Effects of surface warming of a dry snowpack

Changes in air temperature, and hence snow temperature, influence snow stability for skiers. This paper studies how warming in the top 20 cm of a hard `spring' like snowpack and a softer `mid-winter' like snowpack influence the stresses and strains due to a skier load in weak layers 30 and 50 cm below the surface. The temperature effects are studied using a finite element model to predict how the load is transferred through a layered snowpack. The results show that the warming front does not have to extend into the weak layer to have an effect. As the stiffness of the top slab is reduced, the peak stress and peak strain increases in the weak layers. The 30-cm weak layer was more affected by the skier load than the 50-cm layer with an increase in shear stress of 8% in the mid-winter snowpack model and 51% in the spring snowpack model. A model of a real snowpack with a surface wind slab again subject to a skier load showed an increase in shear stress of 32% when a weak layer was present at 22 cm and the top 19 cm was warmed. The increase in stress and strain in the weak layer in all models support the argument that the likelihood of skier-induced avalanche will increase after warming.