There have been a considerable number of avalanches over the weekend but also a lot of activity in the mountains following the French lock-down. As mentioned in an earlier article there is a weak layer present in the snow-pack at altitude on shaded north faces formed during the anticyclonic conditions in late November and it is this layer that caused many of the problems over the last few days.
The Data Avalanche database recorded 32 avalanches between Thursday and Monday. A number were remotely triggered by ski touring parties and some were of an unusually large size for the sector. This is an indication of a widespread persistent weak layer in the snow-pack.
Last Thursday (10 Dec 2020) a ski tourer triggered an avalanche in the 7 Laux backcountry just under a ridge as his group of three were about to ski the slope. He was carried 100 meters down-slope but escaped without injury.
After a snowy Saturday, Sunday was a busy day for the mountain rescue with a return to sunny weather and record numbers of back-country travelers in some areas.
In the Southern French Alps two skiers triggered an avalanche in the Combe du Crachet near the Col du Vars on an east facing slope at 2750 meters altitude. The slope broke on a weak layer of hoar crystals about 2cm deep. The slope is around 37-40°. Neither skiers was injured.
In Monêtier les Bains (Serre Chevalier) three skiers were touring on the Pointe de l'Etendard when they triggered a slide. One of the skiers was partially buried and a second suffered from a knee injury. The skier was rescued by his companions but due to a severe arm and head injury was heliported to hospital in Briançon by the mountain rescue service (PGHM).
Four Soldiers attached to the 7th Bataillon de Chasseurs Alpins based at Varces near Grenoble triggered an avalanche under the col du Chardonnet above Monêtier les Bains around 13h. One skier was completely buried by the slide and another was also carried downhill. They were rescued by their colleagues and the PGHM helicopter took the buried skier to hospital in Briançon for observation.
The PGHM in Modane had to rescue a ski touring party in the Haute Tarentaise near the Grapillon des Merles close to Tignes. Two skiers, part of a group of four, were injured when they triggered at slide at 2700 meters on an east facing slope. One of the skiers was partially buried by the slide, the other suffered a leg injury.
An avalanche that received a lot of media attention was triggered by ski tourers in Courchevel on the Summit of Vizille skiing NE to E facing slopes at 2630 meters altitude. These would normally be open ski runs but obviously with ski resorts closed for Covid they were neither pisted nor avalanche controlled (seems pretty obvious and I'm sure the skiers didn't think otherwise).
The first avalanche occurred on an ENE slope in the bowl under the Suisse chiar. The slide triggered just after a skier. The second slide happened some 20 seconds later and was probably triggered by the first slide on a NE slope in the bowl between the Marmottes and Suisses chair lifts. None of the skiers were caught by the slides which finished on the run out some 100 meters below.
On Monday the units of the PGHM had to fly a rescue missing to the Vallon de l’encoungoura in the Ubaye. A group of ski tourers were climbing the valley when a large avalanche triggered behind the skis of the third skier in the group burying the last three skiers. One skier received first aid treatment directly, the two other skiers were taking to hospital at Digne-les-Bains. One suffered a knee injury and the other chest injuries. The avalanche occurred on a NE slope.
On Tuesday there was a thaw with a southerly air stream accompanied by rain to around 2000 meters, dropping to 1800 meters overnight. This has purged a lot of the snow at lower altitudes with numerous wet snow slides visible today but fragile layers persist at altitude. Note that most of the recent accidents have been over 2500 meters. With a refreeze the mid altitudes should stabilize. The winds from the south to south-west have formed fresh accumulations at altitude and these are sitting on weak layers on North sector slopes. The risk of skier triggered full depth slides should not be neglected on sunny aspects.