Avalanches kill back country recreationalists every year, including skiers, snowboarders, snowshoers, and snowmachiners. All back country users should have knowledge of the basic physics of avalanches to help them evaluate local and regional potential for slides. The foundation of this knowledge comes from understanding how the surrounding environmental conditions in previous weeks, previous days, and the day in question all contribute to snow stability or instability, and how specific factors affect snow on a micro-scale, which determines how snow slopes will behave on a macro-scale. There are two major types of avalanches (excluding debris avalanches from broken cornices and ice formations). These are point releases, or loose snow slides, and slab avalanches. While point releases can be dangerous and should be avoided, slab avalanches are much more catastrophic and account for most of the backcountry avalanche disasters involving humans. Basic physics of point releases are discussed here, followed by a discussion on the basic physics of slab avalanches, and how external factors contribute to the stability or instability of a snow covered slope.
BASIC PHYSICS OF POINT RELEASE AVALANCHES
Point release avalanches, or loose snow slides, begin at one point on a slope and get progressively wider as they proceed down the slope. A fundamental characteristic that must be present for this type of avalanche to occur is a surface layer of cohesionless, or nearly cohesionless, snow (University of Colorado IBS 1975; Fredston and Fesler 1994). An initially small amount of snow begins to move downward when the force of gravity is greater than the forces of cohesion at a particular angle or when debris from above starts the s...
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...ditional weight of one skier crossing at a time.
BIBLIOGRAPHY FOR "THE PHYSICS OF AVALANCHES"
Daffern, T. 1983. Avalanche safety for skiers and climbers. Alpenbooks, Seattle, WA.
Fredston, J.A., and D. Fesler. 1994. Snow sense: a guide to evaluating snow avalanche hazard. Alaska Mountain Safety Center, Anchorage, AK.
Graydon, D., and K. Hanson, editors. 1997. Mountaineering: the freedom of the hills, sixth edition. The Mountaineers,
Seattle, WA.
Perla, R.I., and M. Martinelli. 1976. Avalanche handbook. U.S. Department of Agriculture, Agriculture Handbook 489.
University of Colorado IBS (Institute of Behavioral Science). 1975. Snow avalanche hazard in the United States: a research assessment. Assessment of Research on Natural Hazards, Program on Technology, Environment, and Man, Monograph NSF-RA-E-75-017.
Cross-country skiing is as much of a competitive sport, as it is a back country one. Cross-country skiing is enjoyed by people of all ages, and can be relatively inexpensive. There is no need for lift tickets and with a little maintenance equipment can last for decades. As a result of its broad audience, many people don't realize that physics plays a large role in cross-country skiing. This web page was designed to briefly describe some of the concepts behind the physics of skiing, and give a basic understanding of both the sport and the science.
’[16] ------------------------------------------------------------------------------------------------ Guterson, David, Snow Falling on Cedars, 1994, pp 367. [2] Ibid. , pp. 107.
States on the lee, or down wind, sides of the great lakes receive lake-effect snow every year. For some cities this can push the average snowfall up to 400 inches. During the February storm of this year records were broken for the most snowfall in one storm. For a duration of the storm snow was falling at a rate of six inches or more per hour. Some of the images captured from the event leave some in disbelief that such a thing could even happen. Storms of this magnitude completely shut down all activity. Many areas do not have equipment capable of handling such mass amounts of snow, and even if they do the task is overwhelming. (weather.com 2006)
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