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Cave

Cave

A cave is a naturally occurring hollow area inside the earth. Most caves are formed by some type of erosional process. The most notable exception is hollow lava tubes such as those found in the Hawaiian Islands. The formation of caves depends upon geologic, topographic, and hydrologic factors. These factors determine where and how caves develop, as well as their structure and shape. The study of caves is called speleology. Some caves may be small hillside openings, while others consist of large chambers and interconnecting tunnels and mazes. Openings to the surface may be large gaping holes or small crevices.

Caves hosted in rocks other than limestone are usually formed by water erosional processes. For example, rivers running through canyons with steep walls erode the rock at points where the current is strong. Such caves usually have large openings and are not too deep. Caves of this type can be found in the southwestern United States and were at one time inhabited by prehistoric American Indians known as Cliff Dwellers. Sea caves are formed by waves continually crashing against cliffs or steep walls. Often these caves can only be entered at low tide. Ice caves are also formed in glaciers and icebergs by meltwater that drains down crevices in the ice.

Lava caves, which are often several miles long, form when the exterior of a lava flow hardens and cools to form a roof, but lava below the surface flows out, leaving a hollow tube. Wind or aeolian caves usually form in sandstone cliffs as wind-blown sand abrades the cliff face. They are found in desert areas, and occur in a bottleneck shape with the entrance much smaller than the chamber. Talus caves are formed by boulders that have piled up on mountain slopes. The most common, largest, and spectacular caves are solution caves.

Solution caves form by chemical weathering of the surrounding bedrock as groundwater moves along fractures in the rock. These caves produce a particular type of terrain called karst. Karst terrain primarily forms in bedrock of calcium carbonate, or limestone, but can develop in any soluble sedimentary rock such as dolomite , rock gypsum , or rock salt. The host rock extends from near the earth's surface to below the water table . Several distinctive karst features make this terrain easy to identify. The most common are sinkholes , circular depressions where the underlying rock has been dissolved away. Disappearing streams and natural bridges are also common clues. Entrances to solution caves are not always obvious, and their discovery is sometimes quite by accident.

Formation of karst involves the chemical interaction of air, soil , water, and rock. As water flows over and drains into the earth's surface, it mixes with carbon dioxide from the air and soil to form carbonic acid (H2CO3). The groundwater becomes acidic and dissolves the calcium carbonate in the bedrock, and seeps or percolates through naturally occurring fractures in the rock. With continual water drainage, the fractures become established passageways. The passageways eventually enlarge and often connect, creating an underground drainage system. Over thousands, perhaps millions of years, these passages evolve into the caves seen today.

During heavy rain or flooding in a well-established karst terrain, very little water flows over the surface in stream channels. Most water drains into the ground through enlarged fractures and sinkholes. This underground drainage system sometimes carries large amounts of water, sand, and mud through the passageways and further erodes the bedrock. Sometimes ceilings fall and passageways collapse, creating new spaces and drainage routes.

Not all solution caves form due to dissolution by carbonic acid. Some caves form in areas where hydrogen sulfide gas is released from the earth's crust or from decaying organic material. Sulfuric acid forms when the hydrogen sulfide comes in contact with water. It chemically weathers the limestone, similar to acid rain .

The deep cave environment is often completely dark, has a stable atmosphere, and the temperature is rather constant, varying only a few degrees throughout the year. The humidity in limestone caves is usually near 100%. Many caves contain unique life forms, underground streams and lakes , and have unusual mineral formations called speleothems.

When groundwater seeps through the bedrock and reaches a chamber or tunnel, it meets a different atmosphere. Whatever mineral is in solution reacts with the surrounding atmosphere, precipitates out, and is deposited in the form of a crystal on the cave ceiling or walls. Calcite, and to a lesser degree, aragonite, are the most common minerals of speleothems. The amount of mineral that precipitates out depends upon how much gas was dissolved in the water. For example, water that must pass through a thick layer of soil becomes more saturated with carbon dioxide than water that passes through a thin layer. This charges the water with more carbonic acid and causes it to dissolve more limestone from the bedrock. Later, it will form a thicker mineral deposit in the cave interior as a result.

Water that makes its way to a cave ceiling hangs as a drop. When the drop of water gives off carbon dioxide and reaches chemical equilibrium with the cave atmosphere, calcite starts to precipitate out. Calcite deposited on the walls or floors in layers is called flowstone.

Sometimes water runs down the slope of a wall, and as the calcite is deposited, a low ridge is formed. Subsequent drops of water follow the ridge, adding more calcite. Constant buildup of calcite in this fashion results in the formation of a large sheet-like formation, called a curtain, hanging from the ceiling. Curtain formations often have waves and folds in them and have streaks of various shades of off-white and browns. The streakiness results from variations in the mineral and iron content of the precipitating solution.

