Temporal evolution of crack propagation characteristics in a weak snowpack layer: conditions of crack arrest and sustained propagation

Abstract. For a slab avalanche to release, the system, consisting of a weak layer below a cohesive slab, must facilitate crack propagation over large distances – a process we call dynamic crack propagation. Field measurements on crack propagation at this scale are very scarce. We therefore performed a series of propagation saw test experiments, up to ten meters long, over a period of 10 weeks and analyzed these using digital image correlation techniques. We derived the elastic modulus of the slab (0.5 to 50 MPa), the elastic modulus of the weak layer (50 kPa to 1 MPa) and the specific fracture energy of the weak layer (0.1 to 1.5 J m^-2) with a homogeneous and a layered slab model. During crack propagation, we measured crack speed, touchdown distance and the energy dissipation due to compaction and dynamic fracture (5 mJ m^-2 to 0.43 J m^-2). Crack speeds were highest for PSTs resulting in full propagation and crack arrest lengths were always shorter than touchdown lengths. Based on these findings, an index for self-sustained crack propagation is proposed. Our data set provides unique insight and valuable data to validate models.