Item: Experience with rutschblocks
Title: Experience with rutschblocks
Proceedings: Proceedings of the 1992 International Snow Science Workshop, Breckenridge, Colorado, USA
Authors: J.B. Jamieson and C.D. Johnston
Abstract: During the winters of 1990-1992, rutschblock technique and limitations, variability and precision of rutschblock scores, and applications of rutschblocks to slab stability evaluation were studied in the Cariboo and Monashee Mountains of western Canada. The time required for each test was, under many conditions, reduced to 10 minutes or less by using cords, specialized saws or the tails of skis to cut the two sides and the upper wall of the rutschblock. The median rutschblock score was 4 or less on most days when one or more large dry natural slab avalanches were reported by helicopter skiing guides operating within 30 km of the study area. Also, median rutschblock scores were 4 or less near slabs that had been ski-released and individual scores up to 5 were recorded near recently ski-released slabs. On slopes of 20° to over 40°, median rutschblock scores correlate well with a Swiss stability index; however, rutschblock scores on slopes below 20° are inconsistent with the correlation suggesting a minimum angle for rutschblocks of approximately 20°. In spite of natural variability of rutschblock scores on a particular slope, decreasing the slope angle by 10° tended to increase the rutschblock score by 1. A tendency for higher and more variable scores was noticed near the top of several slopes.
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Keywords: dry slab, rutschblock, slopes
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