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07:51, 26 April 2009: 70.95.116.4 (talk) triggered filter 155, performing the action "edit" on Lava. Actions taken: none; Filter description: Adding links to youtube (examine)

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==External links==
==External links==
{{commons|lava}}
{{commons|lava}}
*[http://www.youtube.com/watch?v=SaQZFaKx69Q Pillow lava formation underwater]
*[http://volcanoes.usgs.gov/Products/Pglossary/aa.html USGS definition of {{okina}}A{{okina}}ā]
*[http://volcanoes.usgs.gov/Products/Pglossary/aa.html USGS definition of {{okina}}A{{okina}}ā]
*[http://volcanoes.usgs.gov/Products/Pglossary/pahoehoe.html USGS definition of Pāhoehoe]
*[http://volcanoes.usgs.gov/Products/Pglossary/pahoehoe.html USGS definition of Pāhoehoe]

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'{{otheruses}} {{wiktionarypar3|lava|aa|pahoehoe}} '''Lava''' is molten [[Rock (geology)|rock]] expelled by a [[volcano]] during an eruption. When first expelled from a volcanic vent, it is a [[liquid]] at [[temperature]]s from 700&nbsp;°C to 1,200&nbsp;°C (1,300&nbsp;°F to 2,200&nbsp;°F). Although lava is quite [[viscosity|viscous]], with about 100,000 times the [[viscosity]] of water, it can flow great distances before cooling and solidifying, because of both its [[thixotropy|thixotropic]] and [[shear thinning]] properties.<ref>{{cite web |url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VCS-4B6CPRP-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=062e0c42281eb5e5d185d5e78aa1e0f7 |title=ScienceDirect - Journal of Volcanology and Geothermal Research : Transient phenomena in vesicular lava flows based on laboratory experiments with analogue materials|publisher=www.sciencedirect.com|accessdate=2008-06-19|last=H. Pinkerton|first=N. Bagdassarov }}</ref><ref>{{cite web|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=5970696|title=Rheological properties of basaltic lavas at sub-liquidus temperatures: laboratory and field measurements on lavas from Mount Etna|publisher=cat.inist.fr|accessdate=2008-06-19}}</ref> A ''lava flow'' is a moving outpouring of lava, which is created during a non-explosive [[effusive eruption]]. When it has stopped moving, lava solidifies to form [[igneous rock]]. The term ''lava flow'' is commonly shortened to ''lava''. [[Explosive eruption]]s produce a mixture of [[volcanic ash]] and other fragments called [[tephra]], rather than lava flows. The word 'lava' comes from Italian, and is probably derived from the [[Latin]] word ''labes'' which means a fall or slide.<ref>[http://www.m-w.com/dictionary/lava Merriam-Webster OnLine dictionary]</ref><ref>[http://dictionary.reference.com/browse/lava Dictionary.com]</ref> The first use in connection with extruded [[magma]] (molten rock below the earth's surface) was apparently in a short account written by [[Francesco Serao]] on the eruption of [[Vesuvius]] between May 14 and June 4, 1737.<ref>[http://www.lindahall.org/events_exhib/exhibit/exhibits/vulcan/9.shtml Vesuvius Erupts, 1738<!-- Bot generated title -->]</ref> Serao described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of the volcano following heavy [[rain]]. [[Image:Pahoeoe fountain edit2.jpg|thumb|right|250px|33 ft (10 m) high fountain of lava, Hawaii, United States]] == Lava composition == [[File:Pāhoehoe and Aa flows at Hawaii.jpg|Pāhoehoe and ʻAʻā lava flows side by side at the Big Island of Hawaii in September, 2007|thumb|300px]] In general, the composition of a lava determines its behavior more than the temperature of its eruption. Igneous rocks, which form lava flows when erupted, can be classified into three chemical types; [[felsic]], intermediate, and [[mafic]]. These classes are primarily chemical; however, the chemistry of lava also tends to correlate with the magma temperature, its viscosity and its mode of eruption. ''[[Felsic]]'' lavas such as [[rhyolite]] and [[dacite]] typically form [[lava spine]]s, [[lava dome]]s or 'coulees' (which are thick, short lavas) and are associated with [[pyroclastic]] (fragmental) deposits. Most felsic lava flows are extremely viscous, and typically fragment as they extrude, producing blocky autobreccias. The high viscosity and strength are the result of their chemistry, which is high in [[silica]], [[aluminium]], [[potassium]], [[sodium]], and [[calcium]], forming a [[polymer]]ized liquid rich in [[feldspar]] and [[quartz]], which thus has a higher viscosity than other magma types. Felsic magmas can erupt at temperatures as low as 650 to 750&nbsp;°C. Unusually hot (>950&nbsp;°C) rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in the [[Snake River Plain]] of the northwestern United States. ''Intermediate'' or [[andesite|andesitic]] lavas are lower in aluminium and silica, and usually somewhat richer in [[magnesium]] and [[iron]]. Intermediate lavas form [[andesite]] domes and block lavas, and may occur on steep composite volcanoes, such as in the [[Andes]]. Poorer in aluminium and silica than felsic lavas, and also commonly hotter (in the range of 750 to 950&nbsp;°C), they tend to be less viscous. Greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and also a greater tendency to form [[phenocrysts]]. Higher iron and magnesium tends to manifest as a darker [[groundmass]], and also occasionally [[amphibole]] or [[pyroxene]] [[phenocryst]]s. ''[[Mafic]]'' or [[basalt]]ic lavas are typified by their high ferromagnesian content, and generally erupt at temperatures in excess of 950&nbsp;°C. Basaltic magma is high in iron and magnesium, and has relatively lower aluminium and silica, which taken together reduces the degree of polymerization within the melt. Owing to the higher temperatures, viscosities can be relatively low, although still thousands of times more viscous than water. The low degree of polymerization and high temperature favors chemical diffusion, so it is common to see large, well-formed phenocrysts within mafic lavas. Basalt lavas tend to produce low-profile [[shield volcano]]es or '[[flood basalt]] fields', because the fluidal lava flows for long distances from the vent. The thickness of a basalt lava, particularly on a low slope, may be much greater than the thickness of the moving lava flow at any one time, because basalt lavas may 'inflate' by supply of lava beneath a solidified crust. Most basalt lavas are of a'a or 'pahoehoe' types, rather than block lavas. Underwater they can form '[[pillow lavas]]', which are rather similar to entrail-type pahoehoe lavas on land. ''[[Ultramafic