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Avalanche Risk YoYo
Posted: 24 January 2012 09:44 AM  
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The avalanche risk really seems to be yoyoing around this year. One moment it is 1 or 2 then it jumps to 4 or 5 only to drop back very quickly. What are the reasons for this? I remember on Pistehors they mentioned that the risk stayed at 3 for the whole season in the Belledonne once.

 
 
Posted: 25 January 2012 04:55 PM   [ # 1 ]  
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Hi Bubb,

The fact that the avalanche risk is ‘yoyoing’ is because we had huge snowfalls. Obviously huge dumps lead to high avalanche danger. But big snowfalls also tend to stabilize quickly and in general a few big snowfalls lead to a much trustworthier snowpack than many small dumps. So: big dumps means lots of powder, initially lots of danger, but in the end a pretty stable snowpack.

 
 
Posted: 26 January 2012 09:26 AM   [ # 2 ]  
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I like Rolf’s answer.

Just from memory we had snow in October but it only really hung around above 2300m and then on North sector slopes. We then had a long period of fine, clear weather and this transformed that snow into a weak layer of goblets or depth hoar. This is typical every autumn/winter and normally sets up the avalanche risk.

What then happened, which is fairly unusual in the French Alps at least, is the first big winter dump, on the 7th December, was about a meter or more of snow. This kind of thickness tends to bridge the underlying weak layer so that it doesn’t present the same danger. Also such snow depths don’t tend to rot out (temperature gradient). We’ve then had subsequent falls but as Rolf said, these have been pretty deep too so during and immediately after the fall the risk goes up, largely due to spontaneous avalanches but once the snow has settled it drops back as there are few weak layers around (maybe some surface hoar formed in the first couple of weeks of January). The warm weather and high altitude rain has also stabilized the snowpack up to 2000+ meters. There have been some slab avalanche reports from the Hautes-Alpes where there has been less snowfall this winter and some pretty big natural slides (which have cleared out some of the last 10 years accumulations of brush wood, yipee).

Still not a single avalanche death in France, lets hope that record continues.