Cave

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Lechuguilla Cave, New Mexico, United States Lechuguilla Cave Pearlsian Gulf.jpg
Lechuguilla Cave, New Mexico, United States

A cave or cavern is a natural void in the ground, [1] [2] specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word cave can refer to smaller openings such as sea caves, rock shelters, and grottos, that extend a relatively short distance into the rock and they are called exogene caves. Caves which extend further underground than the opening is wide are called endogene caves. [3] [4]

Contents

Speleology is the science of exploration and study of all aspects of caves and the cave environment. Visiting or exploring caves for recreation may be called caving, potholing, or spelunking.

Formation types

The formation and development of caves is known as speleogenesis ; it can occur over the course of millions of years. [5] Caves can range widely in size, and are formed by various geological processes. These may involve a combination of chemical processes, erosion by water, tectonic forces, microorganisms, pressure, and atmospheric influences. Isotopic dating techniques can be applied to cave sediments, to determine the timescale of the geological events which formed and shaped present-day caves. [5]

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. This does not, however, impose a maximum depth for a cave which is measured from its highest entrance to its lowest point, as the amount of rock above the lowest point is dependent on the topography of the landscape above it. For karst caves the maximum depth is determined on the basis of the lower limit of karst forming processes, coinciding with the base of the soluble carbonate rocks. [6] Most caves are formed in limestone by dissolution. [7]

Caves can be classified in various other ways as well, including a contrast between active and relict: active caves have water flowing through them; relict caves do not, though water may be retained in them. Types of active caves include inflow caves ("into which a stream sinks"), outflow caves ("from which a stream emerges"), and through caves ("traversed by a stream"). [8]

Speleothems in Hall of the Mountain King of Ogof Craig a Ffynnon, a solutional cave in South Wales. HallOfTheMountainKings.jpg
Speleothems in Hall of the Mountain King of Ogof Craig a Ffynnon, a solutional cave in South Wales.

Solutional

Solutional caves or karst caves are the most frequently occurring caves. Such caves form in rock that is soluble; most occur in limestone, but they can also form in other rocks including chalk, dolomite, marble, salt, and gypsum. Except for salt caves, solutional caves result when rock is dissolved by natural acid in groundwater that seeps through bedding planes, faults, joints, and comparable features. Over time cracks enlarge to become caves and cave systems.

The largest and most abundant solutional caves are located in limestone. Limestone dissolves under the action of rainwater and groundwater charged with H2CO3 (carbonic acid) and naturally occurring organic acids. The dissolution process produces a distinctive landform known as karst , characterized by sinkholes and underground drainage. Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation. These include flowstones, stalactites, stalagmites, helictites, soda straws and columns. These secondary mineral deposits in caves are called speleothems .

The portions of a solutional cave that are below the water table or the local level of the groundwater will be flooded. [9]

Lechuguilla Cave in New Mexico and nearby Carlsbad Cavern are now believed to be examples of another type of solutional cave. They were formed by H2S (hydrogen sulfide) gas rising from below, where reservoirs of oil give off sulfurous fumes. This gas mixes with groundwater and forms H2SO4 (sulfuric acid). The acid then dissolves the limestone from below, rather than from above, by acidic water percolating from the surface.

Primary

Exploring a lava tube in Hawaii. Hawaiian lava tube.jpg
Exploring a lava tube in Hawaii.

Caves formed at the same time as the surrounding rock are called primary caves.

Lava tubes are formed through volcanic activity and are the most common primary caves. As lava flows downhill, its surface cools and solidifies. Hot liquid lava continues to flow under that crust, and if most of it flows out, a hollow tube remains. Such caves can be found in the Canary Islands, Jeju-do, the basaltic plains of Eastern Idaho, and in other places. Kazumura Cave near Hilo, Hawaii 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 rifts, lava molds, open vertical conduits, inflationary, blisters, among others. [10]

Sea or littoral

Painted Cave, a large sea cave, Santa Cruz Island, California Painted cave.jpg
Painted Cave, a large sea cave, Santa Cruz Island, California

Sea caves 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 164 ft) in length, but may exceed 300 metres (980 ft).

