Avalanche is a mass of snow that slides down a mountain slope. Most avalanches result from weather conditions that cause snow on a mountain slope to become unstable. Such disturbances as heavy winds, earth tremors, and explosions can send the snow sliding down the mountain. Skiers have started many avalanches.
There are three chief kinds of avalanches. A dry snow avalanche consists of powdery snow and air that may move faster than 100 miles (160 kilometers) per hour. A wet snow avalanche is a mass of wet, dense snow that typically moves slower than a dry snow avalanche. In a slab avalanche, a solid portion of snow breaks loose as a slab and splits into pieces as it slides.
Experts can often recognize the conditions that lead to avalanches by studying the terrain, snow, and weather in an area. To help control avalanches, they use explosives to reduce snow build-up. They also replant trees on slopes, and erect barriers.
