Avalanche

Avalanches in Montana

When snow accumulation on a slope cannot be supported any longer, the snow support structure may break and fall creating an avalanche. The subsequent rush of unsupported snow can bury and move things in its path. The majority of avalanches do not cause any damage; occasionally however, people and property may fall in their paths.

According to the Montana Disaster and Emergency Services website, “If it is assumed that an accumulation of snow is possible anywhere in Montana, then we can evaluate the potential for hazard solely on the basis of terrain characteristics. The most important factor by far is terrain steepness. Wet snow avalanches can start on slopes of 20 degrees or less, but the optimum slope angle for avalanche starting zones is 25-45 degrees. Slopes steeper than 45 degrees will not normally retain enough snow to generate large avalanches, but they may produce small sluffs that trigger major avalanches on the slopes below. Therefore, all slopes of 20 degrees and greater should be considered as potential avalanche sites.”

History in Gallatin County

The history of avalanches in the Service Area is much more pronounced than that of landslides. Both, however, have occurred. Avalanches are a normal occurrence in the Service Area and typically do not cause significant damage; however, injuries and casualties have occurred. The image below outlines the annual number of fatalities due to avalanches across the US beginning in 1950.

The number of annual fatalities is increasing due to increased use of snowmobiles in the backcountry. Since 1951, 117 people have been killed by avalanches in Montana with numerous additional injuries. The Service Area has experienced 18 fatalities since 1996. Each incident is detailed below.

Date	Location	Damage
4/3/2022	Bozeman	1 caught/ 0 buried/ 0 killed
2/06/2022	West Yellowstone	1 snowmobiler caught, patirally buried-critical, and killed
12/14/2021	Big Sky	2 splitboarders caught, 1 partially buried and fatally injured
2/26/2019	Bridger Range	1 skier caught, partially buried-critical, and killed
4/14/2018	Bridger Range	1 sidecountry rider, partially buried, killed
1/2/2018	S. Madison Range	1 snowmobiler buried and killed
10/7/2017	S. Madison Range	2 skiers caught, 1 killed
1/19/2016	N. Madison Range	1 ski patroller caught, partly buried and killed
4/11/2015	N. Madison Range	1 backcountry tourer caught and killed
1/1/2014	N. Gallatin Range	1 snowmobiler caught and killed
2/14/2011	Bridger Range	1 skier triggered, caught and killed
4/14/2010	N. Madison Range	2 snowmobilers caught, 1 killed
12/10/2009	N. Gallatin Range	1 climber caught, partially buried and killed
2/11/2009	West Yellowstone	3 snowmobilers caught, 1 killed
1/20/2008	N. Madison Range	1 skier triggered, caught, buried and killed
3/3/2007	N. Madison Range	1 skier triggered, caught, buried and killed
12/28/2006	S. Madison Range	2 snowmobilers caught, 1 buried and killed
3/24/2002	S. Madison Range	1 snowmobiler triggered, caught and killed
4/4/2001	Bridger Range	1 skier caught, buried and killed
11/26/1999	N. Madison Range	2 skiers caught, 1 buried and killed
3/9/1996	West Yellowstone	1 snowmobiler buried and killed
2/25/1996	West Yellowstone	1 snowmobiler buried and killed

Probability

The Colorado Avalanche Information Center has compiled statistics on a statewide basis on avalanche fatalities. Montana ranks fifth in the nation with over 50 fatalities from 1950/51 to 2000/01. The top three activities being undertaken at the time of an avalanche were climbing, backcountry skiing, and snowmobiling. Ratings have not been compiled for counties within Montana, however, the historical databases show that Gallatin County is one of the more vulnerable counties in the state from avalanche, particularly in the West Yellowstone and Gallatin Canyon areas. The history of significant incidents noted in the table above demonstrates that the population is most vulnerable to avalanches during the months of December, January, February, and March.