Corrasional or erosional

Salt cave in Mount Sodom Sodom Salt Cave 031712.JPG
Salt cave in Mount Sodom

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. [10] 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

Glacier cave in Big Four Glacier, Big Four Mountain, Washington, c. 1920 Big Four Glacier Ice cave.jpg
Glacier cave in Big Four Glacier, Big Four Mountain, Washington, c. 1920

Glacier caves are formed by melting ice and flowing water within and under glaciers. The cavities are influenced by the very slow flow of the ice, which tends to collapse the caves again. Glacier caves are sometimes misidentified as "ice caves", though this latter term is properly reserved for bedrock caves that contain year-round ice formations.

Fracture

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. [11]

Talus

Talus caves are formed by the openings among large boulders that have fallen down into a random heap, often at the bases of cliffs. [12] These unstable deposits are called talus or scree, and may be subject to frequent rockfalls and landslides.

Anchialine

Anchialine 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 fauna. [13]

Physical patterns

Geographic distribution

Domica Cave in Slovak Karst (Slovakia) Domica Cave 22.jpg
Domica Cave in Slovak Karst (Slovakia)
An entrance of the Torhola Cave in Lohja (Finland) Torhola cave entrance Aug2008.jpg
An entrance of the Torhola Cave in Lohja (Finland)

Caves are found throughout the world, although the distribution of documented cave system is heavily skewed towards those 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 rough 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.

Records and superlatives

Five longest surveyed

  1. Mammoth Cave, Kentucky, US [15]
  2. Sistema Ox Bel Ha, Mexico [15]
  3. Sistema Sac Actun/Sistema Dos Ojos, Mexico [15]
  4. Jewel Cave, South Dakota, US [15]
  5. Shuanghedong Cave Network, China [15]

Ecology

Townsend's big-eared bats in a cave in California Townsends in music hall.jpg
Townsend's big-eared bats in a cave in California
Olms in a Slovenian cave Proteus anguinus Postojnska Jama Slovenija.jpg
Olms in a Slovenian cave

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 fully in caves) and accidentals (animals not in one of the previous categories). Some authors use separate terminology for aquatic forms (for example, stygobites, stygophiles, and stygoxenes).

Of these animals, the troglobites are perhaps the most unusual organisms. Troglobitic species often show a number of characteristics, termed troglomorphic, 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, and cave salamanders such as the olm and 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 fragility of cave ecosystems, 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, 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.

Cave entrances often have typical florae. For instance, in the eastern temperate United States, cave entrances are most frequently (and often densely) populated by the bulblet fern, Cystopteris bulbifera .

Archaeological and cultural importance

Taino petroglyphs in a cave in Puerto Rico Taino petroglyph in cave.jpg
Taíno petroglyphs in a cave in Puerto Rico

Throughout history, primitive peoples have made use of caves. The earliest human fossils found in caves come from a series of caves near Krugersdorp and Mokopane in South Africa. 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 . However, it is not generally thought that these early humans were living in the caves, but that they were brought into the caves by carnivores that had killed them.

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. However, this is now debated (Hopley et al., 2013; Am. J. Phys. Anthrop.). Caves do form in the dolomite of the Ghaap Plateau, including the Early, Middle and Later Stone Age site of Wonderwerk Cave; however, the caves that form along the escarpment's edge, like that hypothesised for the Taung Child, are formed within a secondary limestone deposit called tufa. There is numerous evidence for other early human species inhabiting caves from at least one million years ago in different parts of the world, including Homo erectus in China at Zhoukoudian, Homo rhodesiensis in South Africa at the Cave of Hearths (Makapansgat), Homo neanderthalensis and Homo heidelbergensis in Europe at Archaeological Site of Atapuerca, Homo floresiensis in Indonesia, and the Denisovans in southern Siberia.

