A cave or cavern is a natural underground space large enough for a human to enter. Some people^[who?] suggest that the term cave should only apply to cavities that have some part that does not receive daylight; however, in popular usage, the term includes smaller spaces like sea caves A sea cave, also known as a littoral cave, is a type of cave formed primarily by the wave action of the sea. The primary process involved is erosion. Sea caves are found throughout the world, actively forming along present coastlines and as relict sea caves on former coastlines. Some of the largest wave-cut caves in the world are found on the, rock shelters Rock shelters form because a rock stratum such as sandstone that is resistant to erosion and weathering has formed a cliff or bluff, but a softer stratum, more subject to erosion and weathering, lies just below the resistant stratum, and thus undercuts the cliff, and grottos A grotto is any type of natural or artificial cave that is associated with modern, historic or prehistoric use by humans. When it is not an artificial garden feature, a grotto is often a small cave near water and often flooded or liable to flood at high tide. The picturesque Grotta Azzura at Capri and the grotto of the villa of Tiberius in the Bay.

Speleology Speleology is the scientific study of caves and other karst features, their make-up, structure, physical properties, history, life forms, and the processes by which they form (speleogenesis) and change over time (speleomorphology). The term speleology is also sometimes applied to the recreational activity of exploring caves, but this is more is the science of exploration and study of all aspects of caves and the environment which surrounds the caves. Exploring a cave for recreation or science may be called caving, potholing, or, in Canada and the United States, spelunking (see Caving Caving—also known as spelunking by some in the United States and occasionally potholing in the United Kingdom—is the recreational pastime of exploring wild cave systems. In contrast, speleology is the scientific study of caves and the cave environment).

Types and formation

The formation and development of caves is known as speleogenesis Speleogenesis is the origin and development of caves, the primary process that determines essential features of the hydrogeology of karst and guides its evolution. It often deals with the development of caves through limestone, caused by the presence of water with carbon dioxide dissolved within it, producing carbonic acid which permits the. Caves are formed by various geologic Geology is the science and study of the physical matter and energy that constitute the Earth. The field of geology encompasses the study of the composition, structure, properties, and history of the planet's physical material, the processes by which it is formed, moved, and changed, the history of life on Earth, and human interactions with the processes. These may involve a combination of chemical processes, erosion from water, tectonic forces, microorganisms, pressure, atmospheric influences, and even digging Cave Digging is the practice of enlarging undiscovered cave openings to allow entry. Cave digging usually follows a search of mountains and valleys in karst topography for new caves. Often it takes place underground in places where a large passage has clearly been backfilled with silt, or choked with boulders. Sometimes chisels or explosives can.

Most caves are formed in limestone Limestone is a sedimentary rock composed largely of the mineral calcite . Like most other sedimentary rocks, limestones are composed of grains; however, most grains in limestone grains are skeletal fragments of marine organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and by dissolution Solvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute. As ions dissolve in a solvent they spread out and become surrounded by solvent molecules.

Solutional cave

Solutional caves are the most frequently occurring caves and such caves form in rock that is soluble, such as limestone Limestone is a sedimentary rock composed largely of the mineral calcite . Like most other sedimentary rocks, limestones are composed of grains; however, most grains in limestone grains are skeletal fragments of marine organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and, but can also form in other rocks, including chalk Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under relatively deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores. It is common to find chert or flint, dolomite Dolomite is the name of a sedimentary carbonate rock and a mineral, both composed of calcium magnesium carbonate Ca , marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. It is commonly used for sculpture and as a building material, salt Salt is a mineral that is composed primarily of sodium chloride. It is essential for animal life in small quantities, but is harmful to animals and plants in excess. Salt flavor is one of the basic tastes, making salt one of the oldest, most ubiquitous food seasonings. Salting is an important method of food preservation, and gypsum Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. Rock is dissolved by natural acid in groundwater Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called that seeps through bedding-planes In geology a bed is the smallest division of a geologic formation or stratigraphic rock series marked by well-defined divisional planes separating it from layers above and below. A bed is the smallest lithostratigraphic unit, usually ranging in thickness from a centimeter to several meters and distinguishable from beds above and below it. Beds can, faults In geology, a fault or fault line is a planar fracture in rock in which the rock on one side of the fracture has moved with respect to the rock on the other side. Large faults within the Earth's crust are the result of differential or shear motion and active fault zones are the causal locations of most earthquakes. Earthquakes are caused by energy, joints etc. Over geological epochs cracks expand to become caves or cave systems.

