Karst, area of limestone or dolomite rocks with a unique set of surface and underground features resulting largely from the chemical weathering (particularly solution) of the carbonate rocks. The agent of solution in limestone and dolomite is carbonic acid (H₂CO₃), carbon dioxide dissolved in water, which is contained in rainwater or soil waters. Carbonic acid converts the calcite in the rocks to calcium bicarbonate, which is soluble in water and is readily removed from the rocks. This process of solution (carbonation) usually exploits fractures in the rock, such as joints, bedding planes, and faults, along which water can penetrate. Free movement of water along these fractures, and hence solution, is enhanced in areas of high relief where the rock near the surface is above the local water table. The type site for this landscape feature is Kras, a limestone plateau region in western Slovenia. The name “Kras” means barren, stony ground and is translated into German as karst.

The type of karst landscape in any particular area will depend on the rock type and climate, both past and present. An uneven topography is created by underground drainage and a landscape of caverns, sinks, and hollows results. The humid, temperate karst areas of north-western Europe, which include the northern Pennines of northern England, the Burren in County Clare, Ireland, and the Causses area of central France, have developed extensive underground cave systems and associated swallow holes and (particularly in areas of former glaciation) extensive areas of limestone pavements. In Croatia, where the climate is drier, very large solution hollows, known as poljes, dominate the karst terrain. In the tropics and subtropics, for example Jamaica, Cuba, Vietnam, Malaysia, and Indonesia, the landscape is known as cockpit karst in which large solution hollows, called dolines, are surrounded by low, rounded ridges. In China, Vietnam, and Puerto Rico the karst landscape is characterized by steep-sided pointed hills known as mogotes. See also Limestone Features.