Snow and avalanches in winter 1945/1946

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Snow and avalanches in winter 1945/1946 Bucher, E.; Schild, M.

NATIGIJAL RESZARCB COZiU'CIL OF CANADA

S HOG7 AND AVbLAiiC '3% IIi

A

T

194511946. (Schnee und Lawinen in Kinter 1945/19&6)

Edwin i3ucher an6 I~lelchior Schild t r a n s l a t e d by G.A. Atwater This i s t h e Second of t h e S e r i e s o f T r a n s l a t i o ~ s Prepared f o r t'ne Division of duilding Research.

Ottawa

T h i s i s a r e p o r t from t h e Eidgenossische I n s t i t u t f i b Schnee- und Lawinenforschung ( s w i s s F e d e r a l I n - s t i t u t e f o r Snow and Avalanche Research) Da.vos, S w i t z e r - land, The t r a n s l a t i o n i s published w i t h t h e approval of t h e a u t h o r ,

The National Research Council through i t s D i v i s i o n s of Mechanical Engineering and Buildink Research has a c l o s e l i n k w i t h Eidgenossische I n s t i t u t f u r Schnee- und Lawinenforschung. ldr. G.J. K l e i n o f t h e former D i v i s i o n and t h e w r i t e r have both s p e n t some time a t t h e I n s t i t u t e .

D r , Marcel de Quervain who i s now t h e D i r e c t o r o f t h e I n s t i t u t e s p e n t one y e a r a s a s p e c i a l member o f t h e s t a f f o f t h e D i v i s i o n of Buildink Research d u r i n k 194d and 1949 and l a i d t h e f o u n d a t i o n f o r t h e snow and i c e r e s e a r c h work t o which t n e D i v i s i c n l o o k s forward.

The Swiss I n s t i t u t e h a s been a p i o n e e r i n c o n n e c t i o n w i t h avalanche c o n t r o l work. T h i s work h a s c l o s e r e l e v a n c e t o Canada d e s p i t e t h e d i f f e r e n t c o n d i t i o ~ i s encountered i n t h e two c o u n t r i e s , It i s t h e r e f o r e a p l e a s u r e t o s e e t h i s t r a n s l a t i o n p u b l i s h e d p a r t i c u l a r l y s i r : c e i t i s a t r a n s - l a t i o n o f Report No. 2 o f t h e Swiss I n s t i t u t e which i s n o t g e r n e r a l l y a v a i l a b l e ,

Robert F, Legget, D i r e c t o r ,

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Techo T r a n s o TT-62 I EARLY WINTER

The a r r i v a l of sub-polar a i r massss on the 2Srd

of September brought t h e summer of 1945 t a a c l o s e , With

t e m p e r a t u r e s s t e a d i l y below f r e e z i n g and f r e q u e n t l i g h t

p r e c i p i t a t i o n s , t h e s t a n d a r d t e s t a r e a of t h e Confederate I n s t i t u t e f o r Snow and Avalanche Research s i t u a t e d a t a n e l e v a t i o n of 2540 m e above Lavos was covered w i t h snowo The a g i n g of t h i s f i r s t l a y e r of snow advanced f a i r l y r a p i d l y due t o a l a c k of c o v e r i n g s o t h a t i n t h e p r o f i l e examined on t h e f i r s t of October c o n s i d e r a b l e c o a r s e n i n g of t h e g r a i n s t r u c t u r e could a l r e a d y be observed, dven t h e n i t seemed q u i t e u n l i k e l y t h a t a l a t e r bonding of t h e s e n o n - p l a s t i c t y p e s of snow would o c c u r o Hence, t h e 1945/46 snow cover had a poor Load c a r r y i n g f o u n d a t i o n o

The f i r s t p a r t of October brouglit v a r i a b l e weather w i t h n e g l i g i b l e p r e c i p i t a t i o n s , Iqiarm a i r masses moving i n on t h e s i x t h and s e v e n t h caused a s t a g n a t i o n r e g i o n ( S t a u - l a g e ) which r e s u l t e d i n moderate t o s t r o n g p r e c i p i t a t i o n s , The p r e v a i l i n g winds caused d r i f t s , some q u i t e l a r g e , s o t h a t t h e occurrence of i s o l a t e d wind-slab a v a l a n c h e s was t o be e x p e c t e d - I n f a c t , an avalanche a c c i d e n t i n which a good A l p i n i s t l o s t h i s l i f e h a s a l r e a d y been r e p o r t e d i n t h e r e g i o n of ~ f l n t i s on October t h e s e v e n t h , Dry, warm weather p r e v a i l e d up t o t h e t w e n t i e t h of t h e month. The subsequent

tendency toward foehn winds caused a l i t t l e p r e c i p i t a t i o n w i t h p a i n throughout S w i t z e r l a n d up t o e l e v a t i o n s of about 2500 mo In t h e snow p r o f i l e on t h e f i r s t of November a d i s t i n c t c r u s t f o r m a t i o n on t h e snow s u r f a c e could be

observed, wheraas t h e l a y e r s n e a r the ground u s u a l l y showed s l i g h t cohesiono The mean d i a m e t e r of the g r a i n had i n c r e a s e d and had almost a t t a i n e d t h e magnitude of two millimetres,-,

A r a t h e r l o n g p e r i o d of good weather followed; t h e s o u t h e r n s l o p e s became f r e e from snow up t o an e l e v a t i o n of about 2500 m 0 and t h e n o r t h e r n s l o p e s up t o 2000 m o The p e n e t r a t i o n o f s u b - p o l a r c o l d a i r masses on November 8

caused new p r e c i p i t a t i o n o Much new snow f e l l i n the f o o t - h i l l s of the A l p s and i n t h e g l p i n e r e g i o n n o r t h of t h e fihine-Rhone l i n e and i n t h e ~ d n d n e r Land, whereas t h e

s o u t h e r n Valaisan Valleys and T i c i n o had s l i g h t p r e c i p i t a t i o n o n l y o Thus, t h e r e g i o n above 1500 m o waa f i n a l l y covered w i t h snow d u r i n g t h e n i g h t of November 8/g0

A t o t a l of 72 cmo of nevi1 snow had f a l l e n on t h e

Weissfluhjoch from November 8 t o l l o These new l a y e r s c o u l d

be r e c o g n i z e d i n t h e p r o f i l e f o r t h e f i r s t of December as

f i n e - g r a i n e d l a y e r s , i o e o , a f t e r a p e r i o d of sunny weather b e g i n n i n g on t h e 1 0 t h of November and p a r t i c u l a r l y towards

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Tech, Trans, TT-62

A t e l e v a t i o n s o f 2000 m, i n t h e r e g i o n s of Grau- bfindenvNorth, I n n e r - S w i t z e r l a n d , the Berne and W a a d t l h d e r Alps and o f t h e V a l a i s , where t h e moderate s n o w f a l l o f

movember 8

-

11 formed t h e base, an e x t e n s i v e t r a n s f o r m a t i o n of t h e f l u f f y c r y s t a l s t r u c t u r e o f new snow i n t o a c o a r s e - g r a i n e d c o h e s i o n l e s s l a y e r o c c u r r e d d u r i n g t h e l o n g p e r i o d o f n o n - p r e c i p i t a t i o n , No a v a l a n c h e s were observed with t h e e x c e p t i o n of s m a l l snow c h u t e s on s t e e p g r a s s y s l o p e s , I n t h e months of October and November, which had b e e n t o o dry, t h e t e m p e r a t u r e , r a d i a t i o n and d e g r e e of c l o u d i n e s s had e x e r t e d t h e main i n f l u e n c e on t h e development o f t h e snow- c o v e r , However, t h e p r e c i p i t a t i o n i n December was above average and b r o u g h t a v a r i e t y o f snow c o n d i t i o n s , Westerly weather a t f i r s t caused a s l i g h t i n c r e a s e o f snow i n t h e whole a r e a o f t h e Swiss Alps; t h e Engadine and North Ticfno

was a l s o covered w i t h snow, The subsequent s n o w f a l l s due

t o moderate c o l d a i r masses extended down i n t o t h e v a l l e y s i n t h e V a l a i s r e g i o n and everywhere e l s e on t h e n o r t h s i d e of t h e Alps, whereas T i c i n o and t h e Engadine were n o t touched by i t , I n s i g n i f i c a n t p r e c i p i t a t i o n s followed up t o December 1 2 , A foehn p e r i o d s t a r t i n g on December 1 6 b r o u g h t heavy p r e c i p i t a t i o n s on t h e s o u t h s i d e o f the A l p s o I t a l s o r a i n e d

i n t e r m i t t e n t l y on the n o r t h s i d e up t o 1550 m, above s e a

l e v e l , Rapid changes of a i r masses w i t h d a i l y p r e c i p i t a t i o n s , p a r t i c u l a r l y a t t h e end of the month, f o l l o w e d from t h e 2 0 t h up t o t h e end o f December,

