glaciatie

Glaciation (Dutch: glaciatie) is the process by which large parts of Earth's surface become covered by ice sheets and glaciers. It can be regional, affecting mountains, valleys, and plateaus, or global, when continental ice sheets extend over large portions of the continents. In geological discussions, glaciation also denotes the climactic periods during which such ice growth is sustained, including the advances (glacials) and retreats (interglacials) of ice.

Causes and dynamics: Long-term cooling, atmospheric composition, tectonics, and ocean circulation interact with feedbacks such as increased surface albedo and reduced greenhouse effect to promote ice growth. Orbital variations (Milankovitch cycles) influence the distribution of solar energy at high latitudes and can initiate glacials when conditions persist, often over tens to hundreds of thousands of years. Ice sheets grow when snowfall exceeds melt, after which flow and calving distribute the ice, expanding its reach.

Evidence and impacts: Geological and geophysical records provide evidence for glaciation, including glacial deposits (till, moraines), sculpted bedrock features, drumlins, and varved sediments, as well as isotopic records from marine microfossils and data from ice cores. These indicators help reconstruct past ice extent, duration, and climate context. Glaciation affects sea level, climate, and ecosystems; global cooling generally lowers sea level as water is stored in ice sheets and altered ocean circulation.

Historical scope: Earth’s history features several major glaciations, notably the Neoproterozoic ice ages, the late Paleozoic Ice Age, and the Quaternary glaciations, which show recurring advances and retreats of ice sheets. In the modern era, persistent glaciers remain in high mountains and polar regions, though many are retreating in response to current climate warming.