Modeling the changes in microstructure of snow during metamorphism

Abstract

Since the internal microstructure is important for determining the mechanical, thermal and physical properties of snow, a study was undertaken to develop a physical model that can predict changes in microstructure of snow during metamorphism. The microstructure was defined in terms of the 3-D coordination number, mean grain size, mean bond radius and mean neck length. For situations where temperature gradients were small, a mixture theory was used to calculate the rates of change in grain size and bond size. These calculated results were then compared with experimental data and found to adequately predict changes in microstructure while subjected to small temperature gradients. When temperature gradient effects dominate, a physical model was developed, which calculated sublimation and deposition rates on neck and grain surfaces. This model was found to give results that represent what happens in snow under TG conditions. However, a lack of data to date has precluded a thorough evaluation. For mechanical effects, another physical model was developed to determine the deformation within the bonds and necks. These models have been incorporated into the SNOWPACK program, which was developed by the Swiss Federal Institute for Snow and Avalanche Research at Davos Switzerland as a tool for assisting avalanche hazard forecasters.