III.

Cave Detection

The presence of caves in limestone regions may be detected by means of clues provided by the topography of the land. In such a region the roofs of large caverns may collapse and leave depressions and troughs at the surface of the ground. Natural bridges, another phenomenon of cave regions, may remain after the collapse of a tunnel bearing an underground stream. The Natural Bridge in Virginia is a classic example of this type of formation.

In the phenomenon known as disappearing streams, which is a common feature in areas underlain by caves, whole watercourses may vanish down sinks, or sinkholes, leading to the underground caverns. The sinks are indicative of caves below. Because of the capture of the surface waters by the subterranean drainage system, some cave regions have a rather dry, dusty, poorly vegetated appearance. Such regions are said to have a karst topography, a name derived from a famous cave region along the Adriatic Sea in Italy and Slovenia. Steep-walled sinks called cenotes, found in Yucatán, Mexico, constituted a chief source of water for the Maya peoples.

Caves are sometimes discovered underwater. In such cases, the caves were once dry but became completely flooded because of changes in water tables or in sea level. Mining operations sometimes encounter caves deep below ground.