Lava tube
Overview
 
Lava tubes are natural conduits through which lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 travels beneath the surface of a lava flow, expelled by a volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave
Cave
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...

-like channel.

Lava tubes have been reported from the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

.
Lava tubes are a type of lava cave
Lava cave
A lava cave is any cave formed in volcanic rock, although in typical usage it is reserved for caves formed by volcanic processes, which are more properly termed volcanic caves...

 formed when an active low-viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 lava flow develops a continuous and hard crust, which thickens and forms a roof above the still-flowing lava stream.
Encyclopedia
Lava tubes are natural conduits through which lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 travels beneath the surface of a lava flow, expelled by a volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave
Cave
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...

-like channel.

Lava tubes have been reported from the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

.

Formation

Lava tubes are a type of lava cave
Lava cave
A lava cave is any cave formed in volcanic rock, although in typical usage it is reserved for caves formed by volcanic processes, which are more properly termed volcanic caves...

 formed when an active low-viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 lava flow develops a continuous and hard crust, which thickens and forms a roof above the still-flowing lava stream. Tubes form in one of two ways: by the crusting over of lava channel
Lava channel
A lava channel is a stream of fluid lava contained within marginal zones of static lava or levees. The initial channel may not contain levees per se, until the parental flow solidifies over what develops into the channel and creates simple levees. This initial levee allows for the building of a...

s, and from pahoehoe flows where the lava is moving under the surface.

Lava usually leaves the point of eruption in channels. These channels tend to stay very hot as their surroundings cool. This means they slowly develop walls around them as the surrounding lava cools and/or as the channel melts its way deeper. These channels can get deep enough to crust over, forming an insulating
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

 tube that keeps the lava molten and serves as a conduit for the flowing lava. These types of lava tubes tend to be closer to the lava eruption point.

Further away from the eruption point, lava can flow in an unchanneled, fanlike manner as it leaves its source, which is usually another lava tube leading back to the eruption point. Called pahoehoe flows, these areas of surface-moving lava cool, forming either a smooth or rough, ropy surface. The lava continues to flow this way until it begins to block its source. At this point, the subsurface lava is still hot enough to break out at a point, and from this point the lava begins as a new "source". Lava flows from the previous source to this breakout point as the surrounding lava of the pahoehoe flow cools. This forms an underground channel that becomes a lava tube.

Characteristics

A broad lava-flow field often 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 drains downslope and leaves partially empty cave-like conduits beneath the ground.

Such drained tubes commonly exhibit step marks on their walls that mark the various depths at which the lava flowed, known as flow ledges or flow lines depending on how prominently they protrude from the walls. Lava tubes generally have pahoehoe floors, although this may often be covered in breakdown from the ceiling. A variety of speleothem
Speleothem
A speleothem , commonly known as a cave formation, is a secondary mineral deposit formed in a cave. Speleothems are typically formed in limestone or dolostone solutional caves.-Origin and composition:...

s may be found in lava tubes including a variety of stalactite
Stalactite
A stalactite , "to drip", and meaning "that which drips") is a type of speleothem that hangs from the ceiling of limestone caves. It is a type of dripstone...

 forms generally known as lavacicles, which can be of the splash, shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

 tooth, or tubular variety. Lavacicles are the most common of lava tube speleothems. Drip stalagmite
Stalagmite
A stalagmite is a type of speleothem that rises from the floor of a limestone cave due to the dripping of mineralized solutions and the deposition of calcium carbonate. This stalagmite formation occurs only under certain pH conditions within the underground cavern. The corresponding formation on...

s may form under tubular lava stalactites, and the latter may grade into a form known as a tubular lava helictite
Helictite
A helictite is a speleothem found in limestone caves that changes its axis from the vertical at one or more stages during its growth. They have a curving or angular form that looks as if they were grown in zero gravity...

. A runner is a bead of lava that extrudes from a small opening and then runs down a wall. Lava tubes may also contain mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 deposits that most commonly take the form of crusts or small crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

s, and less commonly, as stalactites and stalagmites.

Lava tubes can be up to 14–15 m (45.9–49.2 ) wide, though are often narrower, and run anywhere from 1–15 m (3.3–49.2 ) below the surface. Lava tubes can also be extremely long; one tube from the Mauna Loa
Mauna Loa
Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately , although its peak is about lower than that...

 1859 flow enters the ocean about 50 kilometres (31.1 mi) from its eruption point, and the Cueva del Viento - Sobrado system on Teide
Teide
Mount Teide , is a volcano on Tenerife, Canary Islands. Its summit is the highest point in Spain, the highest point above sea level in the islands of the Atlantic, and it is the third highest volcano in the world measured from its base on the ocean floor, after Mauna Loa and Mauna Kea located in...

, Tenerife
Tenerife
Tenerife is the largest and most populous island of the seven Canary Islands, it is also the most populated island of Spain, with a land area of 2,034.38 km² and 906,854 inhabitants, 43% of the total population of the Canary Islands. About five million tourists visit Tenerife each year, the...

 island, is over 18 kilometres (11.2 mi) long, due to extensive braided maze areas at the upper zones of the system.

A lava tube system in Kiama, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, consists of over 20 tubes, many of which are breakouts of a main lava tube. The largest of these lava tubes is 2 metres (6.6 ft) in diameter and has columnar jointing due to the large cooling surface. Other tubes have concentric
Concentric
Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another...

 and radial
Radial
Radial can refer to:* Vector , a line* Radius, adjective form of* A radial pattern is one that appears to radiate from a point, like the spokes from the hub of a wheel* A bearing from a waypoint, such as a VOR...

 jointing features. The tubes are infilled due to the low slope angle of emplacement.

