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.
http://www.dailymotion.com/video/x19yoqk_2014-01-slab-avalanche-triggering-mechanism_tech