Field observation and modelling of weak-layer evolution

Abstract

For operational snow-cover simulations, an adequate modelling of the evolution of buried weak layers is of crucial importance. Therefore, the processes governing snow metamorphism within weak layers before and after burial must be known in detail. At the study site of the Swiss Federal Institute for Snow and Avalanche Research, 2540 ma.s.l., a 2 cm thick weak layer of column-grown cup-shaped crystals formed beneath a thin crust in mid-January 1996. Exposed to near-surface processes for about 4 weeks, the layer was buried on 8 February and persisted in the snowpack until mid-April. Numerous temperature profiles and characterizations of both the weak and the adjacent layers were performed in situ. Snow-grain samples, as well as larger snow blocks, were taken to the cold laboratory for further analysis of the texture. The shear strength of the buried weak layer was also investigated by means of shear-frame tests. The field observations and measurements are compared with model simulations of snow temperature and stratigraphy. The comparison shows potential and problems in the modelling of weak-layer evolution.