Examples

  • Iceland
    • Surtshellir
      Surtshellir
      Surtshellir is a lava cave located in western Iceland, around 60 km from the settlement of Borgarnes. Approximately a mile in length, it is the longest such cave in the country. While mentioned in the medieval historical-geographical work Landnámabók, Eggert Ólafsson was the first to give a...

       - For a long time, this was the longest known lava tube in the world.
    • Víðgelmir
      Víðgelmir
      Víðgelmir is a lava tube situated in Western Iceland in the Hallmundarhraun lava field, ca. 2 km. Southeast from Fljótstunga farm in Hvítársíða, Borgarfjörður. The roof of the lava tube has collapsed, creating two large openings near its north end which are the only known entrances...

       - Another long lava tube of Iceland.
  • Portugal
    • Gruta das Torres
      Gruta das Torres
      The Gruta das Torres , is a lava cave, a geological formation of volcanic origin formed from the flow and cooling of subterranean magma rivers. This formation is located outside the parish of Criação Velha, in the municipality of Madalena, on the western flanks of the island of Pico...

       - Lava tube system of the Azores
      Azores
      The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...

      .
  • Spain
    • Cueva del Viento
      Cueva del Viento
      Cueva del Viento-Sobrado underground complex is the largest lava tube in the European Union and one of the largest in the world. It is the fifth largest in the world behind a series of caves in Hawaii. It was created by lava flows from Pico Viejo, next to Mt. Teide...

       - 17 km lava tube. Tenerife, Canary Islands
  • USA
    • Lava River Cave
      Lava River Cave (Arizona)
      Lava River Cave is a lava tube cave in northern Arizona's Coconino National Forest. At approximately long, it is the longest cave of this kind known in Arizona. The cave was discovered by some lumbermen in 1915. The cave has also historically been referred to as "Government Cave" due to its...

       in Arizona
      Arizona
      Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

      's Coconino National Forest
      Coconino National Forest
      The Coconino National Forest is a 1.856-million acre United States National Forest located in northern Arizona in the vicinity of Flagstaff. Originally established in 1898 as the "San Francisco Mountains National Forest Reserve", the area was designated a U.S...

    • Lava Beds National Monument - The site of the largest concentration of lava tubes in the United States
    • Kazumura Cave
      Kazumura Cave
      Kazumura Cave is a lava tube and has been surveyed at 40.7 miles long and 3,614 feet deep making it the longest and deepest lava tube in the world. The cave is located on the island of Hawaii on the eastern slope of Kilauea. Kilauea is the most recently active volcano on the Big Island...

       - Not only the world's most extensive lava tube, but has the greatest linear extent of any cave known
    • Lava River Cave
      Lava River Cave
      The Lava River Cave near Bend, Oregon, is part of the Newberry National Volcanic Monument, which is managed by the United States Forest Service. The cave is an excellent example of a lava tube. At 5,211 feet in length, the northwest section of the cave is the longest continuous lava tube in Oregon...

       in Oregon
      Oregon
      Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

      's Newberry National Volcanic Monument
      Newberry National Volcanic Monument
      Newberry National Volcanic Monument was designated on November 5, 1990, to protect the area around the Newberry Volcano in the United States. It was created within the boundaries of the Deschutes National Forest and is managed by the U.S. Forest Service...

       - Newberry National Volcanic Monument
    • Ape Cave
      Ape Cave
      Ape Cave is a lava tube located in Gifford Pinchot National Forest just to the south of Mount St. Helens in Washington state. Its passageway is the longest continuous lava tube in the continental United States, at . Ape Cave is a popular hiking destination with beautiful views of the Mount St....

      , Washington - May be the third longest lava tube in the continental United States
      United States
      The United States of America is a federal constitutional republic comprising fifty states and a federal district...


  • Earth's moon - Scientific evidence suggests the moon
    Moon
    The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

     has many lava tubes and one location in particular, the Marius Hills
    Marius Hills
    The Marius Hills are a set of volcanic domes located in Oceanus Procellarum on Earth's Moon. The domes are thought to have formed from lavas fairly more viscous than those that formed the Lunar mare. These domes average approximately 200–500 m in height. The Marius Hills take their name from the...

    , has been proposed as being suitable location for a human colony
    Colonization of the Moon
    The colonization of the Moon is the proposed establishment of permanent human communities on the Moon. Advocates of space exploration have seen settlement of the Moon as a logical step in the expansion of humanity beyond the Earth. Recent indication that water might be present in noteworthy...

    .

See also

  • Lava cave
    Lava cave
    A lava cave is any cave formed in volcanic rock, although in typical usage it is reserved for caves formed by volcanic processes, which are more properly termed volcanic caves...

  • Speleology
    Speleology
    Speleology is the scientific study of caves and other karst features, their make-up, structure, physical properties, history, life forms, and the processes by which they form and change over time...

  • Speleothem
    Speleothem
    A speleothem , commonly known as a cave formation, is a secondary mineral deposit formed in a cave. Speleothems are typically formed in limestone or dolostone solutional caves.-Origin and composition:...

  • Caving
    Caving
    Caving—also occasionally known as spelunking in the United States and potholing in the United Kingdom—is the recreational pastime of exploring wild cave systems...

  • Geology of the Moon
    Geology of the Moon
    The geology of the Moon is quite different from that of the Earth...

  • Lunar lava tube
    Lunar lava tube
    Lunar lava tubes are sub-surface tunnels on the Moon that are believed to have formed during basaltic lava flows. When the surface of a lava tube cools, it forms a hardened lid that contains the ongoing lava flow beneath the surface in a conduit-shaped passage. Once the flow of lava diminishes, the...

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