Effects of temperature on fracture in dry slab avalanche release

Abstract

Field experience shows that snow temperatures have important influences on snow stability and the potential for propagating shear fractures. Part of the influence is with respect to metamorphism and bond formation. However, in this paper I consider temperature effects on fracture and the relation to snow slab stability at two scales: (1) microscale fractures of individual bonds or chains of bonded grains which lead to strain‐softening behavior prior to organization of failure into large‐scale failure planes or zones and (2) large‐scale imperfections already undergoing strain‐softening in failure zones in weak layers underneath snow slabs. When fracture at both scales is considered, two important results emerge. First, increasing slab temperatures may decrease slab stability by decreasing the effective slab stiffness (modulus). Second, increasing temperature in the weak layer (strain‐softening) failure zone decreases failure toughness (but not strength) also decreasing stability. The first result shows how slab avalanches can release by temperature increases without the weak layer being directly affected by warming. The second result gives a partial explanation of decreasing frequency of slab avalanche failures as weak (failure) layer temperatures decrease. Both results are supported by field measurements.