Avalanche hazard evaluation and prediction at Rogers Pass

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Avalanche hazard evaluation and prediction at Rogers Pass Schaerer, P.

NATIONAL RESEARCH COUNCIL CANADA

DIVISION OF BUILDING RESEARCH

THE AVALANCHE HAZARD EVALUATION AND PREDICTION AT ROGERS FASS P. S c h a e r e r This i s a j o i n t r e p o r t o f . t h e Department of P u b l i c Works and t h e N a t i o n a l Research Council I n t e r n a l Report No. 227 of t h e D i v i s i o n of B u i l d i n g Research Ottawa December 1961

The Trans-Canada Highway through G l a c i e r National Park, B r i t i s h Columbia, w a s designed and c o n s t r u c t e d by t h e Federal Department of Public Works, Because t h e highway would have t o c r o s s numerous avalanche p a t h s , t h e Department began, a s e a r l y a s 1953, preliminary observations on t h e snow cover, weather and avalanche c o n d i t i o n s t h a t would be encountered and i n t h e w i n t e r of 1955-1956, e s t a b l i s h e d a r e g u l a r observation program t o provide t h e information r e q u i r e d f o r t h e s p e c i f i c a t i o n of t h e avalanche defences.

I n 1956, t h e National Research Council, i n response t o a r e q u e s t from t h e Department of Public Works, s u p p l i e d some of t h e s p e c i a l instruments r e q u i r e d f o r t h e observations. About t h a t time, t h e Division of Building Research of t h e Council r e - c r u i t e d t o i t s s t a f f a c i v i l e n g i n e e r t r a i n e d i n Switzerland. i n road c o n s t r u c t i o n . The s e r v i c e s of t h i s e n g i n e e r , M r . Schaerer, were o f f e r e d t o t h e Department of Public Works. I n 1357 he was

seconded t o t h a t department and given t h e t a s k of recommending t o them t h e avalanche defence f o r the highway. Through M r .

Schaerer and valuable c o n t a c t s w i t h D r .

M.

R. de Quervain, D i r e c t o r o f t h e Swiss Federal I n s t i t u t e f o r Snow and Avalanche Research, t h e valuable experience of t h e Swiss was a p p l i e d t o t h e problem a t Glacier.

!Phe development of t h e avalanche defence f o r t h e Trans-Canada Highway through t h e park a r e a , and t h e a s s o c i a t e d snow cover, weather and avalanche o b s e r v a t i o n s r e q u i r e d f o r t h e s p e c i f i c a t i o n of t h a t defence, was t h e f i r s t p r o j e c t of i t s kind t o be undertaken i n Canada. I t i s probable t h a t t h i s p r o j e c t w i l l serve a s a model if s i m i l a r p r o j e c t s should be undertaken i n t h e f u t u r e . A 1 1 t o o o f t e n , t h e experience obtained i n such work i s n o t recorded i n a f o r m t h a t w i l l make

it

r e a d i l y a v a i l - a b l e . The National Research Council welcomed t h e chance t o a s s i s t i n t h e program a t G l a c i e r and t o have t h e o p p o r t u n i t y t o prepare such a record.

One very important p a r t of avalanche defence i s t h e e v a l u a t i o n and p r e d i c t i o n of t h e avalanche hazard. Although

it was t h e r e s p o n s i b i l i t y o f t h e Parks Branch of t h e Department of Northern A f f a i r s and National Resources, t o organize and operate t h i s s e r v i c e a f t e r t h e Highvlray was completed, it was necessary t o p r e d i c t t h e c h a r a c t e r of t h i s s e r v i c e i n d e s i g n i n g t h e o v e r - a l l defence system. Furthermore, such a s e r v i c e had t o be a v a i l a b l e during t h e period when t h e o b s e r v a t i o n s r e q u i r e d f o r s p e c i f y i n g t h e defence system were made, and while t h e de- f e n c e s and Highway were c o n s t r u c t e d . The experience obtained i n avalanche hazard e v a l u a t i o n and p r e d i c t i o n d u r i n g t h a t p e r i o d , and t h e r o l e t h a t

it

plays i n t h e o v e r - a l l defence system, i s

'This r e p o r t i s one of a s e r i e s r e p o r t i n g t h e work

a t G l a c i e r . It r e p r e s e n t s s i n g u l a r l y c l o s e c o - o p e r a t i o n between t h e Department of P u b l i c Works and t h e D i v i s i o n of B u i l d i n g

Research, c o - o p e r a t i o n which

it

i s a p l e a s u r e t o acknowledge i n t h i s way.

Ottawa

December 1961

Robert P. Legget

TABLE OF CONTENTS TERRAIN 1. Climate Zone. 2. Snowfall.

3.

Temperature.

4.

Wind.

AVALANCHES A T ROGERS PASS

P e r i o d s of Avalanche A c t i v i t y

SOME FUNDUIENTAL CONSIDERATIONS TO THE AVALANCHE HAZARD

EVALUATION AND PREDICTION

The T e s t i n g Method The A n a l y t i c Method

ORGANIZATIOII OF THE OBSERVATIONS Snow and Weather Observations

Observations a t Rogers Pass Summit and a t G l a c i e r S t a t e of t h e Weather

Observations a t F l a t Creek and Stoney Credk Observations on Mount Abbott

S p e c i a l Observations Records

S u r v e y of t h e Avalanches Personnel

CAUSES OF THE AVALANCHES Rupture Zones

Climate Areas The Snow Cover The Snowfall Wind

Temperature

Spring Thaw Avalanches S p e c i a l Avalanches AVALANCHE \ITARNING

The Avalanche Hazard F o r e c a s t Highway Closures

ANTICIPATED ORGANIZATION AND RESPONSIBILITIES OF THE AVALANCHE

WARNING SERVICE

R e s p o n s i b i l i t i e s of t h e Avalanche Warning S e r v i c e Personnel

Snow Cover and Weather Observations

Effec-t of Avalanche Warning on Highway T r a f f i c Avalanche Warning f o r S k i e r s

Table

o f

Contents (Contld) ACKNOWLEDGMENTS

REFERENCES

APPENDIX I: S e l e c t i o n o f t h e Mountain Observatory

APPENDIX 11: Equipment and Methods of Observations

APPENDIX 111: The Weather Forecast

APPENDIX I V : Mount Green Avalanche

THE A V A U N C H Z HAZARD EVALUATION AND PREDICT1 ON AT ROGERS PASS

2. _{S c h a e r e r}

I n t h e e a r l y 1 9 5 0 f s , c o n s i d e r a t i o n was g i v e n t o t h e use of Rogers Pass a s a p o s s i b l e r o u t e t h r o u g h t h e S e l k i r k Range f o r t h e Trans-Canada Higl~tvay. The p a s s , t h e l o w e s t and s h o r t e s t r o u t e through t h e S e l k i r l c s , i s l o c a t e d between t h e

towns of Golden and Revelstolce i n B r i t i s h Columbia. The

summit of t h e B s s i s n e a r t h e town of G l a c i e r i n G l a c i e r N a t i o n a l Park ( p i g s , 1 and 2 ) .

The d i s c o v e r y of t h e Pass by Major A . B. Rogers d u r i n g h i s survey f o r t h e Canadian P a c i f i c Railway enabled t h a t company t o complete t h e f i r s t r a i l w a y l i n k between

Eas-tern Canada and t h e West Coast i n 1885. The l i n e through t h e 'Pass was used. u n t i l 1916 when it was abandoned on t h e completion of t h e Connaught Tunnel.

