Switzerland: thin snow pack primes avalanche time bomb

In a press release issued on the 19th April 2011 the Swiss Snow and Avalanche Research Institute (SLF) highlighted how a winter marked by above average temperatures and a thin snow pack led to an explosive situation by early March where the majority of fatal avalanches were recorded. It is a message we at PisteHors.com repeated throughout the season in our snow report threads. The number of deaths in Switzerland is already equivalent to the long term annual average despite fewer risk 3 and 4 avalanche days.

Avalanches, such as this on in the Simplon on a north slope above 2500m, were easy to trigger by one or more backcountry travellers at the end of winter 2011. (Photo: C.Höhener, 06.03.2011)

2010/2011: A Year of exceptionally poor snow cover

At the time of writing the snow cover in the Swiss Alps is very poor. Above 2000 m. the figure is 50% of the long term average. Between 1000 and 2000 m. there is just 25% of the normal snow depth. A number of weather stations (for example Andermatt, Arosa, Grimsel, Hasliberg, Ulrichen, Weissfluhjoch) are either snow free for the first time at this period of the season or have never recorded so little snow. Records go back 60 years in some cases.

Winter 2010/2011 started relatively early. Above 2000 m. mountains were already snow covered from the start of October. In particular the south of the Alps had considerable snow fall during October and November. In December it snowed frequently to low altitudes, much of Switzerland even woke up on the 25th to a “White Christmas”. By the end of the month snow depths were either average or above average.

Avalanche Risk Level as a % of Total Days (1/12 - 15/4)

Avalanche risk: fragile snow pack at the end of winter

At New Year the base was well stabilized in most areas. Generally snowfall was less than average in January and February. During this the dry spell there was little avalanche risk over much of the Swiss mountains except for mid January when it rained to 2000 m. leading to numerous wet snow avalanches and creating spring-like snow conditions. Even at the start of February snow depths below 2000 m. were exceptionally poor. During the long period of fine weather the a strong temperature gradient transformed the snow pack into facets and this constituted a weak layer for the fresh snow that fell at the end of February. The avalanche risk was significant right through to April for winter sports enthusiasts.

The majority of avalanche accidents occurred at the end of winter; and the majority of fatal accidents were in the South of the Valais where the old snow layers were particularly fragile. Compared with previous years, there were more Low (1/5) and Medium (2/5) risk days and consequently Considerable (3/5) and High (4/5) days were less frequent.

Avalanche at Bourg St Pierre (VS) in which 4 people died and 1 is still missing

A number of serious avalanches at the end of winter

By mid-April, 110 avalanches involving 179 victims had been reported to the SLF. 25 people were killed in 15 incidents. 1 person is still missing. 41 other people were injured. 10 people died on risk 2 days and 15 on risk 3 days. Avalanche victims were practicing the following activities: 2 off piste skiers, 17 ski tourers (incl. snow shoeing), 1 climber, 1 heliskier, 4 unknown (ski tour/snow shoe).
The number of victims is equivalent to the long term annual average. The most serious incident occurred at Valsorey close to Bourg-Saint-Pierre which killed 4 people with 1 still missing.

Posted by on Wednesday, 20 April, 2011 at 11:32 AM

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