Glaciers

Glaciers are persistent masses of ice that form on land by the compaction and recrystallization of snow over many years. Snow accumulates in excess of melting, is transformed into firn, and gradually becomes glacial ice. Gravity drives the flow of the ice, causing deformation and movement that can transport ice downslope and through basins. The surface often features crevasses, seracs, and meltwater channels.

Glaciers occur in two major settings: mountain or alpine regions and polar regions. In mountains, valley glaciers inhabit valleys and can sculpt landscapes through erosion and deposition. In polar regions, ice sheets and ice caps cover large areas of land. The world’s largest glaciers are parts of the Antarctic and Greenland ice sheets. All glacier types respond to climate through changes in accumulation and ablation (melting and sublimation).

Key concepts in glacier dynamics include the accumulation zone, where snowfall adds ice, and the ablation zone, where melting and sublimation remove ice. The equilibrium line separates these zones. Ice moves by internal deformation and, near the base, by sliding over the bedrock. This movement produces features such as crevasses, moraines, and, when glaciers terminate in the sea, calving icebergs.

Glaciers are important indicators of climate change, act as freshwater stores, and shape landscapes through erosion and deposition. They are monitored via satellite observations, field measurements, and ice-core analyses, which help scientists track changes in extent, volume, and flow over time.