sinking of the Earth's surface in response to geologic or man-induced causes. When subsidence occurs in great belts, providing troughs for the accumulation of sediments, the resulting features are termed geosynclines; (geosyncline) nonlinear subsidence produces basins and irregular depressions. Subsurface solution during cave formation may lead to a series of subsidence features at the ground surface, which, collectively, are termed karst (q.v.) topography. Similar effects can be produced by mining or by the extraction of water or petroleum by means of wells. Subsidence also has been produced by the irrigation of virgin areas of alluvial deposits; initial water penetration causes reorientation of constituent particles and a consequent compaction of sediment in the wetted areas. See also geosyncline.