Although t h e snow cover a l r e a d y e x i s t f n g on t h e n o r t h s i d e o f t h e Alps a t t h e b e g i n n i n g o f t h e month had

s l i g h t i n c r e a s e s on s e v e r a l o c c a s i o n s , t h e r e g i o n s below 1800 m, on t h e s o u t h s i d e of t h e Alps were n o t snowed i n u n t i l t h e b e g i n n i n g of December, The s n o w f a l l s l a s t i n g

from the 1 8 t h t o t h e 2 0 t h , however, became v e r y e x t e n s i v e , Owing t o s n o w f a l l s i n 9 e c e m b e ~ t o t a l l i n g 220 cm, (sum of t h e d a i l y s n o w f a l l ) t h e d e p t h I n d i c a t o r (gauge r o d ) of t h e t e s t a r e a on W e i s s f l u h j o c h showed an i n c r e a s e from

68 cm, t o 133 cm, Already t h e September snow had changed

t o d e p t h h o a r throughout, and i n t h e l a y e r o f October snow, t o o , analogous c r y s t a l s c o u l d b e determined, whepeas t h e

t w ~ sun c r u s t s

-

a s shown by t h e snow p e n e t r o m e t e r r e s i s t a n c e

-

were i n a s t a t e o f d i s i n t e g r a t i o n , The November snow was

c o a r s e - g r a i n e d , whereas t h e December l a y e r s , e x c e p t f o r r e - c e n t f a l l s o f f l u f f y new snow, showed a f i n e - g r a i n e d s t r u c t u r e ( c f , p r o f i l e o f Jan, 3, 1 9 4 6 ) ,

S i n c e t h e b e g i n n i n g of December v e r y d i f f e r e n t

development c o u l d be observed on sunny and shady s l o p e s o

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Techo Trans, TT-62

up t o 2500 m e above s e a l e v e l t h e pre-November snow l a y e r s i n the western, e a s t e r n and n o r t h e r n r e g i o n s changed i n t o d e p t h h o a r . As the new s n o w f a l l s of December were p a r t i a l l y accompanied by s t r o n g winds, l a r g e snow d r i f t s r e s u l t e d , p a r t i c u l a r l y on s l o p e s f a c i n g n o r t h and i n v a l l e y s o These snow d r i f t s , depending on t h e i r s i z e and t h e i n c l i n a t i o n of s l o p e , r o l l e d down a s avalanches on t h e c o h e s i o n l e s s d e p t h hoar l a y e r d u r i n g one of t h e December s n o w f a l l s , Thus,

r i g h t a f t e r t h e moderate s n o w f a l l s o f December 5

-

7 s e v e r a l wind-slab avalanches occurred on t h e s e v e n t h and e i g h t of December. This r a r e c u r r e d A a f t e ~ t h e p r e c i p i t a t i o n s of the

1 9 t h t o 22nd, and t h e 2 6 t h t o t h e 31st of Decembero For t h e ~ e r i o d of time under c o n s i d e r a t i o n no avalanches with c a s u i a t i e s OF p r o p e r t y damage took p l a c e i n t h e canton-of Graubmden i n s p i t e of t h i s dangerous s i t u a t i o n , Not l e a s t among the r e a s o n s f o r t h i s i s t h e f a c t t h a t weather c o n d i t i o n s d u r i n g t h i s time were n o t fe.vourable f o r s k i i n g *

The f o l l o w i n g circumstances must be c o n s i d e r e d when a n a l y z i n g t h e snow cover c o n d i t i o n s over t h e remainder of the n o r t h e r n s i d e of t h e Alps

During December no c o a r s e n i n g of t h e snow c r y s t a l s took p l a c e i n t h e r e g i o n of t h e Glarner Alps and t h e

A l p s t e i n ; a l l l a y e r s remained f i n e - g r a i n e d and had bonded c o n s i d e r a b l y o

I n t h e V a l a i s a d i s t i n c t i o n must be made between t h e lower p a r t , where t h e s i t u a t i o n showed no d e v i a t i o n from t h e c o n d i t i o n s elsewhere on t h e n o r t h e r n s i d e of t h e A l p s , t h e s o u t h e r n v a l l e y s , where a l r e a d y a t t h e end of December a depth hoar l a y e r of unusual b e a u t y covered t h e ground, and t h e Goms, where t h e metamorphosis took p l a c e slowly due t o t h e abundance of t h e f i r s t s n o w f a l l s o

Moreover, t h e p r e c i p i t a t i o n s due t o f o e h n on December 18

-

20, which had a l s o brought a s l i g h t i n c r e a s e i n snow d e p t h t o t h e V a l a i s had no a p p r e c i a b l e i n f l u e n c e on the f u r t h e r development of t h e snow c o v e r ,

Three a c c i d e n t s occurred i n December on t h e n o r t h s i d e of t h e Alps: on December 2 i n t h e S a l f i s c h Valley,

December 13

47

t h e A l b r i s t h o r n and December 1 6 on the

Klingenstock

.,

1) C f . Saving of l i f e

a t

t h e Klingenstock by-. K O Scho i n "Die ~ 8 r ~ e r e r z i e h u n g ~ ~ Vol, 24, No, 2 , Feba 1946, Verlag P a u l Haupt, Berno

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Techo Trans, TT-62

T w n i n g now t o t h e s o u t h e r n s i d e o f the Alps, t h e December foehn l a s t i n g from t h e 18

-

20 b r o u g h t more t h a n one and a h a l f metres of new snow t o n o r t h T i c i n o a t

e l e v a t i o n s around 140Q m o The i n c r e a s e i n t h e Sngadine was

a b o u t one t h i r d of t h i s v a l u e and w a s s t i l l l e s s i n t h e V a l a i s , I n g e n e r a l t h e new snow s e t t l e d q u i t e r a p i d l y o

A few avalanches o n l y were observed owing t o t h e good bonding

of t h o e a r l i e r s n o w f a l l s i n t h e T i c i n o o N e v e r t h e l e s s , under t h e i n f l u e n c e of t h e s o u t h e r l y storms accompanying t h e s e p r e c i p i t a t i o n s a v e r y dangerous p e r i o d was t o be e x p e c t e d

immediately a f t e r t h e s n o w f a l l s , I n t h i s c o n n e c t i o n t h e avalanche a c c i d e n t of December 26 on Monte Baro may be r e - c a l l e d ,

Summarizing t h e c o n d i t i o n s a t t h e end of t h e e a r l y w i n t e r p e r i o d i t should be k e p t i n mind t h a t a f i m b a s e p r e v a i l e d o n l y i n the T i c i n o and G l a r n e r Alps-Alpstein a r e a ;

t h e snow cover throughout t h e r e s t of S w i t z e r l a n d had n o t much c a r r y i n g s t r e n g t h a t t h e b e g i n n i n g of mid-winter

The December of moderate s n o w f a l l s was f o l l o w e d by a January i n which t h e p r e c i p i t a t i o n s i n t h e V a l a i s and

T i c i n o exceeded t h e y e a r l y average v a l u e s ; i n t h e r e s t of S w i t z e r l a n d a s much a s 50 p e r c e n t l e s s than normal c o u l d be r s c o r d e d D This d i f f e r e n c e was caused by t h e f o l l o w i n g atmospheric c o n d i t i o n s :

Up t o t h e 1 0 t h of t h e month fair rrveathel~ p r e v a i l e d i n t h e t o t a l a r e a of thu Alps, From t h e 1 0 t h t o t h e 1 2 t k

s e v e r a l f r o n t s of a s e r i e s of cyclones p a s s e d over S w i t z e r l a n d and with t h e i r maritime a i r masses caused s e v e r a l p r e c i p i t a - t i o n s a t r e l a t i v e l y h i g h t e m p e r a t u r e s , I n t h e V a l a i s t h i s weather r e s u l t e d i n moderate i n c r e a s e of t h e snow d e p t h ; i n t h e r e s t ~f t h e Alps t h e i n c r e a s e was slight, A f t e r t h e n o r t h s i d e of t h e Alps had had i t s h e a v i e s t s n o w f a l l of

t h e month from t h e 1 2 t h t o t h e 1 5 t h , wapm a i r masses f l o w i n g i n from t h e Mediterranean r e g i o n b e g i n n i n g on t h e 1 7 t h ,

caused a s t a g n a t i o n r e g i o n on t h e s o u t h s i d e w i t h c o n t i n u i n g p r e c i p i t a t i o n i n Goms and Engadine, A subsequent f o e h n

b r o u g h t a f u r t h e r moderate s n o w f a l l t o t h e s e r e g i o n s , A f t e r a few days of sunny weather a n o t h e r s e r i e s of f r o n t s from tha 2 9 t h on r e s u l t e d i n l i g h t s n o w f a l l s throughout t h e Alps* These s n o w f a l l s were most e f f e c t i v e i n t h e w e s t e r n and

r a g e 5

Tech, T r a n s , TT-62 The i r r e g u l a r c o u r s e of t h e weather i n the v a r i o u s g e o g r a p h i c a l s e c t i o n s n e c e s s a r i l y r e s u l t e d i n a d i v e r g e n t development of t h e snow cover on b o t h s i d e s of t h e Alp moun- t a i n s ,

