In reply to UKC Articles: Thanks Mark.
I understand you are describing the mechanism which 'anchors' the lowest layer(s) of a snowpack. These are the irregularities at the ground's surface which act on the base of the snowpack.
You are also suggesting that these layer(s) next to the ground are broken by the protruding boulders, such that the ground layer doesn't slide readily.
I'm still a little unsure about how these protruding boulders anchor the layers *above* the lowest layer of the snowpack.
I'd welcome your comments on the following:-
1. Once the ground features are covered by the initial layer, subsequent snowpack layers are anchored by the bonds between snow layers and the bonds within the snowpack. The protruding rocks now become sources of weakness because they do not provide support for these upper layers and are 'holes in the snowpack'.
2. The snow around these rocks is weaker too, which means the bonds between these boulders and the snowpack are weaker. This is because of the action of the heat from the rocks acting on the snow around the boulders (the snow crystals become 'sugary' and lack strength).
3. There is a variable snowdepth, especially following the process where the terrain irregularities are covered - described here
http://www.fsavalanche.org/NAC/techPages/articles/12_ISSW_Eckerstorfer.pdf
which is problematic for stability. Shallower snow is a source of instability, because weaker layers of snow are closer to the surface at these points and more easily triggered. A further issue is that propogation occurs more readily from shallower snow into deeper snow.
Putting it together, the protruding rocks can be areas of weakness in a snowpack (shallower snowpack & weaker bonds - 'sugary' snow).
Thinking about an avalanche path:-
In an avalanche path start zone, exposed and shallow buried rocks can form 'trigger' or zones of weakness.
Further down an avalanche path, as the avalanche speeds up to over 200km/h, boulders can still act as a source of weakness in the snowpack by allowing an avalanche to step-down on these weakneses in the snowpack to deeper layers. Of course, they also provide something solid to hit as a victim is carried in the avalanche flow.
Finally, in the deposition zone, rocks are terrain traps where the victim can be buried deeper.