 1 1 i I i i 1 i 1 X. ! ! I •! i ! ! i i i i ! : ; ; i _30 M i l — -1 j 1 i i — , i M f- - r r r - ^ H r|+- \ ! +4̂ - -44^4- :;!!;.; -J—L_J i_l ' • i ! • i i -&Q- ! 1 : : 1 i 4CXT , i l : : • J i 1 r t f 4+-r 1 1 i : ; 1 : i i i 1 i -40-—»rt—A—IV =^=zFzt= =̂V± . • ! / 1 1 (-H/+ i | i -t-+- IT^I 1 •/! Ml i X ± i , T : SiZEtjnor 3 = E ^ j — | | | |—4-1 ~ ' — p n M4~i r 4_4- 4 — X I ± t ± t _ • „ — ^ r t r r t i | jl1• i i 1 1 i I HH SH-^TXTH-H-! J — 4 ± - x L x — ^ X I L L X • J 1 I ' Ml -"zrzrrz 4 ^ x- ~n~i ± h : r- S a i m p| g. N o..4^ ' ' M i l l zjzzjz T + i z f x M : ^ p =fl=iyt ZZrZXXXixZT^a*^ 14- j i / , ,144X4X7——-j——•—Wage. • 1 •• M : Tr j j [_/_|— - j j ! | - 1 1 | • — 1 I 1 j M i ! ; r r - p r -hp rrrt--+4-^- -Al 1 M - • | : 4-̂  P i " ^ ''A mn " h7 .0 t : i l . X i l X " ~T~ j M j 1 : : ! • i | i j 1 M | i 1 j | • i 1 M MM • -+TTT- V...JT J T ^ 1 • M : • • , — n - p — ^ T t H — ^ X x i X X X z i i — H r r — - r * i — H 4-—No of Pebbles Counted. ' ' S — J — ' , i , : / l i< M''|TM 1 tTT^tTTi^l1' l l 11 11 1 "H" ^ j " " h T 1 M , 1 i i ; ^4 - j - -y4- J±fx4j ̂ ^ M ^ M - I - i t xf====i=^z=EiE= , | ; M i h'- ! 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KEFCENCES B A S E L I N E . * I - A U . B L * A C E O N T H E N O R T H S t D E O F C E E E K P.I.*» - S O U T H E N D or C O N C R E T E B A K - P . X . * 4 - P . I . * 1 8 - E D G E O F R O A D P.T.*W- P.X.»33 - NoETH SIDE or CCEEK. P . I . * 8 * - P . I . « 3 5 - O N ElDGE , N O Z T H *IDE O F C E . P . I . * » S - NOE.TH S I D E O F C K . E E K . P . r . * 3 ? - O N T H E T K A l L . y.T.*A\ - S I C N P O S T C B \ « c l c T o t O BASE, LINE * a R T . * K - N o E T H E N D O F T l W B E K O V E C e i J B B L e c e e a c GeiD B.C. HYDBO © P.I. - POINT OF INTERSECTION s.iw. - SEISWC LINES. Fost TbpocWiPHx AtAP :- S E E L O O L W O O O PLAN 15-8<S , DOME: Roe. u.B.O BRITISH COLUMBIA DEPARTMENT OF HIGHWAYS GEOTECHNICAL AND MATERIALS BRANCH RUBBLE OC. TKAVEFCSE. "THE BAKK IER l " G A K I B A L D I PAKkL AEEA SCALE ~ ; , l"*833 ' l ^ £ 1 / 8 / I 9 T 3 - P ° O J N O ;°-i;v3H| C R - . V . X G N C Rl j89984|j_~._ .' S E I S M I C L I N E * l -I • -I • • ~t — : r : O — t : : : I: • i • :t.-: B e i r o c k . ----- :if?°o ̂ — ; S l o p * > - —I : — - i . 1 / /e^oo ^ s ereeJfc -1 . . . : i : S . l . . * » NOTE: LOCATIOK OF S B S H I C L I N E S , S E E DRW'C K. - S9984 - l~l . . '<oElS'MlC LINE BRITISH COLUMBIA DEPARTMENT OF HIGHWAYS GEOTECHNICAL AND MATERIALS BRANCH E U B B L E C ^ E E k L S E 1 S K I C S L S R . V E Y T H E " B K ^ ^ E K . " D CPAV. N scv.£7;:.r = 5©* 2 3 / 7 / / 9 T 3 • 1 C TRACED i FROJ '.0 j ==-0 V j H J * W . : \ G NO 1 e CHECKEO i FILE NO O l - 0 - 5 8 A '"ffli j No |Sfic«: *»- \ RLJ89985 REVISIONS -.