Item: Morphology of crystal growth and grain bonding in snow
Title: Morphology of crystal growth and grain bonding in snow
Proceedings: 2002 International Snow Science Workshop, Penticton, British Columbia
Authors: E. E. Adams and D. A. Miller, Montana State University, Bozeman, Montana
Abstract: Microstructure is of paramount importance to the structural stability of a snowpack. We have scrutinized microstructure at the grain and bond scale with the aid of optical and scanning electron microscopes (SEM). SEM images of fractured samples of equilibrium growth form snow distinctly demonstrate that failure occurs at the grain boundary bonds in this type of snow. Earlier laboratory studies of large flat ice crystals placed in a supersaturated vapor environment have demonstrated that numerous crystals developed across the surface and all displayed the same crystallographic orientation as the parent crystal. This led to a dominant grain growth theory for a kinetic growth snow layer. In this study, SEM images of depth hoar crystals grown in a snowpack expose a very complex geometry near the kinetic crystal bond sites, which smootWy transition to the large striated crystal. It is suggested that these bond areas are comprised of less optimally oriented crystals, which nucleated on the parent grains, but have had their growth truncated by the dominant growth grains. Stress concentrations and potentially small bond to grain ratios imply a weaker structure when compared to SEM images of an equilibrium morphology snowpack. Primary nucleation sites in snow are conjectured to be at high-energy areas associated with grain boundaries.
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Keywords: snow and ice, snow crystal, snow crystal growth, snow crystal structure, snow metamorphism
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