Probabilistic evaluation of snow-slab stability on mountain slopes

The results from a numerical-probabilistic experiment aimed at evaluating avalanche-release probabilities are presented in order to show the problems and the possibilities of such an approach. A snow slab on a mountain slope is modeled as a thin elastic non-moment shell resting on a three-dimensional hard underlying surface. The thickness of snow is considered as an inhomogeneous Gaussian spatial random field with a predetermined covariance that was obtained previously by field measurements. The stress distribution sigma(x, y) is calculated by solving the equations of equilibrium using a finite-difference method with a mesh of lines of curvature on a mountain slope. As a criterion of avalanche release, exceeding some threshold value of stress sigma(thres) by the calculated value sigma(x, y) is applied. The field P(sigma(x, y) > sigma(thres); x, y) derived, using the Monte-Carlo method, is regarded as a measure of the spatial distribution of avalanche-release probability. This simulation scheme at present has no claim to forecast avalanche release but may be used to pinpoint the importance of snow distribution on a slope.