Measurements of weak layer fracture energy

Dry-snow slab avalanches release by a sequence of fractures. The two main parameters which are initially of fundamental importance for the fracture process are the weak layer specific fracture energy and the stiffness of the overlying slab. So far, only few values of weak layer fracture energy exist, mainly because the stiffness of the slab cannot easily be determined. We have performed about 150 propagation saw tests to obtain the weak layer fracture energy from measurements of critical crack length, slab thickness and density. To estimate the stiffness of the slab needed to calculate the energy release rate, we used snow micro-penetrometer measurements. The values of the effective elastic modulus ranged from 1.8 to 12 MPa. The specific fracture energy of the weak layer was evaluated using a finite element (FE) model. For our weak layer/slab configurations we obtained specific fracture energies on the order of 1 J m− 2. These values are large compared to the only previously published value based on field measurements of 0.07 J m− 2. However, comparison with an independent approach using a video sequence of one fracture test confirmed our results. Many more measurements are needed for a comprehensive dataset of weak layer fracture energy.