rock|Ultramafic]]'' lavas such as [[komatiite]] and highly magnesian magmas which form [[boninite]] take the composition and temperatures of eruptions to the extreme. Komatiites contain over 18% magnesium oxide, and are thought to have erupted at temperatures of 1600&nbsp;°C. At this temperature there is no polymerization of the mineral compounds, creating a highly mobile liquid with viscosity as low as that of water. Most if not all ultramafic lavas are no younger than the [[Proterozoic]], with a few ultramafic magmas known from the [[Phanerozoic]]. No modern komatiite lavas are known, as the Earth's mantle has cooled too much to produce highly magnesian magmas. ===Lava behavior=== [[Image:PahoehoeLava.jpg|thumb|right|150px|Toes of a pāhoehoe advance across a road in [[Kalapana, Hawaii|Kalapana]] on the east rift zone of [[Kilauea|Kīlauea]] Volcano in [[Hawaii|Hawaii,United States.]]]] The viscosity of lava is important because it determines how the lava will behave. Lavas with high viscosity are [[rhyolite]], [[dacite]], [[andesite]] and [[trachyte]], with cooled basaltic lava also quite viscous; those with low viscosities are freshly erupted [[basalt]], [[carbonatite]] and occasionally [[andesite]]. Highly viscous lava shows the following behaviors: *tends to flow slowly, clog, and form semi-solid blocks which resist flow *tends to entrap [[Volcanic gas|gas]], which form [[vesicle]]s (bubbles) within the rock as they rise to the surface *correlates with explosive or [[phreatic]] eruptions and is associated with [[tuff]] and [[pyroclastic]] flows Highly viscous lavas do not usually flow as liquid, and usually form explosive fragmental ash or [[tephra]] deposits. However, a degassed viscous lava or one which erupts somewhat hotter than usual may form a lava flow. Lava with low viscosity shows the following behaviors: *tends to flow easily, forming puddles, channels, and rivers of molten rock *tends to easily release bubbling gases as they are formed *eruptions are rarely pyroclastic and are usually quiescent *volcanoes tend to form broad shields rather than steep cones There are three forms of low-viscosity lava flows: ''{{okina}}a{{okina}}ā'', ''pāhoehoe'', and ''pillow lava''. They are described in relation to basaltic flows from Hawaii, shown in the following sections. Lavas also may contain many other components, sometimes including solid crystals of various minerals, fragments of exotic rocks known as [[xenolith]]s and fragments of previously solidified lava. ==Volcanic morphologies== [[Image:Lava entering sea - Hawaii.png|thumb|right|250px|Lava entering the sea to expand the [[Hawaii (island)|big island of Hawaii]], [[Hawaii Volcanoes National Park]].]] The physical behavior of lava creates the physical forms of a lava flow or volcano. More fluid basaltic lava flows tend to form flat sheet-like bodies, whereas viscous rhyolite lava flows forms knobbly, blocky masses of rock. General features of [[volcanology]] can be used to classify volcanic edifices and provide information on the eruptions which formed the lava flow, even if the sequence of lavas have been buried or metamorphosed. [[Image:Three Waikupanaha and one Ki lava ocean entries w-edit2.jpg|thumb|250px|left|Lava enters [[Pacific]] at [[Hawaii (island)|the Big Island of Hawaii]] ]] The ideal lava flow will have a [[breccia]]ted top, either as pillow lava development, autobreccia and rubble typical of ''{{okina}}a{{okina}}ā'' and viscous flows, or a vesicular or frothy carapace such as [[scoria]] or [[pumice]]. The top of the lava will tend to be glassy, having been flash frozen in contact with the air or water. The centre of a lava flow is commonly massive and crystalline, flow banded or layered, with microscopic groundmass crystals. The more viscous lava forms tend to show sheeted flow features, and blocks or breccia entrained within the sticky lava. The crystal size at the centre of a lava will in general be greater than at the margins, as the crystals have more time to grow. The base of a lava flow may show evidence of hydrothermal activity if the lava flowed across moist or wet substrates. The lower part of the lava may have vesicles, perhaps filled with minerals ([[amygdule]]s). The substrate upon which the lava has flowed may show signs of scouring, it may be broken or disturbed by the boiling of trapped water, and in the case of soil profiles, may be baked into a brick-red [[terracotta]]. Discriminating between an intrusive [[Sill (geology)|sill]] and a lava flow in ancient rock sequences can be difficult. However, some sills do not usually have brecciated margins, and may show a weak metamorphic aureole on both the upper and lower surface, whereas a lava will only bake the substrate beneath it. However, it is often difficult in practise to identify these metamorphic phenomenon because they are usually weak and restricted in size. [[Peperite|Peperitic]] sills intruded into wet sedimentary rocks, commonly do not bake upper margins and have upper and lower autobreccias, closely similar to lavas. ==={{okina}}A{{okina}}ā=== ''{{okina}}A{{okina}}ā'' (also spelled ''aa'', ''a{{okina}}a'', ''{{okina}}a{{okina}}a'' and ''a-aa'', {{pronounced|ˈʔɑʔɑː}} in [[Hawaiian English]], from [[Hawaiian language|Hawaiian]] meaning "stony with rough lava", but also to "burn" or "blaze") is one of three basic types of flow lava. {{okina}}A{{okina}}ā is [[basalt]]ic lava characterized by a rough or rubbly surface composed of broken lava blocks called [[clinker]]. [[Image:Aa large.jpg|thumb|left|274px|Glowing {{okina}}a{{okina}}ā flow front advancing over pāhoehoe on the coastal plain of [[Kilauea|Kīlauea]] in [[Hawaii|Hawai{{okina}}i]], United States.]] The loose, broken, and sharp, spiny surface of an {{okina}}a{{okina}}ā flow makes [[hiking]] difficult and slow. The clinkery surface actually covers a massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an {{okina}}a{{okina}}ā flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an {{okina}}a{{okina}}ā flow. Accretionary lava balls as large as 3 metres (10 feet) are common on {{okina}}a{{okina}}ā flows. {{okina}}A{{okina}}ā is usually of higher viscosity than pāhoehoe. Pāhoehoe can turn into {{okina}}a{{okina}}ā if it becomes turbulent from meeting impediments or steep slopes. The sharp, angled texture makes {{okina}}a{{okina}}ā a strong radar reflector, and can easily be seen from an orbiting satellite (bright on [[Magellan probe|Magellan]] pictures). {{okina}}A{{okina}}ā lavas typically erupt at temperatures of 1000 to 1100&nbsp;°C {{clear}} ===Pāhoehoe=== [[Image:Pahoehoe lava.jpg|thumb|200px|right|Pāhoehoe lava from Kīlauea flowing through a tube system down Pulama Pali, Hawaii, United States.]] ''Pāhoehoe'' (also spelled ''pahoehoe'', {{pronEng|pəˌhoʊeˈhoʊe}}, Hawaiian English, from Hawaiian, meaning "smooth, unbroken lava") is [[basalt]]ic lava that has a smooth, billowy, undulating, or ropy surface. These surface features are due to the movement of very fluid lava under a congealing surface crust. A pāhoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. It also forms [[lava tube]]s where the minimal heat loss maintains low viscosity. The surface texture of pāhoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture. With increasing distance from the source, pāhoehoe flows may change into {{okina}}a{{okina}}ā flows in response to heat loss and consequent increase in viscosity. Pahoehoe lavas typically have a temperature of 1100 to 1200&nbsp;°C. The rounded texture makes pāhoehoe a poor radar reflector, and is difficult to see from an orbiting satellite (dark on Magellan pictures). ===Pillow lava===<!-- This section is linked from [[Volcano]] --> [[Image:Nur05018.jpg|thumb|right|170px|Pillow lava ([[NOAA]])]] ''Pillow lava'' is the [[Pillow structure|lava structure]] typically formed when lava emerges from an [[submarine volcano|underwater volcanic vent]] or [[subglacial volcano]] or a lava flow enters the ocean. However, pillow lava can also form when lava is erupted beneath thick glacial ice. The viscous lava gains a solid crust on contact with the water, and this crust cracks and oozes additional large blobs or "pillows" as more lava emerges from the advancing flow. Since water covers the majority of [[Earth]]'s surface and most volcanoes are situated near or under bodies of water, pillow lava is very common. {{clear}} == Lava landforms == Because it is formed from viscous molten rock, lava flows and eruptions create distinctive formations, landforms and topographical features from the macroscopic to the microscopic. ===Volcanoes=== [[Image:Arenallong.jpg|thumb|right|The [[Arenal Volcano]], Costa Rica, is a [[stratovolcano]].]] {{main|Volcano}} Volcanoes are the primary landforms built by repeated eruptions of lava and ash over time. They range in shape from [[shield volcano]]es with broad, shallow slopes formed from predominantly effusive eruptions of relatively fluid basaltic lava flows, to steeply-sided [[stratovolcano]]es (also known as composite volcanoes) made of alternating layers of ash and more viscous lava flows typical of intermediate and felsic lavas. A [[caldera]], which is a large subsidence crater, can form in a stratovolcano, if the magma chamber is partially or wholly emptied by large explosive eruptions; the summit cone no longer supports itself and thus collapses in on itelf afterwards. Such features may include volcanic crater lakes and lava domes after the event. However, calderas can also form by non-explosive means such as gradual magma subsidence. This is typical of many shield volcanoes. ===Cinder and spatter cones=== {{main|Volcanic cone}} [[Cinder cone]]s and spatter cones are small-scale features formed by lava accumulation around a small vent on a volcanic edifice. Cinder cones are formed from [[tephra]] or [[Volcanic ash|ash]] and [[tuff]] which is thrown from an explosive vent. Spatter cones are formed by accumulation of molten volcanic slag and cinders ejected in a more liquid form. ===Kīpukas=== {{main|Kīpuka}} Another [[Hawaiian English]] term derived from the [[Hawaiian language]], a kīpuka denotes an elevated area such as a hill, ridge or old lava dome inside or downslope from an area of active volcanism. New lava flows will cover the surrounding land, isolating the kīpuka so that it appears as a (usually) forested island in a barren lava flow. ===Lava domes=== {{main|Lava dome}} [[Image:Valle Grande dome.jpg|thumb|right|250px|A forested lava dome in the midst of the Valle Grande, the largest meadow in the [[Valles Caldera|Valles Caldera National Preserve]], New Mexico, United States.]] Lava domes are formed by the extrusion of viscous felsic magma. They can form prominent rounded protuberances, such as at [[Valles Caldera]]. As a volcano extrudes silicic lava, it can form an ''inflation dome'', gradually building up a large, pillow-like structure which cracks, fissures, and may release cooled chunks of rock and rubble. The top and side margins of an inflating lava dome tend to be covered in fragments of rock, [[breccia]] and ash. Examples of lava dome eruptions include the [[Novarupta]] dome, and successive lava domes of [[Mount St Helens]]. ===Lava tubes=== {{main|Lava tube}} 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 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 kilometres 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 Kīlauea, and significant, extensive and open lava tubes of Tertiary age are known from North [[Queensland]], [[Australia]], some extending for 15 kilometres. === Lava cascades and fountains === [[Image:Lavafall.jpg|thumb|left|150px|A lava cascade in Hawaii, United States]] [[Image:Villarrica lava fountain.jpg|thumb|right|Lava fountain within [[Villarrica (volcano)|Villarrica]]'s crater]] The eruptions of lava are sometimes attended by peculiarities which impart to them much additional grandeur. Instances have occurred in which the molten stream has plunged over a sheer precipice of immense height, so as to produce a glowing cascade exceeding (in breadth and perpendicular descent) the celebrated [[Niagara Falls]]. In other cases, the lava, instead of at once flowing down the sides of the mountain, has been first thrown up into the air as a [[lava fountain]] up to several hundred metres in height (see [[volcanic cone]]). ===Lava lakes=== {{main|Lava lake}} Rarely, a volcanic cone may fill with lava but not erupt. Lava which pools within the caldera is known as a lava lake. Lava lakes do not usually persist for long, either draining back into the magma chamber once pressure is relieved (usually by venting of gases through the caldera), or by draining via eruption of lava flows or pyroclastic explosion. There are only a few sites in the world where permanent lakes of lava exist. These include: *[[Mount Erebus]], [[Antarctica]] * [[Pu'u 'Ō'ō]] and formerly [[Kilauea|Kīlauea]] volcanoes, [[Hawaii|Hawai{{okina}}i]] *[[Erta Ale]], [[Ethiopia]] *[[Nyiragongo]], [[Democratic Republic of Congo]] [[Image:Dikes-large.jpg|thumb|right|250px|[[Shiprock]], New Mexico, United States: a volcanic neck in the distance, with radiating dike on its south side. Photo credit: [[United States Geological Survey|USGS]] Digital Data Series]] == Unusual lavas == Four types of unusual volcanic rocks have been recognised as erupting onto the surface of the Earth: * [[Carbonatite]] and [[natrocarbonatite]] lavas are known from [[Ol Doinyo Lengai]] volcano in [[Tanzania]], which is the sole example of an active carbonatite volcano.