We all know that avalanches are dangerous. Some of us may have even experienced one. However, even backcountry enthusiasts may not fully understand how avalanches form. Understanding the ways in which avalanches may occur is essential for taking steps toward their prevention.
Technically speaking, an avalanche is any amount of snow sliding down a mountainside—similar to a landslide, but with snow rather than earth. There are two types of avalanches.
- A Surface Avalanche happens when a layer of snow with different properties slides over another layer of snow. Think: when dry, powdery snow slides over a dense, wet, or icy layer.
- A Full-Depth Avalanche happens when the entire snow cover, regardless of the properties of individual layers, slides over the ground.
Both types of avalanches are extremely dangerous. Though large, full-deptch avalanches are, quite obviously, the most dangerous, small, surface avalanches can also cause severe injury and death. Though you may not be buried, you could be pushed off a cliff, into a depression, or into rocks and trees. It is essential to understand how avalanches work, as well as the danger scale, in order to practice safe and informed backcountry exploration.
Avalanches occur when a layer of snow cannot support its own weight. The snow can be loosened by a person’s step, a loud sound, or a gust of wind, causing the snow to loosen. Most avalanches begin with a weakened layer within or on top of the snowpack, which collapses under the weight of higher/surface layers or of itself.