HR: 0830h
AN: NG31A-0605    [PDF]
TI: On the Universality of Power-Law Exponents for Snow Avalanches
AU: * Birkeland, K
EM: kbirkeland@fs.fed.us
AF: USDA Forest Service National Avalanche Center, P.O. Box 130, Bozeman, MT 59771 United States
AU: Rosenthal, W
EM: walter@icess.ucsb.edu
AF: Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106 United States
AB: Snow avalanches are a significant natural hazard in the world's mountainous regions. In the United States, snow avalanches kill more people on an average annual basis than other earth movement hazards such as landslides or earthquakes. Understanding the relationship between avalanche frequency and magnitude can be helpful for avalanche planning and zoning, in addition to improving our understanding of these complex phenomena. Previous research demonstrates that frequency/magnitude relationships for snow avalanches can be described by power-laws, similar to other natural hazards like earthquakes, rockfalls and forest fires. In fact, in these early investigations some researchers have suggested that a universal power-law exponent might exist for snow avalanches. This poster utilizes an extensive snow avalanche dataset covering nearly 30 avalanche seasons at 29 different locations to examine the idea of the universality of power law exponents. The investigation covers a wide range of spatial and temporal scales. Spatial scales range from a single avalanche path to a network of observers measuring avalanches in mountain ranges throughout the western United States, while temporal scales investigated vary from a single snow avalanche season to over 30 seasons of data. For the single site and single path scale, this study uses data from Mammoth Mountain, California and Berthoud Pass, Colorado. Avalanche fracture depth is used to represent avalanche magnitude in this research. Our results demonstrate several points. First, snow avalanche frequency/magnitude relationships can be described with robust power-laws. This is especially evident when the data from all the sites for all the years is combined. Second, individual sites, with areas on the order of 10 square km, demonstrate unique power-laws with exponents ranging from less than 2 to around 5, suggesting that the universality perceived by others may due to chance and limited data. Third, the smaller spatial scale of individual slide paths within these larger areas also have their own power-laws, shedding light on the practical problem of why some avalanche paths tend to produce proportionally more large avalanches than other paths. Finally, for an individual area, power-laws exist for individual seasons and change from year-to-year. This latter result may be helpful for relating avalanche activity to climatological indices which might then prove useful for forecasting the nature of upcoming avalanche seasons.
DE: 1863 Snow and ice (1827)
DE: 3220 Nonlinear dynamics
DE: 3250 Fractals and multifractals
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting