Geography
What is a glacier?
Quick answer
A glacier is a huge, slow-moving river of ice. It forms on land where more snow falls than melts, and it carves valleys as it creeps downhill.
In one sentence
A glacier is a large mass of ice that flows very slowly down a valley or across land.
Explained
High in cold mountains or near the poles, snow can fall for years without melting completely. New snow buries the old, and its weight squeezes the lower layers into hard, dense ice. When the ice gets thick enough, gravity makes it move. It flows downhill like a very slow river, usually only a few centimetres to a few metres a day.
snow
mountain
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Glaciers are powerful. As they creep along, they scrape and carry rocks, shaping the land. They carve wide U-shaped valleys, leave behind piles of rocky debris called moraines, and gouge out bowls that fill with water to become lakes. In places where glaciers once reached the sea, they carved deep inlets called fjords, such as in Norway. The surface cracks into deep gaps called crevasses, which make glaciers dangerous to walk on without a guide.
There are two main types. Valley glaciers flow down mountain valleys, as in the Alps, the Andes and the Himalayas. Ice sheets are enormous domes of ice that cover whole regions, like Antarctica and Greenland. About a tenth of Earth's land is covered by glacier ice, and glaciers hold roughly two-thirds of the world's fresh water. Meltwater from some glaciers feeds rivers that millions of people depend on.
Today many glaciers are shrinking, or retreating, because the world is warming (see global warming and climate). Melting ice from land adds water to the sea, which raises sea levels. The Aletsch Glacier in Switzerland, the longest in the Alps, is one of many that have shortened over the last century.
Glaciers are part of the water cycle: snow falls, ice stores the water for a long time, and meltwater flows back to the sea. Find out more about the frozen ends of the world in the polar regions.
Examples
| Glacier | Where | Fact |
|---|---|---|
| Aletsch | Switzerland | longest in the Alps |
| Perito Moreno | Argentina | big glacier that ends in a lake |
| Jakobshavn | Greenland | one of the fastest-flowing |
| Lambert | Antarctica | one of the largest |
Common mistakes
- "Glaciers are frozen lakes." They are made of compacted snow and they move.
- "A glacier is the same as sea ice." Glaciers form on land; sea ice freezes from sea water.
- "Glaciers only exist at the poles." There are glaciers on high mountains near the equator, such as in the Andes.
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Glaciers
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How does a glacier form?
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