The v a l l e y s a s s o c i a t e d w i t h t h e Pass a r e narrow and have s t e e p s i d e s . Because of heavy s n o w f a l l i n t h e a r e a

w i n t e r and s p r i n g a v a l a n c h e s a r e a common o c c u r r e n c e , I n 1953, t h e Department of P u 3 l i c Ihiorlcs, r e s p o n s i b l e f o r t h e c o n s t r u c t i o n of t b e highway i n G l a c i e r N a t i o n a l P a r k , began a s t u d y of t h e l o c a t i o n of each avalanche s i t e and t h e c o n d i t i o n s under which t h e a v a l a n c h e s o c c u r , M r . N. C. Gardner was i n charge of t h e s e o b s e r v a t i o n s , I n 1956, when t h e d e c i s i o n was made t o c o n s t r u c t t h e higllv~ay throug-11 t h e P a s s , t h e Department of P u b l i c 1,filorks e s t a b l i s h e d a n avalanche o b s e r v a t i o n s t a t i o n

at G l a c i e r . The o b s e r v a t i o n program was e n l a r g e d

t o

o b t a i n t h e i n f o r m a t i o n r e q u i r e d f o r t h e s p e c i f i c a t i o n and d e s i g n of t h e defence system. An avalanche h a z a r d f o r e c a s t r o u t i n e

was e s t a b l i s h e d f o r t h e p r o t e c t i o n of t h e avalanche o b s e r v e r s , s u r v e y o r s and c o n s t r u c t i o n crew,

The N a t i o n a l Research Council, through i t s D i v i s i o i l of B u i l d i n g Research, co-operated i n t h e o r g a n i z a t i o n of t h e avalanche o b s e r v a t i o n s t a t i o n . I n i t i a l l y , t h e N a t i o n a l Research Council c o n t r i b u t e d i n f o r m a t i o n and a p p a r a t u s f o r t a k i n g t h e n e c e s s a r y weather and snow c o v e r o b s e r v a t i o n s ; when t h e a u t h o r

joined t h e Snow and I c e S e c t i o n of t h e D i v i s i o n of B u i l d i n g Research, t h e f o l l v ~ v i n g r e s p o n s i b i l i t i e s were assumed:

1. To make recommendations on t h e t y p e , l o c a t i o n and d e s i g n of t h e defence f o r each avalanche s i t e , To a s s i s t i n

I n A p r i l of 1957, t h e a u t h o r was seconded t o t h e Department of Public !Vorks and joined t h e avalanche observation s t a t i o n a t G l a c i e r on a f u l l - t i m e b a s i s . During t h e w i n t e r s 1957-1958 and 1958-1959 he was r e s p o n s i b l e f o r t h e snow cover, weather and avalanche observations t h a t were made. Based on t h e s e o b s e r v a t i o n s and o t h e r s taken p r i o r t o 1957, a defence p l a n was drawn up and reconmendations made f o r t h e defence a t each avalanche s i t e . This information i s published i n a s e p a r a t e r e p o r t (1). The recommended defence plan included highway c l o s u r e and c o n t r o l o f avalanches w i t h e x p l o s i v e s . The

e v a l u a t i o n and p r e d i c t i o n of t h e avalanche hazard i s t h e r e f o r e a necessary and i n t e g r a l p a r t of t h e avalanche defence. The National Research Council had no r e s p o n s i b i l i t y f o r t h e

o r g a n i z a t i o n of the avalanche hazard p r e d i c t i o n and warning s e r v i c e r e q u i r e d f o r t h e highway b u t it was n e c e s s a r y t o

a n t i c i p a t e t h e n a t u r e of t h i s f u t u r e s e r v i c e when e s t a b l i s h i n g t h e defence f o r each avalanche s i t e . I t was considered t h a t a record of t h e n a t u r e of t h e f u t u r e warning s e r v i c e t h a t had been i n mind when t h e recommendations were prepared f o r t h e avalanche defence works, and a record of t h e experience gained i n avalanche hazard e v a l u a t i o n and f o r e c a s t i n g f o r t h e Rogers Pass a r e a would be valuable t o t h e people r e s p o n s i b l e f o r t h e avalanche warning s e r v i c e f o r t h e completed highway. T h i s

r e p o r t c o n t a i n s t h i s record. I n

it

a r e presented:

( a ) a d e s c r i p t i o n of t h e weather and snow cover observa- t i o n s -taken,

( b ) a summary of experience gained i n making t h e

avalanche hazard e v a l u a t i o n and f o r e c a s t during t h e period when t h e NRC was d i r e c t l y a s s o c i a t e d w i t h t h e f i e l d o b s e r v a t i o n s ,

( c ) a n o u t l i n e of t h e o r g a n i z a t i o n and d u t i e s of t h e f u t u r e avalanche warning s e r v i c e which had been i n mind when planning t h e complete defence system. R e s p o n s i b i l i t i e s f o r snow and weather o b s e r v a t i o n s and f o r avalanche hazard e v a l u a t i o n and f o r e c a s t were t r a n s -

f e r r e d from t h e Department of Public Works and t h e National Research Council t o t h e National Parks Branch of t h e Department of Northern A f f a i r s and National Resources on 2 October 1959.

TERRAIN

The v a l l e y s (Table I ) ad j o i n i n g Rogers Pass run i n a g e n e r a l east-west d i r e c t i o n . The mountains, mainly of q u a r t z i t e rock, with s t e e p s i d e s and bands of bold c l i f f s , r i s e between 8,000 and 10,000

f t

above sea l e v e l . Water has

carved numerous g u l l i e s i n t o t h e mountain s i d e s and h a s deposited decomposed rock i n a l l u v i a l f a n s i n t h e v a l l e y below. Timber

covers most of t h e mountain s i d e s below 6500 f t except f o r t h e g u l l i e s and many a r e a s where f r e q u e n t avalanches h i n d e r t h e growth of t r e e s ( F i g s . 3,

4 ,

5 ) .

TABLE I

VALLEYS AND ELEVATIONS AT ROGERS PASS

-

The average width of t h e v a l l e y s i s 800 f t a t t h e bottom. A t some p l a c e s t h e mountain s i d e s approach one a n o t h e r t o form a narrow V-shaped v a l l e y w i t h t h e r i v e r flowing between t h e s t e e p t a l u s s l o p e s and s h a r p l y r i s i n g

roclcfaces. One of t h e s e narrow d e f i l e s l i e s between Mount Tupper and Mount MacDonald on t h e e a s t s i d e of Rogers Pass (Fig.

3 )

and a n o t h e r important one i s formed by t h e s i d e s of F i d e l i t y and F o r t i t u d e Mountains a t t h e west boundary of G l a c i e r National Park. Apart from two s h o r t s e c t i o n s , each 2 miles l o n g , t h e highway was constructed on t h e n o r t h s i d e of t h e v a l l e y s .

1. Climate Zone.

-

A. Roch ( 2 ) h a s divided t h e mountain

a r e a of t h e western United S t a t e s i n t o t h r e e d i f f e r e n t c l i m a t i c zones. The S e l k i r k Mountains a r e i n t h e n o r t h e r n e x t e n s i o n of t h e middle zone. This zone i s c h a r a c t e r i z e d by heavy snowfalls w i t h moist t o dry snow, medium temperatures which a r e only

Valley Columbia River and Beaver River Bear Creek I l l e c i l l e w a e t River E l e v a t i o n above Sea l e v e l , f t 2600 2800 2800 4 350 1500 2200 3800 4350 Location Golden t o Beaver River junction Beaver River junction t o Rogers Pass Summit Revelstoke t o A l b e r t Canyon t o G l a c i e r -to

Rogers Pass Sumrnit

Distance, m i l e s 40

7

20 1 8 1.6

occasionally below O°F and s t r o n g winds on t h e mountains.

2. Snowfall.

-

Rogers Pass i s i n one of t h e h i g h e s t s n o v ~ f a l l a r e a s i n Canada. The average t o t a l snowfall f o r t h e w i n t e r , measured a t G l a c i e r over a 30-year period between

1321 and 1950, i s 342 i n . The maximum t o t a l snowfall observed was 680 i n . measured i n t h e w i n t e r of 1953-54.

A t t h e 4000-ft l e v e l of t h e v a l l e y snowfall u s u a l l y begins a t t h e end of October and ceases a t t h e end of April.

Summer snowfalls may occur on t h e mountains a t 7000

f t ,

b u t t h i s soon melts. A t t h i s a l t i t u d e , f o r a n average y e a r , snow covers t h e ground from t h e end of September u n t i l the end of June.

There a r e no y e a r l y r e c u r r i n g periods of maximum snowfall i n t e n s i t y . Snowfalls have been recorded d a i l y f o r one month and periods of t w o weeks d u r a t i o n have passed with- out snowfall. Storms w i t h heavy snowfalls a r e i n f r e q u e n t . During w i n t e r s of l i g h t snovifall two storms may occur y i e l d i n g 12 i n . of snow i n a 24-hr period. Winters of heavy snowfall produce 8 t o 10 such storms. A snowfall of more t h a n 20 i n . i n 24 h r i s a r a r e occurrence.

