An avalanche occurs when loose snow and ice suddenly move down a slope. Each year, avalanche hazards can cause multiple winter fatalities. As a matter of physics, snow and ice can succumb to gravitational forces leading to deadly consequences. 8 out of 10 avalanches occur after a storm when new snow is added to existing snow cover on a slope. How do avalanches occur?
Where Do Avalanches Occur?
Avalanches occur in most any region where snow will cling to a sloped surface. In mountainous terrain, thousands of avalanches of various sizes can occur every year. Hillsides with a slope of 35 to 40 degrees are the most dangerous for avalanches. Steeper slopes tend to not have the snow cling to the surface.
How Can Avalanches Be Prevented?
Steeply sloped surfaces are danger zones for potential avalanches. Trees can help to prevent snow from moving down the slope of a hill by becoming an anchor.
Avalanche Safety Resources
Avalanche Facts
According to the state of Colorado, avalanches generally occur on slopes greater than 25 degrees in inclination. The most common slope is between 35 and 45 degrees.
The steepness of a slope, its aspect (which direction it faces), the slopes shape and its natural features are all important in determining whether a slope can slide. Of all of these, the steepness, or slope angle, is the most important.And according to the National Weather Service, the number of avalanches reported in the United States is between 1,200 and 1,800. The number of avalanches that actually occur, however, are probably 100 to 1000 times that number.
Most slab avalanches occur on slopes with starting zone angles between about 30 and 45 degrees, but slabs occasionally occur on slopes less than 30 degrees.
Slopes steeper than about 50 to 60 degrees tend to sluff snow constantly, and slopes about 25 degrees or less are generally not steep enough. Skiing and snowboarding are fun on slopes in the 30-40 degree range, thus we have our dilemma. We like to go where the slab avalanches most often occur.
