Influence of weak-layer heterogeneity on snow slab avalanche release: application to the evaluation of avalanche release depths

Abstract

ABSTRACT. The evaluation of avalanche release depths constitutes a great challenge for risk assessment in mountainous areas. This study focuses on slab avalanches, which generally result from the rupture of a weak layer underlying a cohesive slab. We use the finite-element code Cast3M to build a mechanical model of the slab/weak-layer system, taking into account two key ingredients for the description of avalanche release: weak-layer heterogeneity and stress redistribution via slab elasticity. The system is loaded by increasing the slope angle until rupture. We first examine the cases of one single and two interacting weak spots in the weak layer, in order to validate the model. We then study the case of heterogeneous weak layers represented through Gaussian distributions of the cohesion with a spherical spatial covariance. Several simulations for different realizations of weak-layer heterogeneity are carried out and the influence of slab depth and heterogeneity correlation length on avalanche release angle distributions is analyzed. We show, in particular, a heterogeneity smoothing effect caused by slab elasticity. Finally, this mechanically based probabilistic model is coupled with extreme snowfall distributions. A sensitivity analysis of the predicted distributions enables us to determine the values of mechanical parameters that provide the best fit to field data.

Evaluation of slope stability with respect to snowpack spatial variability

“…distributions, Gaume et al [2012Gaume et al [ , 2013a were able to reproduce avalanche release depth distributions from field observations which proved to be very useful for long-term hazard mapping, for instance, using statistical-dynamical simulations [Meunier and Ancey, 2004;Eckert et al, 2010]. These results thus confirmed the major influence played by the heterogeneity of weak layer mechanical properties on avalanche release size.…”

“…The model, based on the stochastic finite element method, was initially developed to compute avalanche release depth distributions required as input of avalanche flow models for hazard mapping [Gaume et al, 2012[Gaume et al, , 2013a. In this paper, we extended it to focus on the avalanche release probability as a function of snowpack properties and their spatial variations, in view of avalanche forecasting.…”

“…Hence, to investigate slope stability and avalanche release size, measured variations in snow properties have been used as input for numerical models of slab-weak layer systems [Failletaz et al, 2004;Zaiser, 2004, 2007;Chiaia and Frigo, 2009;Gaume et al, 2012Gaume et al, , 2013a. By coupling results of a mechanical model accounting for variations in the mechanical properties of the weak layer with observed snowfall GAUME ET AL.…”

Modeling of crack propagation in weak snowpack layers using the discrete element method

“…However, we checked numerically that, as soon as fracture arrest occurs within the column, the crack propagation distance is almost independent of the column length. For instance, if a propagation distance of 0.7 m is observed for a column length of 1.5 m, it will be the same for a column of 2.5 m. This is true as soon as the column length is higher than the length over which edge effect are observed (length typically lower than 1 m, Gaume et al, 2013). The experiments and the simulations confirm that dense and hard snow slabs are more prone to wide-spread crack propagation than soft slabs.…”

“…van Herwijnen et al, 2010;. On the other hand, theoretical and numerical models, based on fracture mechanics or strength of material approaches, were developed to investigate crack propagation and avalanche release (McClung, 1979;Chiaia et al, 2008;Gaume et al, 2013Gaume et al, , 2014b. While substantial progress has been made, application with regard to avalanche forecasting or hazard mapping is still hindered in part by our lack of understanding of the dynamic phase of crack propagation.…”