A valley is low-lying land in between hills or mountains. It is usually narrow and slopes in a particular direction. Valleys can be shallow with gentle slopes or deep with steep slopes. They often have a river flowing through them. Such valleys are called river valleys.
A glacier is a large area of thick ice which slides slowly down a valley towards lower levels. It is formed when snow remains frozen for a long period of time and accumulates into a dense mass of ice. Glaciers are found on every continent of the world, except Australia. Glaciers change the shape of the land they pass through due to the abrasive action of the ice and sediments in them on the landscape. A glacier is sometimes called a moving river of ice.
An Avalanche is the rapid and sometimes deadly flow of ice down a slope of a hill or a mountain. It is caused when a large mass of snow accumulates on a mountain and topples down due to its enormous weight. It can be triggered by human activity, snowpack (hardened snow) and weather conditions. An avalanche becomes bigger as it moves further down. It accumulates trees, earth and rocks as it moves and can be fatal to anyone in its path.
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