ETYM French glacier, from glace ice, Latin glacies.
A slowly moving mass of ice.
Tongue of ice, originating in mountains in snowfields above the snowline, which moves slowly downhill and is constantly replenished from its source. The scenery produced by the erosive action of glaciers is characteristic and includes glacial troughs (U-shaped valleys), corries, and arętes. In lowlands, the laying down of moraine (rocky debris once carried by glaciers) produces a variety of landscape features.
Glaciers form where annual snowfall exceeds annual melting and drainage. The snow compacts to ice under the weight of the layers above.
Under pressure the ice moves plastically (changing its shape permanently). When a glacier moves over an uneven surface, deep crevasses are formed in rigid upper layers of the ice mass; if it reaches the sea or a lake, it breaks up to form icebergs. A glacier that is formed by one or several valley glaciers at the base of a mountain is called a piedmont glacier. A body of ice that covers a large land surface or continent, for example Greenland or Antarctica, and flows outward in all directions is called an ice sheet.