Thurston Lava Tube,
Big Island, Hawaii, USA.
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
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Thurston Lava Tube,
Big Island, Hawaii, USA.
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Molten rock (magma) that pours or oozes onto the Earth's surface is called lava.
The viscousity of the lava depends on its silica content. Low-silica basalt lava has a low viscousity 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. Overflows of lava from these streams solidify quickly and plaster on to the channel walls, building natural levees or ramparts.
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| Image: Thurston Lava Tube, Big Island, Hawaii, USA. |
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 fluid much longer than surface flows. Tubefed lava can be transported for great distances from the eruption sites.
If liquid lava stops rising from its source deep inside the earth, the kernel of - still molten - lava moving beneath the crust of the lava flow will coninue to drain downhill and leave an open lava tube cave at the end.
This caves caves can be entered at the beginning, the end, through vents where gases from the lava left the tube and of course at roof collapses. This collapses are rather common, as the roof is rather thin. Also the durability of this caves is rather low, they are gone in less than 10.000 years.
The most famous spot 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 61.407 m long and has a height difference of 1102 m from end to end. With this statistics it is the deepest cave of the USA and the 8 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 metres below surface!
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