What Is a Glacier?

A glacier is a large persistent body of ice. Originating on land, a glacier flows slowly due to stresses induced by its weight. The crevasses and other distinguishing features of a glacier are due to its flow. Another consequence of glacier flow is the transport of rock and debris abraded from its substrate and resultant landforms like cirques and moraines. A glacier forms in a location where the accumulation of snow and sleet exceeds its ablation (melting and sublimation) over many years, often decades or centuries. A glacier is distinct from sea ice and lake ice that form on the surface of bodies of water.

The word glacier comes from French. It is derived from the Vulgar Latin glacia and ultimately from Latin glacies meaning ice. The processes and features caused by glaciers and related to them are referred to as glacial. The process of glacier establishment, growth and flow is called glaciation. The corresponding area of study is called glaciology. Glaciers are important components of the global cryosphere.

On Earth, 99% glacial ice is contained within vast ice sheets in polar regions, but glaciers may be found in mountain ranges of every continent except Australia. In the tropics, glaciers occur only on high mountains.

Glacial ice is the largest reservoir of freshwater on Earth. Many glaciers store water during one season and release it later as meltwater, a water source that is especially important for plants, animals and human uses when other sources may be scant.

Because glacial mass is affected by long-term climate changes, e.g., precipitation, mean temperature, and cloud cover, glacial mass changes are considered among the most sensitive indicators of climate change and are a major source of variations in sea level.