Slush 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 Institute (NGI) has started a research program on these topics. Thirty-four slush avalanches with known locations 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 grains, and hard layers or crusts of ice in snow cover or on the ground, are critical conditions for slush avalanche release. Intense rain, falling on cohesionless new snow on these substrata, is the most striking feature of current weather situations. 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: 1) Sudden release from crown surface, 2) drainage of snow-embanked, water-saturated snowfields through narrow outlets and 3) rapid headward growth from first point of release. Enlargements and confinements along the avalanche tracks were caused by distinctly defined features in the tracks.
Slush 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 Institute (NGI) has started a research program on these topics.Thirty-four slush avalanches with known locations 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 grains, and hard layers or crusts of ice in snow cover or on the ground, are critical conditions for slush avalanche release. Intense rain, falling on cohesionless new snow on these substrata, is the most striking feature of current weather situations.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: 1) Sudden release from crown surface, 2) drainage of snow-embanked, water-saturated snowfields through narrow outlets and 3) rapid headward growth from first point of release.Enlargements and confinements along the avalanche tracks were caused by distinctly defined features in the tracks.
ABSTRACT. Slushflows -Oowing mixtures of water and snow -are a major natural hazard in Norway. Knowl edge gathered by the Norwegian Geotechnical Institute during 25 years of slushOow consulting and research is presented. The variation in regional occurrence is described and related to climatic premises and ground conditions. The principal ideas about slushf10w relea e, down-slope propagation and run-out are outlined. They are closely related to the rate and duration of water supply, snowpack properties and geomorphic factors. Slushf10w release is caused by basal shear failure aided by water pressure to cause loss of basal support and finally tensile failure through the snowpack. Our methods of hazard evaluation and acute-hazard prediction and warning are summarized, including the estimation of water supply based on meteorological data. The results of a worldwide questionnaire on slushflows, literature studies and scientific contacts, indicate that slushf10ws occur in all countries having a seasonal snow cover and that the results of our studies in Norway have a general validity.
ABSTRACT. Slushflows -Oowing mixtures of water and snow -are a major natural hazard in Norway. Knowl edge gathered by the Norwegian Geotechnical Institute during 25 years of slushOow consulting and research is presented. The variation in regional occurrence is described and related to climatic premises and ground conditions. The principal ideas about slushf10w relea e, down-slope propagation and run-out are outlined. They are closely related to the rate and duration of water supply, snowpack properties and geomorphic factors. Slushf10w release is caused by basal shear failure aided by water pressure to cause loss of basal support and finally tensile failure through the snowpack. Our methods of hazard evaluation and acute-hazard prediction and warning are summarized, including the estimation of water supply based on meteorological data. The results of a worldwide questionnaire on slushflows, literature studies and scientific contacts, indicate that slushf10ws occur in all countries having a seasonal snow cover and that the results of our studies in Norway have a general validity.
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