Alternate meanings: Cave (disambiguation)
The outside world viewed from a cave
A cave is a natural underground void.
Cave types and formation
Caves are formed by geologic processes. These may involve a combination of chemical processes, tectonic forces and atmospheric influences.
Some caves are formed at the same time as the surrounding rock. These are called primary caves.
Lava tubes are formed through volcanic activity. They are the most common primary caves. Lava flows downhill and the surface cools down and becomes hard. The lava now flows inside its crust, until the eruption ends. The liquid lava inside the crust flows out and leaves a hollow tube. The most important lava tubes are found on Hawaii (Big Island). Kazumura Cave near Hilo is the longest and deepest lava tube of the world and also the eighth longest cave of the United States.
Blister caves are also formed through volcanic activity.
Secondary caves are formed inside the rock after the rock itself has formed by processes which removes material such as solution and erosion.
Erosion is a mechanical form of weathering which is caused by the abrasive action of wind or water.
- Sea caves are very common at all coasts of the world, but as they are restricted to the zone where waves work on the rocks of the coast they are generally rather small.
- Ice caves occur in and under glaciers, formed by melting. They are also influenced by the very slow flow of the ice which tends to close the caves again.
Solutional caves may form anywhere with rock which is soluble, and are most prevalent in limestone, but can also form in other material, including chalk, dolomite, marble, loess, ice, granite, salt, lava, sandstone, and gypsum. The most common process of cave formation is karstification, which is the solution of rocks by rain water.
Cave formation in limestone occurs because limestone dissolves under the action of rainwater and groundwater charged with CO2 (carbonic acid) and naturally occurring organic acids. The dissolution process produces a distinctive landform known as karst and characterized by sinkholes, sinking streams, and underground drainage.
Limestone solution is the single most important process forming caves and the origin of the great majority of all caves on Earth. The reason for this abundance is the facts that limestone is so common and the slowness of the solution process. If it was faster, the lifespan of limestone caves would be much shorter and their number much lower.
Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation, including the most common and well-known stalactites and stalagmites. These secondary mineral deposits in caves are called speleothems. The world's most spectacularly decorated cave is generally regarded to be Lechuguilla Cave (New Mexico, USA).
Lechuguilla and nearby Carlsbad Caverns are now believed to be examples of another type of solutional cave. They were formed by acid rising from below, where reservoirs of oil give off sulfurous fumes, rather than by acidic water percolating from the surface.
Caves are sparse in South America, Antarctica, but are found widely in Europe, Asia, and United States, France, Italy, the UK etc.). It is likely that many more systems remain to be discovered, especially in China, which, despite containing around half the world's exposed limestone - more than 1,000,000 km2 - has hardly been explored underground.
Cave inhabiting animals can be categorized as troglobites (cave limited-species), troglophiles (species which can live their entire lives in caves, but also occur in other environments), trogloxenes (species which utilize caves, but must leave the caves to complete their life cicle) and accidentals. Some authors use separate terminology for aquatic forms (i.e., stygobites, stygophiles, stygoxenes).
Of these animals, the troglobites are among the most fascinating of organisms. Troglobitic species often show a suite of characters, termed troglomorphies, associated with their adaptation to subterranean life. Among these characters are a loss of pigment (often resulting in a pale or white coloration), loss of eyes (or at least of optical functionality), elongation of appendages, and an enhancement of other senses (such as ability to sense vibrations in water). Aquatic troglobites (or stygobites), such as the endangered Alabama cave shrimp, live in bodies of water found in the caves and are fed by detritus washed into the caves, and be the feces of bats and other cave inhabitants.
Bats, like the Gray bat and Mexican Free-tailed Bat, are trogloxenes, and are commonly found in caves, but forage outside of the caves. Some species of cave crickets are classified as trogloxenes, as they roost in caves by day and forage above ground at night.
Caves are visited by many surface-loving animals, including humans. These are usually relatively short-lived incursions, due to the lack of light and sustenance.
Caves can reach considerable dimensions. Of the cave systems that have been discovered so far, the most extensive is Mammoth Cave (Kentucky, USA) with 560km of passages.
The deepest known cave (2004) is the Voronya Cave (Abkhazia, Georgia), with a depth of 1,830m. The Lamprechtsofen Vogelschacht Weg Schacht in Austria (1632m) and Gouffre Mirolda - Lucien Bouclier cave in France (1626m) also deserve mention.
The deepest individual vertical drop within a cave, is 516m in the Lukina jama, which is in the Velebit mountain, in Croatia. The largest individual cavern found is Sarawak Chamber, in the Gunung Mulu National Park (http://www.forestry.sarawak.gov.my/forweb/np/np/mulu.htm) (Sarawak, Borneo, Malaysia), a sloping, boulder strewn chamber with an area of approximately 600m by 400m and a height of 80m. Sarawak often also claims Deer Cave (Mulu) and Gua Niah in the Niah National Park (http://www.forestry.sarawak.gov.my/forweb/np/np/niah.htm) to be of record_breaking dimensions, but there must be good alternative candidates in China and Papua New Guinea.
Archaeological and social importance
Caves are also an archaeological treasure house as primitive people used caves as their shelter and sometimes burial place. Items placed in caves are protected from climate and scavanging animals. One example is the Great Cave of Niah, which is one of the largest limestone caves in the world as well as an archaeological treasure house. It was here that archaeologists discovered the evidence of Man’s existence dating back 40,000 years.
Caving is the sport of cave exploration.
- About Gua Niah (http://www.thingsasian.com/goto_article/article.1462.html)
- British Caving Association (BCA) (http://www.british-caving.org.uk/), UK
- Classification of Caves (http://www.showcaves.com/english/explain/Speleology/Classification.html) Very detailed list of cave types with links to further information
- National Speleological Society (NSS) (http://www.caves.org/), US
- NSS Geo2 Committee on Long and Deep Caves (http://www.pipeline.com/~caverbob/) A website with numerous pages on cave world records, e.g., the longest and deepest caves; compiled by Bob Gulden
- Ogof Ffynnon Ddu (http://ogof.net/) A virtual tour of Ogof Ffynnon Ddu, the deepest cave in the UK
- The Virtual Cave (http://www.goodearthgraphics.com/virtcave.html) A site with exceptional photography by Dave Bunnell, the editor of the NSS News. Make a virtual caving trip!