On t h e W e l s s f l u h j o c h t h e i n c r e a s e i n t h e snow c o v e r d e p t h i n t h e month of J a n u a r y amounted t o o n l y 29 cm, F u r t h e r - more, transi'orrnations took p l a c e w i t h i n t h e snow cover which gave a s p e c i a l c h a r a c t s r t o t h e l a t e r development, While t h e September, October, and hovember l a y e r s c o n t i n u e d t o form a l o o s e b a s e l a y e r , t h e December l a y e r s ( e s p e c i a l l y l a y e r X I I a ) had s e t t l e d and becmie w e l l bonded under t h e i n f l u e n c e of h i g h t e m p e r a t u r e s d u r i n g t h e f o e h n p e r i o d of J a n u a r y 7 t o 1 2 , 'The J a n u a r y f a l l s , too, would have g i v e n no r e a s o n f o r c o n c e r n f o r t h e upper p a r t o f t h e p r o f i l e i f

i t had not been f o r t h e s u r f a c e h o a r of about 2 mml. t h i c k n e s s ,

which formed d u r i n g t h e c l e a r days and n i z t l t s of J,anuary 24

-

28, and which l z y between t h e two l a y e r s I a and I b t h u s

c o n s t i t u t i n g a dangerous middle l a g e r 1 ) , F o r t u n a t e l y , s u c h h o a r l a y e r s n o r m a l l y o c c u r o n l y r e g i o n a l l y ; f o r example, on

t h e e x p e r i m e n t a l f i e l d Bflschalp (1900 m , e l e v a t i o n ) t h e y were n o t i c e a b l e t o a f a r l e s s e x t e n t ,

No l a r g e r a v a l a n c h e s were r e c o r d e d d u r i n g t h i s month, Oniy some l e s s dangerous, wet, new snow a v a l a n c h e s r e s u l t e d from t h e foehn i n f l u x o f 7 J a n u a r y ,

More f a v o u r a b l e t h a n i n Graubanden was t h e snow cover development i n t h e r e s t o f t h e . Alps, Depth h ~ a r c o u l d nowhere be d e t e c t e d , and t h e more r e c e n t l a y e r s were w e l l cemented, However, t h e s t r u c t u r e s o f t h e p r o f i l e s i n t h e s o u t h e r n V a l a i s and t h e Engadine were l e s s s t a b l e , s i n c e i n t h e meantime t h e Deceidber l a y e r had become c o a r s e - g r a i n e d and t h e newest l a y e r s , t o o , a p p a r e n t l y c o u l d n o t bond a p p r e c i a b l y , but t h e r e was no g r e a t i n c r e c s e i n new snow, which d o u b t l e s s would have c a u s e d t h e snow cover t o b r e a k ,

Consequently, no dangerous s i t u a t i o n s appeared i n J a n u a r y b e c a u s e wherever t h i c k l a y e r s o f new snow p r e v a i l e d t h e s u p p o r t i n g l a y e r s were v e r y f i r m and i n a l l o t h e r c a s e s where t h e bottom l a y e r s gave r e a s o n s f o r c o n c e r n t h e y were s u b j e c t e d t o no a p p r e c i a b l e o v e r l o a d , Only i n t h e V a l a i s was p r o p e r t y damage known t o have been c a u s e d by t h r e e a v a l a n c h e s ,

But now February r e s u l t e d i n a sudden, a s w e l l a s a fundamental change i n t h e c o u r s e o f t h e w i n t e r , s i n c e d u r i n g t h a t month

-

w i t h t h e e x c e p t i o n of t h e T i c i n o

-

a s much new snow C311 a s i n a l l t h e o t h e r w i n t e r months from

1) Cf, "Eine Lawine i s t niedergegangen" ( A n Avalanche h a s f a l l e n ) by D r , Marcel de Q u e r v a i n , Magazine,

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December t o May, I n most r e g i o n s of t h e Alps f t brought t h e g r e a t m a j o r i t y o f avalanches f o r t h e recorded w i n t e r :

February became t h e o n l y s p e c i f i c mid-wintss month,

During t h e f i r s t f s u s days weather from t h e west brought i n t e r n i t t e n t foehn wfnds, O n t h e 6 t h a s l o w l y fn-

c r e a s i n g s t a g n a t i o n r e g i o n began t o form which brought stormy

W,N,tV, wfnds, This s i t u a t i o n c o n t i n u e d u n t i l t h e 1 3 t h and caused heavy snowfalls, p a r t i c u l a r l y on t h e 9 t h o A f t e r a s h o r t h i g h p r e s s u r e c o n d f t f o n w l t h f u ~ t h e r l f g h t s n o w f a l l s e a s t o f Oberhasli-.Euzern warmel. a i r masses whfch had g a t h e r e d a t h i g h a l t i t u d e s once more r e s u l t e d i n cloudy weather on t h e 8 8 t h and i n a p e r i o d of contfnuous p r e c i p i t a t i o n l a s t i n g

u n t i l t h e 2 5 t h w i t h p r e v a i l i n g west and n o r t h w e s t winds,

From t h e 2 5 t h on w e s t e r l y weather p r e v a f l e d w i t h i n t e r m i t t e n t c l e a r i n g and foehn winds, The s o u t h s i d e of t h e Alps r e c e i v e d t h e f i r s t moderate p r e c i p i t a t f o n s o f t h e month,

Both p r e c i p f t a t i o n p e r i o d s b r o u g h t a c e r t a i n i n - c r e a s e of snow t o v a r i o u s r e g i o n s o f the Alps: on t h e n o r t h s i d e of the Alps about t h e same m o u n t of snow f e l l i n e a c h p e r i o d , whereas, f n the v a l l e y s t h e f i r s t s n o w f a l l was

moderate and t h e second was heavy ( a t 800 m, e l e v a t i o n , 40

and 118 cm,, r e s p e c t i v e l y ) , The p c f n t o f maximum snow d e p t h o c c u r r e d d u r i n g t h e second p r e c i p i t a t i o n perf od f o r most r e g i o n s of t h e n o r t h s i d e of t h e Alps, The s n o w f a l l s were s h o r t and m o d e ~ a t e between B e d r e t t o and Faido d u r f n g t h e f i r s t p e r i o d , The Engadine s h a r e d c o n s i d e r a b l y I n t h e

p r e c i p i t a t i o n a t the b e g i n n i n g of t h e month, These r e s u l t e d i n maxfmwn snow d e p t h s on t h e s e v e n t h of February f o p

e l e v a t f s n s o f 1800 m,

No l e s s i n t e r e s t i n g w i l l be t h e e x a m i n a t i o n o f t h e q u e s t i o n s o f t h e i n f l u e n c e t h e tremendous masses o f new snow e x e r t e d on t h e e x i s t i n g snow cover w i t h i t s r e g i o n a l l y so d l f f e r e n t s t ~ u c t u s s

-

and p a r t i c u l a r l y , whether t h e coarse- g ~ a i n e d d e p t h h o a r l a y e r s n e a r the ground bonded t o g e t h e r under t h i s new l o a d , and t o what* e x t e n t t h e avalanches d u r i n g and a f t e r t h e s e s n o w f a l l s c o u l d be c o n s i d e r e d a

d i r e c t consequence o f t h e snow cover development of t h e p r s - c e d i n g months, These q u e s t i o n s become more u n d e r s t a n d a b l e when i t i s c o n s i d e r e d t h a t t h e q u a n t i t y o f new snow i n

F e b r u a ~ y a t t h e e x p e r i m e n t a l f i e l d on Wei s s f l u h j o c h e x e r t e d a praessure on t h e bottom l a y e r s o f 382 kg,/&

F i r s t , t h e c o n d i t i o n s a p p e a r i n g on the s tarldalad

t e s t a r e a w i l l t e considelaed, A comparison o f botch p ~ o f i l e s of t h e month r e p o r t e d c l e a r l y shows t h e g r e a t jump i n t h e

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on February 1 t o 270 cm, on RIarch 1, The e a r l y w i n t e r

l a y e r s ( ~ e p t e m ' a a r to ~ o v e m b e r ) had n o t y e t bonded: on t h e c o n t r a r y , t h e i r s t l w c t u r e had become p a r t i a l l y l o o s e r s i n c e +,he formation of d e p t h h o a r had now s e i z e d t h e October

l a y e r s too and the two sun c l a u s t s had a l r e a d y begun t o b r e a k up, Thus, the upper p a r t of t h a snow cover was s t a b l e b u t

t h e l o o s e g r a n u l a r b a s e and the h o a r l a y e r on l a y e r I a

