Heat flow from wet to dry snowpack layers and associated faceting

Abstract

Layers of faceted crystals adjacent to crusts form the failure layers for some unexpected dry-slab avalanches. This paper focuses on the case of facets that form when dry snow overlies wet snow. From a basic equation for heat flow in solids, the approximate freezing time of the wet layer is derived. Seven experiments are described in which a wet layer was placed between two dry-snow layers in a cold laboratory. Measured freezing times are comparable to the freezing times from the approximate solution assuming that latent heat from the irreducible water content flowed up. In four of the experiments, evidence of faceting was observed at the base of the upper dry snow layer within 5 hours and before the wet layer froze. In all seven experiments faceting was observed in the upper dry layer after the wet layer froze. Simulations performed with the snowcover model SNOWPACK yield freezing times that agree reasonably with the approximate solution and allow the influence of various parameters on the results to be explored. In addition, simulated temperatures and grain evolution are compared with observations, showing good agreement. © International Glaciological Society.