Glaciation

Glaciation is the process by which glaciers form, advance, and retreat, and the broader climatic intervals during which large ice sheets cover substantial portions of the Earth's surface. It includes both alpine glaciation in mountains and continental-scale glaciation that can span entire regions or continents.

Glaciers form where snowfall exceeds melting over many years, turning snow into firn and eventually into ice. The glacier grows when accumulation exceeds ablation and shrinks when ablation exceeds accumulation. The location of the equilibrium line and the internal flow of ice determine whether a given glacier thickens, thins, or remains stable.

Continental glaciation, including ice sheets, affects large-scale topography and can cause crustal rebound after ice loss. Alpine glaciation reshapes valleys and mountain landscapes, producing features such as cirques, aretes, and U-shaped valleys. The most extensive glaciations in Earth’s recent history occurred during the Pleistocene, with recurring advances and retreats that influenced sea level and climate.

Evidence for past glaciations includes glacial till and outwash, striated and polished bedrock, and a suite of landforms such as moraines and drumlins. On longer timescales, isotopic records from ocean sediments and other proxies track global temperature and ice-volume changes.

Glaciation exerts profound climatic and ecological effects, sequestering freshwater as ice, lowering sea level during peak phases, and altering atmospheric and ocean circulation patterns. It also shapes habitats and human land use, leaving a legacy in landscapes that persists long after ice has retreated.