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(Shortened abstract) Snow slab avalanches release after the failure andcollapse of a weak layer buried below a cohesive snow slab. This results in thepropagation of a subsidence, known as a collapse wave or anticrack. The slabmay eventually break and detach from the rest of the snowpack, provided thatthe slope is steep enough to enable gravity to overcome the friction. The onlytheoretical framework to date (Heierli 2005) proposed an explicit solution forthe propagation speed in steady state which could not account for weak layerproperties, was not mathematically bounded for certain values of the physicalconstants involved, and could not explain the newly uncovered supersheartransition for steep slopes. Here, a new model for the stationary propagationof anticracks is set up, so as to account for the anticrack speed regime on theone hand, and the supershear regime on the other hand, the existence of whichhas been recently revealed and ascertained by numerical simulations. Theresults presented here seem consistent with most of the available data, andhighlight the role that the compaction of the weak layer can play in reducingthe anticrack speed. On the contrary, by storing energy upon failure andsuddenly releasing it at the crack tip, the weak layer elasticity could helpjustify the higher speeds sometimes observed in both regimes. Finally, a moreaccurate model is proposed, based on the modelling of both the slab and theweak layer as Timoshenko beams; although its complexity prevents us fromsolving it analytically, it provides enlightening insights into the mechanicalprocesses at work at the interface between both layers, from astrength-of-materials perspective. This analysis is a first step towards abetter understanding of the underlying mechanisms of propagation of cracks inslab avalanches, and towards more accurate avalanche size and occurrencepredictions.

A theoretical framework for dynamic anticrack and supershear propagation in snow slab avalanches