As you ski around on a layer of fresh powder every wondered what lies beneath your feet? Well this video is the snow equivalent of Jaws for skiers. Just 60-80cm under your skis is a layer of metastable hoar crystals. All is fine as long as they are not disturbed, for example by a passing skier.
The scenario in the video is typical of the current conditions at altitude (above 1800 - 2100 meters), in this case a west facing slope in the Maurienne at 2500 meters. In the first part of the video the tester pushes a probe into the fresh snow sitting on the weak layer, the weak layer below immediately collapses releasing the slab. Note the slab has been cut on the side and rear.