-

which was s t i l l p r e s e n t b u t had n o t become important due t o

i t s n e g l i g i b l e s i z e

-

was s t i l l r a t h e r dangerous,

The development of the snow cover i n t h e lower r e g i o n s o f t h e Parsenn a r e a took p l a c e more o r l e s s i n t h e

same way, The p r o f i l e s o f Bfischalp and Davos show a

c h a r a c t e r s i m i l a r t o t h a t of t h e Weissfluhjoch, t h e essen- t i a l d i f f e r e n c e b e i n g the l a y e r of hoar on t h e Baschalp which i s n o t between t h e bonded l a y e r s b u t forms t h e cover of t h e l o o s e b a s e ,

The avalanches observed d u r i n g t ~ i s time can be

d i v i d e d i n t o t h r e e p e r i o d s , The f i r s t began a f t e r t h e

moderate s n o w f a l l s from January 29 t o February 1, The new

snow f e l l on the h o a r l a y e r which was formed a t t h e end of January and t h e e f f e c t s of t h i s were a l l t h e more unfavour- a b l e because t h e s e p r e c i p i t a t i o n s were accompanied by h i g h wlnds and were t h e r e f o r e d e p o s i t e d i n h e a v i l y wind-packed

formo I n the following days, p a r t i c u l a r l y on February 1,

a number of t y p i c a l small wind-slab avalanches were observed

above 2200

m,

Some of t h e s e s l i d down w i t h o u t any e x t e r n a l d i s t u r b a n c e , o t h e r s were r e l e a s e d by d i s t a n t o r nearby pas- sage of s k i e r s , A l l examinations o f the breakage a r e a s r e - v e a l e d t h e same p a t t e r n : t h e mass of new snow which had been wind-packad t o a d e p t h of 50

cm,

had s l i d down on t h e l a y e r of h o a r ( ~ e i f b l u m e n d e c k e )

,

A 1 though t h e s e avalanches were n o t verly g r e a t t h e y c o u l d s t i l l be dangerous f o r t h e s k i e r because t h e l o c a l i n s t a b i l i t y was d i f f i c u l t t o e s t i m a t e and breakages o c c u r r e d even on r e l a t i v e l y f l a t s l o p e s , No avalanches w i t h c a s u a l t i e s o r p r o p e r t y damage were r e c o r d e d o

The second avalanche p e r i o d of t h e recorded

month s t a r t e d w i t h t h e heavy snowfalld beginning on 4

February, This p e r i o d s u b s e q u e n t l y brought l a s t w i n t e r

P s

l a r g e s t and m o s t f r e q u e n t avelanches

,

The b u l l e t i n i s s u e d on 8 February read: " O w f n g t o heavy s n o w f a l l s avalanches

were p r e v a l e n t throughout the Alps, The danger of avalanches

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Froin t h e 8 t h t o t h e 1 0 t h exceedir-gly l a r g e wind s l a b s broke away, wf t h few e x c e p t i o n s , on each of the f a m i l i a r " avalanche s l o p e s o f t h e Farsenn r e g i o n , These r e s u l t e d i n c a s u a l t i e s a s w e l l a s c o n s i d e r a b l e p r o p e r t y

damage, The examination of some o f t h e s e c t f o n s showed

t h a t the snaw masses i n lo.wel- r e g i o n s and on sunny s l o p e s s l i d down on t h e l o o s e d e p t h h o a r base, whereas a t h i g h e r eleva+,f 0113, p a r t i c u l a r a l y on shady e l o p e s , t h e h o a r s e r v e d p r i m a ~ i l y a s a a l i d i n g l ~ g o r , and the ccrnpact December

-

January l a y e r was c u b k o :he base o n l y by t h e dynamic impact of' t h e slfdia:g snow masses, Of t h e s erlies of a v a l a n c h e s

observed, two deselave s p e c i a l mantion:: an February 8 t h e

Schiahorrl avalanclle was r e l e a s e d by a demoPi t f on b l a s t with whf c h t h e Palasenn s e r v i c e opened the D o ~ f t & l i - r o u t s , The br~sak-away o c c u r r e d a t the e a s t e r n sdge o f t h e a v a l a n c h e d e f e n c e s and t h e snow massea flowed down tc t h e t r e e l i n e w i t h o u t S n f l i c t i n g any damage, Less f o p t u n a t e was the d e s c e n t of t h e d o u b l e avalanche which o c c u r r e d two days l a t e r a t t h e G o r f b e r g - S a l e z e r Horn and i n vihich n con- a t . n ~ c t i o n worlssr l o s t h i s l i f e y - ) ,

The t h i r d avalanche p e r i o d of t h i s month c o l n c f d e d w i t h t h e heavy snows i v h f ~ h f e l l d u r i n g t h e l a s t t e n days

and which extended f a r i n t o the v a l l e y s , These days o f

maximum snow cover would have p a s s e d without any n o t e - tiro~thy a v a l a n c h e s i f i t ; had n o t been f o r the l a r g e Schaf-

g avzianche which cage d c w ~ on February 24,

The sno~v cover i n t h e G l a r n e r Alps and i n t h e alp st el^ r e g i o n , which had developed ipp t o t h e b e g i n n i n g of Februai-y r v i t h o u t d i s con t i n u a u s Y trcatf f ' i c a t i o n , had t o

r v i t h s t m d a s e v e r e t e s t , The T i l a s t , s n o w f a l l i n February r e s u l t e d i n an i n c r e a s e i n the snow cover of a b o u t 80 cm,

a t an e l e v a t i o n o f 1800 m o Owing t o h i g h t e m p e r ~ t u r e ( t h e z e r o d e g r e e

( c )

isotheran pose a t time:: t o 1508 rn, above s e a b e v e l ) a good s e ~ t l e m a n ~ o f new l a y e r s was p o s s i b l e ; no a v a l a n c h e s were observed d u r i n g t h a t %%me,

Tnus, f a v c u r a b l e c o n d i t i o n s were a% s c estabhisried f o r t h e seconci p r e c i p i t a t i o n p e r i o d , b1rorn the 2 B s t t o t h e 2 6 t h

vepy c o n s f d e r a b l e amsunts ef n s w snsw f e l l i n thns f o o t h i l l r e g i o n o f t h e Alps, amounting t o 160 cm, on t h e ~ c h v d g a l p

(1900

d,

180 cm, a t Mettmen-Ga~ichte (1565 m,

1

and i n -

c r e a s i n g r;he snow c o v e r b y about 120 crn, The f i r m s t r u c t u r e o f t h e snow cover below 2000 m, w a s s u f f i c i e n t t o w i t h s t a n d t h e enormous new l o a d , Only i n s i g n i f i c a n t l o o s e snsw

a v a l a n c h e s could b e o b s e r v e d on s t e e p s l o p e s a t t h e s e e l e v a - t i o n s . However, t h i s i n c r e a s e l e d t o o v e r l s a d i f i g and t o some n o t e w o r t y a v a l a n c h e s a t e l e v a t i o n s where t h e wfnd caused

cons1 d e ~ a b l e d r i f t s ,

-

-

=

m

o

Head of the Parsenla

s e r v i c a i n " ~ & t i ~ k e i t s b e r ~ c h t d e s Par- s e n n d i e n s t e s i m % i n t e r ~ 9 4 5 / 4 6 " ,

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9

Techo T r a n s o TT-62 The p r o f i l e s t r u c t u r e i n t h e middle and western p a r t s of t h e n o r t h e r n s i d e of t h e Alps, t h e lower V a l a i s , and Goms was c o n s i d e r e d more f a v o u r a b l e i n comparison w i t h tlie s t a n d a r d r e g i o n G r a u b b d e n - ~ o r t h due t o t h e l a c k of h o a r l a y e r and t h e f i r m n e s s of the lower b a s e , The f a c t t h a t t h e course of t h e weather i n those r e g i o n s p a r a l l e l e d t h e condi- t i o n s p r e v a i l i n g i n ~ r a u b h d e n - ~ o r t h s e r v e s t o e x p l a i n t h e i r corrasponding snow c o v s r and avalanche developments d u r i n g b7ebruaryo The snow masses s e t t l e d q u i t e r a p i d l y i n those r e g i o n s owing t o r e l a t i v e l y h i g h t e m p e r a t u r e s o The base

experienced a bonding a t t h e same time t h a t a comprsssion

of t h e upper bayors took p l a c e , On March 1, t h e r a f o r e , t h e p r o f i l e s of t h e s e r e g i o n s , w i t h a b a s e , c o n s i d e r a b l y b e t t e r bonded than t h e bas8 i n ~ r a u b b d e n - ~ o r t h , b u t much l o o s e r

than t h a t of t h e n o r t h - e a s t e r n r e g i o n of the f o o t h i l l s o f

t h e Alps, showed a v a r y s t a b l e c h a r a c t e r The avalanches observad d u r i n g b o t h p e r i o d s of s n o w f a l l and t h e c a s u a l t i e s and damage caused by them m i g h t be c o n s i d e r e d s l i g h t , Only t h a Gadmen Valley of t h e Berne h i g h l a n d s a c t u a l l y s u f f e r e d

from avalanches, e s p e c i a l l y from February 21 t o 24, when

n o t l e s s t h a n n i n s avalanches blocked the road between

Gadmen and W e s ~ e n t h a l No human s e t t l e m e n t s were des t r o y e d , and s i n c e the i n h a b i t a n t s c a r e f u l l y avoided l e a v i n g the i p

d w e l l i n g s d u r i n g t h i s most dangerous time no human l i f e was l o s t , The l a r g e s t avalanche i n the Berne k i g h l a n d s descended

on February 9 t h on t h e n o r t h s i d e of the Mahrenhorns, It

c a r r i e d away approximately 50 cubic metres of woodland and

overspread the Gadmen Valley a t Nessenthal t o a d e p t h of 5 m o

over an a r e a of 180 m o l o n g and 300 m e wide, Despite t h e f a c t t h a t snow storms c o n s i d e r a b l y r e s t r i c t e d s k i i n g d u r i n g the most dangerous p e r i o d a p a r titularly t r a g i c a c c i d e n t occurred the n a t u r e of which s e r v e s a s a warning a g a i n s t t r a v e r , s i n g sCeep s l o p e s d u r i n g snow storms and p e r i o d s of poor - v i s i b i l i t y , p a r t i c u l a r l y a t night,, This was the a c c i d e n t of February 23rd which occurred i n t h e G a n t r i s t r e g i o n ,

