An avalanche is when a lot of rock, snow, or ice falls down a mountain. A large avalanche can move at speeds of 80 miles per hour. It causes damage to everything in its path. That includes trees, land, animals, and people.

There are many different kinds of avalanches. Whatever starts the avalanche decides the type of avalanche.

A slab avalanche mostly happens after a deep snowstorm. The snowstorm causes the ice and snow to move. They will start to move downhill. The slab will be about half the size of a football field. The slab avalanche is very dangerous.

A loose snow avalanche is small. It may be called a sluff avalanche. Most of the time, but not always, this type is not dangerous.

An icefall avalanche happens when a glacier flows over a cliff. When the ice breaks and falls, an avalanche may happen. This type is often very large. The icefall avalanche can travel many miles.

There are wet and dry avalanches. A wet avalanche happens when warm weather causes the snow to melt. The wet snow will move down the side of a mountain. A dry avalanche is like a sluff avalanche made of frozen dry snow.

A glide avalanche happens when a bunch of snow slides down a mountain. It is slow moving. It may take several days to glide downhill.