What Are Four Factors for an Avalanche to Occur?

There are three basic types of avalanches. The first, and most deadly, is a slab avalanche, where harder, more cohesive snow settles on on a softer, weaker layer that can't support it. The second, and generally the least dangerous but fastest moving, is a loose snow avalanche, composed of mostly loose, powdery snow. The third type is a wet snow avalanche which occurs when warm temperatures melt the top layer and loosen bonds between the layers of snow.

Slope

• Slope is the single most important factor involved in the likelihood of an avalanche. While avalanches can occur on mountains with a slope angle between 25 and 60 degrees, most happen between 35 and 45 degrees, with 38 degrees being the prime slope angle. Skiers and boarders must be careful because many of the exciting runs have angles greater than 35 degrees. The slope profile is also important. If the slope is convex, as opposed to concave, there is a greater chance of an avalanche.

Ground Surface and Snowpack

• The type of ground under the snow is like the anchor holding the snow to the ground. The rougher or rockier the ground, the more friction there will be to hold the snow in place. Smooth ground means less friction and a greater chance of an avalanche. Snowpack refers to the type of snow. At high levels, snow will most likely be in different layers, so look for signs that pose an avalanche threat: a heavy top layer, which could be on top of a powdery layer, or a wet top layer that releases a handful of water when you squeeze it.

Weather

• Weather is the architect of avalanches. It makes the snowpack, the different layers of snow. Thus, it's a smart idea to know the weather patterns for even a few weeks before traveling in avalanche country. Snow and rain add to the weight and instability of a snowpack. Rain falling on powdery snow is extremely dangerous. Heavy winds carrying snow from one spot to another adds weight to an existing snow pack, making it more unstable. Prolonged periods above freezing can lead to wet avalanches.

Human

• Most avalanches that catch or kill people are caused by people because they underestimate the possibility of an avalanche. While ignorance accounts for some fatalities, not knowing what signs to look for or taking the proper precautions accounts for more. Some simple precautions can mean the difference between life and death. Keep an eye on the weather. When going up a mountain, try to go through patches of thick trees. When descending, take low-angle routes and, if in avalanche terrain, spread out and move from island of safety to island of safety.