The magnitude and t h e frequency of t h e 24-hr snow- f a l l s a t G l a c i e r during t h e w i n t e r s between 1953 and 1960 a r e shown i n Table 11.

TABLE I1

FREQUENCY OF SNO\VPALLS AT GILACIER

o Records of t h e w i n t e r 1954-55 include only snowfalls a f t e r

1 January 1955. Winter 1953/54 1954/55 1955/56 1956/57 1957/58 1958/59 1359/60 T o t a l Snowfall of t h e Winter i n . 680 310 336 341 321 442 368 Number of Days with Snowfalls

Less than 4 i n . 56 35" 42 47 74 85 84 More than 20 i n . 2

-

-

1

-

-

-

4 t o 1 2 i n . 44 17* 30 17 26 41 29 1 2 t o 20 i n . 7

-

-

3 1 3 1

Storms with a h i g h snowfall r a t e a r e u s u a l l y of s h o r t d u r a t i o n . A day with heavy s n o v ~ f a l l i s normally followed by

a period of l i g h t snowfall. Records from 1930 t o 1960 show

t h a t t h e maximum t o t a l snowfall a t G l a c i e r f o r a 5-day period was j u s t under 70 i n .

It i s p o s s i b l e t h a t once i n 20 y e a r s a w i n t e r with very heavy s n o ~ ~ f a l l could occur when t h e above-mentioned snow- f a l l amounts a r e exceeded. On 21 January 1935, 35 i n . of snow were recorded i n a 24-hr p e r i o d , b u t t h i s extreme r a t e h a s n o t been observed s i n c e .

3. Temperature.

-

The mean monthly w i n t e r temperatures

a t G l a c i e r f o r t h e

30-yr

period 1921 t o 1950 a r e given i n Table 111.

TABLE I11

MEAN

TEPIIPERATURES OF THE WINTER MONTHS

The temperature i s below OOP only a few times d u r i n g t h e

w i n t e r and t h i s cold weather u s u a l l y does n o t continue f o r more t h a n a week. The lowest temperature e v e r measured a t G l a c i e r was -33OP.

The temperature d u r i n g a snowstorm normally ranges between 20 and 32OF. A f t e r a s t o m has ended it i s u s u a l f o r t h e cloudy weather t o continue and t h e temperature t o change r e l a t i v e l y slowly, The temperature f r e q u e n t l y r i s e s d u r i n g a

snowstorm and t h e snowfall i n t h e v a l l e y s changes t o r a i n . MeanTemperature,

OP

4. Wind.

-

Most snorrfalls a r e accompanied by s o u t h e r l y and w e s t e z : m i n d s of v a r i a b l e speed. Large amounts of snow

can d r i f t over t h e mountain r i d g e s and be deposited on t h e l e e s i d e . Heavy s n o v ~ f a l l s may occur w i t h no s i g n i f i c a n t wind,

Peb. 18.6

AVALANCHES AT ROGERS PASS Nov.

25,2

F i r s t s t u d i e s r e v e a l e d t h a t t h e avalanche hazard t o t h e highviay through Rogers Pass would be h i g h and would equal

March 26.8 Dec. 17.5 A p r i l 35.8 Jan. 13.6

t h e worst c o n d i t i o n s encountered on highways and r a i l r o a d s kept open during t h e w i n t e r i n t h e mountainous a r e a s of

Switzerland, A u s t r i a and Western United S t a t e s , The highway would have t o c r o s s t h e f o l l o w i n g number of avalanche paths:

9 s i t e s where avalanches of dangerous s i z e occur more than once each w i n t e r .

21 s i t e s where avalanches of minor s i z e occur once o r more t h a n once each w i n t e r . Large avalanches occur o c c a s i o n a l l g , b u t n o t every w i n t e r .

1 3 s i t e s where avalanches occur only under severe con- d i t i o n s and n o t every w i n t e r . The avalanches would be l a r g e i n most c a s e s .

31 s i t e s where avalanches occur only o c c a s i o n a l l y under severe c o n d i t i o n s . The snow t h a t would r e a c h t h e highway would u s u a l l y be a i r b o r n e and l i t t l e would be deposited on t h e highway.

TOTAL

74 avalanche s i t e s ,

I n t h i s r e p o r t , t h e l o c a t i o n of t h e avalanche s i t e

i s given by t h e highway mileage from t h e e a s t boundary of G l a c i e r National Park. Most of t h e s i t e s have a name and have been f u l l y described (1)-

The avalanche hazard i s v e r y high a t t h e two

d e f i l e s where t h e v a l l e y has a narrow V-shape and t h e highway

i s l o c a t e d a t t h e bottom of t h e l o n g , s%eep mountain s i d e . These two most a c t i v e avalanche a r e a s a r e l o c a t e d :

( a ) Below Mount Tupper between Mile 1 0 and Mile 1 3 ( F i g s .

3

and

4 ) .

( b ) On t h e south s i d e of F i d e l i t y Mountain immediately west .of G l a c i e r National Park.

Avalanches may reach t h e highway a t both s e c t i o n s during and a f t e r every s i g n i f i c a n t snowfall, p a r t i c u l a r l y a f t e r snowfalls of more t h a n 1 0 i n . accompanied by wind,

Between and o u t s i d e t h e two a r e a s , t h e avalanche s i t e s a r e more s c a t t e r e d and t h e v a l l e y f l o o r i s wider ( F i g s . 2 and

5 ) .

Avalanches r e a c h t h e highway only under bad condi- t i o n s . Dangerous ones u s u a l l y occur a f t e r snowfalls of more t h a n 24 i n . and d u r i n g t h e snow melting period.

Periods of Avalanche A c t i v i t y

There a r e two avalanche p e r i o d s each year, I n t h e f i r s t p e r i o d , between e a r l y November and l a t e February,

avalanches a r e caused mainly by snoivfalls

,

wind a c t i o n , and r a i n i n a s s o c i a t i o n w i t h snoi8ifalls. I n t h e second p e r i o d , between l a t e Idarch and mid-May, avalanches a r e caused mainly by warm weather and melting of t h e snow,

Records of t h e avalanches a f f e c t i n g t h e railway l i n e between t h e years 1910 and 1952 were s t u d i e d i n t h e o f f i c e of t h e Division Engineer of t h e Canadian P a c i f i c Railway a t Revelstoke, The study revealed a cycle of some y e a r s of

heavy a c t i v i t y followed by y e a r s of few avalanches, Avalanches a f f e c t i n g t h e railway l i n e between Stoney Creek and t h e e a s t

p o r t a l of Connaught h e l , and between t h e west p o r t a l of t h e t u n n e l and I l l e c i l l e w a e t s i d i n g d u r i n g t h e period 1910-1960

a r e p l o t t e d i n Fig, 6 , The graph shows periods of h i g h avalanche a c t i v i t y with maxima 1920, 1935 and 1952, The observations

r e q u i r e d f o r t h e defence planning of t h e highway appear t o have been made during a period of low avalanche a c t i v i t y ,

SOME FUNDAMENTAL CONSIDERATIONS TO THE AVALANCHE HAZARD

EVALUATION AND PREDICTION

The technique of observing d i f f e r e n t snow and weather f a c t o r s and e v a l u a t i n g from them t h e l i k e l i h o o d of

avalanche occurrences i s c a l l e d "avalanche hazard f o r e c a s t i n g w by t h e U,S, F o r e s t Service, An avalanche i s caused by

d i f f e r e n t f a c t o r s which a r e i n t e r r e l a t e d c l o s e l y . C e r t a i n r u l e s have been e s t a b l i s h e d through experience concerning t h e dependence of t h e avalanche hazard on t h e s e f a c t o r s , b u t t h e f o r e c a s t i n g of avalanches i s s t i l l a n a r l - , r a t h e r than a science. It r e q u i r e s a c e r t a i n s k i l l which i n c l u d e s a thorough understanding of t h e behaviour of snow on t h e ground, t h e

t e r r a i n , t h e weather i n t h e mountains, and t h e i r i n t e r -

r e l a t i o n s h i p . -)

The hazard can be evaluated q u i t e a c c u r a t e l y f o r t h e time of observation, b u t t h e p r e d i c t i o n of t h e f u t u r e hazard i s only a s good a s t h e weather f o r e c a s t , I n p r a c t i c e , t h e avalanche hazard f o r e c a s t e r has t o assume t h a t t h e weather w i l l follow a c e r t a i n p a t t e r n and h i s p r e d i c t i o n i s based on t h i s .

