Physical Processes in Snowpacks During Rain or Melt Events
Abstract
Observations during rain-on-snow indicate three evolutionary regimes of snow behavior, immediate avalanching, delayed avalanching, and a return to stability. Immediate avalanching occurs within minutes of the onset of rain. This is important information for avalanche control technicians; the avalanches release several hours before, liquid water has penetrated to the sliding layer. Delayed avalanches release several hours after rain has started. The delay varies depending on the rate of increasing stress associated with additional precipitation, and the time taken for water to penetrate and weaken the snowpack. Avalanche activity is rare after continuation of rain for 15 hours or more. This return to stability occurs after a drainage system has been established. Infiltration is not uniform and water penetrates through localized channels that often occupy less than 50% of the total volume of the snowpack. Runoff starts much sooner than would be predicted if wetting was homogeneous. Insitu measurements of deformation indicate that the strain rate in low density snow often increases without increased normal loading. Forces other than gravity must contribute to the deformation. This important finding is supported by measurements on slopes that show that the usual assumption that snow behaves as a linear, isotropic, viscous material is incorrect. A new theory involving thermodynamically induced strain is suggested. Snow, Rain-On-snow, Avalanches, Infiltration, Deformation, Rheology.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 10, 1994
- Accession Number
- ADA275445
Entities
People
- H. Conway
Organizations
- University of Washington