French avalanche expert Alain Duclos has posted another of his interesting videos on slab triggering. This is on a west facing slope on the 16th January 2019 at 2900 meters in the Vanoise. Alain disturbs the thin weak layer until the whole area collapses triggering the slab.
Alain says "it is not always easy to make these videos, but I was probing the snowpack with my pole and I thought it was really suspicous so I got the camera out". What we can see is about 50cm of fresh snow on the old base from before Christmas. The important thing is the fragile layer, probably depth hoar that formed on the interface between the old and new layers of snow. It is this weak layer that gives the slab the energy to slide. Alain's snow saw could be your skis, the weak layer collapses over a wider
area, the size of which decides how big the slab will be.