The a u t h o r , f a m i l i a r with t h e S w i s s method of

avalanche hazard f o r e c a s t i n g , was pleased t o have t h e oppor- t u n i t y t o co-operate with people who received t h e i r t r a i n i n g i n avalanche hazard f o r e c a s t i n g from t h e United S t a t e s F o r e s t s e r v i c e , During f r e q u e n t d i s c ~ s s i o n s

i t

became e v i d e n t t h a t

t h e e v a l u a t i o n of t h e avalanche hazard can be approached by two d i f f e r e n t methods, t h e t e s t i n g method and t h e a n a l y t i c method.

The T e s t i n g Method

The t e s t i n g method i s t h e b a s i s of technique used by t h e Swiss Snow and Avalanche Research I n s t i t u t e , and i s widely used f o r avalanche warning i n o t h e r c o u n t r i e s

( 3 ) .

The

avalanche hazard f o r e c a s t i s based on snow cover observations. These o b s e r v a t i o n s , u s u a l l y c a l l e d t h e snow p r o f i l e , show i f

t h e r e a r e u n s t a b l e l a y e r s which raigJbt c o l l a p s e and cause

avalanches. The s t a b i l i t y of t h e snow cover can be t e s t e d a t any time when t h e c o n d i t i o n s warrant it. Weather f a c t o r s such a s snowfall, wind and t e n p e r a t u r e a r e used t o determine i t s

s t a b i l i t y between observations. Experience and t e s t s have

sho-m which f a c t o r s may l e a d t o a f r a c t u r e and which c o n d i t i o n s c o n t r i b u t e t o s t a b i l i z a t i o n . The s i m 2 l e s t a p p l i c a t i o n o f t h e t e s t i n g method i s t h e d i r e c t t e s t i n g of t h e s t a b i l i t y of a s l o p e .

This t e s t i n g method has t h e f o l l o w i n g advantages: ( a ) The a c t u a l m a t e r i a l , t h e snow on t h e ground, i s

s t u d i e d . This m a t e r i a l can be observed by anyone and i t s c o n d i t i o n s a r e c l e a r l y v i s i b l e .

( b ) It i s u n i v e r s a l and can be a p p l i e d t o any avalanche

a r e a .

llountain climbers and f e e l i n g f o r snow need recognize whether t h e l i k e l y t o s l i d e .

slciers who u s u a l l y have a only l i t t l e t r a i n i n g t o snow on a given s l o p e i s The disadvantages of t h e t e s t i n g method a r e : ( a ) I n a c c u r a t e deterinination of t h e avalanche hazard

i f t h e s t a b i l i t y of t h e s l o p e s i s n o t t e s t e d con- t i n u o u s l y .

( b ) A b a s i c understanding of snow behaviour under

d i f f e r e n t weather c o n d i t i o n s and t e r r a i n i s r e q u i r e d . The Analytic Method

The a n a l y t i c method has been developed mainly by t h e U.S. P o r e s t Service ( 4 ,

5 ) .

It was found t h a t most avalanches a r e caused by snowfalls and occur e i t h e r d u r i n g

o r immediately a f t e r storms. A method was developed, t h e r e f o r e , by which t h e occurrence of t h e s e d i r e c t a c t i o n avalanches

could be f o r e c a s t e d a c c u r a t e l y . A number of d i f f e r e n t con- t r i b u t i n g f a c t o r s have t o be observed and t h e avalanche hazard i s evaluated from t h e magnitude of each f a c t o r . The s t a b i l i t y of t h e o r i g i n a l snon cover i s only one of t h e s e , The i n f l u e n c e of each f a c t o r i s found by a n a l y z i n g

Lhc

avalanche c o n d i t i o n s over a few winters. The ? o r e c a s t i n g l ~ l @ s

i.n

t l i i s repo?.d fo,- s p r i n g thaw avalanches, and a l s o f o r Mount Green and Crossovar avalanches

a r e examples of t h e a n a l y t i c method (Appendices I V , V ) . This method i s s i m i l a r t o t h a t used i n f o r e c a s t i n g t h e f o r e s t f i r e hazard.

The a n a l y t i c method has t h e following advantages :

( a ) Good r e s u l t s a r e obtained f o r t h e f o r e c a s t of d i r e c t a c t i o n avalanches. The chances of whether o r n o t a d i r e c t a c t i o n avalanche w i l l occur can be p r e d i c t e d more a c c u r a t e l y t h a n by t h e t e s t i n g method,

( b ) A f t e r many y e a r s of experience r u l e s can be found t o e v a l u a t e t h e hazard f o r a given avalanche a r e a , These r u l e s can o f t e n be a p p l i e d by a n observer w i t h a l i t t l e t r a i n i n g . Rules f o r t h e time when avalanches should be c o n t r o l l e d by e x p l o s i v e s can a l s o be e s t a b - l i s h e d and be a p p l i e d by t h e people i n charge of t h i s

defence

.

( c ) The method i s s u i t a b l e f o r p r e d i c t i n g t h e avalanche hazard when a n a c c u r a t e weather f o r e c a s t i s a v a i l a b l e . The method has t h e f o l l o w i n g disadvantages:

( a ) Many weather o b s e r v a t i o n s a r e r e q u i r e d , Numerous instruments and f r e q u e n t observations may make

avalanche hazard f o r e c a s t i n g appear t o be a s p e c i a l s c i e n c e . Amateurs, such a s s k i e r s , may be d i s - couraged from o b t a i n i n g t h e knowledge on avalanche occurrences n e c e s s a r y f o r t h e i r orm s a f e t y ,

( b ) The method cannot p r e d i c t some delayed a c t i o n avalanches caused by changes i n t h e snow cover, u n l e s s t h e observers c o n s i d e r very c a r e f u l l y t h e s t a b i l i t y of t h e snow cover.

( c ) There i s a danger t h a t avalanche f o r e c a s t i n g w i l l

become a mechanical process and human good sense w i l l be l o s t . The f a c t o r s t h a t cause avalanches a r e r e l a t e d i n such a complex way t h a t it i s

impossible t o a c c u r a t e l y e x p r e s s t h i s r e l a t i o n s h i p a n a l y t i c a l l y , a s t h e r e a r e always odd c o n d i t i o n s t o which t h e r u l e s cannot be a p p l i e d .

( d ) The value of f a c t o r s causing t h e avalanches i n one a r e a may n o t be t h e same i n a n o t h e r a r e a . Experience gained through o b s e r v a t i o n s over a few w i n t e r s i s u s u a l l y r e q u i r e d before t h i s method can be a p p l i e d t o any s i t e .

I,!Iost avalanche warning s e r v i c e s use both methods. The avalanche hazard i s b a s i c a l l y evaluated w i t h t h e t e s t i n g method, and supplemented by t h e a n a l y t i c method t o improve t h e accuracy. During t h e survey, t h e avalanche hazard on Rogers Pass was evaluated and p r e d i c t e d mainly by t h e t e s t i n g method, vri-bh good r e s u l t s . Rules could be e s t a b l i s h e d a t some s i t e s which allowed a more a c c u r a t e e v a l u a t i o n o f t h e avalanche hazard. The experience obtained i n e v a l u a t i n g t h e avalanche hazard and t h e r u l e s e s t a b l i s h e d a r e recorded i n t h i s r e p o r t .

I t i s hoped t h a t t h i s record w i l l a s s i s t t h e Rogers Pass

Avalanche Hazard Evaluation and F o r e c a s t i n g Group i n developing a working combination of t h e t e s t i n g and a n a l y t i c methods.

ORGANIZLlTIOIT OP THE OBSERVATIONS Snow 2nd Weather Observations

The headquarters f o r t h e avalanche o b s e r v a t i o n s t a t i o n was a t G l a c i e r i n t h e camp of t h e Department of 32u'olic Worlrs. This st;ation made t h e r e q u i r e d o b s e r v a t i o n s on t h e snow cover and weather, surveyed t h e avalanches t h a t occurred, and prepared t h e avalanche hazard f o r e c a s t .

