Thesis Committee

Ian Baker, Ph.D. (Chair)

Mary R. Albert, Ph.D.

Harold J. Frost, Ph.D.

Zoe R. Courville, Ph.D.

Abstract

Investigation of snow properties can be applied to understand the climate change issues and snow avalanche prediction. Most of the snow properties, i.e. thermal and mechanical, are directly linked to the microstructure of snowpack and those properties evolve simultaneously with deformation of the snow and its metamorphism. Thus, this dissertation primarily explores the characterization of snow microstructural evolution under the effects of temperature gradient and overburden. Snow structural evolutions were monitored by the techniques of scanning electron microscopy (SEM), X-ray computed microtomography (micro-CT) and numerical simulation. The temperature gradient setup constructed for this work, commercial compression stage and commercial cooling stage were used to simulate the natural boundary conditions within snow layers. Of the different types of metamorphism that may occur in snow layers, temperature gradient metamorphism (TGM) is perhaps the most significant one. The snow layer undergoing TGM will lose its strength and transform into a weak layer, which is the microstructural cause of avalanches. 1-D arrays of ice spheres were used as a reproducible approach to observe snow microstructural evolution and investigate the mass transfer process. By controlling temperatures on both sides of ice spheres, different vapor transfer directions were studied. Our experiments demonstrated the mass transfer processes and microstructural evolutions under alternating and unidirectional temperature gradient. We also investigated the effects of temperature gradient on natural snow. The specific surface area (SSA) was used to characterize the TGM. The magnitude of the temperature gradient and the initial snow type both influence the evolution of the SSA. The trend in the SSA is controlled by two mechanisms, grain growth and the formation of complex surface. For the relationship between the structure of snow and its mechanical properties, there are two aspects of this field of particular interest: the structure of snow determines its mechanical properties such as elasticity and viscosity, and the structure of snow evolves under an applied load. Micro-CT images, complemented with SEM images, demonstrate that the mechanical properties of snow depend on the density, the SSA, and the bond formation. During our interrupted compression tests, the SSA decreased more rapidly than that determined for snow metamorphism without an overburden. It is clearly evident that pressure sintering of snow contributes to accelerated sintering and coarsening processes.