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Snow failure is the result of gradual damage accumulation culminating in macroscopic cracks. The failure type strongly depends on the rate of the applied load or strain. Our aim was to study the microstructural mechanisms leading to the macroscopic loading rate dependence. We modeled snow failure and the concurrent acoustic emissions for different loading rates with a fiber bundle model and compared the model results to laboratory experiments. The fiber bundle model included two time-dependent healing mechanisms opposing the loading-induced damage process: (a) sintering of broken fibers and (b) relaxation of load inhomogeneities due to viscous deformation. The experimental acoustic emissions features could only be reproduced correctly if both healing mechanisms were included in the model. We conclude that both sintering and viscous deformation at a microscopic level essentially contribute to the macroscopic loading- and strain-rate dependent behavior of snow.

Plain Language Summary Snow slab avalanches originate from an initial crack in a weak snow layer followed by subsequent crack propagation within the snowpack. Understanding how this initial crack arises is essential for understanding the formation of spontaneous avalanches and subsequently also for avalanche hazard management. We used a numerical model mimicking the snow microstructure (fiber bundle model) to model snow failure experiments, where the load applied to the snow samples increased at different speeds until the samples failed. The crackling noise (or acoustic emissions) produced by the formation or growth of microscopic cracks within the snow was used to assess the damage process in the snow. We included in the model sintering and viscous deformation. Sintering means that two ice particles bond almost immediately upon contact, allowing the healing of cracks in snow. Viscous deformation means that ice deforms with time also at a constant force and, due to this, concentrations of forces in the snow are smoothed out over time. The model could reproduce the experiments only if both sintering and viscous deformation of ice were considered. We conclude that both mechanisms essentially contribute to snow failure and are of crucial importance for understanding snow failure and thus predicting avalanche release.