A contribution to the prediction of slush avalanches

Symposium on Snow and Ice Processes at the Earth's Surface. Sapporo 1984Slush avalanches, primarily known from uninhabited arctic and mountainous regions, every year cause damage to man and property in Norway. Seeking objective criteria to identify their hazard zones, and methods for their prediction and control, the Norwegian Geotechnical In stitute (NGI) has started a research program on these topics. Thirty-four slush avalanches with known loca tions of crown surface have been investigated with regard to geomorphic and climatic characteristics. Starting zones, crown surfaces and tracks were classified according to geomorphic conditions important to avalanche release and motion. Weak cohesionless snowpacks of coarse grain s, and hard la yers or crusts of ice in snow cover or on the ground, are cr itica l conditions for slush avalanche release. Intense rain, falling on cohesionless new snow on these substrata, is the most striking feature of current weather sit uations. The main starting zones were drainage channels, sloping bogs, depressions and open fields. Channel-like, scar-like or bowl-like features appeared in the snow cover due to avalanche release. Three main types of release were identified: I) Sudden release from crown surface, 2) drainage of snow-emba nked , water-satu rated snowfields through narrow outlets and 3) rapid head ward growth from first point of release. En largements and confinements along Ihe avalanche tracks were caused by distinctly defined features in the tracks