Cave
Exogene caves are smaller openings that extend a relatively short distance underground (such as rock shelters).
These may involve a combination of chemical processes, erosion by water, tectonic forces, microorganisms, pressure, and atmospheric influences.
[4] It is estimated that a cave cannot be more than 3,000 metres (9,800 ft) vertically beneath the surface due to the pressure of overlying rocks.
Such caves can be found in the Canary Islands, Jeju-do, the basaltic plains of Eastern Idaho, and in other places.
Other caves formed through volcanic activity include rifts, lava molds, open vertical conduits, inflationary, blisters, among others.
A special case is littoral caves, which are formed by wave action in zones of weakness in sea cliffs.
Elsewhere, in places such as Thailand's Phang Nga Bay, solutional caves have been flooded by the sea and are now subject to littoral erosion.
Erosional caves are those that form entirely by erosion by flowing streams carrying rocks and other sediments.
[9] Many caves formed initially by solutional processes often undergo a subsequent phase of erosional or vadose enlargement where active streams or rivers pass through them.
[11] Talus caves are formed by the openings among large boulders that have fallen down into a random heap, often at the bases of cliffs.
As the world's expanses of soluble bedrock are researched by cavers, the distribution of documented caves is likely to shift.
For example, China, despite containing around half the world's exposed limestone—more than 1,000,000 square kilometres (390,000 sq mi)—has relatively few documented caves.
For instance, in the eastern temperate United States, cave entrances are most frequently (and often densely) populated by the bulblet fern, Cystopteris bulbifera.
The cave sites of Sterkfontein, Swartkrans, Kromdraai B, Drimolen, Malapa, Cooper's D, Gladysvale, Gondolin and Makapansgat have yielded a range of early human species dating back to between three and one million years ago, including Australopithecus africanus, Australopithecus sediba and Paranthropus robustus.
The first early hominid ever found in Africa, the Taung Child in 1924, was also thought for many years to come from a cave, where it had been deposited after being predated on by an eagle.
This may have allowed rapid expansion of humans out of Africa and colonization of areas of the world such as Australia by 60–50,000 years ago.
Archaeologists have uncovered relationships between paintings of dots and lines, in specific areas of resonance, within the caves of Spain and France, as well as instruments depicting paleolithic motifs,[31] indicators of musical events and rituals.
Clusters of paintings were often found in areas with notable acoustics, sometimes even replicating the sounds of the animals depicted on the walls.
The human voice was also theorized to be used as an echolocation device to navigate darker areas of the caves where torches were less useful.
[34] During the 20th century musicians began to explore the possibility of using caves as locations as clubs and concert halls, including the likes of Dinah Shore, Roy Acuff, and Benny Goodman.
[citation needed] Unlike today, these early performances were typically held in the mouths of the caves, as the lack of technology made depths of the interior inaccessible with musical equipment.
[35] In Luray Caverns, Virginia, a functioning organ has been developed that generates sound by mallets striking stalactites, each with a different pitch.
