Improved Kinematics in a Weak Interface Model for Stratified Snow Packs

The danger of dry snow slab avalanches is dependent on the conditions of the snow cover in alpine regions. Whether an avalanche is triggered from its own weight, wind or additional loads as backcountry skiers depends strongly on the conditions of the so-called weak layer. These porous and faceted layers grow as surface and depth hoar and are buried by densified snow layers, the so-called slab. In terms of mechanical properties, the slab has a relative high stiffness and tensile strength, while the weak layers with their low densities are more compliant and prone to collapse. These so-called anti-cracks nucleate in the weak layer and propagate afterwards through the slope until the slab ruptures and the avalanche is released.

Providing an efficient stability assessment of stratified snowpacks demands for a mechanical model that can capture both the anti-crack nucleation and propagation. We present a highly efficient and accurate model based on the weak interface models from fracture mechanics, which is able to render stresses and energy release rates in snow packs in real time. The improved kinematics of the weak layer in combination with an improved derivation of the energy release rate enable one to substitute finite element computations in avalanche mechanics. In particular, the model covers the effect of the layering order on both the extensional and bending stiffness of the slab. It can be used for externally-loaded slopes and for stability tests such as the propagation saw test.