In southern Africa, early modern humans regularly used sea caves as shelter starting about 180,000 years ago when they learned to exploit the sea for the first time. [23] The oldest known site is PP13B at Pinnacle Point. 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. Throughout southern Africa, Australia, and Europe, early modern humans used caves and rock shelters as sites for rock art, such as those at Giant's Castle. Caves such as the yaodong in China were used for shelter; other caves were used for burials (such as rock-cut tombs), or as religious sites (such as Buddhist caves). Among the known sacred caves are China's Cave of a Thousand Buddhas [24] and the sacred caves of Crete.

Caves and acoustics

The importance of sound in caves predates a modern understanding of acoustics. 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, [25] 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. [26] Dots of red ochre are often found in spaces with the highest resonance, where the production of paintings was too difficult. [27]

Caves continue to provide usage for modern-day explorers of acoustics. Today Cumberland Caverns provides one of the best examples for modern musical usages of caves. Not only are the caves utilized for reverberation, but for the dampening qualities of their abnormal faces as well. The irregularities in the walls of the Cumberland Caverns diffuse sounds bouncing off the walls and give the space an almost recording studio-like quality. [28] 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. [29] In Luray Caverns, Virginia, a functioning organ has been developed that generates sound by mallets striking stalactites, each with a different pitch. [30]

See also

Related Research Articles

<span class="mw-page-title-main">Karst</span> Topography from dissolved soluble rocks

Karst is a topography formed from the dissolution of soluble carbonate rocks such as limestone, dolomite, and gypsum. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. More weathering-resistant rocks, such as quartzite, can also occur, given the right conditions.

<span class="mw-page-title-main">Stalactite</span> Elongated mineral formation hanging down from a cave ceiling

A stalactite is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble and that can be deposited as a colloid, or is in suspension, or is capable of being melted, may form a stalactite. Stalactites may be composed of lava, minerals, mud, peat, pitch, sand, sinter, and amberat. A stalactite is not necessarily a speleothem, though speleothems are the most common form of stalactite because of the abundance of limestone caves.

<span class="mw-page-title-main">Speleology</span> Science of cave and karst systems

Speleology is the scientific study of caves and other karst features, as well as their composition, structure, physical properties, history, ecology, 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 properly known as caving, potholing, or spelunking. Speleology and caving are often connected, as the physical skills required for in situ study are the same.

<span class="mw-page-title-main">Sinkhole</span> Geologically-formed topological depression

A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water enters into underground passages known as ponor, swallow hole or swallet. A cenote is a type of sinkhole that exposes groundwater underneath. Sink and stream sink are more general terms for sites that drain surface water, possibly by infiltration into sediment or crumbled rock.

<span class="mw-page-title-main">Stalagmite</span> Elongate mineral formation found on a cave floor

A stalagmite is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites are typically composed of calcium carbonate, but may consist of lava, mud, peat, pitch, sand, sinter, and amberat.

<span class="mw-page-title-main">Inner Space Cavern</span> Cave in Georgetown, Texas, United States

Inner Space Cavern is a karst cave located in Georgetown, Texas. The cavern was formed by water passing through Edwards limestone. The cavern is estimated to be around 20-25 million years old but were only open to the surface since the late Pleistocene period 14,000–45,000 years ago.

Krubera Cave is the second-deepest-known cave on Earth, after the Veryovkina Cave. It is located in the Arabika Massif of the Gagra Range of the Western Caucasus, in the Gagra District of Abkhazia, an occupied region of Georgia.

<span class="mw-page-title-main">Cenote</span> Natural pit or sinkhole that exposes groundwater underneath

A cenote is a natural pit, or sinkhole, resulting when a collapse of limestone bedrock exposes groundwater. The term originated on the Yucatán Peninsula of Mexico, where the ancient Maya commonly used cenotes for water supplies, and occasionally for sacrificial offerings. The name derives from a word used by the lowland Yucatec Maya—tsʼonoʼot—to refer to any location with accessible groundwater.

Phreatic is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption.