The largest and most abundant solutional caves are located in limestone. Limestone dissolves under the action of rainwater and groundwater Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called charged with H₂CO₃ (carbonic acid Carbonic acid is the inorganic compound with the formula H2CO3 (equivalently OC2). It is also a name sometimes given to solutions of carbon dioxide in water, which contain small amounts of H2CO3. The salts of carbonic acids are called bicarbonates (or hydrogen carbonates) and carbonates. It is a weak acid. Carbonic acid is sometimes confused with) and naturally occurring organic acids An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids whose acidity is associated with their carboxyl group -COOH. Sulfonic acids, containing the group -SO2OH, are relatively stronger acids. The relative stability of the conjugate base of the acid determines its acidity. Other groups. The dissolution process produces a distinctive landform known as karst Karst topography is a landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite, characterized by sinkholes A sinkhole, also known as a sink, shake hole, swallow hole, swallet, doline or cenote, is a natural depression or hole in the earth's surface caused by karst processes - the chemical dissolution of carbonate rocks. Sinkholes may vary in size from less than 1 to 300 meters both in diameter and depth, and vary in form from soil-lined bowls to, and underground drainage. Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation. These include flowstones Flowstones are composed of sheetlike deposits of calcite formed where water flows down the walls or along the floors of a cave. They are typically found in "solution", or limestone caves, where they are the most common speleothem. However, they may form in any type of cave where water enters that has picked up dissolved minerals, stalactites A stalactite (from the Greek stalasso, , "to drip" and meaning "that which drips") is a type of speleothem (secondary mineral) that hangs from the ceiling of limestone caves. It is a type of dripstone, stalagmites A stalagmite (from the Greek stalagma , "drop" or "drip") is a type of speleothem that rises from the floor of a limestone cave due to the dripping of mineralized solutions and the deposition of calcium carbonate. The corresponding formation on the ceiling of a cave is known as a stalactite. If these formations grow together,, helictites, soda straws and columns. These secondary mineral deposits in caves are called speleothems A speleothem , commonly known as a cave formation, is a secondary mineral deposit formed in a cave. Speleothems are typically formed in limestone or dolostone solutional caves.

The portions of a solutional cave that are below the water table The water table is the level at which the groundwater pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the groundwater in a given vicinity. It usually coincides approximately with the 'phreatic surface', but can be many feet above it. As water infiltrates through pore spaces in the soil, it first or the local level of the groundwater will be flooded.^[1]

The world's most spectacularly decorated cave is generally regarded to be Lechuguilla Cave Lechuguilla Cave is, as of August 2007, the fifth longest cave (126.1 miles ) known to exist in the world, and the deepest in the continental United States (1,604 feet (489 m)), but it is most famous for its unusual geology, rare formations, and pristine condition in New Mexico The state's total area is 121,412 square miles . The eastern border of New Mexico lies along 103° W longitude with the state of Oklahoma, and three miles (5 km) west of 103.5° W longitude with Texas. On the southern border, Texas makes up the eastern two-thirds, while the Mexican states of Chihuahua and Sonora make up the western third, with. Lechuguilla and nearby Carlsbad Cavern Carlsbad Caverns National Park is a United States National Park in the Guadalupe Mountains in southeastern New Mexico. The primary attraction of the park for most visitors is the show cave, Carlsbad Caverns. Visitors to the cave can hike in on their own via the natural entrance, or take the elevator directly to the Underground Lunchroom some 750 are now believed to be examples of another type of solutional cave. They were formed by H₂S (hydrogen sulfide Hydrogen sulfide is the chemical compound with the formula H2S. It is a colorless, very poisonous, flammable gas with the characteristic foul odor of rotten eggs. It often results from the bacterial breakdown of organic matter in the absence of oxygen, such as in swamps and sewers (anaerobic digestion). It also occurs in volcanic gases, natural) gas rising from below, where reservoirs of oil give off sulfurous fumes. This gas mixes with ground water and forms H₂SO₄ (sulfuric acid Sulfuric acid is a strong mineral acid with the molecular formula H2SO4(aq). It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion. Principal uses include lead-acid). The acid then dissolves the limestone from below, rather than from above, by acidic water percolating from the surface.

Primary cave

Some caves are formed at the same time as the surrounding rock. These are sometimes called primary caves.

