A microstructural approach to predict dry snow metamorphism in generalized thermal conditions

Abstract

Dry snow metamorphism has traditionally been classified by the thermal environment encountered in the snowpack. Snow experiencing a predominantly macroscopically isothermal environment develops a different microstructure than snow that is subjected to a significant temperature gradient. As such, previous research has evaluated snow metamorphism based upon select thermal gradient-dependent processes, when in reality, there is a continuum of physical processes simultaneously contributing to metamorphism. In previous research, a discrete temperature-gradient transition between the two thermal environments has been used to activate separate morphological analyses. The current research focuses on a unifying approach to dry snow metamorphism that is applicable to generalized thermal environments. The movement of heat and mass is not prescribed, but is allowed to develop naturally through modeling of physical processes. Equilibrium forms and the transition to kinetic growth are considered with this model. Metamorphism predictions under macroscopically isothermal conditions are presented followed by a definition for the transition to kinetic growth. Density, grain size, bond size, and temperature dependencies are each examined in an isothermal metamorphism environment. The same physical model is then used to define a smooth transition between isothermal and temperature gradient environments. Microstructural and environmental parameters that influence transition to kinetic growth are examined. The correlation with established trends and experiments in each environment is excellent. The microstructural model is a new tool capable of evaluating metamorphism for a broad range of microstructural parameters and thermal environments.