The f i r s t problem vras t o s e l e c t t h e s i t e s f o r snow and weather observations. The i d e a l observatory should be l o c a t e d n e a r t h e r u p t u r e zone of t h e avalanches v~herz th e observations a r e r e p r e s e n t a t i v e of t h e avalanche a r e a . S t a f f accommodation should be n e a r t h e o b s e r v a t i o n a r e a s o t h a t

observations can be c a r r i e d ou-b continuously and s p e c i a l measurements made a t any r e q u i r e d time, This i d e a l s i t e would be on t h e mountains between GOO0 and 7000 f t above sea l e v e l and 3000 f t h i g h e r t h a n -the v a l l e y , w i t h a b u i l d i n g f o r t h e s t a f f and a c c e s s by road o r a e r i a l t r a m a y , Because time and funds were n o t a v a i l a b l e f o r tlie c o n s t r u c t i o n of such a major p r o j e c t , and t h e su-rvey of t h e avalanches a l o n g t h e f u t u r e highway was t h e inore import-ant t a s k , it was

decided t o e s t a b l i s h t h e avalanche o b s e r v a t i o n s t a t i o n i n t h e v a l l e y . S i t e s a e r e chosen f o r d a i l y observations and two a d d i t i o n a l s i t e s were choser a t t h e a l t i t u d e of t h e avalanche r u p t u r e zone a t which r e g u l a r weekly observations o r d a i l y could be made, when c o n d i t i o n s vrananted it. The p r i n c i p l e of keeping t h e number of ~ S s e r v a t i o n s w i t h i n t h e c a p a c i t y of t h e observation group i*Jas a p p l i e d a t a l l -Limes, Experience shoiired t h a t d a i l y observsL'io;zs should be kept t o a rriinimum b u t t h a t t h e y should be r e l i a b l e and complete. A d e s c r i p t i o n

Rogers Fass Summit.

-

The summit o f Rogers Pass was chosen a s

-

t h e c e n t r a l observatory where a l l b a s i c observations were made. It was l o c a t e d a t a n a l t i t u d e of 4300 f t i n t h e middle

o f t h e 1200-ft wide v a l l e y runs from south t o n o r t h (Fig. 2 ) . Prom t h i s l o c a t i o n t h e weather c o n d i t i o n s on both s i d e s of t h e pass could be observed. It was assumed t h a t t h e f u t u r e headquarters of t h e highway maintelzance s t a f f and t h e avalanche warning s e r v i c e would be l o c a t e d a t t h e summit of t h e p a s s , and it would be an advantage t o have t h e observatory c l o s e a t hand. A t e s t p l o t 100 by 150 f t with a small s h e l t e r

and

i n s t r u n e n t stand was e s t a b l i s h e d - i n October 1957 and

observations began i n t h e w i n t e r of 1957-1958 (Fig.

7 ) .

Daily observations were made between 8 and 1 0 a.m. by p a t r o l s from Glacier.

Rogers Pass Summit i s moderately exposed t o wind;

observations on t h e depth of new snow had t o be made i n a s h e l t e r e d a r e a behind t h e cabin. A p r o t e c t i v e fence was

e r e c t e d around t h e a r e a where t h e snow cover was s t u d i e d , b u t

it was s t i l l d i s t u r b e d by animals, p a r t i c u l a r l y b e a r s . Glacier.

-

The survey camp a t G l a c i e r on t h e west s i d e of Rogers Pass, 3800 f t above sea l e v e l , was t h e headquarters of t h e s t a f f making t h e avalanche observations (Fig. 8 ) . It w a s

l o g i c 6 1 t h a t continuous weather and snow o b s e r v a t i o n s should be made n e a r t h e camp, p a r t i c u l a r l y when temperature and

~ r e c i ~ i t a t i o n observations have been made a t G l a b i e r f o r t h e p a s t 40 years. Twice d a i l y observations taken a t G l a c i e r i n d i c a t e d t h e weather c o n d i t i o n s on t h e west s i d e of Rogers - Fass.

P l a t Creek.

-

P l a t Creek i s a park warden s t a t i o n on t h e west

-

_{s i d e of Rogers Bss,}

₉

_{miles from t h e summit a t an a l t i t u d e of}

3100 f t . Daily observations were taken t h e r e by t h e warden on a p l o t c l o s e t o h i s house.

The purpose of t h e s e o b s e r v a t i o n s was t o determine any d i f f e r e n c e between t h e c o n d i t i o n s i n t h e I l l e c i l l e w a e t Valley and those observed a t G l a c i e r and a t t h e summit.

Stone7 Creek.

-

Stoney Creek i s a park warden s t a t i o n on t h e

-

e a s t s i d e of Rogers Pass, 6 miles f r o m t h e summit and 3650 f t above sea l e v e l . Daily observations were taken t h e r e by t h e warden on a p l o t c l o s e t o h i s house.

The purpose of t h e s e o b s e r v a t i o n s was t o determine any s i g n i f i c a n t d i f f e r e n c e between t h e c o n d i t i o n s observed on t h e summit and on t h e e a s t s i d e of t h e pass.

1101;mt Abbott.

-

P o s s i b l e s i t e s f o r a rnountain observatory a r e

7 . -

-

discussed i n Appendix I. Nount Abbott, 6800

f t

above sea

t r a i l was a v a i l a b l e , and a c c e s s i n w i n t e r was s h o r t ( P i g . 2 ) .

A c a b i n was b u i l t t h e r e i n September 1956 ( F i g . g ) , and a

t e s t p l o t was e s t a b l i s h e d on a t e r r a c e 200 f t below t h e c a b i n .

A r a d i o telephone connected t h e o b s e r v a t o r y w i t h t h e head-

q u a r t e r s a t G l a c i e r . m e o b s e r v a t o r y was occupied c o n t i n u o u s l y d u r i n g t h e w i n t e r of 1956-57, b u t o n l y d u r i n g storms and t h e snow-melt period i n t h e f o l l o w i n g two w i n t e r s . Weekly

i n s p e c t i o n s were made when no o b s e r v e r l i v e d t h e r e . The o b s e r v a t i o n s t a k e n a t Mount Abbott i n d i c a t e d t h e snow cover and t h e weather c o n d i t i o n s a t t h e a l t i t u d e o f t h e r u p t u r e zone f o r t h e avalanches.

Balu Pass.

-

A second mountain o b s e r v a t o r y was e s t a b l i s h e d a t Balu Pass, 6600 f t above s e a l e v e l (Fig. 1 0 ) . T e s t p l o t s were s t a k e d o u t on b o t h s i d e s of t h e p a s s where t h e snow p r o f i l e was surveyed monthly d u r i n g t h e w i n t e r 1957-1958. A

c a b i n was b u i l t a t t h e summit of t h e pass i n September 1958. This o b s e r v a t o r y served p r i m a r i l y f o r wind o b s e r v a t i o n s a s Mount Abbott was a n u n s a t i s f a c t o r y s i t e f o r such measurements.

The wind speed and d i r e c t i o n were measured w i t h a s t a n d a r d anemovane and recorded on a n E s t e r l i n e Angus r e c o r d e r i n December 1958 and J a n u a r y 1959. S p e c i a l wind t e l e m e t e r i n g equipment was developed f o r t h i s o b s e r v a t o r y by t h e Radio and E l e c t r i c a l Engineering D i v i s i o n , NRC, and i n s t a l l e d i n September 1959 ( 6 ) . Information on t h e wind speed and d i r e c t i o n was

t h u s t r a n s m i t t e d t o G l a c i e r by r a d i o . The s t a t i o n performed w e l l i n t h e f o l l o w i n g w i n t e r , and needed o n l y o c c a s i o n a l

i n s p e c t i o n . The absence of i c i n g on t h e anemovane o f f e r e d some encouragement t h a t t h e wind equipment might be i n s t a l l e d on a more exposed and remote mountain w i t h d i f f i c u l t a c c e s s , e . g . , on t h e r i d g e of Mount Abbott.

An e x t e n s i v e s t u d y on t h e c o n d i t i o n s c a u s i n g s p r i n g thaw avalanches was conducted a t Balu Pass i n May 1959.

