The Cosmique couloir is one of the classic Chamonix ski descents: 800 m long, steep, sustained, and constantly very exposed. Although in the past it was considered extreme skiers only territory, today’s insane Chamonix standards have progressively pushed people’s limits to the point that, on a good day, it’s full of tracks by lunchtime.
Depending on snow conditions, entering the couloir normally requires one or two rappels. When there’s a lot of snow though, and it’s stable, you can drop in right at the entrance. The top section is around 50 degrees. Although it mellows out to around 45 degrees for a long middle section, and becomes gradually less steep until the Bossons Glacier, it’s never less than around 40 degrees. You are in a ‘no fall zone’ for around 400 m. Even if the consequences of falling anywhere along its length can be serious, this sections is particularly dangerous.
When my friends Alex and Sophie arrived at the entrance of the couloir, the snow was still untracked. According to the avalanche bulletin, the risk was low at that altitude, and they hadn’t seen any recent signs of avalanche activity. That increased their confidence, and pushed them in higher-consequence terrain.
Alex went first, and as he rappelled he jumped on the snow, and caused a very small pocket slab to release and tumble softy down the couloir. He made a platform for himself about 20 m down. The snow under his skis was soft, and he didn’t feel any layers with his ski pole. Once off the rope, he decided to ski the upper section conservatively. As he descended, the pitch of the couloir eased off and he felt the snow become less stable. Instead of skiing the fall line, Alex decided to ski cut to his left, just in case there was another small pocket like the one he rappelled through. He identified an island of safety near a rock, on the other side of the couloir, and skied across. Sophie was watching him from above.
As he approached the rock, he heard a whoomp. It’s a terrifying sound. It’s an obvious sign of strong instability in the snowpack. It’s generated by a layer of snow collapsing on the one below. Alex knew what was happening. Suddenly a crack broke at his knees, and propagated across the slope. The snow began pulling at his legs. In a matter of seconds everything below him was in motion as if the slope had come to life. Alex was able to hold steady in place holding precariously on his edges at the crown fracture of the avalanche. A few seconds later a powder cloud exploded at the bottom of the couloir. Everything fell silent.
From 50 meters above, Sophie shouted down to see if Alex was okay. He replied he was, although it was a very close call. Alex is an experienced and careful skier and mountaineer. He underestimated the size of the pocket slab he was going to find, as it turned out to be a sizable slab. Despite his understanding of the low avalanche risk, he never let his guard down. Rappelling down was definitely the safest option.
They could have perhaps stayed on the rope a bit longer. Alex made an effective ski cut, which was also the correct thing to do. Ski cutting is an advanced skill. You need to know exactly where to cut. If he had cut too low, he would have been caught in the slab. You’re never completely safe in avalanche terrain, even when the risk is low .