<span class="mw-page-title-main">Troglofauna</span> Species that lives in caves and similar subterranean environments

Troglofauna are small cave-dwelling animals that have adapted to their dark surroundings. Troglofauna and stygofauna are the two types of subterranean fauna. Both are associated with subterranean environments – troglofauna are associated with caves and spaces above the water table and stygofauna with water. Troglofaunal species include spiders, insects, myriapods and others. Some troglofauna live permanently underground and cannot survive outside the cave environment. Troglofauna adaptations and characteristics include a heightened sense of hearing, touch and smell. Loss of under-used senses is apparent in the lack of pigmentation as well as eyesight in most troglofauna. Troglofauna insects may exhibit a lack of wings and longer appendages.

<span class="mw-page-title-main">Sistema Dos Ojos</span> Flooded cave system at the coast of the Yucatan Peninsula, Mexico

Dos Ojos is part of a flooded cave system located north of Tulum, on the Caribbean coast of the Yucatán Peninsula, in the state of Quintana Roo, Mexico. The exploration of Dos Ojos began in 1987 and still continues. The surveyed extent of the cave system is 82 kilometers (51 mi) and there are 28 known sinkhole entrances, which are locally called cenotes. In January 2018, a connection was found between Sistema Dos Ojos and Sistema Sac Actun. The smaller Dos Ojos became a part of Sac Actun, making the Sistema Sac Actun the longest known underwater cave system in the world.

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 dissociation of the calcium carbonate in the limestone.

<span class="mw-page-title-main">Caving in New Zealand</span>

Caving in New Zealand is an established hobby as well as being a part of commercial tourism.

<span class="mw-page-title-main">Underground lake</span> Lake under the Earths surface

An underground lake or subterranean lake is a lake underneath the surface of the Earth. Most naturally occurring underground lakes are found in areas of karst topography, where limestone or other soluble rock has been weathered away, leaving a cave where water can flow and accumulate.

<span class="mw-page-title-main">Solutional cave</span> Type of cave

A solutional cave, solution cave, or karst cave is a cave usually formed in the soluble rock limestone. It is the most frequently occurring type of cave. It can also form in other rocks, including chalk, dolomite, marble, salt beds, and gypsum.

<span class="mw-page-title-main">Subterranean fauna</span>

Subterranean fauna refers to animal species that are adapted to live in an underground environment. Troglofauna and stygofauna are the two types of subterranean fauna. Both are associated with hypogeal habitats – troglofauna is associated with terrestrial subterranean environment, and stygofauna with all kind of subterranean waters.

There are a number of terms that are used in connection with caves, caving and speleology. The following is an incomplete list.

<span class="mw-page-title-main">Sistema Huautla</span> Cave system in the southern Mexican state of Oaxaca

Sistema Huautla is a cave system in the Sierra Mazateca mountains of the southern Mexican state of Oaxaca. As of April 2021 it was the deepest cave system in the Western Hemisphere, 1,560 metres (5,120 ft) from top to bottom, with over 55 miles of mapped passageways.

<span class="mw-page-title-main">Fissure</span> Long, narrow crack opening on a planetary surface

A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word fissura, which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes.

<span class="mw-page-title-main">Cave diving regions of the world</span> Regions of the world where known cave diving venues exist

Cave diving is underwater diving in water-filled caves. The equipment used varies depending on the circumstances, and ranges from breath hold to surface supplied, but almost all cave diving is done using scuba equipment, often in specialised configurations with redundancies such as sidemount or backmounted twinset. Recreational cave diving is generally considered to be a type of technical diving due to the lack of a free surface during large parts of the dive, and often involves planned decompression stops. A distinction is made by recreational diver training agencies between cave diving and cavern diving, where cavern diving is deemed to be diving in those parts of a cave where the exit to open water can be seen by natural light. An arbitrary distance limit to the open water surface may also be specified. Despite the risks, water-filled caves attract scuba divers, cavers, and speleologists due to their often unexplored nature, and present divers with a technical diving challenge.

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