The f a m i l i a r avalanches of Goms a i d n o t occur a t t h i s time; only t h e " ~ i l ~ e r s b & c h l i avalanche" between

B l i t z i n g e n and Selkingen descended i n l e r g e p r o p o r t i o n s on February 1 0 , I t f i l l e d up t h e t r a c k s of t h e Furka-

Oberalp r a i l w a y and t o r e down t h e conducting w i r e s

,

T r a f f i c could n o t be resun~ed u n t i l the evening of February 1 5 a f t e r 4850 c u b i c metres of avalanche snow had been

removed

S u r p r i s i . n g l y , i n d i s t r i c t s of c e n t r a l S w i t z e r l a n d ,

where t h e r e w 3 . s much snow and many avalanches, no damage

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The f a c t t h a t s n o w f a l l s accompanied by storms even a t p l a c e s which have n o t been considered avalanche s l o p e s , can cause dangerous d r i f t s the t r a v e r s i n g of which must sometimes r e s u l t i n s e r i o u s snow s l i d e s i s shown by the avalanche a c c i d e n t a t Balmberg on February 24,

The manner i n whfch t h e r e l a t i v e l y moderate snos- f a l l s of February on t h e f f lam s t r u c t u r e of the snow cover

i n n o r t h Ticino l e d t o a f u r t h e r c o n s o l f d a t i o n need n o t be explained i n d e t a i l , The snow cover o f 185 cm, t h i c k n e s s a t the experimental f i e l d i n B e d r e t t o (1435 m , ) i n d i c a t e s a de- gree of bonding l e a v i n g n o t h i n g t o be d e s i r e d , Thus, o n l y f i v e avalanches were observed d u r i n g the whole month by the boundary s e r v i c e on the i~ e x t e n s i v e p a t r o l s , These avalanches came down i n the f a m i l i a r avalanche t r a c k s of V i l l a , Ronca and Valleggia without i n f l i c t i n g any damage,

F i n a l l y , t h e c o n d i t i o n s i n the southern v a l l e y s of t h e V a l a i s and i n t h e Engadine remain t o be consideredo During the who3.e month a development v e r y d i f f e r e n t from a l l o t h e r r e g i o n s took p l a c e w i t h r e s p e c t t o p r e c i p f t a t i o n ,

changes i n t h e snow s t r u c t u r e and avalanche formation, A t

f i r s t , the s n o w f a l l s a t the beginning of February were c o n s i d e r a b l e , The snow cover i n c r e a s e a t 1800 m, amounted

t o approximately 60 cm, The d e p o s i t of snow masses a t the

beginning o f February, whi c h due t o s t r o n g winds was very

i r r e g d a r a t e l e v a t f o n s corresponding t o those of t h e V a l a i s , and whlch took p l a c e c h i e f l y on s l o p e s f a c i n g e a s t , immediately caused g r e a t avalanche d e s c e n t s over the known t r a c k s of t h e Z e m a t t Valleyo

That t h e r e were few avalanches i n t h e Engadine i n February i s due t o r e l a t i v e l y s m a l l snow depths, Of course,

the s l i g h t e s t overload s u f f i c e d t o break t h e l o o s e b a s e which has a l r e a d y been mentfoned s e v e r a l times, I n ' f a c t s e v e r a l

avalanches were observed, the l a r g e s t descending on February 1 2 i n Val S u l s a n a and t a k i n g t h r e e l i v e s ,

February was marked by heavy s n o w f a l l s , Owing t o

the c o n t i n u o u s l y heavy snow f a l l s a favourable bonding of t h e

l a y e r s o f new snow was p o s s i b l e , Thus, only a few avalanches

occurred, p a i > t i c u l a r l y i n r e g i o n s where t h e e a r l y w i n t e r l a y e r s showed v e r y l o o s e s t r a t i f i c a t i o n o r where t h e snow masses s e t t l e d on s u r f a c e hoar formed a t the end of Januaryo

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I11

LATE

ViINTLH

I n c o n t r a s t t o E'ebruary, Idlarch showed l i t t l e p r e c i p i t a t i o n on t h e n o r t h s i d e of tile A l p s ; however, t h e s o u t h s i d e r e c e i v e d an e x c e s s of a b o u t 40 p e r c e n t above nornlal , '('he 1s t , 2nd and 3 r d brouqht p r e c i p i t a t i o r i s t h r o u g h o u t S w i t z e r l a n d which were lieavy i n t h e s o u t h e r n and e a s t e r n part; o f t h e V a l a i s , moderate on t h e solfith s i d e of S t , G o t t h a r d , and n e ; l i ; i b l e i n t h e r e m a i n i n g r e g i o n s of t h e A l p s , The v a l l e y s o f t h e V a l a i s and t h e s o u t h e r n boundary r e g i o n s of t h e Berne Alps a t t a i n e d t h e i r .naxirnum snow c o v e r d u r i n g t h e s e f o u r d a y s , While on t h e n o r t h s i d e or" t h e Alps c o n t i n u o u s sunny o r s l i ~ h t l y c l o u d y , warm w e a t h e r u p t o t h e end o f t h e month c a u s e d a s t e a d y d e c r e a s e of t h e snow c o v e r , a i r masses co:ning i n from t h e s o u t h e a s t b r o u g h t d a i l y p r e c i p i t a t i o n s f r o m t h e 4 t h t o t h e 1 5 t h i n T i c i n o and p a r t i a l l y a l s o i n t h e d n g a d i n e , These r e s u l t e d f i n a l l y i n maxirr~urn snow d e p t h f o r t h e s e r e ~ i o r l s

-

i n t h e Engadine o n l y

above 2000 m , P a r t i c u l a r a t t e n t i o n must be p a i d t o t h e snow cover o f idlarch 1 5 on t h e s o u t h s i d e of t h e G o t t h a r d b e c a u s e t h e r e were 270 cm, snow i n B e d r e t t o and 225 cm,

i n k i r o l o ,

From March 1 5 on, t h e w e a t h e r changed i n t h e s e p r e c i p i t a t i o n r e s i o n s t o o , The b r i g h t w e a t h e r p r e v a i l i n g u p t o t h e end o f t h e month c a u s e d a r a p i d d e c r e a s e i n t h e

d e p t h o f t h e snow,

March was t h e t i m e of' most i n t e n s e s e t t l e m e n t

and bonding of a l l l a y ~ r s of t h e snow c o v e r on W e i s s f l u h j o c h , With a t o t a l of 31 cm, new snow, 1 8 cm, of which was a t t r i - b u t e d t o t h e s n o w f a l l of Svlqrch 2, t h e t o t a l d e p t h of t h e snow c o v e r d e c r e a s e d by one h a l f rnetce, The p r o c e s s o f

s e t t l i n g was c a u s e d by f r e q u e n t t e m p e r a t u r e s above f r e e z i n g , The p r o f i l e of A p r i l 1 s h o u l d r e p r e s e n t t h e p o i n t of maxi- mum b o n d i n g , The whole p r o f i l e h a s t h e t y p i c a l foram of a f i r m snow c o v e r s t r u c t u r e t h e L1,;'iiperature g r a d i e n t o f which, n e v e r t ' h e l e s s , i n d i c a t e s t h a t s p r i n g i s a p p r o a c h i n g and s h o u l d soon s o f t e n t h e s t i l l s t r o n g snow c o v e r ,

