Basins

A basin is a natural low area of the Earth's surface that can collect water and sediments. In geography, the term is used for several related concepts: drainage basins (watersheds) that collect precipitation and funnel it to rivers; endorheic basins with no outlet to the sea; and geological basins formed by crustal subsidence that may fill with sediments or host lakes and seas. Ocean basins are the largest-scale depressions on the planet and anchor the topology of the ocean floor.

Drainage basins define how water moves across landscapes and support ecosystems and human use. They include all land drained by a river and its tributaries and are delineated by topography. Endorheic basins drain internally through evaporation or infiltration rather than to the ocean, creating inland lakes or salt flats. Structural and sedimentary basins form where the crust subsides and sediments accumulate, sometimes hosting groundwater, oil and gas, or shallow lakes.

Sedimentary basins are a major class of geological basins and are important in stratigraphy and resource geology. Groundwater basins contain aquifers that store freshwater and supply wells. Ocean basins, encompassing the major oceans, are vast depressions that contain seawater and influence global climate and ocean circulation.

Notable examples include the Great Basin in western North America, an inland and endorheic region; the Amazon and Congo basins, which drain large portions of South America and central Africa; and the Mississippi River Basin in the United States. The Caspian Basin underlies the Caspian Sea region and is among the largest sedimentary basins.

Basins are central to water resources, climate research, biodiversity, and energy. They evolve over geological time through tectonic activity, erosion, and sedimentation, and their boundaries influence hydrology and land use.