<human>:  How does an avalanche work?
<bot>: An avalanche is a rapid flow of snow, ice, and rocks down a mountainside. The avalanche is caused by the instability of the snowpack, which is created when new snowfall is not strong enough to support the weight of the existing layers of snow and ice. This can be caused by a variety of factors such as wind, temperature, terrain, and the presence of water. Once an avalanche is triggered, gravity and the friction of the snow cause it to flow rapidly down the slope, sometimes at speeds of over 100 miles per hour. Avalanches may carry snow, rocks, and other debris with them, making them potentially destructive and dangerous.