<ref>http://www.geology.sdsu.edu/how_volcanoes_work/Unusual%20lava.html Vic Camp, ''How volcanoes work'', Unusual Lava Types, San Diego State University, Geology</ref> * Copper [[sulfide]] bearing lavas have been recognised from [[Chile]] and [[Bolivia]]<ref>Guilbert, John M. and Charles F. Park, Jr.; 1986, ''The Geology of Ore Deposits'', W. H. Freeman, pp556-557, ISBN 0-7167-1456-6</ref> * [[Iron]] oxide lavas are thought to be the source of the [[iron ore]] at [[Kiruna]], [[Sweden]], erupted in the [[Proterozoic]], and in Chile associated with highly alkaline igneous rocks<ref>Guilbert, John M. and Charles F. Park, Jr.; 1986, ''The Geology of Ore Deposits'', W. H. Freeman, pp404-405, ISBN 0-7167-1456-6</ref> *Olivine [[nephelinite]] lavas are a unique type of lava that is thought to have come from much deeper in the [[mantle (geology)|mantle]] of the [[Earth]].<ref>[http://gsc.nrcan.gc.ca/volcanoes/cat/feature_volcano_e.php Catelogue of Canadian volcanoes - Stikine Volcanic Belt: Volcano Mountain] Retrieved on [[2007-11-23]]</ref> The term "lava" can also be used to refer to molten "ice mixtures" in eruptions on the icy satellites of the Solar system's gas giants<ref>McBride and Gilmore (Ed.); 2007, ''An introduction to the Solar System'', Cambridge University Press, p. 392</ref>. ==Hazards== Lava flows are enormously destructive to property in their path but generally move slowly enough for people to get out of their way, so casualties caused directly by active lava flows are rare. Nevertheless injuries and deaths have occurred, either because people had their escape route cut off, because they got too close to the flow<ref name=usgs> [http://volcanoes.usgs.gov/Hazards/What/Lava/lavaflow.html Lava Flows and Their Effects] USGS</ref> or, more rarely, if the lava flow front travelled too quickly. This notably happened during the eruption of [[Nyiragongo]] in Zaire (now [[Democratic Republic of Congo]]) on [[10 January]] [[1977]] when the crater wall was breached during the night and the fluid lava lake in it drained out in less than an hour. Flowing down the steep slopes of the volcano at up to 100&nbsp;km/h, the lava swiftly overwhelmed several villages whilst their residents were asleep. As a result of this disaster, the mountain was designated a [[Decade Volcano]] in 1991<ref name=hvo> [http://hvo.wr.usgs.gov/volcanowatch/2002/02_01_31.html Nyiragongo -- Could it happen here?] USGS Hawaiian Volcano Observatory</ref>. Deaths attributed to volcanoes frequently have a different cause, for example volcanic ejecta, [[pyroclastic flow]] from a collapsing lava dome, [[lahar]]s, poisonous gases that travel ahead of lava, or explosions caused when the flow comes into contact with water<ref name=usgs />. ==Towns destroyed by lava flows== [[Image:Kalapana house destroyed by lava.jpg|thumb|right|260px|Lava can easily destroy entire towns. This picture shows one of over 100 houses destroyed by the lava flow in [[Kalapana, Hawai'i|Kalapana, Hawai{{okina}}i]], United States, in 1990.]] *[[Kaimū, Hawai'i|Kaimū, Hawai{{okina}}i]] Destroyed by the eruption of the [[Kīlauea volcano]] in 1990. (abandoned) *[[Kalapana, Hawaii|Kalapana, Hawai{{okina}}i]] Destroyed by the eruption of the [[Kīlauea volcano]] in 1990. (abandoned) *[[Kapoho, Hawai'i|Kapoho, Hawai{{okina}}i]] Destroyed by a lava flow from an eruption of [[Kīlauea]] on [[January 28]], [[1960]]. (abandoned) *[[Keawaiki, Hawai'i|Keawaiki, Hawai{{okina}}i]] (abandoned) *[[Koae, Hawai'i|Koa{{okina}}e, Hawai{{okina}}i]] (abandoned) *[[San Sebastiano al Vesuvio|San Sebastiano al Vesuvio, Italy]] Destroyed in 1944 by the most recent eruption of [[Mount Vesuvius]] during the Allies' occupation of southern [[Italy]]. (rebuilt) *[[Daraga, Albay|Cagsawa]], [[Philippines]] <ref>[http://www.tourism.gov.ph/explore_phil/place_details.asp?content=thingstodo&province=32 Philippines Government Tourism website]</ref> ==Towns partially destroyed by lava flows== *[[Catania, Italy]], in the eruption [[Mount Etna]] in 1669 (rebuilt) *[[Goma|Goma, Democratic Republic of Congo]], in the eruption of [[Nyiragongo]] in 2002 *[[Heimaey|Heimaey, Iceland]], in the 1973 [[Eldfell]] eruption (rebuilt) *[[Royal Gardens, Hawaii|Royal Gardens, Hawai{{okina}}i]], by the eruption of [[Kilauea]] in 1986-87 (abandoned) *[[Parícutin]] (village after which the volcano was named) and [[Nuevo San Juan Parangaricutiro, Michoacán|San Juan Parangaricutiro]], Mexico, by [[Parícutin]] from 1943-1952. ==Towns destroyed by tephra== *[[Pompeii]], Italy in the eruption [[Mount Vesuvius]] in 79 AD *[[Herculaneum]], Italy in the eruption [[Mount Vesuvius]] in 79 AD *[[Sumbawa Island]], Indonesia in the eruption [[Mount Tambora]] in 1815 AD *[[Joya de Cerén|Cerén]], El Salvador in the eruption of [[Lake Ilopango|Ilopango]] between 410 and 535 AD<ref>Bundschuh, J. and Alvarado, G. E (editors) (2007) ''Central America: Geology, Resources and Hazards'', volume 1, p.56, London, Taylor and Francis</ref> .... ==References== {{reflist|2}} {{1911}} ==External links== {{commons|lava}} *[http://volcanoes.usgs.gov/Products/Pglossary/aa.html USGS definition of {{okina}}A{{okina}}ā] *[http://volcanoes.usgs.gov/Products/Pglossary/pahoehoe.html USGS definition of Pāhoehoe] *[http://volcano.und.edu/vwdocs/vwlessons/havo.html Volcanic landforms of Hawai{{okina}}i] *[http://volcanoes.usgs.gov/Hazards/What/Lava/lavaflow.html USGS hazards associated with lava flows] *[http://hvo.wr.usgs.gov/volcanowatch/2002/02_01_31.html Hawaiian Volcano Observatory Volcano Watch newsletter article on Nyiragongo eruptions, 31 January 2002] *[http://www.worldvolcanoes.info/map.html Google Maps Plot of World Volcanoes] *[http://link.brightcove.com/services/link/bcpid687239786/bclid736245450/bctid736245427 National Geographic lava video] Retrieved 23 August 2007 [[Category:Volcanology]] [[Category:Igneous rocks]] [[Category:Glassforming liquids and melts]] [[ar:حمم بركانية]] [[bg:Лава]] [[ca:Lava]] [[cs:Láva]] [[co:Lava]] [[cy:Lafa]] [[da:Lava]] [[de:Lava]] [[et:Laava]] [[es:Lava]] [[eo:Lafo]] [[fa:گدازه]] [[fr:Lave]] [[fur:Lave]] [[gl:Lava]] [[ko:용암]] [[hr:Lava]] [[id:Lava]] [[is:Hraun]] [[it:Lava]] [[he:לבה]] [[sw:Lava]] [[la:Lava]] [[lv:Lava]] [[lb:Lava]] [[lt:Lava]] [[lmo:Lava]] [[hu:Láva]] [[mr:लाव्हा]] [[ms:Lava]] [[nl:Lava]] [[nds-nl:Lava]] [[ja:溶岩]] [[no:Lava]] [[nn:Lava]] [[nds:Lava]] [[pl:Lawa]] [[pt:Lava]] [[ro:Lavă]] [[ru:Лава]] [[scn:Lava]] [[simple:Lava]] [[sk:Láva]] [[sr:Лава]] [[fi:Laava]] [[sv:Lava]] [[ta:லாவா]] [[te:లావా]] [[th:หินหลอมเหลว]] [[tr:Lav]] [[uk:Лава]] [[zh:熔岩]]'