Observations a t Rogers Pass Summit and a t G l a c i e r

The d e s c r i p t i o n of t h e equipment and rnetliods used f o r t h e snow cover and weather o b s e r v a t i o n s a r e given i n Appendix 11. The f o l l o w i n g d a i l y o b s e r v a t i o n s were t a k e n a t

t h e two o b s e r v a t o r i e s :

A i r temperature :

-

d a i l y maximum temperature

-

d a i l y minimum temperature

-

temperature a t t h e time of o b s e r v a t i o n P r e c i p i t a t i o n :

-

d e p t h of new snow

-

d e n s i t y o r s p e c i f i c g r a v i t y of new snow

-

t o t a l s n o w f a l l from t h e beginning of a storm ( s t o r m s t a k e )

-

s e t t l e m e n t of new snow

-

r a i n f a l l Snow cover: Wind : S t a t e of t h e Weather

-

t o t a l snow d e p t h

-

s e t t l e m e n t of t h e snow c o v e r

-

snow temperature

-

s u r f a c e of t h e snow ( e . g . s o f t , c r u s t )

-

d e p t h of p e n e t r a t i o n of a f o o t p r i n t o r d e p t h of p e n e t r a t i o n of t h e f i r s t s e c t i o n of t h e ramsonde

-

a s h a l l o w snowpit was dug and t h e h a r d - n e s s and s h e a r s t r e n g t h of t h e

d i f f e r e n t snow l a y e r s were t e s t e d whenever such o b s e r v a t i o n s were r e q u i r e d

-

windspeed

-

wind d i r e c t i o n

-

o b s e r v a t i o n s on t h e d i r e c t i o n and t h e magnitude of snow movements on mountain r i d g e s (snow f l a g s ) and i n t h e v a l l e y whenever v i s i b i l i t y

p e r m i t t e d .

D a i l y o b s e r v a t i o n s on p r e c i p i t a t i o n and a i r tempera- t u r e were continued d u r i n g t h e summer.

The complete p r o f i l e of t h e snow c o v e r was surveyed twice a month on Rogers Pass Summit.

Observations a t F l a t Creek and Stoney Creek

The f o l l o w i n g d a i l y o b s e r v a t i o n s were t a k e n a t t h e two p a r k warden s t a t i o n s :

-

maximum t e m p e r a t u r e

-

minimun temperature

-

d e p t h of new snow

-

t o t a l snowfall from b e g i n n i n g of a storm

-

r a i n f a l l

-

t o t a l snow d e p t h

Observations were n o t made on some days d u r i n g t h e w i n t e r and measurements were d i s c o n t i n u e d d u r i n g t h e summer.

Observations on Mount Abbott

The same d a i l y observations made a t Rogers Pass Summit and a t G l a c i e r were made, on llount Abbott when t h e observatory was occupied. A t o t h e r t i m e s , p r e c i p i t a t i o n and temperature were measured w i t h recording i n s t r u u e n t s . The snow p r o f i l e was surveyed weekly.

S p e c i a l Observations

The r u p t u r e zones of avalanches were v i s i t e d when- e v e r t h e avalanche hazard made such v i s i t s f e a s i b l e . The p r o f i l e s of t h e snow cover i n t h e s e a r e a s were s t u d i e d and compared w i t h t h e p r o f i l e s taken a t Rogers ?ass Summit and

Mount Abbott

.

Records

A l l observations were recorded on s p e c i a l forms

( i s 11, 1 2 ,

13).

The observations on t h e snow cover and t h e weather were p l o t t e d a g a i n s t time. A l l r e c o r d s were s t o r e d a t t h e avalanche observation s t a t i o n a t G l a c i e r and were t r a n s f e r r e d t o t h e Department of Northern A f f a i r s and National Resources on 2 October 1959.

Survey of t h e avalanches

Recording a l l avalanches along t h e proposed highway was t h e primary work of t h e avalanche o b s e r v a t i o n s t a t i o n .

These avalanches were surveyed f r e q u e n t l y by p a t r o l s and

recorded i n a s p e c i a l book. Those d e p o s i t i n g snow n e a r o r on t h e highway right-of-way were t r a c e d on l o c a t i o n plans. The l o c a t i o n of t h e f r a c t u r e zone and t h e path of some important avalanches were t r a c e d on photographs ( P i g ,

1 4 ) .

It was important t o know n o t only t h e d a t e b u t t h e

hour when t h e avalanches had occurred. The time could be

obtained f a i r l y a c c u r a t e l y by d a i l y and o f t e n twice d a i l y p a t r o l s between Mile

11.5

and 1 7 , and p a t r o l s through o t h e r a r e a s when avalanches could be expected.

Personnel

The s t a f f of t h e avalanche observation s t a t i o n averaged s i x men d u r i n g t h e w i n t e r and t h r e e d u r i n g t h e

summer. These numbers were r e q u i r e d f o r s a f e t y reasons. F a t r o l s through avalanche a r e a s should be done by a t l e a s t two o r more men. A t l e a s t two should be a t t h e mountain observatory when occupied d u r i n g storm p e r i o d s .

I t was foimd t h a t h a l f of t h e s t a f f should have a good knowlkdge of s k i i n g and be experienced i n mountain

t r a v e l . The o t h e r s need only a f a i r knowledge i n s k i i n g b u t must be p h y s i c a l l y f i t f o r t h e work.

CAUSES OP THE AVALANCHES

Observations showed t h a t avalanches a r e caused by

t h e same f a c t o r s a s i n o t h e r c o u n t r i e s s o t h a t experience gained by o t h e r o r g a n i z a t i o n s i n t h e f o r e c a s t i n g o f avalanches can

be a p p l i e d t o Rogers Pass. I n t h i s s e c t i o n , t h e f a c t o r s which c o n t r i b u t e t o t h e development of avalanches a r e summarized and those of p a r t i c u l a r importance f o r t h e avalanche hazard f o r e - c a s t a t Rogers Pass a r e emphasized, T h i s summary i s n o t meant t o be a general handbook on avalanche hazard f o r e c a s t i n g ; it i s addressed t o those who r e q u i r e an i n t r o d u c t i o n t o t h e con- d i t i o n s a t t h e pass. The r u l e s t h a t a r e given h e r e a r e based on a l l a v a i l a b l e o b s e r v a t i o n s and can probably be improved with more experience.

Rupture Zones

Rogers Fass has an upper and lower zone from which avalanches can s t a r t t o s l i d e . A t e r r a c e with a s l i g h t i n c l i n e , l o c a t e d between 5500 and 6500 f t d i v i d e s t h e s e t w o zones on

many of t h e mountain s l o p e s ( P i g s . 15, 1 6 ) . &lost avalanches s t a r t i n g t o s l i d e i n t h e lower zone r u p t u r e on t h e c l i f f s o r a t t h e t o e o f c l i f f s . The upper zone c o n t a i n s s t e e p s l o p e s r i s i n g from 6500 f t t o t h e mountain r i d g e s . Many small avalanches t h a t o r i g i n a t e i n t h e upper zone s t o p on t h e

t e r r a c e between t h e two zones. A knowledge of t h e two d i f f e r - e n t r u p t u r e zones i s important t o p r e d i c t avalanches caused by high temperatures. I t was observed f r e q u e n t l y t h a t t h e

temperature in t h e lower zone was h i g h enough t o cause avalanches, whereas i n t h e upper zone t h e temperature was s o low t h a t t h e

snow was s t i l l s t a b l e , Climate Areas

A t Rogers Pass t h e r e a r e two major c l i m a t e a r e a s ,

and t h e avalanche hazard f o r each should be evaluated s e p a r a t e l y . The two a r e a s a r e :

-

t h e Tupper a r e a on t h e e a s t s i d e of t h e P a s s ,

-

t h e I l l e c i l l e w a e t Valley on t h e west s i d e of t h e Pass.