-r-rr l4,SOQ £pS. \ 9,300 £Ps. SEtSKJC JJNE *4- « 4 * 5 , PJ.'AO °/s 105 E. \,SOO _&ft _ S..AOO -fps. . i " . : . r - V i - ; . !' : • ! XS.,500 $\>s- SE1SK IC U N E * l O 81 _ J J i s o ' . f r o m •J . Rubble Cr. *9 —+— —I 7,COO fps. . _ : . . . U - •I :: ; M . O O O jpi.';. ••I- : - .U . ' „ . - l : . . . i « B / . : S l o p e \Q.SOO £ps. NOTE.- LOCATION OF SEISHIC. ' :XINES ; . . S E I S K I O U l N E *"9 BRITISH COLUMBIA DEPARTMENT OF HIGHWAYS GEOTECHNICAL AND MATERIALS BRANCH R U B B L E . CfCEEkL S E I S H I C S U R V E Y "THE *B/OS.E:\HK." 0 S C A L E 5 o • | D A - E 2 4 / 7 / / 9 ? 3 c T R A C E D i P ? O J N O -E ' J v : H CJ=-.v: \G S 3 e C H E C K E D 1 t.u -.a O l - U - S B A V 9 No |s-»,-A - ' - . .... ... ..... • . K.j8998G|§;> P : E V ' S L O N S 82 "Tt* . : : : ! : • - . 1 :Li. :zz::\; '~- -• = >l£pO_£pi . e,s~oo *Ps. \Q>,00O 5?s. , . _u . i - —t.: - - -1 - rrr.r-- -~ . i - _SELSMIC. LINE * G <S.L. J *><S,*'7,.*e.,*ll AK.E. COMMON) 1 . . . . 1. 1 ii.. :' ::: i . - • - - | - - . j : • • 1 . i . :: r : -• * • i i::. " . i . ... ... • ! • •;• j. f " 1 _ • i * I' "•!:" i i .. *! *:: '. i. 1 ~ " ~ r r " 7 " " | ' "*"—;— • • i -"•I. . . . S E I S K I C L l N! E * 7 . IS.I-. *C , * 7 J'»8 J « - l l AK.E.I COKKON) NOTE- LOCAXVOM :OF S E i s n c — r u n e s j " S E E . - t i z v / ' c ; ; - V - c a BRITISH COLUMBIA DEPARTMENT OF HIGHWAYS GEOTECHNICAL AND MATERIALS BRANCH £ 8 B B U E C R 1 E E K . T H E E . * B A f c K . i E g L " mz ^ ;r-.\** So' I-"^E477/I973 83 K G,000 Sps . -.X-:. I: ; :.V;|;' ,:; S l U S 9,fOO fps- _ 4 ; ' t r _ _ S E . I S H I C . U N E . * U. L l6-l_.»S/*7, »8,*ll, ARE. CDMOU;; J : NOTE.: LOCATION OT^ S E I S M I C — \ L.TNES , S E E " •'DTZXN"S. : I '- K - 8 9 9 £ 4 - | - \ . » BRITISH COLUMBIA DEPARTTv'iENT OF HIGHWAYS v^rS^. GEOTECHNICAL AND MATERIALS BRANCH R U B B L E CSEEEXKL S E 1 S A M C 5 i l ^ V £ Y c 1 1 scAt£v;.M»*50' l"-' ; s^4/7 / W l ? ? . c TPACEO « O J NO - • •• H :-*.v.G E CHECKED ^ OWH-58 A • -at- j No j Sc * 1 | REVISIONS :;• V Slope. #1 « 3 * 4 •5 , a , : n,sooips. SEISKIC _UNE ̂ E A <S.L_. • 1 2 * * 1 3 A C E COHMON) 84 :l ;i:..:L-.- : !:: : : ' —77V • • • - i - . ..j. • - i • : . . I. • _ i - - i ' ...... *4 *» 4 M L . -r-.v .1/ i t . _ . I • } • ••-. • : t : - : : : : ; : : i - ... • ... j: -SEISMIC LINE. ..* 13___ (S,U-*I2.A, -.13,*K; ACE. Ctl<WON> -i « 4 «9 t 528 5 r o m " ; B r i d g e . I.50O £ps. %200 SpS. i :. t . . t S . \ » . * 1 2 ^ , » B , « l 4 . A C E C O f V W M ) ~ — r r j . —". „ -. I j\. ][•: V M X : | X : 4 4 N O T E - L O C A T I O N ,• O F S E \ < S M 1 C . . - U N T ^ - - - S E E - —Dtws: :. £-83984-I-V 1|- BRITISH COILSVSBJA DEPARTTVENT Of HIGHWAYS ^JfS- GEOTECHNICAL AND MATERIALS BRANCH R U B B L E C T ^ E E k L S E I S M I C S l i K V E Y T H E * B A K K I E K . " SCALE o 5Q' [ D A T E g 4 / 7 / I 9 T 3 I R E G H w OI-H-58A L E G E N D : -0.32 sec- 0.32 sec AREA COVERED BY PROTOTYPE SLIDE DEBRIS POSITION OF LEADING EDGE OF MODEL SLIDE AND TIME AFTER RELEASE POSITION