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'{{otheruses}} {{wiktionarypar3|lava|aa|pahoehoe}} '''Lava''' is molten [[Rock (geology)|rock]] expelled by a [[volcano]] during an eruption. When first expelled from a volcanic vent, it is a [[liquid]] at [[temperature]]s from 700&nbsp;°C to 1,200&nbsp;°C (1,300&nbsp;°F to 2,200&nbsp;°F). Although lava is quite [[viscosity|viscous]], with about 100,000 times the [[viscosity]] of water, it can flow great distances before cooling and solidifying, because of both its [[thixotropy|thixotropic]] and [[shear thinning]] properties.<ref>{{cite web |url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VCS-4B6CPRP-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=062e0c42281eb5e5d185d5e78aa1e0f7 |title=ScienceDirect - Journal of Volcanology and Geothermal Research : Transient phenomena in vesicular lava flows based on laboratory experiments with analogue materials|publisher=www.sciencedirect.com|accessdate=2008-06-19|last=H. Pinkerton|first=N. Bagdassarov }}</ref><ref>{{cite web|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=5970696|title=Rheological properties of basaltic lavas at sub-liquidus temperatures: laboratory and field measurements on lavas from Mount Etna|publisher=cat.inist.fr|accessdate=2008-06-19}}</ref> A ''lava flow'' is a moving outpouring of lava, which is created during a non-explosive [[effusive eruption]]. When it has stopped moving, lava solidifies to form [[igneous rock]]. The term ''lava flow'' is commonly shortened to ''lava''. [[Explosive eruption]]s produce a mixture of [[volcanic ash]] and other fragments called [[tephra]], rather than lava flows. The word 'lava' comes from Italian, and is probably derived from the [[Latin]] word ''labes'' which means a fall or slide.<ref>[http://www.m-w.com/dictionary/lava Merriam-Webster OnLine dictionary]</ref><ref>[http://dictionary.reference.com/browse/lava Dictionary.com]</ref> The first use in connection with extruded [[magma]] (molten rock below the earth's surface) was apparently in a short account written by [[Francesco Serao]] on the eruption of [[Vesuvius]] between May 14 and June 4, 1737.<ref>[http://www.lindahall.org/events_exhib/exhibit/exhibits/vulcan/9.shtml Vesuvius Erupts, 1738<!-- Bot generated title -->]</ref> Serao described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of the volcano following heavy [[rain]]. [[Image:Pahoeoe fountain edit2.jpg|thumb|right|250px|33 ft (10 m) high fountain of lava, Hawaii, United States]] == Lava composition == [[File:Pāhoehoe and Aa flows at Hawaii.jpg|Pāhoehoe and ʻAʻā lava flows side by side at the Big Island of Hawaii in September, 2007|thumb|300px]] In general, the composition of a lava determines its behavior more than the temperature of its eruption. Igneous rocks, which form lava flows when erupted, can be classified into three chemical types; [[felsic]], intermediate, and [[mafic]]. These classes are primarily chemical; however, the chemistry of lava also tends to correlate with the magma temperature, its viscosity and its mode of eruption. ''[[Felsic]]'' lavas such as [[rhyolite]] and [[dacite]] typically form [[lava spine]]s, [[lava dome]]s or 'coulees' (which are thick, short lavas) and are associated with [[pyroclastic]] (fragmental) deposits. Most felsic lava flows are extremely viscous, and typically fragment as they extrude, producing blocky autobreccias. The high viscosity and strength are the result of their chemistry, which is high in [[silica]], [[aluminium]], [[potassium]], [[sodium]], and [[calcium]], forming a [[polymer]]ized liquid rich in [[feldspar]] and [[quartz]], which thus has a higher viscosity than other magma types. Felsic magmas can erupt at temperatures as low as 650 to 750&nbsp;°C. Unusually hot (>950&nbsp;°C) rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in the [[Snake River Plain]] of the northwestern United States. ''Intermediate'' or [[andesite|andesitic]] lavas are lower in aluminium and silica, and usually somewhat richer in [[magnesium]] and [[iron]]. Intermediate lavas form [[andesite]] domes and block lavas, and may occur on steep composite volcanoes, such as in the [[Andes]]. Poorer in aluminium and silica than felsic lavas, and also commonly hotter (in the range of 750 to 950&nbsp;°C), they tend to be less viscous. Greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and also a greater tendency to form [[phenocrysts]]. Higher iron and magnesium tends to manifest as a darker [[groundmass]], and also occasionally [[amphibole]] or [[pyroxene]] [[phenocryst]]s. ''[[Mafic]]'' or [[basalt]]ic lavas are typified by their high ferromagnesian content, and generally erupt at temperatures in excess of 950&nbsp;°C. Basaltic magma is high in iron and magnesium, and has relatively lower aluminium and silica, which taken together reduces the degree of polymerization within the melt. Owing to the higher temperatures, viscosities can be relatively low, although still thousands of times more viscous than water. The low degree of polymerization and high temperature favors chemical diffusion, so it is common to see large, well-formed phenocrysts within mafic lavas. Basalt lavas tend to produce low-profile [[shield volcano]]es or '[[flood basalt]] fields', because the fluidal lava flows for long distances from the vent. The thickness of a basalt lava, particularly on a low slope, may be much greater than the thickness of the moving lava flow at any one time, because basalt lavas may 'inflate' by supply of lava beneath a solidified crust. Most basalt lavas are of a'a or 'pahoehoe' types, rather than block lavas. Underwater they can form '[[pillow lavas]]', which are rather similar to entrail-type pahoehoe lavas on land. ''[[Ultramafic rock|Ultramafic]]'' lavas such as [[komatiite]] and highly magnesian magmas which form [[boninite]] take the composition and temperatures of eruptions to the extreme. Komatiites contain over 18% magnesium oxide, and are thought to have erupted at temperatures of 1600&nbsp;°C. At this temperature there is no polymerization of the mineral compounds, creating a highly mobile liquid with viscosity as low