An avalanche is a falling mass of material such as snow, rock, or debris. Avalanches occur when the weight of a packed mass of material causes a section of the material to shear off. As the material travels across the landscape, it can do a significant amount of damage, and avalanches are a major concern in some regions of the world.
The word “avalanche” comes from the Romansh language of Switzerland, and it originally referred specifically to a falling mass of snow. Over time, people have adopted the term to refer to landslides of rock and debris as well. Avalanches continue to be an issue in Switzerland, and they also occur in parts of North America, and in any other regions where there are large mountain ranges.
For an avalanche to occur, several conditions must be satisfied. The mass of material must be on a slope with a significant angle, and it must be weakened by its own weight. Earth tremors, shock waves from engines and explosions, or even a skier's passage can trigger a critical weakness as the mass of material reaches a tipping point and shears off. As the avalanche travels down the slope, it can pick up more material, becoming larger and more dangerous.
In a snow avalanche, the snow may be a tightly packed chunk, in which case it is known as a slab avalanche, or a looser mass of flowing snow, in a powder avalanche. Unstable snow is an issue of concern in recreation areas because skiers, snowboarders, and other people out in the winter are at risk of being caught in avalanches. Many governments monitor avalanche-prone regions carefully for early warning signs of avalanches, posting warnings to alert people to the danger level.
Some regions practice avalanche control. An event may be deliberately triggered with a targeted explosion so that it can occur harmlessly when no people are around, or barriers may be installed on frequently-used slopes to slow or stop the progress of falling materials.
Traveling on the edge of trails reduces the risk of being caught, because avalanches tend to follow the path of least resistance along the middle of the trail. If caught, people should jettison skiing and snowboarding gear, and use a swimming motion to try to stay on top of the falling snow. In cases where it is impossible to stay on top of the snow, the chest should be thrust out with a deep breath, and a hand should be used to cover the face to create breathing room.
If victims are rescued within 15 minutes, their chances of survival are very good. For this reason, carrying avalanche beacons is recommended, as the beacon can help rescuers find a victim quickly. People should also travel with partners in regions with unstable snow and rock, and they should pack shovels so that witnesses can quickly dig down to rescue victims, since every minute counts.