Most snowstorms approach t h e Pass from t h e west and southwest and d e p o s i t a g r e a t e r amount of new snow i n t h e I l l e c i l l e w a e t Valley t h a n i n t h e Tupper a r e a . Observations d u r i n g t h e two w i n t e r s between 1957 and 1959 showed t h a t t h e average t o t a l s n o w f a l l i n t h e Tupper a r e a was 80 p e r c e n t of 3

t h e snowfall measured i n t h e I l l e c i l l e w a e t - Valley. A s l e s s s n o w f a l l i s r e q u i r e d t o cause avalanches on Mount Tupper, t h e avalanche hazard i s u s u a l l y about e q u a l i n b o t h a r e a s .

Occasional storms from t h e n o r t h and e a s t d e p o s i t more snow i n t h e Tupper a r e a t h a n on t h e west s i d e of Rogers Pass.

Observations a t t h e s u m m i t give a good i n d . i c a t i o n of weather c o n d i t i o n s on t h e e a s t s i d e of Rogers Pass. A

s p e c i a l o b s e r v a t o r y i n Stoney Creek i s n o t e s s e n t i a l , b u t

a d d i t i o n a l o b s e r v a t i o n s on t h e e a s t s i d e of Mount Tupper would be u s e f u l f o r a c o n t r o l .

Generally h i g h e r p r e c i p i t a t i o n on t h e west s i d e of Rogers Pass t h a n t h a t measured a t t h e summit; i n d i c a t e s a need f o r a d d i t i o n a l weather o b s e r v a t i o n s on t h e west s i d e , e i t h e r a t G l a c i e r o r a t F l a t Creek. The d i f f e r e n c e i n p r e c i p i t a t i o n a t G l a c i e r and a t F l a t Creek i s n o t s i g n i f i c a n t . Since F l a t Creek i s a l i t t l e warmer, r a i n sonetimes f a l l s h e r e when t h e r e i s s n o w f a l l a t G l a c i e r . G l a c i e r i s , t h e r e f o r e , a more s u i t a b l e s t a t i o n f o r weather o b s e r v a t i o n s w i t h t h e a d d i t i o n a l advantage of having been a c l i m a t o l o g i c a l s t a t i o n f o r o v e r 40 y e a r s . The Snow Cover

Frequent s n o w f a l l s w i t h f a i r l y c o n s t a n t t e m p e r a t u r e s d u r i n g and a f t e r each s n o w f a l l u s u a l l y produce a s t a b l e snow cover. The t y p i c a l snow p r o f i l e h a s l a y e r s w i t h i n c r e a s i n g s t r e n g t h toviard t h e ground ( F i g . 1 3 ) . Snow w i t h a h i g h d e g r e e of metamorphism ( d e p t h h o a r , s u g a r snow) forming l a y e r s w i t h low s t r e n g t h a r e n o t o f t e n observed. Unstable l a y e r s c a u s i n g avalanches may develop from t h e f o j ~ o w i n ~ c o n d i t i o n s :

( a ) Snow c o v e r s t h e mountains i n September and e a r l y October, and cold w e a t h e r w i t h l i t t l e s n o w f a l l p e r s i s t s d u r i n g October and November. The snow i n t h e avalanche r u p t u r e zones changes i n t o depth h o a r t h u s c r e a t i n g a n u n s t a b l e base f o r f u t u r e s n o v ~ f a l l s . This s i t u a t i o n i s t y p i c a l f o r t h e Rocky Mountain

a r e a b u t a p p e a r s only o c c a s i o n a l l y i n t h e S e l k i r k s . I t was observed i n t h e Rogers Pass a r e a i n t h e w i n t e r of 1957-58, b u t t h e u n s t a b l e snow covered s m a l l a r e a s only.

( b ) Cold weather i n J a n u a r y and February w i t h a p e r i o d of no s n o w f a l l f o r two o r more weeks may cause con- s i d e r a b l e me-tamorphism of t h e snow a t t h e s u r f a c e .

T h i s snow l a y e r h a s low cohesion and may f r a c t u r e l a t e r under t h e weight of new snow o r d u r i n g t h e

snow-melt period. Such a c o n d i t i o n was observed i n February 1957 and was t h e cause of numerous s p r i n g thaw avalanches i n ?flay of t h a t y e a r .

( c ) A period of r a i n o r sunshine occurs r e s u l t i n g i n a c r u s t which forms a s l i d i n g s u r f a c e f o r w i n t e r

a n d s p r i n g a v a l a n c h e s , p a r t i c u l a r l y i n t h e lower r u p t u r e zone.

Although u n s t a b l e l o o s e l a y e r s a r e i n f r e q u e n t l y observed i n t h e Rogers Pass a r e a , t h e snow p r o f i l e proved t o be important a s t h e b a s i s f o r t h e d a i l y avalanche hazard f o r e c a s t . The ram r e s i s t a n c e of t h e whole snow c o v e r and t h e p r o f i l e of t h e upper

5

f t (150 cm) was surveyed once p e r week. Since t h e p r o p e r t i e s of snow d e e p e r t h a n 5 f t from

t h e s u - f a c e do n o t change v e r y r a p i d l y , it was found n e c e s s a r y t o observe t h e complete p r o f i l e o n l y once p e r month.

I n f l u e n c e d by r a i n and sun, t h e p r o f i l e a t t h e summit o b s e r v a t o r y d i d n o t always r e p r e s e n t t h e c o n d i t i o n s i n t h e r u p t u r e zone of t h e avalanches. Snow p r o f i l e s from t h e t e s t p l o t on nlount Abbott and from s l o p e s of d i f f e r e n t exposure i n t h e r u p t u r e zone proved more u s e f u l .

Experience showed t h a t when t h e snow c 6 v e r was more t h a n 4 f t deep, o b s e r v a t i o n s on t h e s e t t l e m e n t were n o t n e c e s s a r y f o r t h e avalanche hazard f o r e c a s t i n g .

The ground had t o be covered w i t h a c e r t a i n d e p t h of snow b e f o r e avalanches could i n c r e a s e and a t t a i n t h e speed n e c e s s a r y t o r e a c h t h e v a l l e y and t h e highway. The observed d e p t h s f o r t h e period 1957 t o 1959 a r e given i n Table I V .

These o b s e r v a t i o n s i n d i c a t e t h a t Mount Abbott

r e q u i r e s a snow d e p t h of a b o u t 2 8 i n . (70 cm) b e f o r e a v a l a n c h e s from t h e upper zones r e a c h t h e v a l l e y . A s i m i l a r d e p t h observed a t t h e summit a p p e a r s t o be n e c e s s a r y before a v a l a n c h e s from t h e lower r u p t u r e zone can r e a c h t h e highway, It must be noted t h a t avalanches from t h e upper zone may r e a c h t h e h i g h - way even when t h e r e i s no snow i n t h e v a l l e y .

The Snowfall

The m a j o r i t y of a v a l a n c h e s a r e caused by s n o w f a l l s .

It was observed t h a t under "normal" c o n d i t i o n s , a v a l a n c h e s may o c c u r a t Rogers Pass i f t h e amounts cf new snow l i s t e d i n

SNOW DEPTHS WHEN THE FIRST AVALANCHES REACHED THE VALLEY

e x i s t when t h e snow c o v e r i s s t a b l e and t h e temperature i s

below 32°F and almost c o n s t a n t . The f i g u r e s given i n t h e t a b l e a r e based on t h e e x p e r i e n c e s of t h r e e w i n t e r s only. Lack of i n f o r m a t i o n on t h e wind made

it

d i f f i c u l t t o a n a l y z e o b s e r v a t i o n s f r o n w i n t e r s p r e v i o u s t o 1957.

