Item: The mass of maximum avalanches
Title: The mass of maximum avalanches
Proceedings: Proceedings of the 1982 International Snow Science Workshop, Bozeman, Montana, USA
Authors: Peter Schaerer, National Research Council of Canada, 3904 West 4th Ave., Vancouver, British Columbia, Canada V6R IP5
Abstract: Since 1966 the National Research Council of Canada measured the mass of snow brought down by individual avalanches at 45 avalanche paths at Rogers Pass, B.C. In addition, observations were available of avalanches on the railway track at Rogers Pass since 1909. The analysis of the data of the largest avalanches in each path demonstrated that avalanches that occur less frequently than on the average once in 12 years much exceed the mass of the usual large ones which occur once in 3 to 10 years. Plotting the annual maximum avalanches against a frequency distribution would underestimate the mass of a 30 year or longer maximum avalanche. Such avalanches often surprise by their size. The incline of the slope of the starting zone was found to have a strong influence on the size of maximum avalanches. The exposure with respect to wind was secondary in influence. The. roughness of the ground proved to be insignificant. From the observations and a study of the mass of avalanches which appeared to have occurred only once in the past 100 years, the following empirical relation was developed: M=C·SYA; where: Mis the mass of a maximum avalanche, in tonne; S is the 30-year maximum water equivalent of snow in the starting zone, in m; A is the surface area of the starting zone + track, in m2, Values of the coefficient C for a 1OO-year maximum avalanche are: 120 for inclines less than 40° 80 for inclines 41 ° to 45° 60 for inclines greater than 45°.
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Keywords: starting zone, wind, slope
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