Lava tubes Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like channel are formed through volcanic A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, ash and gases to escape from below the surface activity and are the most common 'primary' caves. The lava Lava is molten rock expelled by a volcano during an eruption. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at temperatures from 700 °C to 1,200 °C . Up to 100,000 times as viscous as water, lava can flow great distances before flows downhill and the surface cools and solidifies. The hotter lava continues to flow under that crust, and if most of the liquid lava beneath the crust flows out, a hollow tube remains, thus forming a cavity. Examples of such caves can be found on the Canary Islands The Canary Islands (pronounced /kəˈnɛəriː ˈaɪləndz/, colloquially also known as the Canaries; Spanish: Islas Canarias, pronounced [ˈislas kaˈnarjas]; 28°06′N 15°24′W / 28.1°N 15.4°W , Hawaii The Island of Hawaiʻi, also called the Big Island or Hawaiʻi Island , is a volcanic island (the eastern-most and southern-most in the Hawaiian islands chain) in the North Pacific Ocean. With an area of 4,028 square miles (10,432 km²), it is larger than all of the other Hawaiian Islands combined and is the largest island in the United States, and many other places. Kazumura Cave near Hilo Hilo is the second-largest CDP in the State of Hawaiʻi and the largest settlement on the island of Hawaiʻi with a population of 40,759 during the 2000 census is a remarkably long and deep lava tube; it is 65.6 km long (40.8 mi).

Lava caves, include but are not limited to lava tubes. Other caves formed through volcanic activity include rift caves, lava mold caves, open vertical volcanic conduits, and inflationary caves.

Sea cave or littoral cave

Sea caves A sea cave, also known as a littoral cave, is a type of cave formed primarily by the wave action of the sea. The primary process involved is erosion. Sea caves are found throughout the world, actively forming along present coastlines and as relict sea caves on former coastlines. Some of the largest wave-cut caves in the world are found on the are found along coasts around the world. A special case is littoral caves, which are formed by wave action in zones of weakness in sea cliffs. Often these weaknesses are faults, but they may also be dykes or bedding-plane contacts. Some wave-cut caves are now above sea level because of later uplift. 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. Sea caves are generally around 5 to 50 metres (16 to 160 ft) in length but may exceed 300 metres (980 ft).

Corrasional cave or erosional cave

Corrasional or erosional caves are those that form entirely by erosion by flowing streams carrying rocks and other sediments. These can form in any type of rock, including hard rocks such as granite. Generally there must be some zone of weakness to guide the water, such as a fault or joint. A subtype of the erosional cave is the wind or aeolian cave, carved by wind-born sediments. 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.

Glacier cave

Glacier caves occur in ice and under glaciers and are formed by melting. They are also influenced by the very slow flow of the ice, which tends to close the caves again. (These are sometimes called ice caves, though this term is properly reserved for caves that contain year-round ice formations).

Fracture cave

Fracture caves are formed when layers of more soluble minerals, such as gypsum, dissolve out from between layers of less soluble rock. These rocks fracture and collapse in blocks of stone.

Talus cave

Talus caves are the openings between rocks that have fallen down into a pile, often at the bases of cliffs (called "talus").

Anchihaline cave

Anchihaline caves are caves, usually coastal, containing a mixture of freshwater and saline water (usually sea water). They occur in many parts of the world, and often contain highly specialized and endemic faunas.

Patterns

• Branchwork caves resemble surface dentritic stream patterns; they are made up of passages that join downstream as tributaries. Branchwork caves are the most common of cave patterns and are formed near sinkholes where groundwater recharge occurs. Each passage or branch is fed by a separate recharge source and converges into other higher order branches downstream.^[2]
• Angular Network caves form from intersecting fissures of carbonate rock that have had fractures widened by chemical erosion. These fractures form high, narrow, straight passages that persist in widespread closed loops.^[2]
• Anastomotic caves largely resemble surface braided streams with their passages separating and then meeting further down drainage. They usually form along one bed or structure, and only rarely cross into upper or lower beds.^[2]
• Spongework caves are formed as solution cavities are joined by mixing of chemically diverse water. The cavities form a pattern that is three-dimensional and random, resembling a sponge.^[2]
• Ramiform caves form as irregular large rooms, galleries, and passages. These randomized three-dimensional rooms form from a rising water table that erodes the carbonate rock with hydrogen-sulfide enriched water.^[2]

Geographic distribution

Caves are found throughout the world, but only a portion of them have been explored and documented by cavers. The distribution of documented cave systems is widely skewed toward countries where caving has been popular for many years (such as France, Italy, Australia, the UK, the United States, etc.). As a result, explored caves are found widely in Europe, Asia, North America, and Oceania but are sparse in South America, Africa, and Antarctica. This is a great generalization, as large expanses of North America and Asia contain no documented caves, whereas areas such as the Madagascar dry deciduous forests and parts of Brazil contain many documented caves. 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.

