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A cave or cavern is a natural underground space large enough for a human to enter. The term applies to
natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like
rock shelters, sea caves, and grottos.
Speleology 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
Types and formation
The formation and development of caves is known as speleogenesis. Caves are formed by various
geologic processes. These may involve a combination of chemical processes, erosion from water,
tectonic forces, microorganisms, pressure, atmospheric influences, and even digging.
Most caves are formed in limestone by dissolution.
Solutional Caves
Solutional caves are the most frequently occurring caves and such caves form in rock that is soluble,
such as limestone, but can also form in other rocks, including chalk, dolomite, marble, salt, and gypsum.
Rock is dissolved by natural acid in groundwater that seeps through bedding-planes, faults, joints and so
on. 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 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.[1]
The world's most spectacularly decorated cave is generally regarded to be Lechuguilla Cave in New
Mexico. Lechuguilla 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 ground water and forms H 2SO4 (sulfuric acid). The acid
then dissolves the limestone from below, rather than from above, by acidic water percolating from the
Primary Caves
Some caves are formed at the same time as the surrounding rock. These are sometimes called primary
Lava tubes are formed through volcanic activity and are the most common 'primary' caves. The lava 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, Hawaii, and many other places. Kazumura
Cave near Hilo 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 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 cave in Big Four Glacier, Big Four Mountain, Washington, ca. 1920
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").
Anchialine cave
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
Physical 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 threedimensional rooms form from a rising water table that erodes the carbonate rock with hydrogensulfide enriched water.[2]
Pit caves (vertical caves, potholes, or simply "pits") consist of a vertical shaft rather than a horizontal
cave passage. They may or may not be associated with one of the above structural patterns.
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, and so on.).
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.