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Lava Tubes
Lava tube on the way down the Chain of Craters Road
Hawaii, Hawaiian Islands
 
Earth's Natural Wonders in Australia & Oceania
World's longest lava tube: Kazumura Cave
Length of Kazumura Cave: 36.9 miles
Drop of Kazumura Cave: 3,605 feet
 
Lava tube on the way down the Chain of Craters Road [1]
   
   
Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow, expelled by a volcano 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-like channel.[3]
Tube is approx 15ft diameter. Kona Coast, Hawaii [2]
 

 

 

Lava tubes are formed when a flow of relatively fluid lava cools on the upper surface sufficiently to form a crust. Beneath this crust, which by dint of being made of rock is an excellent insulator, the lava can continue to flow as a liquid. When this flow occurs over a prolonged period of time the lava conduit can form a tunnel-like aperture or lava tube, which can conduct molten rock many kilometers from the vent without cooling appreciably. Often these lava tubes drain out once the supply of fresh lava has stopped, leaving a considerable length of open tunnel within the lava flow.

Lava tubes are known from the modern day eruptions of Kilauea, and significant, extensive and open lava tubes of Tertiary age are known from North Queensland, Australia, some extending for 15 kilometers.[4]

Lava tubes are formed when an active low-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 channels, 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 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.[3]

 

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 speleothems may be found in lava tubes[4] including a variety of stalactite forms generally known as lavacicles, which can be of the splash, shark tooth, or tubular variety. Lavacicles are the most common of lava tube speleothems. Drip stalagmites may form under tubular lava stalactites, and the latter may grade into a form known as a tubular lava helictite. 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 deposits that most commonly take the form of crusts or small crystals, and less commonly, as stalactites and stalagmites.

Lava tubes can be up to 14-15 metres wide, though are often narrower, and run anywhere from 1-15 m below the surface. Lava tubes can also be extremely long; one tube from the Mauna Loa 1859 flow enters the ocean about 50 km (over 30 miles) from its eruption point, and the Cueva del Viento - Sobrado system on Teide, Tenerife island, is over 18 km long, due to extensive braided maze areas at the upper zones of the system.

A lava tube system in Kiama, Australia, consists of over 20 lava tubes, many of which are breakouts of a main lava tube. The largest of these lava tubes is 22 m in diameter and has columnar jointing due to the large cooling surface. Other tubes have concentric and radial jointing features. The tubes are infilled due to the low slope angle of emplacement.[3]

 

Written and produced by Donald B. MacGowan; videography by Frank Burgess and Donald MacGowan; Narration by Frank Burgess; Original Music by Donnie MacGowan

DrBlizzardo
August 14, 2008

 

Nahuku, the Thurston Lava Tube, gives the visitor an opportunity for a close-at-hand inspection of the inner plumbing of a volcano. It also makes for an interesting and unique way to escape the noonday heat or afternoon shower briefly. Lava tubes form when the outer crust of a flowing river of lava begins to cool and crust over, but the lava continues to flow beneath it; when the flow has completely drained away, the lava tube is left behind.

Thurston lava tube is a remarkably large, well-preserved and accessible example of a lava tube-type cave. An easy, 0.3 mile trail (about a 15 minute hike) winds through lush fern forest alive with singing bird and buzzing insects, down into a collapse crater entering the lava tube and slipping about 300 feet through the well-lighted, floored cave, popping up through a skylight in the tube and returning to the parking lot. A very easy walk and certainly a "must see" for any visitor to the park.

 

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References
 
1. Flickr-Lava Tubes -Creative Commons Attribution License-retrieved 6/27/2009
2. Flickr-Kona Coast lava tube-Creative Commons Attribution License-retrieved 6/27/2009
3. Wikipedia- Lava Tubes- Creative Commons Attribution/Share-Alike License
4. Lava. (2008, May 7). New World Encyclopedia. Retrieved 11:39, July 29, 2009 from http://www.newworldencyclopedia.org/entry/Lava?oldid=703913.
 
 
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