Record lengths, depths, pitches and volumes

• The cave system with the greatest total length of surveyed passage is Mammoth Cave (Kentucky, USA) at 591 kilometres (367 mi) in length. This record is unlikely to be surpassed in the near future, as the next most extensive known cave is Jewel Cave near Custer, South Dakota, at 225 kilometres (140 mi).^[3]

• The longest surveyed underwater cave is the Ox Bel Ha Cave System in Yucatán, Mexico at 180 km (110 mi).^[3] The record has been exchanged several times with Sistema Sac Actun, currently at 172 kilometres (107 mi).

• The deepest known cave (measured from its highest entrance to its lowest point) is Voronya Cave (Abkhazia), with a depth of 2,191 metres (7,188 ft).^[4] This was the first cave to be explored to a depth of more than 2 kilometres (1.2 mi). (The first cave to be descended below 1 kilometre (0.62 mi) was the famous Gouffre Berger in France.) The Illyuzia-Mezhonnogo-Snezhnaya cave in Abkhazia, (1,753 metres or 5,751 ft) and the Lamprechtsofen Vogelschacht Weg Schacht in Austria (1,632 metres or 5,354 ft) are the current second- and third-deepest caves. The deepest cave record has changed several times in recent years.

• The deepest vertical shaft in a cave is 603 metres (1,978 ft) in Vrtoglavica Cave in Slovenia. The second deepest is Patkov Gušt at 553 metres (1,814 ft) in the Velebit mountain, Croatia.

• The largest room ever discovered is the Sarawak chamber, in the Gunung Mulu National Park (Miri, Sarawak, Borneo, Malaysia), a sloping, boulder strewn chamber with an area of approximately 700 by 400 metres (2,297 by 1,312 ft) and a height of 80 metres (260 ft). The nearby Clearwater Cave System is believed to be the world's largest cave by volume, with a calculated volume of 30,347,540 m3.

• The largest passage ever discovered is in the Son Doong Cave in Phong Nha-Ke Bang National Park in Quang Binh Province, Vietnam. Explored by joint Vietnamese-British cave scientists of the British Cave Research Association, it is 4.6 km (2.9 mi) in length, 80 m (260 ft) high and wide over most of its length, but over 140 m (460 ft) high and wide for part of its length.^[5]

Ecology

Cave-inhabiting animals are often categorized as troglobites (cave-limited species), troglophiles (species that can live their entire lives in caves, but also occur in other environments), trogloxenes (species that use caves, but cannot complete their life cycle wholly in caves) and accidentals (animals not in one of the previous categories). Some authors use separate terminology for aquatic forms (e.g., stygobites, stygophiles, and stygoxenes).

Of these animals, the troglobites are perhaps the most unusual organisms. Troglobitic species often show a number of characteristics, termed troglomorphies, associated with their adaptation to subterranean life. These characteristics may include a loss of pigment (often resulting in a pale or white coloration), a loss of eyes (or at least of optical functionality), an elongation of appendages, and an enhancement of other senses (such as the ability to sense vibrations in water). Aquatic troglobites (or stygobites), such as the endangered Alabama cave shrimp, live in bodies of water found in caves and get nutrients from detritus washed into their caves and from the feces of bats and other cave inhabitants. Other aquatic troglobites include cave fish, the Olm, and cave salamanders such as the Texas Blind Salamander.

Cave insects such as Oligaphorura (formerly Archaphorura) schoetti are troglophiles, reaching 1.7 millimetres (0.067 in) in length. They have extensive distribution and have been studied fairly widely. Most specimens are female but a male specimen was collected from St Cuthberts Swallet in 1969.

Bats, such as the Gray bat and Mexican Free-tailed Bat, are trogloxenes and are often found in caves; they forage outside of the caves. Some species of cave crickets are classified as trogloxenes, because they roost in caves by day and forage above ground at night.

Because of the fragile nature of the cave ecosystem, and the fact that cave regions tend to be isolated from one another, caves harbor a number of endangered species, such as the Tooth cave spider, Liphistiidae Liphistius trapdoor spider, and the Gray bat.

Caves are visited by many surface-living animals, including humans. These are usually relatively short-lived incursions, due to the lack of light and sustenance.