as that of water. Most if not all ultramafic lavas are no younger than the [[Proterozoic]], with a few ultramafic magmas known from the [[Phanerozoic]]. No modern komatiite lavas are known, as the Earth's mantle has cooled too much to produce highly magnesian magmas. ===Lava behavior=== [[Image:PahoehoeLava.jpg|thumb|right|150px|Toes of a pāhoehoe advance across a road in [[Kalapana, Hawaii|Kalapana]] on the east rift zone of [[Kilauea|Kīlauea]] Volcano in [[Hawaii|Hawaii,United States.]]]] The viscosity of lava is important because it determines how the lava will behave. Lavas with high viscosity are [[rhyolite]], [[dacite]], [[andesite]] and [[trachyte]], with cooled basaltic lava also quite viscous; those with low viscosities are freshly erupted [[basalt]], [[carbonatite]] and occasionally [[andesite]]. Highly viscous lava shows the following behaviors: *tends to flow slowly, clog, and form semi-solid blocks which resist flow *tends to entrap [[Volcanic gas|gas]], which form [[vesicle]]s (bubbles) within the rock as they rise to the surface *correlates with explosive or [[phreatic]] eruptions and is associated with [[tuff]] and [[pyroclastic]] flows Highly viscous lavas do not usually flow as liquid, and usually form explosive fragmental ash or [[tephra]] deposits. However, a degassed viscous lava or one which erupts somewhat hotter than usual may form a lava flow. Lava with low viscosity shows the following behaviors: *tends to flow easily, forming puddles, channels, and rivers of molten rock *tends to easily release bubbling gases as they are formed *eruptions are rarely pyroclastic and are usually quiescent *volcanoes tend to form broad shields rather than steep cones There are three forms of low-viscosity lava flows: ''{{okina}}a{{okina}}ā'', ''pāhoehoe'', and ''pillow lava''. They are described in relation to basaltic flows from Hawaii, shown in the following sections. Lavas also may contain many other components, sometimes including solid crystals of various minerals, fragments of exotic rocks known as [[xenolith]]s and fragments of previously solidified lava. ==Volcanic morphologies== [[Image:Lava entering sea - Hawaii.png|thumb|right|250px|Lava entering the sea to expand the [[Hawaii (island)|big island of Hawaii]], [[Hawaii Volcanoes National Park]].]] The physical behavior of lava creates the physical forms of a lava flow or volcano. More fluid basaltic lava flows tend to form flat sheet-like bodies, whereas viscous rhyolite lava flows forms knobbly, blocky masses of rock. General features of [[volcanology]] can be used to classify volcanic edifices and provide information on the eruptions which formed the lava flow, even if the sequence of lavas have been buried or metamorphosed. [[Image:Three Waikupanaha and one Ki lava ocean entries w-edit2.jpg|thumb|250px|left|Lava enters [[Pacific]] at [[Hawaii (island)|the Big Island of Hawaii]] ]] The ideal lava flow will have a [[breccia]]ted top, either as pillow lava development, autobreccia and rubble typical of ''{{okina}}a{{okina}}ā'' and viscous flows, or a vesicular or frothy carapace such as [[scoria]] or [[pumice]]. The top of the lava will tend to be glassy, having been flash frozen in contact with the air or water. The centre of a lava flow is commonly massive and crystalline, flow banded or layered, with microscopic groundmass crystals. The more viscous lava forms tend to show sheeted flow features, and blocks or breccia entrained within the sticky lava. The crystal size at the centre of a lava will in general be greater than at the margins, as the crystals have more time to grow. The base of a lava flow may show evidence of hydrothermal activity if the lava flowed across moist or wet substrates. The lower part of the lava may have vesicles, perhaps filled with minerals ([[amygdule]]s). The substrate upon which the lava has flowed may show signs of scouring, it may be broken or disturbed by the boiling of trapped water, and in the case of soil profiles, may be baked into a brick-red [[terracotta]]. Discriminating between an intrusive [[Sill (geology)|sill]] and a lava flow in ancient rock sequences can be difficult. However, some sills do not usually have brecciated margins, and may show a weak metamorphic aureole on both the upper and lower surface, whereas a lava will only bake the substrate beneath it. However, it is often difficult in practise to identify these metamorphic phenomenon because they are usually weak and restricted in size. [[Peperite|Peperitic]] sills intruded into wet sedimentary rocks, commonly do not bake upper margins and have upper and lower autobreccias, closely similar to lavas. ==={{okina}}A{{okina}}ā=== ''{{okina}}A{{okina}}ā'' (also spelled ''aa'', ''a{{okina}}a'', ''{{okina}}a{{okina}}a'' and ''a-aa'', {{pronounced|ˈʔɑʔɑː}} in [[Hawaiian English]], from [[Hawaiian language|Hawaiian]] meaning "stony with rough lava", but also to "burn" or "blaze") is one of three basic types of flow lava. {{okina}}A{{okina}}ā is [[basalt]]ic lava characterized by a rough or rubbly surface composed of broken lava blocks called [[clinker]]. [[Image:Aa large.jpg|thumb|left|274px|Glowing {{okina}}a{{okina}}ā flow front advancing over pāhoehoe on the coastal plain of [[Kilauea|Kīlauea]] in [[Hawaii|Hawai{{okina}}i]], United States.]] The loose, broken, and sharp, spiny surface of an {{okina}}a{{okina}}ā flow makes [[hiking]] difficult and slow. The clinkery surface actually covers a massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an {{okina}}a{{okina}}ā flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an {{okina}}a{{okina}}ā flow. Accretionary lava balls as large as 3 metres (10 feet) are common on {{okina}}a{{okina}}ā flows. {{okina}}A{{okina}}ā is usually of higher viscosity than pāhoehoe. Pāhoehoe can turn into {{okina}}a{{okina}}ā if it becomes turbulent from meeting impediments or steep slopes. The sharp, angled texture makes {{okina}}a{{okina}}ā a strong radar reflector, and can easily be seen from an orbiting satellite (bright on [[Magellan probe|Magellan]] pictures). {{okina}}A{{okina}}ā lavas typically erupt at temperatures of 1000 to 1100&nbsp;°C {{clear}} ===Pāhoehoe=== [[Image:Pahoehoe lava.jpg|thumb|200px|right|Pāhoehoe lava from Kīlauea flowing through a tube system down Pulama Pali, Hawaii, United States.]] ''Pāhoehoe'' (also spelled ''pahoehoe'', {{pronEng|pəˌhoʊeˈhoʊe}}, Hawaiian English, from Hawaiian, meaning "smooth, unbroken lava") is [[basalt]]ic lava that has a smooth, billowy, undulating, or ropy surface. These surface features are due to the movement of very fluid lava under a congealing surface crust. A pāhoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. It also forms [[lava tube]]s where the minimal heat loss maintains low viscosity. The surface texture of pāhoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture. With increasing distance from the source, pāhoehoe flows may change into {{okina}}a{{okina}}ā flows in response to heat loss and consequent increase in viscosity. Pahoehoe lavas typically have a temperature of 1100 to 1200&nbsp;°C. The rounded texture makes pāhoehoe a poor radar reflector, and is difficult to see from an orbiting satellite (dark on Magellan pictures). ===Pillow lava===<!