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Topic – Avalanches and Landslides

Read the Following Selection

Read about avalanches and landslides, or click on the play button below to listen aloud.

Avalanches and Landslides

How are avalanches and landslides similar and different?

The Material That Falls

An avalanche is made of falling snow, ice, and rocks. A landslide is made of falling soil and rocks.

Where the Material Falls

Snow in an avalanche and soil in a landslide both fall down a slope. The slope is the side of a mountain or a tall hill.

What Makes the Material Fall

A landslide can damage structures such as roads.

Imagine a mountainside covered with snow that does not move. The snow resists the pull of gravity, so it does not fall down the slope. A large snowfall can add a lot of snow on top of the snow that was already there. The snow on the mountainside is now so heavy that it cannot resist gravity, so gravity pulls the snow down the slope.

Landslides are also caused by precipitation. Rain or melting snow can lead to a landslide. The particles of soil on a dry slope rub against each other. Friction between the soil particles keeps the particles from moving. When the soil gets wet, there is water between the particles of soil. The water reduces the friction, so gravity can pull the soil down.

A Trigger Event

A loud noise can trigger an avalanche

Avalanches and landslides are usually started by a trigger event. The trigger event is something that makes the snow or soil unstable, so that gravity can start to pull it down the slope.

A trigger event is usually something that causes vibrations. The vibrations could come from an earthquake, an erupting volcano, or even a very loud sound. These vibrations make the snow or soil unstable, then gravity causes an avalanche or landslide.

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