Rheological Properties of Low Density Snow

• Main Author: Conway, Howard
• Other Authors: WASHINGTON UNIV SEATTLE DEPT OF GEOPHYSICS
• Format: Text
• Language: English
• Published: 1998
• Subjects: Snow; Ice and Permafrost; *SNOW; *RHEOLOGY; AVALANCHES; LOW DENSITY; SLOPE STABILITY; RAIN ON SNOW; SNOW DENSIFICATION; Ice; permafrost
• Online Access: http://www.dtic.mil/docs/citations/ADA366132; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA366132

Widespread slab avalanches up to 1m deep often release immediately after the onset of rain on new snow. Measurements show that on first wetting the densification rate increases by about three orders of magnitude. It is likely that the initial burst of densification is a result of rapid structural changes and grain rearrangement. Abrupt changes in the mechanical properties are also likely but measurements show that only the upper 0.15m or less of the snowpack has been affected at the time of avalanching. We have not detected changes at the sliding layer. Results from an elastic slip-weakening model show the slab modulus may have a controlling influence on slope stability. It is evident that the mechanical properties of both the weak layer and the slab control slope stability. We have investigated the evolution of snow slope stability during storms by tracking the shear strength at a potential weak layer and the shear stress imposed by the weight of the overburden. Preliminary tests with the model are promising and State highway avalanche technicians plan to use it operationally at Snoqualmie Pass in the Washington Cascades during the coming winter.