Item: Evolving shear strength, stability and snowpack properties in storm snow
Title: Evolving shear strength, stability and snowpack properties in storm snow
Proceedings: Proceedings of the 2006 International Snow Science Workshop, Telluride, Colorado
Authors: Catherine Brown and Bruce Jamieson, Dept. of Geology and Geophysics, University of Calgary, Dept. of Civil Engineering, University of Calgary
Abstract: There is a lack of measurements on the rapidly changing mechanical and physical properties of non-persistent instabilities in storm snow. Given the importance of these weak layers in creating snowpack instabilities on which natural avalanches can release, there is a need to better understand and quantify the evolution of layer properties. After identifying unstable layers with a tilt-board test, we measured changes in layer shear strength over time with a shear frame test. We performed up to 13 sets of 12 shear frame test arrays for seven separate storm snow weak layers at the Mt. Fidelity study plot in the Columbia Mountains of British Columbia, Canada. This resulted in over 430 shear frame tests, with sampling up to twice daily, in the winter of 2006. Snowpack properties, including overlying load, densities, temperature gradient and crystal types, of the weak layer and adjacent layers were measured, along with ambient weather conditions. Observations show higher density layers with smaller crystals above and below the weak layer, and weak layers tended to have a lower density and consist of large, precipitation particles. We measured an average rate of strengthening in non-persistent layer of 143 Pa/d. Results indicate a strong correlation between strengthening in weak layers and the stress induced by overlying load.
Keywords: non-persistent weak layers, storm snow, shear strength, stability indices
Digital Abstract Not Available