Pierre Muller is a high mountain guide but also a doctor and first aider. He worked for 20 years as a first aider for the PGHM (High Mountain Gendarmerie Platoon) in Briançon then in Chamonix. He publishes
Secours en avalanche
, published in February by Glénat editions.
LE
FIGARO.-
A deadly avalanche occurred at the Armancette glacier
, in the commune of Contamines-Montjoie in Haute-Savoie.
Is this type of avalanche surprising?
Pierre MULLER.-
Yes, and this type of large-scale avalanche, in these weather conditions, is not frequent.
What happened was that a small cold snowslide went very high, and caused an overload in a fragile area.
That snow must have pulled what's called the trigger that kicked off an old slab.
This old plate, from the beginning of winter, had remained cold and crumbly, and therefore fragile, despite the spring, because it is a north face, therefore in the shade, very high up.
This old fragile layer had little chance of breaking, and the risk yesterday, although the slope is known for its avalanches, was very low.
How are avalanches triggered?
There must be a slope of more than 30° - that of Armancette reaches 35° - and a good amount of snow.
Then it's the quality of the snow that comes into play, and that depends on how it landed, with or without wind, warmed up or not, with a strong gradient or not.
Sometimes the heat can cause small drops to bead up in the snow and make the snowpack heavier.
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Otherwise, the wind can also break the dendrites, these star-shaped snowflakes that cling to each other.
The snow then becomes crumbly, like coarse salt.
This type of snow rests in the north faces of the Alps, at more than 3000 meters of altitude.
It is often formed at the beginning of winter, during an anticyclone, when the ground is even less cold than the snow.
This fragile layer, in general, is forgotten until spring when it is transformed with the warming into a very compact snowfield.
The avalanche risk was rated 2 out of 5 at this altitude, and therefore qualified as limited by Météo France. Was the accident unforeseeable?
What people struggle to understand is that avalanche risk is an occurrence.
Météo France provides a BERA, an avalanche risk assessment bulletin.
This estimate is calculated in particular in the stations where the trackers make readings, above 3000 in general therefore.
But at more than 3000 meters of altitude, where the terrain is more subject to wind, cold, sun and rapid changes, the reliability is less good.
There is always a risk therefore, especially at high altitude.
To understand, let's take the comparison of a minefield.
If with a risk of 4/5 we have fifty mines on a piece of land, we will only have five with a risk of 2/5.
The risk is much lower, but it still exists.
In the case of the Armancette glacier, the plate could have held out until the summer.
The Miage domes at 3673 meters and the Armancette glacier.
Mayeul Aldebert / Le Figaro
The thickness of the layer above the brittle layer is generally solid.
But the snowpack is not homogeneous.
There are places where this fragile layer will be under three meters of snow and in this case, 15 skiers can pass over it without anything happening.
But sometimes the snow has been carried by the wind, and the risk of overloading and collapse is greater.
The committed skiers were really unlucky, and I could have been there myself, especially this Easter weekend in April, when the weather conditions are excellent and the snow very stable for this climb which is a great classic mountaineering route.
The guides were not reckless.
When you go to the mountains, you necessarily take a risk, even a minimal one, it's inherent in the mountains.
And sometimes there are six deaths like yesterday, but compared to the hundreds of thousands of people who were in the mountains this weekend, the risk remains moderate.
Can global warming make the avalanche phenomenon even more unpredictable?
Generally speaking, the January weather yo-yos, with successive winter and spring temperatures, make the snow very difficult to read.
There is also this phenomenon of yellow snow, loaded with sand from the Sahara, which weakens layers in the snowpack.
But Sunday's avalanche has nothing to do with global warming.
It was cold at altitude, above zero, it was a normal April day.
Read alsoWhat were the deadliest avalanches in France?
It should also be noted that there is no increase in avalanche accidents, even with the spectacular boom in ski touring after the Covid, when the resorts closed.
Hikers leave with safety equipment, are made aware.
How do you manage this avalanche risk as a mountain guide?
Most of the time, we analyze the weather report, with the avalanche risk forecast and the observations we make ourselves in the mountains.
Afterwards, we adapt the race to the level of the customers and their expectations.
Even by respecting this way of doing things, we can one day be fooled.
But Sunday's situation is so exceptional and unique that it is difficult to draw conclusions.
This is the unpredictable part of the mountain.
We cannot guarantee risk 0 as a guide.
And regular customers are aware of this and know that they are reducing the risk with a professional, but not eliminating it.
It should nevertheless be remembered that the risk remains really very moderate, compared to the number of practitioners.