Of c o u r s e , t h e e f f e c t of t h e w e a t h e r was more pronounced i n t h e lower r e g i o n s , Thus, t h e development a t a n e l e v a t i o n of a b o u t 2000 m , was r o u g h l y two weeks ahead o f t h e c o n d i t i o n s on t h e s t a n d a r d t e s t a r e a , The snow cover was a l r e a d y wet t h r o u g h o u t by 20 March and t h e p r o f i l e of t h e f i r s t of A p r i l p r o v e s t h a t t h e d i s i n t e g r a t i o n p r o c e s s was a l r e a d y i n f u l l swing, The m e l t i n g p r o c e s s at an e l e v a t i o n o f 1500 m , had a l r e a d y s t a r t e d a t t h e b e g i n n i n g o f t h e month and c a u s e d a d e c r e a s e i n t h e snow c o v e r o f a b o u t f i f t y p e r c e n t d u r i n g t h e month,

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Tech, Transct TT-62

Avalanche danger w a s n o t e p t i r o l y overcome a t t h e

beginning o f the m~rlthn I n t h e f'ilast days of Ivlalach a number

of wind-slab avalanches were observed above 200Q m, some of which w e r a r e l e a s e d by s k i e r s while ~ t l i q p s descended w i t h o u t b e i n g ele eased by extcrna.l. c a u s e s , In lower r e g i o n s r a d i a t i o n and h e a t a c t ~ d so s t r o n g % y % h a t t h e s l i d i n g of t h e whole snow cover was c o n s i d e r e d p o s s i b l e because of the h e a t e d g ~ o u n d ,

Idany wet wind s l a b avalanches were observe -' on the second

and t h i ~ d i n ? Davoso A s the i n f l u e n c e of ?!I.;.::;.- and r a d i a t i o n

e f f ' e c t s i n c r e a s e d t h e s e s c c u ~ > ~ a d on ' - " i l : ~ , g k i a ~ ' s 7. opo s ,, A s f a r H S i s knobnun no damage was c a u s e d o

The e a r 2 . y d i s lntegpat-~n of th2 s n r ~ ~ , ~ c,';i*Vc.,r ';

b e observed i n a1.l parts of' t h e Alpine kegion y{'r;icl-~ ,ill. Mzrch

had t h e same p r a o i p i t a t i o n c o n d i t i o n s a s Graubunden-1?ol3t'i;, I n the south~drl: 811d c e n t r a l V a l a i s t h e g r e a t snovrfalls of

3 ?$arch (125 c430 fell S.n B r i g t h a t day on ground which had

becorns f r e e f r o x snow (apepen Boden)) oince rnora r e l e a s e d t h e

f ?

' ' T a ~ c b ~ ~ a n d b ava3.anchesq ( 4 2 3 c u b i c m e t r e s of exczvated matepin l ) ths ' ~ t - 1 ,den-Sch.litan avakanche" (746 c u b i c me t z e s ) t h e l'Sc'nusr:.-

L un:i tlia " ~ f a i c h e n z u g avalanche

"

(2200 c u b i c rtls t r e e ) chj. cl-:

cams ;Lorn on t L o t r a c k s o f t h e 7-isp-Zermatt r a i l r o a d , ancl whe~ne

a house w a s darringeci a % t h e Simplora,=.roat: through a f u r t h e r des=- c e n t a t Gab%" The r a p i d d i s i n t e g r a t i o n of t h e snow cover i n t h i s d i a b r i c t began on t h e f o r n t h of Fharch, I t i s noteworthy t h a t ? ' no d e s t r l i c t i v e a a a l a u c h e s came down i n t o t h e v a l l . e y a 1-71

G s m s at tlna.L bime i n s p i t e of t h e abundance of snow,

uf..'nat were t h e consequences of' the heavy s n o w f a l l s on t h e soutll s i d e cf $he A l p s which c o n t i n u e d up t o t h e

middle uf t h e rnolzth"?s a l r e a d y p o i n t e d o u t , the snow cover h e r e showed a f i r m s t ~ u c t u r e , T!e d a i l y q u a n t i t i e s of new

sncw sf 2

-

40 c m o f e l l a t t e m p e r a t u r e s around

zero"^

and

Z ~ F C windo Thus, tho mcst f a v o u r a b i s c o ~ d i t i o n s f o r uniform

" I - % -

l a y e r s sand

__

, . > I s e t t l e m e n t were g i v e n , This time, t o o , t h e snow c o v e r ~ v , ~ L s t o o d t h e new l o a d , No avalanches were obselaved,

The change of weathers i n the r::.11Ci.r2.32 o f t h e m ~ n t h c o n s i d e ~ a b l y a c c e l e r a t e d t h e d i a i n t e g r a t i i : ) n ol: t h e snow cover s o t h a t t h e t o t a i d e p t h sf t h e snow up t o t h e f i r s t of AppEl decraeassd by a b o u t 40 ern: cies;rpi:t;e, CiLc;l p r e c i p i t a - t i o n s of t h e f i r s t h a l f of !!Iar@h, The " ~ v a l a n c h e B u l l e t i n ! ' of 29 March i s r e p r e s e n t a t i v e of t h e c o n d i t i o n s p r e v a i l i n g a t t h e end ~f March:

'"ri th.9 whole A l p i n e r e g i o n v e r y f a v o u r a b l e c o n d i t i o n s for s p r i n g s k i i n g p r e v a i l o Ho-vrever, calaeful c o n s i d e r a t i o n should be given when e n t o r i n g s t e e p s l o p e s exposed t o ' t h e suntb

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Tech. Trans. TT-62

A p r i l was c h a r a c t e r i z e d b y a g r e a t l a c k of p r e - c i p i t a t i o n and g r e a t sun r a d i a t i o n , The whole of c e n t r a l

Europe was under t h e i n f l u e n c e of s u b - t r o p i c a l warm air. masses which were i n t e r r u p t e d o n l y s p o r a d i c a l l y by c o l d a i r masses which h a d l i t t l e e f f e c t on t h e w e a t h e r , Up t o t h e 2 5 t h b r i g h t weather p r e v a i l e d i n t e r r u p t e d b y p r e c i p i t a t i o n s b e g i n n i n g on A p r i l 18. From t h e 2 6 t h t o t h e end of t h e

m o n t h foehn c o n d i t i o n s w i t h c o n t i n u o u s , moderate p r e c i p i t a - t i o n s p r e v c . i l e d on t h e s o u t h s i d e of t h e Alps b r i n g i n g

snow i n n o r t h T i c i n o above 1500

m,

and i n t h e Engadine

above 2000 m o

This g e n e r a l t e n d e n c y of t h e w e a t h e r s o f c o u r s e which r e s u l t e d , f o r example, i n a mean t e m p e r a t u r e f o r

t h e month about 1 0 7 degree t o o h i g h (-0-6 i n s t e a d of - 2 , 3 ° ~ ) a l s o causeci s ~ 3 ~ ; - r r a c i d d i s i n t e g r a t i o n o On \ \ ; e i s s f l u h j o c h

t h i s disinte;:r:?.tioli .lsJ a l r e a d y s t a r t e d a t t h e b e g i n n i n g

of t h e month i , i t h a w e t t i n g of t h e whole snow c o v e r , The snow p r o f i i e o f t h e f i r s t of Itlay c l e a r l y sliows t r a c e s of

t h i s development, Tlie thorough w e t t i n g , t h e n o t i c e a b l e

d e c r e a s e i n t h e snow p e m trc:,;? t c r b i 23i; ~ : L L c.2 ~cnd p a r t i c u l a r l y t h e pronounced i c e lamina i n d i c a t e an a l r e a d y advanced d i s - i n t e g r a t i o h , The l o s s of snow d e p t h of about 50 cm, o c c u r r e d mainly a t t h e expense of t h e upper l a y e r s I I I a , b and I I b ;

t h e l a y e r s I I a , Ib, Ia, and t h e December l a y e r s a l s o d e c r e a s e d s l i g h t l y i n s i z e . Thus, t h e d i s i n t e g r a t i o n t o o k p l a c e a s

u s u a l f r o m t o p t o bottom,

In lower r e g i o n s t h e snow c o v e r d e c r e a s e d more r a p i d l y i n d e p t h , A t a n e l e v a t i o n of 2000 mb where t h i s

c o v e r s t i l l amounted t o 1 1 5 cmo a t t h e b e g i n n i n g of t h e month, a c o v e r of 25 cmo c o u l d s t i l l b e measured on t h e f i r s t of May ( ~ f i s c h a l ~ )

-

s h o r t l y b e f o r e becoming f r e e from snow d u r i n g June

-

whereas t h e t e s t a r e a a t Davos was a l -

r e a d y f r e e from snow on 1 2 A p r i l o

I n t h e r e m a i n i n g r e g i o n s of t h e AJps, a l s o , t h e m e l t i n g of t h e snow c o v e r took place v e r y r a p i d l y , s o t h a t

t h e mean snow boundary a l r e a d y ascended i n t h e Zngadine

t o

2100

m o ,

i n n o r t h e r n T i c i n o t o 1500 m o and i n t h e r e m a i n i n g r e g i o n s t o 1800 m. The i n t e n s i t y of t h e snow c o v e r d i s - i n t e g r a t i o n i n t h e two months March and A p r i l may be

i l l u s t r a t e d by t h e c o n d i t i o n s p r e v a i l i n g i n B e b e t t o , 1435

m.

