Background information from: the WSL Institute for Snow and Avalanche Research SLF and the Swiss Association of Cableway Operators, Seilbahnen Schweiz,
29.02.2012
High temperatures
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Eine Gleitschneetafel kann als
Lawine abstürzen, wenn die treibende Kraft infolge des Gewichtes grösser wird
als die rückhaltenden Kräfte. (Davos Frauenkirch, Dezember 2011; Photo SLF/S.
Margreth)
Une plaque glissante peut se transformer en avalanche lorsque la force d’entraînement
sous l'effet de la gravité devient plus importante que les forces de retenue.
(Davos Frauenkirch, décembre 2011; photo SLF/S. Margreth)
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Increased danger of full-depth and wet snow avalanches
Temperatures have been climbing appreciably in the
night of Tuesday, February 28, 2012. There has been many releases of full-depth
and wet snow avalanches. The safety experts responsible for the ski resorts and
roads exercise great care in their meticulous daily assessment of the avalanche
situation. Snow sport participants venturing off piste are urged to give due
consideration to the spring-like avalanche conditions as well.
General
- The occurrence of gliding snow is relatively easy to identify because of
the formation of horseshoe-shaped fractures in the snowpack, which are also
known as glide cracks. It is difficult to predict, however, when the slow
sliding movement will accelerate and give rise to a full-depth avalanche. Such
avalanches release entirely without warning, moreover, even before the opening
of a glide crack that has been apparent for a long time in advance. Full-depth
avalanches can occur at any time of day or night and are generally natural.
Even the slow gliding movement of the snow can pose a danger because of the
immense pressure being exerted on objects such as cableway masts or similar.
- The severity of snow gliding observed this winter is thought likely to
arise only every 30 years or so. It is attributable to ground that was not
frozen when the snow cover formed in some places, and to very heavy one-time
snowfalls.
- During each of the next few days, the danger of wet snow avalanches will
also increase significantly under the influence of warming. These avalanches
can reach medium size and endanger exposed parts of transportation routes.
Significance and action
- Full-depth avalanches present a major challenge to the safety experts
responsible for the ski resorts and roads because they are difficult to
predict, and only little experience has been accumulated to date.
- Mindful of their enormous responsibility, the safety authorities make a
detailed and very cautious assessment of the avalanche situation every day.
They are aware of the variability in the avalanche situation in individual
regions, caused by differences in the strength of the snowpack, typically
because of the altitude of a ski resort (high alpine, alpine or prealpine), the
influence of different aspects, and variations due to the effects of wind.
- If an acute danger exists, the authorities monitor the situation
carefully and take action as necessary, which can entail closing potentially
endangered areas.
- The more frequent closure of ski slopes and roads is therefore to be
expected. It is essential that instructions issued by the safety authorities
are observed.
Recommended behaviour when engaging in winter sports outside marked and
open pistes
- As regards full-depth avalanches: avoid or spend as little time as
possible in terrain below glide cracks in particular
- As regards wet snow avalanches: finish backcountry touring and off-piste
activities early (no later than midday)
- Pay attention to the current
avalanche bulletin
Further information
Further advice
WSL Institute for Snow and Avalanche Research SLF:
Julia Wessels, Communication, +41 (0)81
417 02 86 wessels@slf.ch
or
Cornelia Accola, Communication, +41
(0)81 417 02 34, cornelia.accola@slf.ch
Seilbahnen Schweiz SBS:
Roman Weissen, Media Office, +41 (0)31
359 23 14, +41 (0)79 239 41 00,
roman.weissen@seilbahnen.org
