Hunting Mach cones in supershear snow slab avalanches with numerical modelling.

Snow slab avalanches, caused by the failure of a weak snow layer buried beneath a cohesive slab, are very difficult to predict and by far the deadliest type of snow hazard. Recently, numerical simulations and observations of real-scale avalanches showed evidence of a transition from a sub-Rayleigh to intersonic fracture. The sub-Rayleigh regime is driven by weak layer collapse and slab bending, a process often referred to as anticrack propagation. On the other side, the intersonic regime is characterized by a mode II (shear) crack propagating at a velocity higher the slab’s shear wave speed. This process, well documented in strike-slip earthquakes, is often referred to as supershear. Here, we use numerical simulation and reproduction of avalanche experiments to provide additional insights into supershear fracture, by revealing and investigating Mach cones appearing in the snow slab during this regime, further consolidating the supershear avalanche theory. Furthermore, we analyse the effect of slab layering on crack propagation speed and Mach cone characteristics. Beyond enhancing process understanding, this work may also provide valuable insights for experimentalists on how to visualize Mach cones in snow fracture experiments.