-- This section is linked from [[Volcano]] --> [[Image:Nur05018.jpg|thumb|right|170px|Pillow lava ([[NOAA]])]] ''Pillow lava'' is the [[Pillow structure|lava structure]] typically formed when lava emerges from an [[submarine volcano|underwater volcanic vent]] or [[subglacial volcano]] or a lava flow enters the ocean. However, pillow lava can also form when lava is erupted beneath thick glacial ice. The viscous lava gains a solid crust on contact with the water, and this crust cracks and oozes additional large blobs or "pillows" as more lava emerges from the advancing flow. Since water covers the majority of [[Earth]]'s surface and most volcanoes are situated near or under bodies of water, pillow lava is very common. {{clear}} == Lava landforms == Because it is formed from viscous molten rock, lava flows and eruptions create distinctive formations, landforms and topographical features from the macroscopic to the microscopic. ===Volcanoes=== [[Image:Arenallong.jpg|thumb|right|The [[Arenal Volcano]], Costa Rica, is a [[stratovolcano]].]] {{main|Volcano}} Volcanoes are the primary landforms built by repeated eruptions of lava and ash over time. They range in shape from [[shield volcano]]es with broad, shallow slopes formed from predominantly effusive eruptions of relatively fluid basaltic lava flows, to steeply-sided [[stratovolcano]]es (also known as composite volcanoes) made of alternating layers of ash and more viscous lava flows typical of intermediate and felsic lavas. A [[caldera]], which is a large subsidence crater, can form in a stratovolcano, if the magma chamber is partially or wholly emptied by large explosive eruptions; the summit cone no longer supports itself and thus collapses in on itelf afterwards. Such features may include volcanic crater lakes and lava domes after the event. However, calderas can also form by non-explosive means such as gradual magma subsidence. This is typical of many shield volcanoes. ===Cinder and spatter cones=== {{main|Volcanic cone}} [[Cinder cone]]s and spatter cones are small-scale features formed by lava accumulation around a small vent on a volcanic edifice. Cinder cones are formed from [[tephra]] or [[Volcanic ash|ash]] and [[tuff]] which is thrown from an explosive vent. Spatter cones are formed by accumulation of molten volcanic slag and cinders ejected in a more liquid form. ===Kīpukas=== {{main|Kīpuka}} Another [[Hawaiian English]] term derived from the [[Hawaiian language]], a kīpuka denotes an elevated area such as a hill, ridge or old lava dome inside or downslope from an area of active volcanism. New lava flows will cover the surrounding land, isolating the kīpuka so that it appears as a (usually) forested island in a barren lava flow. ===Lava domes=== {{main|Lava dome}} [[Image:Valle Grande dome.jpg|thumb|right|250px|A forested lava dome in the midst of the Valle Grande, the largest meadow in the [[Valles Caldera|Valles Caldera National Preserve]], New Mexico, United States.]] Lava domes are formed by the extrusion of viscous felsic magma. They can form prominent rounded protuberances, such as at [[Valles Caldera]]. As a volcano extrudes silicic lava, it can form an ''inflation dome'', gradually building up a large, pillow-like structure which cracks, fissures, and may release cooled chunks of rock and rubble. The top and side margins of an inflating lava dome tend to be covered in fragments of rock, [[breccia]] and ash. Examples of lava dome eruptions include the [[Novarupta]] dome, and successive lava domes of [[Mount St Helens]]. ===Lava tubes=== {{main|Lava tube}} 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 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 kilometres 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 Kīlauea, and significant, extensive and open lava tubes of Tertiary age are known from North [[Queensland]], [[Australia]], some extending for 15 kilometres. === Lava cascades and fountains === [[Image:Lavafall.jpg|thumb|left|150px|A lava cascade in Hawaii, United States]] [[Image:Villarrica lava fountain.jpg|thumb|right|Lava fountain within [[Villarrica (volcano)|Villarrica]]'s crater]] The eruptions of lava are sometimes attended by peculiarities which impart to them much additional grandeur. Instances have occurred in which the molten stream has plunged over a sheer precipice of immense height, so as to produce a glowing cascade exceeding (in breadth and perpendicular descent) the celebrated [[Niagara Falls]]. In other cases, the lava, instead of at once flowing down the sides of the mountain, has been first thrown up into the air as a [[lava fountain]] up to several hundred metres in height (see [[volcanic cone]]). ===Lava lakes=== {{main|Lava lake}} Rarely, a volcanic cone may fill with lava but not erupt. Lava which pools within the caldera is known as a lava lake. Lava lakes do not usually persist for long, either draining back into the magma chamber once pressure is relieved (usually by venting of gases through the caldera), or by draining via eruption of lava flows or pyroclastic explosion. There are only a few sites in the world where permanent lakes of lava exist. These include: *[[Mount Erebus]], [[Antarctica]] * [[Pu'u 'Ō'ō]] and formerly [[Kilauea|Kīlauea]] volcanoes, [[Hawaii|Hawai{{okina}}i]] *[[Erta Ale]], [[Ethiopia]] *[[Nyiragongo]], [[Democratic Republic of Congo]] [[Image:Dikes-large.jpg|thumb|right|250px|[[Shiprock]], New Mexico, United States: a volcanic neck in the distance, with radiating dike on its south side. Photo credit: [[United States Geological Survey|USGS]] Digital Data Series]] == Unusual lavas == Four types of unusual volcanic rocks have been recognised as erupting onto the surface of the Earth: * [[Carbonatite]] and [[natrocarbonatite]] lavas are known from [[Ol Doinyo Lengai]] volcano in [[Tanzania]], which is the sole example of an active carbonatite volcano.