S n o w

C o v e r

S t a b i l i t y,

A v a l a n c h e

I n i t ia t i o n

a n d

F o r e c a s t i n g

Precipitationat Passlevelchangedto rainat 1500 on January
24. Rain, first on December 22, 1992 and againon January3
hadcausedthesnow deeperthan60 cm to settleand become
relatively homogeneous. Justpriortorain about 55cm of
snow hadaccumulatedon a thin layerof facetedcrystals that
had formed duringcold weatherearlier. A number of slabs
releasedatthefacetedlayer,especiallyon steeperslopes,dur-
ingthecoldpartof thestorm. Howeveractivityincreasedcon-
siderablyat theonsetof rainandmanyslabsupto 60 cmdeep
releasedboth naturallyand artificiallyat this time.
Figure 3a shows theevolution of creepprofiles thathave
beenconstructedfrommeasurementsofshoepositions
on a 36ºslope.Material lines have been drawn at hourly
intervals to show the evolutionof deformation in the snow-
pack overthree hours centered around the onset ofrain.
The shoes deepest in the snowpack were set above a rain
crustonDecember22nd.Theothershoeswereplaced
sequentially after snow accumulated on January 3rd, 20th,
21stand 24th.The shoe near the surface was placed two
hours before rain started.

Fig. 3b vertical
(showthe range
of motion expected usingthe usual constitutive assumptions for
snow on a 36 degree slope. We think theapparently anomalous
motion is a result of metamorphic and/or capillary strain acting
independently of gravity.

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