The effect of daytime warming on snowpack creep

Snowpack warming is, besides loading by precipitation and wind-transport, one of the major triggers contributing to natural avalanche release. Established release mechanisms for sponta- neous slab avalanches strongly depend on deformation rates in weak layers, which are affected by temperature changes. In general, snow can adjust to low deformation rates without weakening. Once a critical rate is exceeded snow exhibits strain softening and ultimately brittle fracture. Failure of a weak layer is an important prerequisite to slab avalanche release. Critical slope parallel deformation rates may be reached in weak layers on sufficiently steep slopes due to increased creep in the overly- ing slab, which is heated by solar radiation. Using time lapse photography during the transition from cold mornings to warm sunny afternoons, we monitored vertical and slope parallel displacements of markers on a vertical snow profile on steep slopes. In a case study we present time series of dis- placements that showed increased snowpack creep and slope parallel deformation rates during solar heating of the near surface layers.