Continuous Monitoring of Metamorphic Changes of Internal Snow Structure as a Tool in Avalanche Studies

Abstract

AbstractRelationships between snow structure, climatic factors, and the nature of avalanche events in the San Juan Mountains of Colorado, U.S.A., are analyzed. Physical and mechanical properties of the snow cover have been monitored on a continuous basis by conventional methods as well as through the application of a profiling snow-density gauge. Temperature-gradient metamorphism is the dominant mechanism which determines the character of the local snow structure. Properties unique to well-developed temperature-gradient snow (depth hoar) are discussed. Three specific metamorphic processes are described which contribute to a highly varied and mechanically weak snow structure. Analysis of fracture-line profile data allow general studies of the local snow climate to be compared with the stratigraphy of actual release zones. Fracture-line data support the conclusion that meteorological conditions prevailing at the time of new-snow deposition play a less significant role in the eventual release of slab avalanches than metamorphic processes which influence the snow cover between storm periods. Shear failure zones are consistently composed of weak layers metamorphosed weeks and even months prior to the precipitation event which triggers the release.