Archaeological and cultural importance

Throughout history, primitive peoples have made use of caves for shelter, burial, or as religious sites. Since items placed in caves are protected from the climate and scavenging animals, this means caves are an archaeological treasure house for learning about these people. Cave paintings are of particular interest. One example is the Great Cave of Niah, in Malaysia, which contains evidence of human habitation dating back 40,000 years.^[6] Another, the Diepkloof Rock Shelter in South Africa contains evidence of human habitation and use of symbols dating back 60,000 years.^[7]

In the animal kingdom, caves offer shelter, including uses such as maternity dens.

In Germany some experts found signs of cannibalism in the caves at the Hönne.

Caves are also important for geological research because they can reveal details of past climatic conditions in speleothems and sedimentary rock layers.

Caves are frequently used today as sites for recreation. Caving, for example, is the popular sport of cave exploration. For the less adventurous, a number of the world's prettier and more accessible caves have been converted into show caves, where artificial lighting, floors, and other aids allow the casual visitor to experience the cave with minimal inconvenience. Caves have also been used for BASE jumping and cave diving. The book Caverns of Magic by Hal G. P. Colebatch surveys some of the instances of cave stories in literature and mythology.

Caves are also used for the preservation or aging of wine and cheese. The constant, slightly chilly temperature and high humidity that most caves possess makes them ideal for such uses.

World's longest caves

1. Mammoth Cave, Kentucky^[3]
2. Jewel Cave, South Dakota^[3]
3. Optymistychna Cave, Ukraine^[3]
4. Wind Cave, South Dakota^[3]
5. Lechuguilla Cave, New Mexico^[3]

See also

• Cave Conservancies
• Cave Research Foundation
• Cenote
• Flowstone
• List of caves
• National Speleological Society
• Pit cave
• Speleology
• Speleothem
• Subterranean lake
• Subterranean river

References

1. ^ John Burcham. "Learning about caves; how caves are formed". Journey into amazing caves. Project Underground. http://www.amazingcaves.com/learn_formed.html. Retrieved September 8, 2009.
2. ^ ^{a b c d e} Easterbrook, Don, 1999, Surface Processes and Landforms [2nd edition], New Jersey, Prentice Hall, pp. 207
3. ^ ^{a b c d e f g} World’s Longest Caves List from The National Speleological Society
4. ^ World's Deepest Caves List from The National Speleological Society
5. ^ Owen, James (2009-07-04). "World's Biggest Cave Found in Vietnam". National Geographic News. National Geographic Society. http://news.nationalgeographic.com/news/2009/07/090724-biggest-cave-vietnam.html. Retrieved 2009-07-29.
6. ^ National Geographic. James Shreeve. "The Greatest Journey". March 2006.
7. ^ Texier PJ, Porraz G, Parkington J, Rigaud JP, Poggenpoel C, Miller C, Tribolo C, Cartwright C, Coudenneau A, Klein R, Steele T, Verna C. (2010). "A Howiesons Poort tradition of engraving ostrich eggshell containers dated to 60,000 years ago at Diepkloof Rock Shelter, South Africa". Proceedings of the National Acadademy of Science U S A. 107: 6180–6185. doi:10.1073/pnas.0913047107 PMID 20194764

External links

• Australian Speleological Federation (ASF), AU
• British Caving Association (BCA), UK
• The Mulu Caves Project, A British-Malaysian collaboration to explore the caves of the Gunung Mulu National Park, Sarawak
• Classification of Caves A list of cave types with links to further information
• Journal of Cave and Karst Studies
• National Speleological Society (NSS), US
• International Union of Speleology (UIS).
• Speleological Abstract (SA/BBS) An annual review of the world's speleological literature.
• The Virtual Cave Large educational site with numerous photographs of various types of caves and cave formations and descriptions of how they form.
• cave-biology.org Cave biology (biospeleology) in India.
• Biospeleology; The Biology of Caves, Karst, and Groundwater, by Texas Natural Science Center, The University of Texas at Austin and the Missouri Department of Conservation.
• Tour Caves A Google Map of Commercial Tour Caves in the US.
• French Caves List of Commercial Caves in France.
• Caves of Croatia List and details about longest and deepest caves and pits in Croatia.
• Cathedral Cave Preserve A privately owned speleological research and educational park. US
• The latest news from the caving scene.
• World Cave Database

Categories: Caves | Coastal geography | Erosion landforms | Fluvial landforms

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