The Gornergletscher glacier in SwitzerlandA glacier is a mass of ice that moves slowly downhill. It is made from layers of snow that collect in basins between high mountain peaks. As the layers build up, the snow turns to ice. The ice becomes so thick and heavy, it starts to move. Glaciers move very slowly—just a few metres a day—but they are powerful forces. Some snake down mountain valleys, while others are ice sheets that cover large areas of land. Greenland and Antarctica are covered by ice sheets.
As the glacier moves, it gouges out loose rocks and carries them downhill. These rocks collect together in “dirty” bands called moraines. Where two glaciers meet, their moraines merge together. Further down the valley where the glacier melts (at its snout), all the rocks are dumped in heaps known as end moraines. Where a glacier runs over steeper slopes, cracks, known as crevasses, form on its surface.
About 75% of the world's fresh water is stored in glaciers, ice caps and ice sheets.
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