Avalanche!

Avalanches are one of the few natural disasters we need to be aware of in this area. We don't need to worry about hurricanes or earthquakes or even volcanoes. Even so, many backcountry skiers don't carry avalanche beacons with them. This simple piece of equipment can save your life should you become buried by emitting a faint signal that can be picked up by the rest of your party--assuming they are similarly equipped--allowing them to quickly locate you beneath the snow.

Every year we hear of skiers killed by avalanches and in many cases these deaths could have been avoided had the victims been more aware of the power hidden within those virgin slopes of knee-deep powder. Avalanches are a regular occurrence in the Rockies, particularly on the eastern slopes where colder temperatures and shallower snowpacks provide the ideal situation for avalanches to occur.

Avalanches most commonly occur on slopes of between 30° and 45°, although shallower slopes have also been known to slide. Normally, areas with low snowfall and colder temperatures are the most dangerous. With a shallow snowpack, when the temperature drops severely, a temperature gradient begins to form. This is simply a large variation between the temperature at the surface of the snowpack when compared to deeper temperatures. This causes the individual crystals in the snowpack to re crystallize and thus lowers their ability to bond to neighbouring crystals. In extreme cases, the crystals form depth hoar, which can result in a snowpack with very little strength. These weak layers may be buried by additional snowfalls and will provide a weakness in the snowpack for some time.

Slab avalanches occur under a variety of conditions. Generally, a slab forms on a windblown lee slope. As high winds carry snow along the surface, the individual crystals are broken into much smaller particles. When the wind speed slows down on the lee slope, these crystals are deposited. Since they are much more compact, they tend to pack much tighter and form a cohesive slab of snow. If one of these slabs forms atop a layer of depth hoar, the entire slope may release at once. Slab avalanches are visible on slopes as large fracture lines below which the snow has released.

What causes an avalanche to release? The most simple answer is that there is too much stress on the slope for the snowpack to support it. This can occur naturally as the snowpack slowly accumulates snow and eventually releases on its own. For the backcountry skier however, the slope can release when the weight of a skier cutting across a slope provides just the amount of stress to release a slab. Most accidents are caused by skiers releasing the slopes under which they become buried.

This is a very simplified look at a few of the cause of avalanches. If you're planning a trip into remote areas, either travel with a qualified guide or at least take an avalanche safety course before you go (or both). The mountains can be both exhilarating and dangerous and taking a few precautions may save your life. Both Kananaskis Country and Banff provide current avalanche condition reports--call before you head out!