Item: Observations on buried surface hoar in british colombia, canada: section analyses of layer evolution
Title: Observations on buried surface hoar in british colombia, canada: section analyses of layer evolution
Proceedings: Proceedings of the 1998 International Snow Science Workshop, Sunriver, Oregon
Authors: Robert E. Davis, U.S. Army Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire USA, Bruce Jamieson and Colin Johnston, Department of Civil Engineering, University of Calgary, Calgary Albe
Abstract: Observations on sections cut through buried surface hoar layers over time offer the opportunity to measure microstructural changes associated with strengthening. We present preliminary results of new analyses carried out with measurements on sections from snow sampled every week to ten days from midwinter to late winter over four years, 1995-1998, in British Colombia, Canada. Our measurements focused on changes in basic geometry of buried surface hoar layers, particularly where the buried surface hoar crystals were bonded to the underlying snow. As with previous results, over time the thickness of the layer containing surface hoar crystals decreased as strength increased. In samples from sloping snow, the effect of creep was evident in changing orientation of the cut profiles of buried surface hoar. We attempted to identify bond lines using Kry's criteria to assess bond area density, size and change. Results show that low shear strength of buried surface hoar stems from low area density of bonds at the base of layers of surface hoar crystals. The bond number density increases around the bases of some crystals over the course of several weeks. These measurements seem to support a recent conceptual model involving differential settlement of the buried surface hoar crystals, but evidence was statistically inconclusive pending more measurements.
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Keywords: avalanche, snow metamorphism, snow strength, snow crystal, snow cover structure
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