EFFECTS OF TEMPERATURE ON FRACTURE IN DRY SLAB AVALANCHE RELEASE

Field experience shows that snow temperatures have important influence s on snow stability and the potential for propagating shear fractures. Part of the influence is with respect to metamorphism and bond format ion. 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 t o strain-softening behavior prior to organization of failure into larg e-scale failure planes or zones and (2) large-scale imperfections alre ady undergoing strain-softening in failure zones in weak layers undern eath snow slabs. When fracture at both scales is considered, two impor tant results emerge. First, increasing slab temperatures may decrease slab stability by decreasing the effective slab stiffness (modulus). S econd, increasing temperature in the weak layer (strain - softening) f ailure zone decreases failure toughness (but not strength) also decrea sing stability. The first result shows how slab avalanches can release by temperature increases without the weak layer being directly affect ed by warming. The second result gives a partial explanation of decrea sing frequency of slab avalanche failures as weak (failure) layer temp eratures decrease. Both results are supported by field measurements.