A slow-moving mass of ice formed in higher latitudes and elevations. When snowfall is greater than melting and the increasing amounts of snow become compacted and pressurized it forms firn and ultimately a glacier. As the glacier moves, it carries rocks and soil, and can form u-shaped valleys over geologic time. Glaciers can move at variable rates.
[Ecological Monographs; v64: pp. 149-175: 1994.] [Geological Society of America Bulletin; v103: pp. 1073-1089: 1991.]
Source: Atmospheric Chemistry Glossary