abovs s e a l e v e l , where t h e snow c o v e r amounting t o 270 cm,

on March 15, had m e l t e d by A p r i l 28, which c o r r e s p o n d s t o

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Techo Trans, TT-62

With t h e exception of a few harr'iless wet snc?.?

s l i d e s no avalanches were observed anywhere d u r i n g the tf'L~ol.,-~ month of A p r i l o I n r e g i o n s below 1300 rn, t h e w i n t e r co.,iia

be regarDded a s h a v i n g come t o an end, The l a s t b u l l e t i n was i s s u e d on A p r i l 18:

" N O avalanche danger, e x c e p t f o r shallow wet snow s l i d e s , p r e v a i l s a t t h e p r e s e n t time i n the whole Alpine r e g i o n " ,

ExamPnatisn of the time prof i l 8 show-. !;hat the

d i s i n t s g r a t i o n of t h e snow cover on t h e , i l e i s s f . ~ ~ ~ ~ l j x h was r z t a r d e d once more i n ?,lay and had n o t even been c~.nipleted I n June, due t o c o n s i d e r a b l e s n o w f a l l s i n t h e middle of t h i s month,

Up to May 14 t h e iweather was b r i @ t and warm on

the n o r t h e r n s i d e of t h e Alps w i t h o n l y s l i g h t p r e c i p i t a t i o n s , whereas the s o u t h e r n s i d e had p r e c i p i t a t i o n s almost d a i l y o

Snow $ e l l only above 2500 m o A r c t i c a i r masses caused snow-.

f a l l s on the 1 5 t h and 1 6 t h dorr~n t o e l e v a t i o n s of 1200 m, J-bing the second h a l f of t h e month f r e q u e n t changes of a i r masses a l s o caused nurerous p r e c i p i t a t i o n s w i t h snoif? on b o t h

s i d e s of t h e A l p s down t o 2200 m0 Approximately double t h e normal prwcipi t a t ions cnlne down i n T i c i n o d w i n g May v i l ~ e ~ e a s

the e x c e s s i n t h e remaining p a r t of S w i t z e r l a n d was con- s i d e r a b l y l e s s

June was c h a r a c t e r i z e d b y f r e q u e n t , p a r t i a l 7 - 7 k-ieavy cold a i r p e n e t r a t i o n s o The f i r s t of t h e s e i n ~ ' i . , ~ L:

occurred on t h e 3 r d and caused s n o w f a l l s down t o 240Q m,

The second, on t h e t w e l f t h , caused t h o h e a v i s s t continuous

r a i n of t h e wh'ole suwaer; t h e snow boundary descended i n

t h i s c a s e down t o 1000 m a A f t e r a few o v e r c a s t days a t h i r d c o l d a i r i n f l u x 'Lasting from the 2 1 s t t o t h e 24th a g a i n caused s n o w f a l l down t o 2500 m o and t e m p e r a t u r e s n e a r f r e e z i n g down t o 2000 m o Only on the 2 6 t h d i d tho

temperature r i s e c o n s i d e r a b l y , going a s h i g h a s 17OC a t

2500 m e

A f t e r t h e snow cover up t o June 1 2 t h had d i s - i n t e g r a t e d t o 94 cm, a t t h e expense of l a y e r s I I b and I I a , t h e s n o w f a l l s from t h e 1 2 t h t o 1 7 t h w i t h a t o t a l of 72 cm, .

caused a new i n c r e a s e i n t h e depth of snow t o 123 cm, Although t h e m e l t i n g of t h i s new l a y e r was r e t a r d e d by a f u r t h e r i n c r e a s e of 38 emo ( 2 1 s t

-

25th June) t h e l a s t warm days of t h e month caused t h e -June l a y e r s a s w e l l a s the r e s t of I I a and I I b t o d i s a p p e a r ,

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Tech0 T r a n s o TT-62

A l t e r n a t i n g sunny and cloudy weather w i t h h i g h

ternparatures and i n t e r m i t t e n t r a i n f a l l s a t t a c k e d t h e remaining o l d e s t l a y e r s s o e f f e c t i v e l y t h a t tho t a s t a r e a became f r e e from snow by 12 J u l y . Thus, the snow covar of t h e w i n t e r of 1945/46 l a s t e d 292 days, o r e x a c t l y f o u r - f i f t h s of a y e a r ,

I n lower r e g i o n s where t h e s n o w f a l l s of t h e s e two months came down on snow-free ground t h e i r m e l t i n g took p l a c e much f a s t e p due t o the a d d i t i o n a l e f f e c t of t h e ground h e a t ,

On s t e e p , g r a s s y s l o p e s i s o l a t e d wet snow avalanches o c c u r r e d o Forty-two sheep were l o s t t u one of t h e s e avalanches on

l18ngisalp a t E i n s i e d e l n o

The w i n t e r , which had brought much snow, b u t which v a r i e d g r e a t l y i n development from r e g i o n t o r e g i o n i n the Swiss Alps came h e r e w i t h t o a c l o s e Thus, t h e v a r i e t y of snow c o n d i t i o n s i n t h e Alpine r e g i o n , a s w e l l a s t h e g r e a t s i g n i f i c a n c e of t h e form of the snow cover base was once more demonstratedo The i n c r e a s e i n snow d e p t h g e n e r a l l y r e s u l t s i n an i n c r e a s e d number of a v a l a n c h e s - However, t h e d e c i s i v e f a c t o r concerning s t a b i l i t y i s t h e m e t e o r o l o g i c a l c o n d i t i o n s a t t h e beginning of t h e w i n t e r ,

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Tech a T r a n s TT-62

BIBLIOGRAPIIY

-

H a e f e l i R o : ~ Z t i ~ k e i t s b e r i c h t 1934

-

1937 d e r Schweiz, Komrnis s i o n

far

Schnee- lund Labvinenf o r s c h u n g [ R e p o r t of

A c t i v i t y of t h e S w i s s Comlission f o r Snow a n d Avalanche R e s e a r ~ h ) ~ ~ k a t i o n V v a i s s f l u h j ~ c h Davoso S c h w e i z ,

B a u z e i t u n g , V o l , 110, Noo 8 , . 1 9 3 ' 7 0

Haef e l $ H o : Von d e ~ ~ 8 t i ~ k e i t d e r S t a t i o n h e i s s f luh j o c h

der Schwciz K a m n l i s i o n f

!,b

$@h.nee- und Lawfnenf o r s c h u n g , (On t h e A c t i v i t y aP t h e W e f s s f l u h j s c h S t a t i o n of t h e

Svviss Commission f o r Snow and Avalanche R e s e a r c h ) % , ( S h o r t R e p o r t ) . Schweiz. B a u z e i t u n g o V o l o 111, No 1 5 , A- r a i l 1938

Thams Chr , : U b e ~ d i e S t s a h l u n g s e ig e n s c h a f t e n deza Schnee- decke (On t h e R a d i a t i o n P s s p e r t f e s of t h e Snow Cover) G e r l o B e f t r h g Gssphyso 53, 371 ( 1 9 3 8 ) o

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Neher J o

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N i g g l i , (The Snow a n d f t s ~ d e t a m o ~ p h o s i s

wlch

an I n t r o d ~ l c t P o n b y P ~ o f " ~ D r o P NiggPf

1

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B a e f e E i H o 2 _{b e r d i s}

~ a t i

_{k e i t d e r S t a t i o n Y f e i s s f l u h j o @ h} d e r Schweiz, Kommission P

8

r Schnes- und Lav!inenf o r s c h u n g o S c h w e i z o B a u z e i t u n g , Vole 113, No, 25, 1939 ( s e e Iio0 2 ) '

H a e f e l i R o : Schneomechanik,

m i e

H i n w e i s e n a u f d i e

Erdbaumechanik 1 9 3 g 0 (Snow m e c h a n i c s w i t h r e f e r e n c e t o s o i l m$chani@s 1 9 3 9 , S p e c - i a l R e p o r t f r o m No, 4 )

f i a e f e l i R o und Bucher 23,: Tdodsrne F o r s c h u n g i m Kampfe gegen Lawineno (Modern K e s e a r c h i n t h e F i g h t a g a i n s t A ~ a l a n c h e s ) ~ J a h r b u c h d e s Schweiz, S k i v e r b a n d e s , 1 9 3 9 , l l a e f e l i R o : Wesen mid Aufgaben dela Schnee- und Lawinen- f o r s c h u n g o B e r i c h t d e s V , I n t e r n a t i o n a l e n K o n g r e s s e s f u r R e t t u n g s w e s e n und e r s t o R i l f e b e i u n f & l l e n o (The N a t u r e and Tasks of Snow and Avalanche R e s e a r c h , R e p o r t of t h e V o I n t e r n o Congress f o r Rescue and F i r s t Aid

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Tech.

