Snow Slab Release, its Mechanism and Conclusion for the Arrangements of Supporting Structures

Abstract

The paper presents a model of snow slab release based on the concept of the presence of ground-parallel thin super-weak layers. The fact that the same snow type under same state may or may not fracture under a certain stress unless a critical strain-rate and critical fracture-strain is reached highlights the necessity of stress and strain-rate concentrations. Super-weak layer, which cannot or can only insufficiently transmit the shear stress caused by the overlying snow layers, is considered to provide such concentrations. The model establishes that although the existence of weak layers in a snowpack is a necessary condition, yet it is not sufficient for avalanche formation. A minimum length of the super-weak zone is required for the crack to propagate leading to the release of a slab avalanche Critical crack lengths are found to be of the order of 5 m to 10 m. Critical value of crack length has been found to be dependent on slope, thickness and viscosity of the weak layer. The model does not hold good, if the super-weak zone vanishes. The paper finally discusses the arrangement of supporting structures to minimise the development of super-weak zones.