Item: A Smartphone Application for Estimating the Critical Slope Angle for Avalanche Release
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Title: A Smartphone Application for Estimating the Critical Slope Angle for Avalanche Release
Proceedings: International Snow Science Workshop 2016 Proceedings, Breckenridge, CO, USA
Authors:
- Ron Simenhois [ Coeur Alaska, Juneau, AK, USA ]
- Karl W. Birkeland [ USDA Forest Service National Avalanche Center, Bozeman, MT, USA ]
- Alec van Herwijnen [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
Date: 2016-10-02
Abstract: Once a weak layer has fractured, slope steepness largely dictates whether or not an avalanche will release. Exceeding the critical slope angle, i.e. angle at which the slab overcomes friction, is an essential condition for dry-snow slab avalanche release. Practitioners continually take this into consideration when assessing avalanche terrain and safe travel routes in alpine environments. However, thus far, such assessments rely on rules of thumb, such as avoiding terrain steeper than 30°, rather than actual measurements. Further, research into critical slope angles has been limited and confined to dry-snow and mostly persistent weak layers and harder slabs. To address these limitations, we developed a simple smart phone app to measure the kinetic friction between the detached slab and the bed surface. We used Optical Flow method to track motion of sliding slabs. We assumed Coulomb friction to calculate the friction between the slab and bed surface and derive the critical slope angle. Using our app on existing videos allowed us to compare our measurements with prior friction research, and we found the app was able to estimate friction to within +/- 1° of previous work. Our preliminary field data consist of 16 measurements on decomposed fragments (DF) and moist faceted crystal (FC) weak layers from four pits spaced 10 meters apart on a single slope. The critical slope angle was 35 +/- 1° for the DF layer and 39 +/- 0.5° for the moist FC layer. Our data also show a constant critical slope angle within the initial 0.1 – 0.2 m. of the down-slope motion, and a decreasing critical slope angle shortly afterward. Our smartphone tool provides a method to quickly estimate critical slope angles in the field. Our goal is to link critical slope angles to specific snow cover properties, and to assess spatial and temporal variability in critical slope angle.
Object ID: ISSW16_O17.01.pdf
Language of Article: English
Presenter(s):
Keywords:
Page Number(s): 383-389
Subjects: smartphones avalanche slope slope steepness
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