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lava
lava , molten rock that erupts on the earth's surface, either on land or under the ocean, by a volcano or through a fissure. It solidifies into igneous rock that is also called lava. Before reaching the earth's surface, the mixture of solid and liquid rock, and gases, is known as magma. Lavas are composed chiefly of silica and the oxides of aluminum, iron, magnesium, calcium, sodium, and potassium. Silica, with soda and potash, predominates in the light-colored, acid felsites; iron oxides, lime, and magnesia, in the dark-colored, basic basalts . Rock froth forms on the upper part of a lava flow if bubbles solidify before the gas can escape. Light-colored, glassy froth is pumice ; dark, cindery or slaggy froth, of a coarser texture than pumice, forms what is known as scoriae. Lava flows which solidify as a mass of blocks and fragments with a rough surface are called block lava, or aa; those which solidify with a smooth, ropy, billowy surface are known as corded lava, or pahoehoe. Lava can sometimes cover wide regions through great fissures in the earth's surface, as in the ancient Columbia River plateau of the NW United States, where it is spread over 30,000 sq mi (77,700 sq km) and is up to 5,000 ft (1,524 m) deep. Other such regions are found in the Deccan plateau of India, in E Brazil, and in Iceland. Submarine lavas develop through volcanic activity along the mid-oceanic ridges and plate boundaries, where the mid-oceanic ridges produce more lava than any continental eruptions. Such underwater eruptions also harbor rich fauna unique to the vent area, such as red tube worms and giant clams, whose food supply is based on the hydrogen sulfide abundant in the vent waters. Unique features include black smokers, or hot springs of mineral-rich water that belch out from the ocean ridge where it is most active. In many instances the reasons for the heat and liquidity of magma, its exact source, and the causes of its rise in the earth are not clearly known, though the volcanic activity is often related to seafloor spreading . Other volcanic areas also lie along colliding plate boundaries and around rising magma hot spots. See plate tectonics . |
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"lava." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "lava." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1E1-lava.html "lava." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-lava.html |
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lava
lava Molten rock at the surface of the Earth is called lava. Lavas vary in composition: when they are rich in silica (SiO2) they are highly viscous (sticky); when poor in silica, they have low viscosity. Some lavas contain large amounts of gas; others are gas-free. As lavas erupt the pressure in the magma is reduced and, in the manner of a bottle of fizzy drink (soda) being opened suddenly, the gas bubbles out. Different combinations of viscosity and gasiness lead to a wide variety of behaviours on eruption. Very viscous, gas-rich lavas erupt explosively, as at Mt. St Helen's, because the gas bubbles cannot escape quickly enough and the lava is blown apart. Low-viscosity, gas-poor lavas erupt quietly and flow away in thin sheets. Viscous lavas form thick, slow-moving flows; less viscous lavas form thin faster-moving flows. The surface of a lava flow cools quickly in contact with the air and solidifies rapidly. Continued movement of the lava underneath this surface may cause it to break into blocks, or the surface may become wrinkled and folded to form a ropy texture. Blocky and ropy lavas are often known as aa-aa and pa-hoe-hoe, onomatopoeic Hawaiian words.
Judith M. Bunbury |
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PAUL HANCOCK and BRIAN J. SKINNER. "lava." The Oxford Companion to the Earth. 2000. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. PAUL HANCOCK and BRIAN J. SKINNER. "lava." The Oxford Companion to the Earth. 2000. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O112-lava.html PAUL HANCOCK and BRIAN J. SKINNER. "lava." The Oxford Companion to the Earth. 2000. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O112-lava.html |
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lava
lava Molten rock, normally a silicate, erupted by a volcano. It may be vesicular, glassy, or porphyritic in texture, and varies between acidic and basic in composition. Its behaviour on extrusion and its relief-forming capacity depend largely on its viscosity, which is affected by silica content, temperature, and amount of dissolved gases and solids. Generally, the less viscous the lava the faster the flow, and the more viscous the lava the greater the tendency towards explosive eruption. Two varieties of basaltic lava surface are recognized: ‘aa’, a jagged, stony clinker, bristling with sharp points; and ‘pahoehoe’, characterized by a smooth, ropy appearance. Andesitic and rhyolitic lavas tend to have ‘blocky’ surfaces, characterized by smooth-faceted blocks, 1–5m in diameter.
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AILSA ALLABY and MICHAEL ALLABY. "lava." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "lava." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O13-lava.html AILSA ALLABY and MICHAEL ALLABY. "lava." A Dictionary of Earth Sciences. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-lava.html |
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lava
lava Molten rock, normally a silicate, which is expelled by a volcano. Its behaviour on extrusion and its relief-forming capacity depend largely on its viscosity, which is affected by its silica content, temperature, and the amount of dissolved gases and solids it contains. Generally, the less viscous the lava the faster the flow, and the more viscous the lava the greater the tendency towards explosive eruption.
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MICHAEL ALLABY. "lava." A Dictionary of Ecology. 2004. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "lava." A Dictionary of Ecology. 2004. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O14-lava.html MICHAEL ALLABY. "lava." A Dictionary of Ecology. 2004. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-lava.html |
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lava
lava Molten rock or magma that reaches the Earth's surface and flows out through a volcanic vent in streams or sheets. There are three main types of lava: vesicular, such as pumice; glassy, such as obsidian; and even-grained. Chemically, lavas range from acidic to ultrabasic. Basic lavas have a low viscosity and flow easily, covering large areas. Acidic lavas are highly viscous and rarely spread far.
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"lava." World Encyclopedia. 2005. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "lava." World Encyclopedia. 2005. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O142-lava.html "lava." World Encyclopedia. 2005. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-lava.html |
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lava
lava †stream of molten rock; substance resulting from the cooling of this; fluid matter from a volcano. XVIII. — It. lava (Neapolitan dial.) †stream suddenly caused by rain, the lava stream from Vesuvius, f. lavare LAVE.
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T. F. HOAD. "lava." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. T. F. HOAD. "lava." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O27-lava.html T. F. HOAD. "lava." The Concise Oxford Dictionary of English Etymology. 1996. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O27-lava.html |
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lava
la·va / ˈlävə; ˈlavə/ • n. hot molten or semifluid rock erupted from a volcano or fissure, or solid rock resulting from cooling of this. |
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"lava." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "lava." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O999-lava.html "lava." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-lava.html |
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lava
lava •cadaver, slaver
•halva, salver, salvor
•balaclava, Bratislava, carver, cassava, Costa Brava, guava, Java, kava, larva, lava, palaver
•woodcarver
•clever, endeavour (US endeavor), ever, forever, however, howsoever, never, never-never, sever, Trevor, whatever, whatsoever, whenever, whensoever, wheresoever, wherever, whichever, whichsoever, whoever, whomever, whomsoever, whosoever
•delver, elver
•Denver
•Ava, caver, craver, deva, engraver, enslaver, favour (US favor), flavour (US flavor), graver, haver, laver, paver, quaver, raver, saver, savour (US savor), shaver, vena cava, waiver, waver
•lifesaver • semiquaver
•achiever, beaver, believer, cleaver, deceiver, diva, Eva, fever, Geneva, griever, heaver, leaver, lever, Neva, perceiver, receiver, reiver, reliever, retriever, Shiva, underachiever, viva, weaver, weever
•cantilever
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"lava." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "lava." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O233-lava.html "lava." Oxford Dictionary of Rhymes. 2007. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O233-lava.html |
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