Lava Tubes
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A lava tube, more rarely called a pyroduct, is a 'roofed conduit through which molten lava travels away from its vent'. If
lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
in the tube drains out, it will leave an empty
cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...
. Lava tubes are common in low-
viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...
volcanic systems. Lava tubes are important as they are able to transport molten lava much further away from the eruptive vent than lava channels. A tube-forming lava flow can emplace on longer distance due to the presence of a solid crust protecting the molten lava from atmospheric cooling. Lava tubes are often considered when preparing hazard maps or managing an eruptive crisis.


Formation

A lava tube is a type of
lava cave A lava cave is any cave formed in volcanic rock, though it typically means caves formed by volcanic processes, which are more properly termed volcanic caves. Sea caves, and other sorts of erosional and crevice caves, may be formed in volcanic rock ...
formed when a low-
viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...
lava flow develops a continuous and hard crust, which thickens and forms a roof above the still-flowing lava stream. Three main formation mechanisms have been described: (1) roofing over a lava channel, (2) pāhoehoe lobe extension or (3) lava flow inflation. # When it erupts from a vent, lava usually flows in channels. While the core of the channel tends to stay very hot, its sides cool down rapidly, forming solidified walls called levees. Depending on the activity of the channel, three ways to form a lava tube are possible. If the level of lava flowing inside the channel is stable for a long time, the surface will start to solidify from the levees toward the center of the channel, slowly forming a solid crust. If the level of lava is irregular, the overspill of lava along the levees causes them to grow and eventually join together over the channel. Another way these channels may close is by the accumulation of floating surface crust. This type of lava tube tends to form closer to the eruptive vent. # When pahoehoe lava emplaces, it sometimes form lobes. The formation of aligned pahoehoe lobes that are continuously fed by molten lava may form lava tubes. # During an eruption, when lava flows emplace and their sides cool rapidly and solidify into levees, the pressure of molten lava passing through the flow may cause it to inflate. The surface of the flow then solidifies as it cools, forming a crust, leading to the formation of a lava tube.


Characteristics

A broad lava-flow field often forms a lava tube system that consists of a main lava tube and a series of smaller tubes that supply lava to the front of one or more separate flows. When the supply of lava stops at the end of an eruption, or lava is diverted elsewhere, lava in the tube system sometimes drains downslope and leaves partially or fully empty
cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...
s. Such drained tubes commonly exhibit numerous internal features that can give information on the activity that happened within the tube. Wall linings are thin layers of lava that cover the walls and ceiling of a tube. They form when the tube drains. Each wall lining corresponds to a cycle of drainage and refilling of the tube. Step marks on the walls indicate the various depths at which the lava flowed. These are known as lava benches, flow ledges or flow lines, depending on how prominently they protrude from the walls. Lava tubes generally have pāhoehoe floors, although this may often be covered in breakdown from the ceiling. A variety of
stalactite 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 (chemistry ...
, generally known as lavacicles, can be observed inside lava tubes. They can be of the splash, "shark tooth", or tubular varieties. Lavacicles are the most common lava tube internal feature. Drip
stalagmite 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 ...
s may form under tubular lava stalactites, and the latter may grade into a form known as a tubular lava
helictite A helictite is a speleothem (cave-formed mineral) found in a Solution cave, limestone cave that changes its axis from the vertical at one or more stages during its growth. Helictites have a curving or angular form that looks as if they were gro ...
. A runner is a bead of lava that is extruded from a small opening and then runs down a wall. Lava tubes may also contain
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...
deposits that most commonly take the form of crusts or small
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s, and less commonly, as stalactites and stalagmites. Some stalagmites may contain a central conduit and are interpreted as hornitos extruded from the tube floor. Lava tubes can be up to wide, though are often narrower, and run anywhere from below the surface. Lava tubes can also be extremely long; one tube from the Mauna Loa 1859 flow enters the ocean about from its eruption point, and the Cueva del Viento–Sobrado system on Teide,
Tenerife Tenerife ( ; ; formerly spelled ''Teneriffe'') is the largest and most populous island of the Canary Islands, an Autonomous communities of Spain, autonomous community of Spain. With a land area of and a population of 965,575 inhabitants as of A ...
island, is over long, due to extensive braided maze areas at the upper zones of the system. A lava tube system in
Kiama Kiama may refer to: * Electoral district of Kiama, a seat in the New South Wales Legislative Assembly * Kiama, New South Wales, a town * Kiama (spider), a genus of spiders *Municipality of Kiama The Municipality of Kiama is a local government ar ...
,
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
, consists of over 20 tubes, many of which are breakouts of a main lava tube. The largest of these lava tubes is in diameter and has
columnar jointing Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as Joint (geology), joints, result in the formation of a regular array of polygonal Prism (geometry), prisms, or columns. Columnar join ...
due to the large cooling surface. Other tubes have
concentric In geometry, two or more objects are said to be ''concentric'' when they share the same center. Any pair of (possibly unalike) objects with well-defined centers can be concentric, including circles, spheres, regular polygons, regular polyh ...
and radial jointing features. These tubes are infilled due to the low slope angle of emplacement.


Extraterrestrial lava tubes

Lunar lava tubes have been discovered and have been studied as possible human habitats, providing natural shielding from radiation. Several holes on the lunar surface, including one in the Marius Hills region, have been observed with angled satellite imagery to lead into voids wider than the holes themselves. These are considered as possible collapses into lunar lava tubes. Martian lava tubes are associated with innumerable lava flows and lava channels on the flanks of
Olympus Mons Olympus Mons (; ) is a large shield volcano on Mars. It is over high as measured by the Mars Orbiter Laser Altimeter (MOLA), about 2.5 times the elevation of Mount Everest above sea level. It is Mars's tallest volcano, its tallest planetary mou ...
. Partially collapsed lava tubes are visible as chains of pit craters, and broad lava fans formed by lava emerging from intact, subsurface tubes are also common. Evidence of Martian lava tubes has also been observed on the Southeast Tharsis region and
Alba Mons Alba Mons (formerly and still occasionally known as Alba Patera, a term that has since been restricted to the volcano's summit caldera; also initially known as the Arcadia ring) is a volcano located in the northern Tharsis region of the planet Ma ...
. Caves, including lava tubes, are considered candidate
biotope A biotope is an area of uniform environmental conditions providing a living place for a specific assemblage of flora (plants), plants and fauna (animals), animals. ''Biotope'' is almost synonymous with the term habitat (ecology), "habitat", which ...
s of interest for extraterrestrial life.


Notable examples

* Iceland ** Surtshellir – For a long time, this was the longest known lava tube in the world. * Italy ** Grotta dei Tre Livelli - Famous example of a multiple level lava tube. * Kenya ** Leviathan Cave – At , it is the longest lava tube in Africa. * South Korea ** Manjang Cave – more than long, located in
Jeju Island Jeju Island (Jeju language, Jeju/) is South Korea's largest island, covering an area of , which is 1.83% of the total area of the country. Alongside outlying islands, it is part of Jeju Province and makes up the majority of the province. The i ...
, is a popular tourism spot. * United States ** Kazumura Cave,
Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
– The world's most extensive lava tube, at , it has the greatest linear extent of any known lava cave.


See also

* * * * * *


References


External links

* {{Subterranea Cave geology Volcanic landforms Volcanology