ETYM French cave, Latin cavus hollow, whence cavea cavity. Related to Cage.
An underground enclosure with access from the surface of the ground or from the sea.
Roofed-over cavity in the Earth’s crust usually produced by the action of underground water or by waves on a seacoast. Caves of the former type commonly occur in areas underlain by limestone, such as Kentucky and many Balkan regions, where the rocks are soluble in water. A pothole is a vertical hole in rock caused by water descending a crack; it is thus open to the sky.
Cave animals often show loss of pigmentation or sight, and under isolation, specialized species may develop. The scientific study of caves is called speleology. During the ice age, humans began living in caves leaving many layers of debris that archeologists have unearthed and dated in the Old World and the New. They also left cave art, paintings of extinct animals often with hunters on their trail. See also Altamira. Celebrated caves include the Mammoth Cave in Kentucky, 6.4 km/4 mi long and 38 m/125 ft high; the Caverns of Adelsberg (Postumia) near Trieste, Italy, which extend for many miles; Carlsbad Caverns, New Mexico, the largest in the US; the Cheddar Caves, England; Fingal’s Cave, Scotland, which has a range of basalt columns; and Peak Cavern, England.
Most inland caves are found in karst regions, because limestone is soluble when exposed to ground water. As the water makes its way along the main joints, fissures, and bedding planes, they are constantly enlarged into potential cave passages, which ultimately join to form a complex network. Limestone caves are usually found just below the watertable, wherever limestone outcrops on the surface. The biggest cave in the world is over 70 km long, at Holloch, Switzerland.
Coastal caves are formed where relatively soft rock or rock containing definite lines of weakness, like basalt at tide level, is exposed to severe wave action. The gouging process along the weaker band is exacerbated by subsidence, and the hollow in the cliff face grows still larger because of air compression in the chamber. Where the roof of a cave has fallen in, the vent up to the land surface is called a blowhole. If this grows, finally destroying the cave form, the outlying truncated “portals” of the cave are known as stacks or columns. The Old Man of Hoy (137 m high), in the Orkney Islands, north of Scotland, is a fine example of a stack.