Tuesday, 12 February 2013
This winter has been a record-breaking season for snowfall in the Western Alps. In mid-December the Dauphine newspaper reported that it was the highest level of snowfall pre Christmas in over 50 years. Since then, it has hardly stopped snowing. Indeed in Chamonix, in the first 35 days of the New Year, there were 30 days of bad weather.
The high level of snowfall seems to have coincided with a proportionally high number of avalanche accidents, many of which have been fatal. Last week a skier died at Brevent in Chamonix, and numerous deaths have been reported in Switzerland.
So, is it as simple as high snowfall=high avalanche risk ? Unfortunately no. Looking at other weather and snowpack factors over the recent weeks gives us a much better understanding of why there have been so many accidents.
When snow warms up, it melts. When it then re-freezes it tends to bond with the layer below it, hence stabilising the snowpack. Overall, recent temperatures have been quite cold, for long periods. This has slowed the stabilisation of the snowpack. Lack of sunshine has also meant that snow on sunny aspects has not been receiving as much solar radiation as usually expected.
The exception to this cold was a massive thaw two weeks ago when the freezing level rose to over 2300m. This rise in temperature was so vast there were numerous spontaneous, and skier triggered, avalanches. The thaw (and rain) caused the snowpack to be lubricated and to lose cohesion. It was then slow to re-bond. Since then the temperature has plummetted once again with a morning temperature of -17C in Chamonix two days ago.
The final key reason for the lack of stability in the snowpack recently has been wind activity. Winds above 2000m have been moderate to strong for the majority of January and early February. This has caused a large amount of windslab to form on all aspects. This windslab was widely publicised and those reponsible for the security of the ski areas did as much as possible to control the slopes in the Chamonix area with controlled blasting. However, the recent high snowfalls have merely buried much of this slab. The extra insulation provided by the fresh covering of recent snow has slowed this process even further.
So, what does all this mean ? Is it safe to ski off-piste or not ? In my opinion there is currently some world-class off-piste skiing to be had in Chamonix and the Western Alps, however extreme care should be exercised to minimise the risks. There is no such thing as "safe", as the photo clearly demonstrates. I took this last Friday in Les Contamines. The release was naturally occurring, to full depth, with a crown wall between 3 and 4m high. Note the pisteur on the left to use as scale. This avalanche occurred between pistes in Les Contamines and the debris covered a piste. Whether in-bounds or in the backcountry there are some areas of very fragile snow. Yesterday's Avalanche Bulletin for Haute Savoie warned of slab releases at high altitude to 1m depth.
Selection of ski itineraries is critical at the moment, with low angle slopes being a sensible choice if skiing at altitude. Extra care should be taken when skiing areas uncompacted by regular traffic, and adherence to the advice on the Avalanche Bulletin is very prudent.
Stay safe everyone, and enjoy this epic snow year.