A cave or cavern is a natural opening in the earth large enough for a human to enter.
Caves are found everywhere around the earth.
They are formed by geologic processes, which may involve a combination of chemical processes, erosion from water, tectonic forces, microorganisms, pressure, and atmospheric conditions.
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.
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.
A substantial number of relatively small caves, called volcanic caves, are formed in lava and by the mechanical movement of bedrock.
Corrasional or erosional caves are those that form entirely by erosion by flowing streams carrying rocks and other sediments.
Sea caves are formed by wave action on fractures or other weaknesses in the bedrock of sea cliffs along coastlines.
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.
Talus caves are formed by the openings among large boulders that have fallen down into a random heap, often at the bases of cliffs.
Anchialine caves are caves, usually coastal, containing a mixture of freshwater and saline water (usually sea water).
Caves vary in size, shape and content, but they all include spectacular formations. The two most well-known speleothems are stalactites and stalagmites. A stalactite hangs like an icicle from the ceiling or sides of a cavern. A stalagmite appears like an inverted stalactite, rising from the floor of a cavern. Mnemonics have been developed for which word refers to which type of formation; one is that stalactite has a C for “ceiling”, and stalagmite has a G for “ground”.
Veryovkina Cave is 2,212 meters (7,257 ft) deep and is the deepest-known cave on Earth. Its entrance is situated 2,309 meters (7,575 ft) above sea level in Abkhazia, Georgia.
Krubera Cave is the second-deepest-known cave on Earth after the Veryovkina Cave. It is also located in Abkhazia, Georgia. The difference in elevation of the cave’s entrance and its deepest explored point is 2,197 ± 20 metres (7,208 ± 66 ft).
Mammoth Cave is the world’s longest recorded cave system. It has more than 640 kilometers (400 miles) of surveyed passageways, which is nearly twice as long as the second-longest cave system, Mexico’s Sac Actun underwater cave. It is located in central Kentucky, United States.
Hang Son Đoòng (the name means “Mountain River Cave”) is the world’s largest single cave passage, based on its overall dimensions. It is around 200 metres (655 feet) high, 150 metres (490 feet) wide and has a length of at least 6.5 kilometres (4 miles). Son Đoòng is located in Phong Nha-Ke Bàng National Park, Vietnam.
The Chauvet Cave (a.k.a Caverne du Pont d’arc) is one of the most famous prehistoric rock art sites in the world. With one exception, all of the cave art paintings have been dated between 30,000 and 33,000 years ago. Chauvet contains a total of over 300 paintings and engravings. These were grouped in specific ways. In the most accessible part of the cave, most images are red, with a few black or engraved ones.
Cave of the Crystals or Giant Crystal Cave is a cave in Naica, Chihuahua, Mexico. The cave was discovered in April 2000 by miners excavating a new tunnel for the Industrias Peñoles mining company located in Naica. Cave of the Crystals is connected to the Naica Mine at a depth of 300 meters (980 feet). The main chamber contains giant selenite crystals, some of the largest natural crystals ever found. The cave’s largest crystal found to date is 12 meters (39 feet) in length, 4 meters (13 feet) in diameter and 55 tons in weight.
The Waitomo Glowworm Caves attraction is a cave at Waitomo on the North Island of New Zealand. It is known for its population of Arachnocampa luminosa, a glowworm species found exclusively in New Zealand. The glowworms are the size of ordinary mosquitoes, and millions of them abound inside the cave. This cave is a major tourist attraction and is famous worldwide.
The olm or proteus and is an aquatic salamander. It is also known as the human fish, for its pale, pinkish skin. Olms are entirely aquatic and only found in the waters of caves in the Dinaric Alps—that is, parts of Slovenia, Italy, Croatia, and Herzegovina. They live in the subterranean, freshwater lakes and streams of limestone caves. The water in these caves is slightly acidic, contains high concentrations of oxygen, and ranges in temperature from 5 to 15 °C (41 to 59 °F). Adapted to an aphotic environment, olms usually reside deep within cave systems. They are generally found over 300 meters (985 feet) below surface.
The word “cave” is derived, via Old French, from the Latin cavea meaning hollow place, which comes from cavus meaning hollow.
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.