icesheet

An ice sheet is a large mass of land-based ice that covers more than about 50,000 square kilometers and flows outward under its own weight. Ice sheets are distinct from ice caps, glaciers, and sea ice because they rest on bedrock on land and spread via slow, gravity-driven flow. The two major ice sheets are the Antarctic and Greenland Ice Sheets, which harbor far more ice than smaller regional ice bodies.

Formation and structure begin with snowfall that accumulates year after year. Over time, snow compresses into firn and then into glacial ice. The thickest parts of an ice sheet deform internally and can slide at the bed, causing outward flow that feeds outlet glaciers and ice streams. The interior tends to remain cold and low in melting, while the margins are more dynamic and prone to thinning.

Dynamics and stability are controlled by gravity, ice temperature, bed topography, and subglacial hydrology. Ice moves from thick central regions toward the edges, where calving, melting, and sublimation can reduce mass. Subglacial lakes and channels influence flow patterns. The geometry of the bedrock beneath the ice sheets shapes their outlets and potential responses to climate forcing.

Distribution and volume are dominated by the Antarctic and Greenland sheets, which contain the vast majority of Earth's freshwater ice. Together they dwarfs smaller ice bodies and have the potential to raise global sea levels by many meters if disrupted; estimates often place around 60 meters for Antarctica and about 7 meters for Greenland in extreme scenarios.

Monitoring and research employ satellite gravimetry and altimetry, radar and seismic sounding, and field measurements to assess mass balance, thickness, flow, and responses to climate change.