It only takes a few seconds for one of the most beautiful and peaceful experiences nature has to offer to turn into a disaster. In November of 1998, four experienced young Canadians were cross-country skiing through the spectacular Rocky Mountains in Kokanee Glacier Park, British Columbia. The next moment, the group found itself plummeting down a steep slope, tossed about by one of the most powerful forces in nature: an avalanche.
Three members of the group survived the dangerous wall of flowing ice and snow. But one, Michel Trudeau, the 23-year-old son of Pierre Trudeau, a former prime minister of Canada, was swept into the icy depths of Lake Kokanee. Unfortunately, no one could reach him in time and he drowned.
Trudeau's killer was an enormous mass of snow mingled with ice, soil, pebbles, and possibly boulders that rushed down the mountainside. Known in some regions as a "snowslide," an avalanche is almost always a terrible, destructive event, one that few plants and animals have the ability to survive. Fortunately, avalanches are not everyday occurrences in most mountain regions. They require four specific conditions before the snow can start sliding: a steep slope, deep snow cover consisting of several distinct layers including at least one weak layer, and a trigger. They are, therefore, most common in snowy, mountainous regions, such as the Alps or the Himalayas.
An avalanche occurs when the force of gravity, which is always trying to pull snow downhill, exceeds the force between the molecules of ice that keep snowflakes stuck together. The layers of snow that build up over time, however, aren't all the same. For example, layers of snow laid down during extremely cold temperatures will be different from those deposited during warm spells. The layers will have different moisture levels, and the amount of moisture in the snow affects how well snowflakes bind together. If a lower layer is composed of ice crystals that don't stick together well, the layers of snow on top can suddenly break free and begin coasting downhill.
A common trigger is often nothing more than a loud noise. When the conditions are just right, thunder or even a loud shout can be enough to set the deposit of snow in motion. For this reason, mountain guides often demand that hikers keep absolutely silent when crossing areas where avalanches are common.
Ski resort operators, however, use the ability of noise to set off an avalanche to their advantage. To avoid dangerous accumulations of snow, they trigger small avalanches with explosives, which create shock waves. These shock waves shake the weak layers of a snowpack enough to break the bonds between the layers of snow and initiate a snowslide. This way, there is a lower chance that a hiker or skier could trigger one and die as a result.
Predicting the timing of a natural avalanche is almost impossible. But experienced mountain guides and snow experts can often tell where one is likely to happen. Nearly all avalanches, as much as 90 percent, occur on mountain slopes of 30 to 45 degrees. Almost none happen on slopes of less than 25 degreesi—t's too flat—or on inclines steeper than 50 degrees, where snow never gets a chance to build up.
Avalanches most commonly begin above the tree line, where there are no trees to help hold the snowpack in place. Once an avalanche gets started, however, it can continue down a mountainside well below the tree line, through narrow gullies and along cleared roads. Like anything that falls toward the ground, the farther an avalanche travels, the more speed it picks up. And the faster it travels, the more force it acquires. The largest avalanches move so fast that they can produce a furious wind while the snow tumbles down a mountain, steamrolling almost everything in their paths. Even thick stands of trees are no match for the power of a sizable avalanche.
Entire villages have found themselves buried under several meters of snow in a matter of minutes. Happily, few avalanches take place in areas that are properly maintained, like ski resorts and popular hiking trails. Nevertheless, people are buried alive every year because they were in the wrong place at the wrong time, and did not take precautions.
According to the Colorado Avalanche Information Center, the way to avoid getting caught in an avalanche is to avoid dangerous slopes. If venturing into remote mountains in the winter, you should carry an inexpensive, handheld tool called an inclinometer. Smaller than a paperback book, an inclinometer measures the angle of a mountainside. This simple piece of equipment could save your life.
The Colorado Center, which has a vast amount of experience with avalanches, also recommends you keep an eye out for patterns in the snow that show how it has been laid down. Knowing how to identify snow-covered areas that pose an avalanche risk, however, takes years of experience. A warning sign that is easier to see is bent trees that show where previous avalanches have taken place. Also, snow that makes a cracking or hollow sound could be unstable. You should also watch for rocky outcrops or large trees that could prevent runaway slides. Staying close to these will show you safer routes around dangerous areas.
If, despite these efforts, you are still caught in an avalanche, try first to get to the side of the snowslide, where the force of the moving snow is weakest. Grab onto any heavy object within reach, like a tree or large rock. If that's not possible, "swim" with the avalanche and try to stay on top of the snow.
Although there are many tragic stories like Michel Trudeau's, there are also plenty of examples of people who manage to survive being buried beneath more than a meter of snow. Rescuers found one young woman buried by an avalanche in the mountains of Utah for almost two hours. Although she couldn't remember too many details, experts suspect that, before the avalanche came to a rest, she moved her head and shoulders as much as possible, creating a small pocket beneath the snow with enough air to keep her alive.
The word "avalanche" comes from a word in a French dialect, avalance, which means simply "descent." But the image behind this word is one of a great unstoppable force. It has inspired the name of a professional hockey team, the Colorado Avalanche, and even a sport-utility vehicle, the Chevrolet Avalanche. While the image of tons of rolling snow thundering down a mountainside might be a source of awe and wonder, an avalanche remains one of the most dangerous forces that nature can unleash.