Often, a hanging drop falls directly to the ground. Some calcite is deposited on the ceiling before the drop falls. When the drop falls, another takes its place. As with a curtain formation, subsequent drops will follow a raised surface and a buildup of calcite in the form of a hanging drop develops. This process results in icicle-shaped speleothems called stalactites. The water that falls to the floor builds up in the same fashion, resembling an upside down icicle called a stalagmite.

Of course, there are variations in the shape of speleothems depending on how much water drips from the ceiling, the temperature of the cave interior, rates and directions of air flow in the cave, and how much dissolved limestone the water contains. Speleothems occur as tiered formations, cylinders, cones, some join together, and occasionally stalactites and stalagmites meet and form a tower. Sometimes, when a stalactite is forming, the calcite is initially deposited in a round ring. As calcite builds up on the rim and water drips through the center, a hollow tube called a straw develops. Straws are often transparent or opaque and their diameter may be only that of a drop of water.

Stalagmites and stalactites occur in most solution caves and usually, wherever a stalactite forms, there is also a stalagmite. In caves where there is a great deal of seepage, water may drip continuously. Speleothems formed under a steady drip of water are typically smooth. Those formed in caves where the water supply is seasonal may reveal growth rings similar to those of a tree trunk. Stalactites and stalagmites grow by only a fraction of an inch or centimeter in a year, and since some are many yards or meters long, one can appreciate the time it takes for these speleothems to develop.

The most bizarre of speleothems are called helictites. Helictites are hollow, cylindrical formations that grow and twist in a number of directions and are not simply oriented according to the gravitational pull of a water drop. Other influences such as crystal growth patterns and air currents influence the direction in which these speleothems grow. Helictites grow out from the side of other speleothems and rarely grow larger than 4 in (8.5 cm) in length.

Speleothems called anthodites are usually made of aragonite. Calcite and aragonite are both forms of calcium carbonate, but crystallize differently. Anthodites grow as radiating, delicate, needle-like crystals . Pools of seepage water that drain leave behind round formations called cave popcorn. Cave pearls are formed in seepage pools by grains of sand encrusted with calcite; flowing water moves the grains about and they gather concentric layers of calcite.

See also Erosion; Stalactites and stalagmites

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Cave

Cave

A cave is a naturally occurring hollow area inside Earth. All caves are formed by some type of erosion process. The study of caves is called speleology (pronounced spee-lee-OL-o-gee). While some caves may be small hillside openings, others may consist of large chambers and inter-connecting tunnels and mazes. Openings to the surface may be large gaping holes or small crevices.

Caves have served as shelter for people throughout history. Many religious traditions have regarded caves as sacred and have used them in rituals and ceremonies. Human remains, artifacts, sculptures, and drawings found in caves have aided archaeologists in learning about early humans. A cave discovered in southeastern France in 1994 contains wall paintings estimated to be more than 30,000 years old.

Cave formation

The most common, largest, and spectacular caves are solution caves. These caves are formed through the chemical interaction of air, soil, water, and rock. As water flows over and drains into Earth's surface, it mixes with carbon dioxide from the air and soil to form a mild solution of carbonic acid. Seeping through naturally occurring cracks and fissures in massive beds of limestone in bedrock (the solid rock that lies beneath the soil), the acidic water eats away at the rock, dissolving its minerals and carrying them off in a solution.

With continual water drainage, the fissures become established passageways. The passageways eventually enlarge and often connect, creating an underground drainage system. Sometimes ceilings fall and passageways collapse, creating new spaces and drainage routes. Over thousands, perhaps millions of years, these passages evolve into the caves we see today.

Several distinctive features in the landscape make cave terrain easy to identify. The most common is a rugged land surface, marred by sinkholes, circular depressions where the underlying rock has been dissolved away. Disappearing streams and natural bridges are also common clues. But entrances to solution caves are not always obvious, and their discovery is sometimes quite by accident.

Words to Know

Speleology: Scientific study of caves and their plant and animal life.

Stalactite: Cylindrical or icicle-shaped mineral deposit projecting downward from the roof of a cave.

Stalagmite: Cylindrical or upside down icicle-shaped mineral deposit projecting upward from the floor of a cave.

Cave environment

A deep cave is completely dark, has a stable atmosphere, and has an almost constant temperature. The humidity in limestone caves is usually near 100 percent. Many caves contain unique life-forms, underground streams and lakes, and unusual mineral formations.

Water that makes its way to a cave ceiling hangs as a drop. The damp atmosphere in a cave reacts with that water, forcing the dissolved mineral out of the water solution. The crystalline material that most often remains is called calcite. Calcite deposited on the ceiling creates a hanging icicle-shaped formation called a stalactite (pronounced sta-LACK-tite). Calcite deposited on the floor of a cave builds up to create an upside down icicle-shaped formation called a stalagmite (pronounced

sta-LAG-mite). Stalactites and stalagmites grow by only a fraction of an inch or centimeter a year. In time, two such formations often merge to form a stout floor-to-ceiling column.

