Crack propagation speeds in weak snowpack layers

• Published in: Journal of Glaciology
• Main Authors: Bastian Bergfeld, Alec van Herwijnen, Grégoire Bobillier, Eric Larose, Ludovic Moreau, Bertil Trottet, Johan Gaume, Janic Cathomen, Jürg Dual, Jürg Schweizer
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2022
• Subjects: Avalanches; snow; snow mechanics; Environmental sciences; GE1-350; Meteorology. Climatology; QC851-999; Journal of Glaciology
• Online Access: https://doi.org/10.1017/jog.2021.118; https://doaj.org/article/2bd78ff53b7643b48a3b4cb550536a78

For the release of a slab avalanche, crack propagation within a weak snowpack layer below a cohesive snow slab is required. As crack speed measurements can give insight into underlying processes, we analysed three crack propagation events that occurred in similar snowpacks and covered all scales relevant for avalanche release. For the largest scale, up to 400 m, we estimated crack speed from an avalanche movie; for scales between 5 and 25 m, we used accelerometers placed on the snow surface and for scales below 5 m, we performed a propagation saw test. The mean crack speeds ranged from 36 ± 6 to 49 ± 5 m s−1, and did not exhibit scale dependence. Using the discrete element method and the material point method, we reproduced the measured crack speeds reasonably well, in particular the terminal crack speed observed at smaller scales. Finally, we used a finite element model to assess the speed of different elastic waves in a layered snowpack. Results suggest that the observed cracks propagated as mixed mode closing cracks and that the flexural wave of the slab is responsible for the energy transfer to the crack tip.