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What is a glacier?

A glacier is a large, perennial accumulation of crystalline ice, snow, rock, sediment, and often liquid water that originates on land and moves down slope under the influence of its own weight and gravity. Typically, glaciers exist and may even form in areas where:

  1. mean annual temperatures are close to the freezing point
  2. winter precipitation produces significant accumulations of snow
  3. temperatures throughout the rest of the year do not result in the complete loss of the previous winter’s snow accumulation

Over multiple decades this continuing accumulation of snow results in the presence of a large enough mass of snow for the metamorphism from snow to glacier ice process to begin. Glaciers are classified by their size (i.e. ice sheet, ice cap, valley glacier, cirque glacier), location, and thermal regime (i.e., polar vs. temperate). Glaciers are sensitive indicators of changing climate.

Learn more: USGS Water Science School: Glaciers and Icecaps