cave, a cavity in the earth's surface usually large enough for a person to enter. Caves may be formed by the chemical and mechanical action of a stream upon soluble or soft rock, of rainwater seeping through soluble rock to the groundwater level, or of waves dashed against a rocky shore. Volcanic action (accompanied by the formation of gas pockets in lava or the melting of ice under lava) and earthquakes or other earth movements are also sources of cave formation. Limestone regions almost invariably have caves; some of these are notable for their stalactite and stalagmite formations or for their magnitude and beauty.
The preserved remains of prehistoric humans and animals and indications of early human culture have been discovered in some caves. Caves have served as burial grounds and shelter since prehistoric times. One such cave is Alabama's Russell Cave, where human evidence dates back 9,000 years. Speleology, the scientific study of caves and their plant and animal life, contributes to knowledge of biological adaptation and evolution. Some cave animals lack sight, and both plants and animals living where light is excluded show loss of pigment. Deep cave ecosystems, lacking the sunlight necessary for photosynthesis, depend on bacteria that use chemosynthesis to create energy.
Among famous caves in the United States are Carlsbad Caverns National Park (N.Mex.), Mammoth Cave National Park (Ky.), Wind Cave National Park (Black Hills, S.Dak.), Luray Caverns (Va.), and Wyandotte Cave (Ind.). In Europe there are celebrated caves in Belgium, Dalmatia, Gibraltar, Capri, Sicily, Postojna, and England (Kent's Cavern and Kirkdale). The caves of the Pyrenees and the Dordogne are famed for their prehistoric paintings (see Paleolithic art), and those of Ajanta, India, and Dunhuang, China, for their Buddhist frescoes. Among the deepest known caves are Krubera in the nation of Georgia, which extends more than 6,500 ft (2,000 m) below the surface, and Lamprechtsofen in Austria.
See C. E. Mohr and T. L. Poulson, The Life of the Cave (1966); D. R. McClurg, The Amateur's Guide to Caves and Caving (1973).