Parameterization of the snow fracture energy to model the onset of crack propagation in snowpack models

Année de publication

2026

Snowpack models are widely used to complement field observations in avalanche risk forecasting. They help estimate key indicators related to dry-snow slab avalanche triggering processes, such as failure initiation and crack propagation. In recent decades, several frameworks have been developed to model the onset of crack propagation, typically characterized by the critical cut length (the cut length beyond which an initial crack starts propagating), measurable in the field using the Propagation Saw Test (PST). However, these models often depend on poorly constrained parameters, particularly, the weak layer fracture energy wf. In this work, we relate the fracture energy to snow properties that can be measured directly or simulated by detailed snowpack models. To this end, we compute the min-cut on about 300 three-dimensional snow microstructure images. The min-cut represents the smallest ice interface that would need to be fractured to separate two opposing sides of the structure, and can therefore be interpreted as a proxy of fracture energy. We fitted a relation between the min-cut and snow properties that can be measured or simulated, namely density and grain morphology. The min-cut is then linearly related to the fracture energy wf using measurements from Richter et al. (2019), which track weak layers across multiple seasons and sites using PST and observed profiles. We retrieved wf by inverting the WEAC slab model (Weißgraeber and Rosendahl, 2023): we supply the model with slab characteristics that are either obtained from field measurements or from Crocus snowpack simulations and solve wf for the given PST-derived cut lengths. This yields a relationship between wf and the min-cut, calibrated for the grain types most commonly associated with dry-snow slab avalanche release (faceted crystals and depth hoar) under predominantly Mode I loading conditions. After calibration, wf is evaluated in two slab models of different complexity for their ability to reproduce measured critical cut lengths, using both observed data and Crocus outputs. Although the correlation between min-cut and wf remains moderate (i.e. R of 0.5 at most), likely due to measurement and modeling uncertainties, the parameterization demonstrates an added-value over the use of a constant wf in reproducing realistic critical cut lengths. Moreover, the proposed parameterization performs well for identifying and monitoring weak layers over the course of the season. Its consistent performance across slab models and strong results using Crocus outputs highlight its potential for operational dry-snow slab avalanche hazard monitoring.</div>

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