With any outdoor adventure comes the risk of confronting the more unfavorable elements of nature that are always possible in the wild. Each season has its own form of natural disaster—disasters that are both fascinating in their magnitude and terrifying in their critical mass of destruction. During the winter, this is the avalanche.
Avalanches, however, can be easily avoided with proper information on the subject. These massive snow slides are not a matter of chance, and, with a little knowledge of how and why they occur, you can ensure much safer outdoor activities this winter.
There are two types of avalanches: point release (or sluffs) and slab. Point release avalanches are smaller and are not particularly hazardous; few people are harmed by this form each year. Slab avalanches, however, tend to be very dangerous.
Slab avalanches become possible when the snowpack starts to develop in multiple layers—imagine a layer cake. These layers will consist of a lower, densely packed snow, then a weak layer (a sugary snow called the facet), and then another dense snowpack. These layers develop differently because of variations in weather patterns, precipitation, solar radiation, night-time cooling, and wind.
The top layer, the slab, becomes an avalanche when the facet layer collapses and the slab slides downward. Many different things can trigger the collapse, including additional snow, rain or wind—most avalanches occur during or right after a storm.
The most common trigger is humans.
Avalanches also need a slope to occur. Almost all avalanches occur on 35- to 45-degree slopes, what would be considered a black diamond ski slope. The prime slope for an avalanche is 37 to 38 degrees. It's important to remember, however, that even if you're on a hill free from the dangers of an avalanche, always be aware of the mountains above and beyond you—these slopes could still be triggered and drift snow down to your location.
So, to recap, there are four ingredients required for an avalanche to occur:
- a steep slope—the terrain,
- a slab,
- a weak layer—the snowpack, and
- a trigger—usually the human factor.