Since the start of the season, avalanches have claimed the lives of 35 people, including at least 27 cross-country skiers.
A particularly heavy toll, according to the National Association for the Study of Snow and Avalanches (Anema), which usually lists “12 deaths per year in ski touring”.
Proof of the dangerousness of these avalanches, the overwhelming majority of the victims would not be novices, but people who, on the contrary, know the mountain and its potential risks, according to the association.
On Monday, five people, including two guides and an instructor, perished in two flows on the slopes of the Ecrins in Isère.
On Saturday, the risk of avalanches was particularly high, especially in the northern Alps above 2,200 to 2,400 m, Météo France said in a press release, which, however, no longer figures the risk of flows in this season.
Seven people were still killed during the day after two avalanches in Savoie.
🏔️⚠️ [#Avalanches] ❄️
➡️ High risk Saturday at altitude in the #Alpes du Nord, above 2200 to 2400m.
In the Southern Alps, the avalanche risk will be lower, but not to be neglected.
➡️ Sun, avalanche risk decreases.
📸 @GaetanHeymes
👉🗒️ https://t.co/aF0a6zOX7z pic.twitter.com/kyE5qMslzd
- Météo-France (@meteofrance) May 7, 2021
Usually less frequent in this season, the flows observed in recent days were favored by a disturbance of winter conditions.
A meteorological instability which is explained first of all by the “little winter” that France has just passed through, with frequent snowfall at altitude for a week.
Some may have been particularly abundant over a large part of the Northern Alps.
Thus, the accumulation of snow reached more than 60 cm in the Mont-Blanc massif or even 50 cm in the Savoie department.
Warming temperatures after a snowfall
A snowy episode which was followed by both marked and rapid warmth over the whole of the Alps on Saturday. Temperatures oscillating between 10 and 12 ° have been observed at an altitude of over 2,000 m, particularly in the Northern Alps. "This sudden warming of temperatures has greatly destabilized the snowpack," explains to Parisian Alexandre Flouttard, a forecasting engineer at Météo France. Thus "very many starts of avalanches of snow moistened by the sun and the warmth were observed on Saturday", adds the specialist. Concretely, skiers who "cut a steep slope in snow in the heat can always favor the departure of a cast iron plate", complete in a Météo France bulletin.
Another phenomenon that may have weakened the snowpack in recent months, that of the Saharan sands.
Several upwelling of air from the Sahara have been observed since the beginning of the year in Haute-Savoie, Isère but also in Aude and Puy-en-Velay.
These ocher-colored suspended particles color the snow, but also disrupt the composition of its mantle.
“When you see a deposit of sand on the snowpack, the reflection of the sun on the snow is reduced.
The mantle absorbs solar radiation and heats up faster.
This destabilizes its composition and ultimately increases the risk of leakage, ”explains Alexandre Flouttard.
However, such a phenomenon has not been observed in recent days.
"Atypical avalanche phenomena"
It should be noted, however, that avalanches are not the only cause of the higher number of deaths in the mountains than in other years.
As we had already mentioned in January, the stopping of the ski lifts due to the health crisis resulted in fewer preventive avalanche firing.
The ski areas were therefore not secured, resulting in a greater number of victims on the slopes than in other years.
Read also Twice as many avalanche victims: why the mountain is so dangerous this year
If the avalanche risk should diminish this Sunday, caution remains in order. "The little cloudy and little windy night from Saturday to Sunday will allow a good night freeze-up and therefore a good stabilization of the snowpack in the early hours of the day", reports Météo France, which adds however that "there will be new some departures on steep slopes not yet fully purged ”in the Northern Alps. An avalanche risk cannot therefore be completely ruled out, especially with "even stronger heat in the afternoon and at the end of the day".
“If we no longer quantify the risk of avalanches since April, that does not mean that new flows cannot occur. The risk is still very present, ”insists Alexandre Flouttard of Météo France. The frustration accumulated during confinement such as the return of sunny days could have pushed some to take advantage of the snow, and this when the conditions are not always favorable. Wanting to avoid a particularly deadly next season, Anema, the union of high mountain guides (SNGM) and prevention associations like Chamoniarde keep calling for vigilance in the face of "increasingly atypical avalanche phenomena" .