'

Trans

o

TT-62

9)

Haefeli Ro: Zur 1;Iilachnnik aussergcw&li?7.1.cher Gletscher-

schvsar!:ruz~;.on

(Crz tho

Zlachanics

of

Unusual Glacier

Fluctuations

)

Schkvef

z

Bauzeitung, Vol 115, No

16,

1940,

10)

!.less Eo

:

Le travail de la commission .suisse

pour

itetude

de

la neige et des avalancheso ( m e Work of the

Swiss Cornmis

s

ion on Snow and Avalanche #Research) Journal

forestier suisse

91, 19400

11)

Buchor E o 9

Haefeli R,, Heas

Eo, Jost

C h o

and Winterhalder

R O UO: Lawinen, die Gefahr

f b

den Skifahrer

,

(Avalanches,

the Danger for the Skier)o Issued by Geotechn- Kom-

mission der Schweiz, Naturforschenden Gesellschaft 1940,,

12)

Nigglf P O

:

Schnee und Firn

,

liektoratsrede an

d e r 107

Stiftungsfeier der ~niversitgt

Zurich

19400

(Snow and

Firno Speech of the Rector of the University z b i c h at

the 107th foundation celebration 194Qo Art, Institut

Orell ~ a s s l i

AG.

13)

Haefeli Ro: Die Arbeiten der Station Weissfluhjoch der

Schweizo Schnee-

und. Lawinenfors~hungskommission~

(The work of the Weissfluhjoch StatPon of the Swiss

Research Commission on Snow and Avalanches),

1934

-

1940

Intersylva,

1941

14)

Prohaska Po: Neuere Schnee- und Lawinenforschung in

der Schweiz

Meteorologische Zeitschrift

(Recent

.

Snow and Avalanche Research) Vole

7, 19400

15) Prohaska F o

und Thams Chrcl

:

Neue Untersuchungen fiber

die Strahlungseigenschaften der Schneedecke. (Recent

Investigations on Radiation Properties of the Snow C o ~ e r ) ~

Helvetica Physica Acta, Volo XIIIo

16)

Bucher E o und Jost Cho: Die Erfahrungen in d e ~

khstlichen

~osl8sung

von Lawinen mit ~ i l f e

des b~inenwerfers

,

_{( m e}

Experiences

wf

th the Artificial Release of Avalanches

Using Trench Mortars)

r s ~ Z ~ o ' 1 9

31

July and

1

August

1941. 17)

Miggli

P o

und Rothen Fo: Bericht fiber den Lawinenkurs

ffir Sorstleute vom 15/21e Dezember

19400

(Report

on

the

Course on Avalanches for Forestry P e r ~ o n n e l ) ~

Schweiz,

Zeitschrift f h

Forstwesen,

1941,

Page

-

18

Tech, T r a n s o TT-62

H a e f e l i R , : Spannungs- und ~lastizitgtserscheinun~en

d e r Schneedecke, u n t e r besondeper ~ e r h k s i c h t i g u n g d e r Schneedeckendruckberechriung und verwandter Probleme d e r Erdbauf orschung. ( S t r e s s and P l a s t i c i t y o f ' t h e Snow Cover, w i t h S p e c i a l C o n s i d e r a t i o n of t h e P r e s s u r e C a l c u l a t i o n of t h e Snow Cover and R e l a t e d Problems of S o i l R e s e a r o h ) Schwe,iz, Arschfb, 19420

Bucher

E o

: Die Lawinen d e s Winters 1941/42, (The Avalanches of t h e Winter 1941/42), S p e c i a l R e p r i n t from ''Die Alpen" 1942, Vole 1 2 ,

Bucher E o

,

A r r i g o n i A , , und hrIr" , de Q u e r v a i n , : Die t e c h n i s c h e n I n s t a l l a t i o n s n d e s Eidg, I n s t i t u t e s f b Schnee- und Lawinenf orschung auf Weissf l u h j o c h b e f Davos (The T e c h n i c a l I n s t a l l a t i o n of t h e C o n f e d e r a t e I n s t i t u t e f o r Snow and Avalanche Research a t Vieiss- f l u h j o c h n e a r Davos), Schweizo B a u z e i t u n g , 13; May 1944,

Bucher E o : O f f e n h a l t u n g von A l p e n s t r a s s e n i r n Winter (Keeping t h e Alpine Roads open

i n

W i n t e r ) o Auto- Revue, 8 March 1944, Noo 1 0 ,

Bucher E o z Lawinendienst i n K r i e g s - und F r i e d e n s z e i t e n ,

(Avalanche S e r v i c e i n Nap and Peace ) , "Die Alpen", A p r i l 1944,

Bucher

E,:

Die Anfange d e r s c h w e i z e r i s c h e n S c h n e e ~ A d Lawinenf orschung. (The Reginnings of Swiss Snow and Avalanche R e s e a r c h ) , Leben und Umwelt, V o l , 1, September 1944,

bucher

Eo:

Das Eidg, I n s t i t u t f b S c h e e - und Lawinen- f o r s c h u n g , (The Confederate I n s t i t u t e f o r Snow and Avalanche R e s e a r ~ h ) ~ Echo, March 1944,

B e r i c h t fiber d i e ~ d t i g k e i t d e s E i d g o I n s t i t u t s f b Schnee- und Lawinenf o r s c h u n g o (Report on t h e A c t i v f t y of t h e C o n f e d e r a t e I n s t i t u t e f o r Snow arid Avalanche R e s e a r c h ) , No, 1, h i n t e r 1943 44, "Schweiz, Z e i t -

s c h r i f t f & Forstwesen" No, 5

/

6 , Jahrgang 1945, W o de Q u e r v a i n o : Schnee a l s k r i s t a l l i n e s Aggregat*

(Snow a s C r y s t a l l i n e Aggregate ) , l t E x p e r i e n t i a n Val, 1/7, 1945,

Page

-

1 9

Techo T r c n s , TT-62 2 7 ) B e r i c h t fiber d i e ~ f f t i g k e i t d e s Eidg, I n s t i t u t s f b

Schnee- und Lawinenforschung N r o 2, Winter 1944/45,

( s e e lJoo 2 5 ) llSchvreiz, Z o i t s c h r i f t f b F o r s t v ~ e s e n ~ ?

K O , 12, Jahrgang 1945,

28 ) Bucher

E o

: Auf'gabe und Organisa t i o n d e s Lawinendiens t e s

.

(Task and O r g a n i z a t i o n of t h e Avalanche S e r v i c e ) , lfDfe Alpent1 1946, Vole 1,

2 9 ) Bucher

E o :

Schnee- und Lawinenforschung, (Snow and Avalanche H e s e a r ~ h ) ~ P e s t a l o z z i - K a l e n d e r 194y0 3 0 ) Bucher E o : Technische b e r l e g u n g e n zum Problem d e r

Lawinenbildung ( T e c h n i c a l C o n s i d e r a t i o n s on t h e Problem of Avalanche F o r m a t i o n ) "Berge d e r Welt 11,

Vol. l o

31) M o de Guorvain: Eine Lavrine i s t niedergegangen,

(An Avalanche has f a l l e n ) " P r i s m a n , No, 5, S p e c i a l 13eprint on t h e Occasion of t h e 200th a n n i v e r s a r y

c e l e b r a t f on of t h e S N G 0 ( S o c i e t y of Swiss N a t u r a l i s t s ) ,

32 ) Bucher

E,

: B e r i c h t fiber d i e ~ H t i g k e i t d e s Eidgo I n s t i t u t s f a r Schnee- und Lawinenf orschung i m J a h r e 1945/46 (See Itoo 2 5 ) , "schweiz, Z e i t s c h r i f t f b Forstwesen" Noo 2, Jahrgang 1947 ,

REP ORTS ISSUED

No, 1 Das e i d g e n 8 s s i s c h e I n s t i t u t f b Schnee- und Lawinen- f orschungo (The Confederate I n s t i t u t e f o r Snow and Avalanche Research, I n a u g u r a l R e p o r t ) , October 1946 o

No, 2 D i s k u s s i o n s b e i t r a g zun Lawinenverbau, ( D i s c u s s i o n on Avalanche ~ e f ence ) by Edwin ~ u c h e r

d

January 1947 0

No, 3 Schnee und Lawinen i r n Winter 1945/46, (Snow and Avalanches i n \ l i n t e r 1945/46)" By Edwin Bucher and Melchior S c h i l d , March 1947,

North Side o'f Alps

1

Figure 1

I

I

Tech.Trana. TT-62 @

-

&e/mf&+bcA ZZ*o m @

.

.

.-.-.

Gar/<& /YCZ m @ P'?VOJ rl k 0 S o u t h S i d e o f Alps i ! @ @,/&77 /&So 127 Q)

-

BediuNo N J S rn @ - Zermctf/ /ia m @ --- ZUQZ /7se rrr ~ecrur?der Jdnurt8y /9qs / H i

Fig. 1. Comparlson of Snow Depths at Various Stations o n