I'm not an expert on snow or avalanches, thought I have seen more snow than I ever wanted.. but what this video seems to show is almost a block of ice. If we assume the raised footprints indeed existed, those can only be formed in powder snow. Avalanche can also occur in powder snow but that's not what this video shows...
Yes, that is hard to grasp for me. To my understanding important points are:
-local topography is small depression with rather steep angle, 28 to 30 degrees
-weak, low friction layer of snow was due to local depression steep angle
-wind blown snow filled local depressions (also like in the ravine) and built uniform layer of snow, which was angled like terrain as a whole (lower than traditional avalanche threshold)
-Snow layer above weak layer was deep at the depression, but thin above depression
-Thin top doesn't leave deep and distinct crack line typical to slab avalanche, so it's hard to tell afterwards if any slab was released
-Everything is good as long as snow layer is uniform, this is most important, spontaneous avalanches never occur if layer is uniform
-If you disturb the uniform layer and make cut wide enough
to the deep snow on depression, the layer lose support from below
-If you cut snow, layer is supported only from friction from weak layer and by thin layer above the local depression
-Slab could release immeadiately if the angles are steep enough, but in Dyatlov case angle was not and it didn't come down immediately as they was digging place for tent
-In windy conditions snow accumulated to cut (Wind slab) and increased load so that it overcome support from friction and upper thin layer
-basically it was delayed release of a small snow slab, not avalanche as most of us imagine avalance is
To me this situation is analogous in mechanism and scale to snow sliding from metal roof like in this picture. Metal roof is "weak layer" of low friction, snow is already broken free from top "thin layer" and supported only from below and friction of the metal roof. I wouldn't cut this snow and sleep under it in the cut.