Estimating run-out distances for extreme snow avalanches
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Estimating the run-out distances for snow avalanches is an important task for land use planning in mountaneous areas. The practical requirements are usually to define the run-out for a certain return period, which varies from 20-50 years for highway purposes to 300-1000 years for living areas. The run-out distance of a snow avalanche are both dependent on the topography of the avalanche path, the volume of the avalanche and the physical properties of the snow involved. The pioneering work in establishing a model to estimate the run-out distance was made by Voellmy (1955). His model is a flow model to calculate the velocity and the resulting run-out distance. The input data is both topographic data and selected values for the physical properties of the snow. In his paper he recommended certain values to be used for avalanches having long return periods. Another approach is proposed by Lied and Bakkehøi (1980), who compared the run-out distance of extreme avalanches orny on topographic parameters. This type of model is called a topographical model, in contrast to the Voellmy-type which is a dynamical model.