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Lava Tubes

Lava Tube Caves

en: lava cave; lava tube
de: Lavahöhle (e); Lavaröhre (e)
es: cueva volcánica (f); tubo (m) de lava
fr: grotte (f) de lave; tube (f) de lave
hu: lávabarlang
it: grotta (sf) lavica; tubo (sm) di lava
pt: tubo de lava
ro: pestera (f) vulcanica; tub (n) de lava

Image:  Thurston Lava Tube, Big Island, Hawaii, USA.

Lava Tube Caves or Lava Tubes are  Primary cave formed by large lava flows. Molten rock (magma) that pours or oozes onto the Earth's surface is then called lava. The viscosity of the lava depends on its silica content. Low-silica basalt lava has a low viscosity and can form fast-moving (15-50 km/h), narrow lava streams or spread out in broad sheets up to several miles wide.

During long lasting eruptions, lava flows tend to become channeled into a few main streams. Overflow of lava from these streams solidifies quickly and supports the channel walls, building natural levees or ramparts. So actually the channel is created by the flowing lava itself, a self fupporting process.

Lava streams that flow steadily in a confined channel for many hours to days may develop a solid crust or roof and thus change gradually into streams within lava tubes. Because the walls and roofs of such tubes are good thermal insulators, lava flowing through them can remain hot and flowing, much longer than surface flows. Lava can be transported for great distances from the eruption sites in the tubes.

Image:  Thurston Lava Tube, Big Island, Hawaii, USA.

Lava produces big amounts of gas and steam, and while flowing through the tube this produces a certain air pressure inside. This keeps the tube open but also may press a hole into the covering crust, which is still hot and rather soft. Those venting holes are called hornitos (Spanish for little ovens) or spatter cones. The reason is simple, the gas pressure from below throws small pieces of lava out of the venting holes, which form cones, up to 15m high, on top of the vent. The lava in those cones is formed of layer above layer of spatters.

When the lava flow from the volcano ends, the lava will continue to move and drain the tube downhill. This leaves a partially empty tube which may be called lava tube cave. Lava which is not able to flow out of the tube will remain in the form of solidified pools, flows, or even waterfalls.

Lava tubes can be entered at the beginning and at the end of the tube. Inbetween there are two kinds of openings or skylights, hornitos and roof collapses. Hornitos formed while the lava was still flowing, collapses are a result of susequent erosion. It is easy to differenciate between them, as hornitos do not have much collpsed material at the ground, it was transported away by the flowinf lava stream. Collapses are rather common, as the roof of lava tubes is rather thin, a result of the way it formed. Also the durability of this caves is rather low, they are generally gone in less than 10,000 years. Older tubes are extremely rare.

The most famous place for lava tubes on Earth is Hawai'i. Because of the geography, the lava tubes on Big Island are the biggest in the World.  Kazumura Cave is 65,500m long [2010] and has a height difference of 1,102m [2010] from end to end. With this size it is the deepest cave of the USA and the 8th longest. The second deepest cave of the USA is still a lava tube of Hawai'i, Huehue Cave and many other caves in this list too. Despite this superlatives, lava tubes are never more than a few meters below surface!


See also

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