AND SHAPE OF A DROP OF COLOURED MUD IN THE MODEL SLIDE AND THE TIME AFTER RELEASE OF THE SLIDE O o o J RUBBLE CREEK SLIDE SCALE MODEL SLIDE MOTION AND DEFORMATION Scale 1:10000 FIGURE El 2100 El 2000 El 2000 El 1900 El 1800 El 1800 El 1800 El 1700 El 1700 El 1600 El 1600 El 1400 El 1200 4500 4000 3500 3000 2500 4500 Pi § k j 4000 3500 3000 2500 2000 Line joins upper limit of slide debris on valley slides Slide debris deposited on valley floor x center of gravity Pre - volcanic Ji* surface SECTION C-C 4 t h Lava lobe Pre-volcanic 1^ surface - — ^ SECTION D-D 4500 4O00 3500 3000 2500 2000 k j k 5000 k i ti 4500 4000 3500 5000 ti 4500 4000 3500 3000 3rd Lava lobe & 5000 k! 4500 Pre-volcanic 4000 surface. Apparent dip 13 i 3500 k j ti SECTION E-E 3 r d Lava lobe 5000 4000 Pre volcanic surface. Apparent dip 15° 3 5 0 0 3000 k j ti SEC TIONS A CROSS RUBBLE CREEK VALLEY SECTION E-E E l 4620 5000 k j ti SECTION G-G NOTE : Eor locations of Sections see Eigure 4 R U B B L E C R E E K S L I D E G E O L O G I C S E C T I O N S A L O N G S L I D E P A T H F I G U R E 5 Scale 1:10000  4800 4600 4400 4200 4000 3800 3600 3400 3200 'Ti-V.Red rubble V\— Regular, vertical columns several feet wide. The size of some of these frees indicates that they are over 200 yrs- old- ispg_ Appears to be grey lava 4 600 : ... '---^ r r-y~.-~^ " * — R e d rubble interbanded with darker layers C-ĵ X^X". Well graded, from about 20 ft dia. to -y-'.-y^ ) earthy material / Bonds dip 13"into slope. Bands 2 ft to about 40 ft thick 4400 4200 Slope on which trees grow appears to have once been continuous with wooded talus slope immediately SW of the section. The banding also continues under this slope 4000 3BOO Black lava with closely spaced (0.5 ft.) columnar /oints. Columns plunge at very low angles and generally point towards surface of outcrop Probably neor original flow-surface- Talus on both sides of outcrop Small patch of red rubble Loose volcanic talus SECTION A-A Scot* I"-400' 3600 3400 3200 Cheakamus formation outcrop 4600 Red rub~ ble V.-;- (Only visible'afr---- 4400 o few points J 4200 4000 3800 3600 3400 3200 3000 Overall angle 64* Locally vertical over several hundred feet 46Q0 4400 4200 4000 3800 Center of the lava lobe is probably vertically jointed, grey lava similar to that exposed on the N E wall of the 4th lobe near El 3900 Black, closely jointed lava near flow surface. Columns have variable plunges but usually less than 60° Slabbing due to vertical, open fractures 3600 34 OO 3200 3000 SECTION B-B Possible profiles 1 -* • Scale; 1**400' ^Outcrop of Cheakamus formation Often with thin mantle of Glacio- Fluvial debris. Apparent Dip of NE wall of Rubble Creek volley. n 0 T l: FOR LOtATIOtl Of SECTI0T15 SEE FIGURE ? RUBBLE CREEK SLIDE GEOLOGICAL SECTIONS THROUGH SOURCE AREA FIGURE 3 

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