Underground Cave Definition
The caves continue to be used by modern discoverers of acoustics. Today, Cumberland Caverns offers one of the best examples of modern musical use of caves. Caves are used not only for reverberation, but also for the damping properties of their abnormal faces. Irregularities in the walls of Cumberland`s caves dissipate sounds bouncing off the walls, adding quality to the space and recording almost like a studio.  The caves are significant both in their echo and in their silence. During the 20th century, musicians began to explore the possibility of using the caves as venues as clubs and concert halls, including Dinah Shore, Roy Acuff and Benny Goodman. [ref. Unlike today, these first performances usually took place in the mouths of caves, as the lack of technology made the depths of the interior inaccessible with musical devices.  In one case, a stalagmite suspended from the ceiling of a cave was transformed into a functional organ. Unlike an organ, this instrument reacts percussively like a piano, using chopsticks to beat stalagmites to create different pitches.  These large underground chambers can take hundreds of thousands of years to form. Lava caves include, but are not limited to, lava tubes.
Other caves formed by volcanic activity include fissures, lava forms, open vertical pipes, inflationary bubbles.  Anchialine caves are caves, mainly near the coast, that contain a mixture of fresh and salt water (usually seawater). They are found in many parts of the world and often contain highly specialized and endemic fauna.  The importance of sound in caves predates a modern understanding of acoustics. Archaeologists have discovered relationships between the paintings of dots and lines in specific resonance zones in caves in Spain and France, as well as instruments with Paleolithic motifs, indicating musical events and rituals. Clusters of paintings have often been found in areas with remarkable acoustics, sometimes even the sounds of animals depicted on the walls. The human voice was also theorized to be used as an echolocation device to navigate darker areas of caves where torches were less useful.  Red ochre tips are often found in rooms with the highest resonance, where the production of paints was too difficult. Here, singing is considered the most effective way to explore the caves.  Not all caves are part of karst landscapes.
A considerable number of relatively small caves, called volcanic caves, are formed in lava and by the mechanical movement of bedrock. Other caves are formed in glaciers by melting ice. Still others are caused by the erosive effect of water and wind or by the debris of erosive processes; These are sea caves, aeolian caves, rock shelters and slope caves. Bats, such as the gray bat and Mexican free-tailed bat, are trogloxenes and are often found in caves; They look for food outside the caves. Some types of cave crickets are classified as wrens because they sleep in caves during the day and feed above ground at night. This is a rough generalization, as large parts of North America and Asia do not contain documented caves, while areas such as the dry deciduous forests of Madagascar and parts of Brazil contain many documented caves. As cavers explore areas of the world`s soluble bedrock, the distribution of documented caves is likely to change. For example, although China contains about half of the world`s exposed limestone — more than 1,000,000 square kilometers (390,000 square miles) — has relatively few documented caves. But some distance from the cave, he dropped his pipe, and when he bent down to pick it up, he took a small satin shoe instead. Among these animals, troglobites are perhaps the most unusual organisms. Troglobite species often exhibit a number of characteristics called troglomorphs, associated with their adaptation to underground life.
These properties can include loss of pigment (often with a pale or white tint), loss of eyes (or at least optical functionality), lengthening of appendages, and enhancement of other senses (such as the ability to detect vibrations in water).