F i r s t Avalanches from t h e Upper Rupture Zone

26 November 1357

8 November 1958

18 November 1958 24 October 1959

F i r s t Avalanches from t h e Lower Rupture Zone

12 December 1957 20 November 1958 23 November 1959

Comparisons between o b s e r v a t i o n s from G l a c i e r and Mount Abbott on t h e amount of snow t h a t f e l l d u r i n g a s t o m

show only a slight d i f f e r e n c e between t h e amount measured on t h e mountain and i n t h e v a l l e y below. I n soine storms more snow f a l l s on Mount Abbo-t;t t h a n a t G l a c i e r and v i c e v e r s a . The d i f f e r e n c e i s n o t l a r g e enough t o i n f l u e n c e t h e avalanche hazard f o r e c a s t a s it can be assumed t h a t t h e same amount of new snow f a l l s i n t h e upper and lower avalanche r u p t u r e zones a s

i n

t h e v a l l e y . When r a i n i s measured i n t h e v a l l e y and snow i s f a l l i n g on t h e mountain i t can be assumed t h a t 1 i n . of r a i n corresponds t o 1 2 i n . of snow. Snow Depth on l~lount Abbott 90 cm = 35 i n . 70 cm =L 28 i n . 70 cm = 28 i n . 28 i n . , e s t i m a t e d from o b s e r v a t i o n s made on F i d e l i t y Mountsin. Snow Depth on Rogers P a s s Summit; 73 cm = 29 i n . 70 cm = 28 i n . 73 crn = 29 i n . Rain f o l l o w i n g a s n o w f a l l i n t h e avalanche r u p t u r e zones can s t a r t a v a l a n c h e s w i t h i n one o r two h o u r s of i t s

beginning. I f t h e s n o w f a l l i s n o t more t h a n 1 2 i n . t h e avalanches w i l l probably be s m a l l and w i l l n o t r e a c h t h e highway. Most b i g avalanches $hat blocked r a i l w a y t r a f f i c

i n p r e v i o u s y e a r s r e s u l t e d from heavy s n o w f a l l s followed by r a i n ( e . g . on

1'7

February 1930, 9 t o 1 0 J a n u a r y 1933 and 24 t o 26 January 1935).

TABLE V

AMOUNTS OF SNOWFALL CAUSING AVALANCHES

The s p e c i f i c g r a v i t y of t h e new snow ranges between 0.07 and 0.10. The average s p e c i f i c g r a v i t y of t h e new snow was 0.083 i n t h e w i n t e r of 1957-58 and 0.084 i n t h e w i n t e r of 1958-59.

New

snow with s p e c i f i c g r a v i t i e s lower than 0.07

and h i g h e r t h a n 0.10 a r e more l i k e l y t o cause avalanches. Snow with a low s p e c i f i c g r a v i t y w i l l r e s u l t i n avalanches before t h e amounts of snow i n d i c a t e d i n Table V I a r e reached.

T o t a l Measurement on storm- s t a k e 8'l (20cm) 10" (25cm) 10" (25cm) 16" (40cm) 16" (40cm) 22" (55cm) 32" (80cm) Wind I n f l u e n c e Strong wind No wind Strong wind No wind Strong wind No wind Mostly without wind Snowfall T o t a l f o r 1 2 hours 10" (25cm) 14" (35cm) 16" (40cm) 20" (50cm) 20" (fjOcm) 28" (70cn) 40" (100cm) Avalanche Hazard Hazard 2: Small avalanches a t s i t e s where avalanches occur f r e q u e n t l y , e. g. a t Mount Tupper. Hazard f o r mountain s k i i n g . Hazard 3: Minor

avalanches may occur a t a l l known s i t e s . Smaller avalanches may r e a c h t h e highway a t unprotected s i t e s . Hazard 4: Major

avalanches may occur a t a l l known s i t e s and may reach t h e highway. Hazard

5:

Avalanches of unusual s i z e may reach t h e highway a t a l l lmo~vn and a l s o a t new s i t e s .

Wind

Wind i s a dominant f a c t o r i n t h e build-up of an avalanche s i t u a t i o n . The d i r e c t i o n of t h e p r e v a i l i n g wind i n t h e r u p t u r e zone determined i n most c a s e s whether a c e r t a i n avalanche would s t a r t t o s l i d e a f t e r a snowfall.

Observations a t Rogers Pass Summit showed t h e wind a t t h i s s i t e t o be influenced by t h e mountains and d i r e c t i o n of t h e v a l l e y and n o t n e c e s s a r i l y r e l a t e d t o t h e d i r e c t i o n and speed o f t h e wind i n t h e r u p t u r e zone of t h e avalanches. Therefore, o b s e r v a t i o n s a t an exposed s i t e on t h e mountains a r e r e q u i r e d . During t h e w i n t e r of 1958-59, i n s u f f i c i e n t o b s e r v a t i o n s were made on Balu Pass t o a l l o w a n adequate

c o r r e l a t i o n a t a l l s i t e s between t h e wind speed and d i r e c t i o n and avalanche occurrences.

Observations a t Rogers Pass Summit i n d i c a t e d t h a t a wind of speed g r e a t e r than 8 mph w i l l i n f l u e n c e t h e avalanche hazard. The information c o l l e c t e d d u r i n g t h e avalanche survey

on t h e i n f l u e n c e of wind on t h e avalanche hazard a t some s i t e s

i s sulnmarized i n Tables VI and VII. This information was

obtained from observations on t h e d r i f t i n g of snow on mountain r i d g e s and a s s o c i a t e d c o r n i c e formation and from t h e wind

observations taken a t t h e Balu Pass s i t e . TABLE V I

AVALANCHES AFFECTED BY

WIND

Avalanche S i t e G u l l i e s a t Mount MacDonald Tupper

-

Timber Tupper 1 Pioneer Tupper-Minor Benches IIounds Crossover T r a c t o r shed P,TacDonald-West shoulder Avalanche C r e s t Abbott No. 3 nlount Green F i d e l i t y Lanarlc Highway Mile 10.2-11.7 10.4-10.6 11.3 11.4 11.6 12.0-12.2 12.4 12*

3

12.7-13.0 14.5-15.0 16.3 17.8 20.3 26.0

-

Wind D i r e c t i o n Favourable t o Avalanche Occurrence South West, f o l l o v ~ i n g t h e v a l l e y of Bear Creek TI 11 1 I I I I I I I 11 11 !I ?I Southwest t o s o u t h tt 1 t South t o s o u t h e a s t E a s t Southwrest t o south ';Jest t o southwest West l?/e s t

TABLE V I I

AVALANCHES FROBABLY INFLUENCED BY WIND

( b u t n o t enough o b s e r v a t i o n s t o confirm t h i s ) Temperature I t was found t h a t s p e c i a l a t t e n t i o n i s r e q u i r e d Favourable Wind D i r e c t i o n Southwest t o s o u t h 11 11 I t 11 West West, f o l l o w i n g t h e v a l l e y Avalanche S i t e G r i z z l y Cheops Abbott No. 4 J u n c t i o n Twins .. &

when t h e temperature d u r i n g a s n o w f a l l i s n e a r 32OF, a s a n y r i s e i n temperature could change t h e s n o w f a l l i n t o r a i n , and

Hi&way hlile 13.4 14.5-15.2 17.85 18.7

-

c r e a t e a s e r i o u s avalanche hazard. A s n o w f a l l w i t h tempera- t u r e s below 20°F produced slow s t a b i l i z a t i o n of t h e snow cover.

The i n f l u e n c e of temperature on s p r i n g thaw

a v a l a n c h e s i s d i s c u s s e d i n a s p e c i a l c h a p t e r . High tempera- t u r e s i n t h e s p r i n g cause t h e i c e t o melt and f a l l from t h e c l i f f s . F a l l i n g i c e which reached t h e highway was observed i n t h e Tupper-Timber Avalanche a r e a , hlile 1 0 - 4 t o Mile 1 0 - 8 ,

Most of t h e time t h e temperature on t h e mountains

i s lower t h a n t'ne temperature i n t h e v a l l e y . During some important s n o w f a l l s and sometimes i n s p r i n g t e m p e r a t u r e s were h i g h e r on t h e mountains. Experiences have shotm t h a t a continuous r e c o r d of t e m p e r a t u r e s a t h i g h a l t i t u d e i s a g r e a t a s s e t i n avalanche f o r e c a s t i n g . During t h e avalanche s u r v e y it was n e c e s s a r y t o occupy t h e o b s e r v a t o r y on Mount Abbott a t c r i t i c a l p e r i o d s t o r e p o r t t n e temperature and o t h e r infornla- t i o n t o t h e h e a d q u a r t e r s i n t h e v a l l e y . It would be u s e f u l

i f t h e a i r temperature a t a mountain o b s e r v a t o r y could be t e l e m e t e r e d .

Spring Thaw Avala'nches

The term s p r i n g thaw a v a l a n c h e s i s a p p l i e d t o t h o s e avalanches t h a t o c c u r i n t h e s p r i n g due t o l o s s of cohesion of t h e snow when it m e l t s . S p r i n g thaw a v a l a n c h e s can be