Sometimes the water runs down the slope of the wall, and as the calcite is deposited, a low ridge forms. Subsequent drops of water follow the ridge, adding more calcite. Constant buildup of calcite in this fashion results in the formation of a wavy, folded sheet hanging from the ceiling called a curtain. Curtain formations often have streaks of various shades of off-white and brown.

Cave life

Three different groups of animals use or inhabit caves. Animals in the first group commonly use caves but depend on the outside world for survival. These include bats, birds, bears, and crickets. Those in the second group live their entire life cycle within a cave, generally near the entrance, but are also found living outside caves. Cockroaches, beetles, and millipedes are some examples of this second group. The last group comprises animals that are permanent deep cave dwellers. Because they often live in total darkness, these animals lack skin color and eyes. They rely on their sense of touch to get around. Examples of this group include fish, shrimp, crayfish, salamanders, worms, snails, insects, bacteria, fungi, and algae.

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cave

cave, a cavity in the earth's surface usually large enough for a person to enter. Caves may be formed by the chemical and mechanical action of a stream upon soluble or soft rock, of rainwater seeping through soluble rock to the groundwater level, or of waves dashed against a rocky shore. Volcanic action (accompanied by the formation of gas pockets in lava or the melting of ice under lava) and earthquakes or other earth movements are also sources of cave formation. Limestone regions almost invariably have caves; some of these are notable for their stalactite and stalagmite formations or for their magnitude and beauty.

The preserved remains of prehistoric humans and animals and indications of early human culture have been discovered in some caves. Caves have served as burial grounds and shelter since prehistoric times. One such cave is Alabama's Russell Cave, where human evidence dates back 9,000 years. Speleology, the scientific study of caves and their plant and animal life, contributes to knowledge of biological adaptation and evolution. Some cave animals lack sight, and both plants and animals living where light is excluded show loss of pigment. Deep cave ecosystems, lacking the sunlight necessary for photosynthesis, depend on bacteria that use chemosynthesis to create energy.

Among famous caves in the United States are Carlsbad Caverns National Park (N.Mex.), Mammoth Cave National Park (Ky.), Wind Cave National Park (Black Hills, S.Dak.), Luray Caverns (Va.), and Wyandotte Cave (Ind.). In Europe there are celebrated caves in Belgium, Dalmatia, Gibraltar, Capri, Sicily, Postojna, and England (Kent's Cavern and Kirkdale). The caves of the Pyrenees and the Dordogne are famed for their prehistoric paintings (see Paleolithic art), and those of Ajanta, India, and Dunhuang, China, for their Buddhist frescoes. Among the deepest known caves are Krubera in the nation of Georgia, which extends more than 6,500 ft (2,000 m) below the surface, and Lamprechtsofen in Austria.

See C. E. Mohr and T. L. Poulson, The Life of the Cave (1966); D. R. McClurg, The Amateur's Guide to Caves and Caving (1973).

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cave

cave / ˈkāv/ • n. a large underground chamber, typically of natural origin, in a hillside or cliff. • v. [intr.] 1. explore caves as a sport. 2. short for cave in below. PHRASAL VERBS: cave in (or cave something in) (with reference to a roof or similar structure) subside or collapse or cause something to do this. ∎ fig. yield or submit under pressure: the manager caved in to his demands. DERIVATIVES: cave·like / -ˌlīk/ adj. cav·er n.

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cave

cave Natural underground cavity. There are several kinds, including coastal caves, formed by wave erosion, ice caves, formed in glaciers, and lava caves. The largest caves are formed in carbonate rocks such as limestone.

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cave

cave 2 fall in over a hollow. XVIII. prob. var. of dial. (esp. eastern) calve (XVIII), cauve, which may be of LG. orig.; cf. WFlem. inkalven fall in, Du. afkalven fall away, uitkalven fall out.

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cave

cave 1 underground hollow. XIII. -(O)F. (now ‘cellar’) — L. cava, sb. use of fem. sg. or n. pl. of cavus hollow.

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Cave

Cave

a small group of politicians who break away from the main party; a splinter party.

Example: cave of Adullam, 1866.

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Cave

Cavebehave, brave, Cave, clave, concave, crave, Dave, deprave, engrave, enslave, fave, forgave, gave, grave, knave, lave, Maeve, misbehave, misgave, nave, outbrave, pave, rave, save, shave, shortwave, slave, stave, they've, waive, wave •enclave • exclave • conclave •Redgrave • architrave • Wargrave •Palgrave • palsgrave • aftershave •brainwave • heatwave • microwave

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