<ref>http://www.geology.sdsu.edu/how_volcanoes_work/Unusual%20lava.html Vic Camp, ''How volcanoes work'', Unusual Lava Types, San Diego State University, Geology</ref> * Copper [[sulfide]] bearing lavas have been recognised from [[Chile]] and [[Bolivia]]<ref>Guilbert, John M. and Charles F. Park, Jr.; 1986, ''The Geology of Ore Deposits'', W. H. Freeman, pp556-557, ISBN 0-7167-1456-6</ref> * [[Iron]] oxide lavas are thought to be the source of the [[iron ore]] at [[Kiruna]], [[Sweden]], erupted in the [[Proterozoic]], and in Chile associated with highly alkaline igneous rocks<ref>Guilbert, John M. and Charles F. Park, Jr.; 1986, ''The Geology of Ore Deposits'', W. H. Freeman, pp404-405, ISBN 0-7167-1456-6</ref> *Olivine [[nephelinite]] lavas are a unique type of lava that is thought to have come from much deeper in the [[mantle (geology)|mantle]] of the [[Earth]].<ref>[http://gsc.nrcan.gc.ca/volcanoes/cat/feature_volcano_e.php Catelogue of Canadian volcanoes - Stikine Volcanic Belt: Volcano Mountain] Retrieved on [[2007-11-23]]</ref> The term "lava" can also be used to refer to molten "ice mixtures" in eruptions on the icy satellites of the Solar system's gas giants<ref>McBride and Gilmore (Ed.); 2007, ''An introduction to the Solar System'', Cambridge University Press, p. 392</ref>. ==Hazards== Lava flows are enormously destructive to property in their path but generally move slowly enough for people to get out of their way, so casualties caused directly by active lava flows are rare. Nevertheless injuries and deaths have occurred, either because people had their escape route cut off, because they got too close to the flow<ref name=usgs> [http://volcanoes.usgs.gov/Hazards/What/Lava/lavaflow.html Lava Flows and Their Effects] USGS</ref> or, more rarely, if the lava flow front travelled too quickly. This notably happened during the eruption of [[Nyiragongo]] in Zaire (now [[Democratic Republic of Congo]]) on [[10 January]] [[1977]] when the crater wall was breached during the night and the fluid lava lake in it drained out in less than an hour. Flowing down the steep slopes of the volcano at up to 100&nbsp;km/h, the lava swiftly overwhelmed several villages whilst their residents were asleep. As a result of this disaster, the mountain was designated a [[Decade Volcano]] in 1991<ref name=hvo> [http://hvo.wr.usgs.gov/volcanowatch/2002/02_01_31.html Nyiragongo -- Could it happen here?] USGS Hawaiian Volcano Observatory</ref>. Deaths attributed to volcanoes frequently have a different cause, for example volcanic ejecta, [[pyroclastic flow]] from a collapsing lava dome, [[lahar]]s, poisonous gases that travel ahead of lava, or explosions caused when the flow comes into contact with water<ref name=usgs />. ==Towns destroyed by lava flows== [[Image:Kalapana house destroyed by lava.jpg|thumb|right|260px|Lava can easily destroy entire towns. This picture shows one of over 100 houses destroyed by the lava flow in [[Kalapana, Hawai'i|Kalapana, Hawai{{okina}}i]], United States, in 1990.]] *[[Kaimū, Hawai'i|Kaimū, Hawai{{okina}}i]] Destroyed by the eruption of the [[Kīlauea volcano]] in 1990. (abandoned) *[[Kalapana, Hawaii|Kalapana, Hawai{{okina}}i]] Destroyed by the eruption of the [[Kīlauea volcano]] in 1990. (abandoned) *[[Kapoho, Hawai'i|Kapoho, Hawai{{okina}}i]] Destroyed by a lava flow from an eruption of [[Kīlauea]] on [[January 28]], [[1960]]. (abandoned) *[[Keawaiki, Hawai'i|Keawaiki, Hawai{{okina}}i]] (abandoned) *[[Koae, Hawai'i|Koa{{okina}}e, Hawai{{okina}}i]] (abandoned) *[[San Sebastiano al Vesuvio|San Sebastiano al Vesuvio, Italy]] Destroyed in 1944 by the most recent eruption of [[Mount Vesuvius]] during the Allies' occupation of southern [[Italy]]. (rebuilt) *[[Daraga, Albay|Cagsawa]], [[Philippines]] <ref>[http://www.tourism.gov.ph/explore_phil/place_details.asp?content=thingstodo&province=32 Philippines Government Tourism website]</ref> ==Towns partially destroyed by lava flows== *[[Catania, Italy]], in the eruption [[Mount Etna]] in 1669 (rebuilt) *[[Goma|Goma, Democratic Republic of Congo]], in the eruption of [[Nyiragongo]] in 2002 *[[Heimaey|Heimaey, Iceland]], in the 1973 [[Eldfell]] eruption (rebuilt) *[[Royal Gardens, Hawaii|Royal Gardens, Hawai{{okina}}i]], by the eruption of [[Kilauea]] in 1986-87 (abandoned) *[[Parícutin]] (village after which the volcano was named) and [[Nuevo San Juan Parangaricutiro, Michoacán|San Juan Parangaricutiro]], Mexico, by [[Parícutin]] from 1943-1952. ==Towns destroyed by tephra== *[[Pompeii]], Italy in the eruption [[Mount Vesuvius]] in 79 AD *[[Herculaneum]], Italy in the eruption [[Mount Vesuvius]] in 79 AD *[[Sumbawa Island]], Indonesia in the eruption [[Mount Tambora]] in 1815 AD *[[Joya de Cerén|Cerén]], El Salvador in the eruption of [[Lake Ilopango|Ilopango]] between 410 and 535 AD<ref>Bundschuh, J. and Alvarado, G. E (editors) (2007) ''Central America: Geology, Resources and Hazards'', volume 1, p.56, London, Taylor and Francis</ref> .... ==References== {{reflist|2}} {{1911}} ==External links== {{commons|lava}} *[http://www.youtube.com/watch?v=SaQZFaKx69Q Pillow lava formation underwater] *[http://volcanoes.usgs.gov/Products/Pglossary/aa.html USGS definition of {{okina}}A{{okina}}ā] *[http://volcanoes.usgs.gov/Products/Pglossary/pahoehoe.html USGS definition of Pāhoehoe] *[http://volcano.und.edu/vwdocs/vwlessons/havo.html Volcanic landforms of Hawai{{okina}}i] *[http://volcanoes.usgs.gov/Hazards/What/Lava/lavaflow.html USGS hazards associated with lava flows] *[http://hvo.wr.usgs.gov/volcanowatch/2002/02_01_31.html Hawaiian Volcano Observatory Volcano Watch newsletter article on Nyiragongo eruptions, 31 January 2002] *[http://www.worldvolcanoes.info/map.html Google Maps Plot of World Volcanoes] *[http://link.brightcove.com/services/link/bcpid687239786/bclid736245450/bctid736245427 National Geographic lava video] Retrieved 23 August 2007 [[Category:Volcanology]] [[Category:Igneous rocks]] [[Category:Glassforming liquids and melts]] [[ar:حمم بركانية]] [[bg:Лава]] [[ca:Lava]] [[cs:Láva]] [[co:Lava]] [[cy:Lafa]] [[da:Lava]] [[de:Lava]] [[et:Laava]] [[es:Lava]] [[eo:Lafo]] [[fa:گدازه]] [[fr:Lave]] [[fur:Lave]] [[gl:Lava]] [[ko:용암]] [[hr:Lava]] [[id:Lava]] [[is:Hraun]] [[it:Lava]] [[he:לבה]] [[sw:Lava]] [[la:Lava]] [[lv:Lava]] [[lb:Lava]] [[lt:Lava]] [[lmo:Lava]] [[hu:Láva]] [[mr:लाव्हा]] [[ms:Lava]] [[nl:Lava]] [[nds-nl:Lava]] [[ja:溶岩]] [[no:Lava]] [[nn:Lava]] [[nds:Lava]] [[pl:Lawa]] [[pt:Lava]] [[ro:Lavă]] [[ru:Лава]] [[scn:Lava]] [[simple:Lava]] [[sk:Láva]] [[sr:Лава]] [[fi:Laava]] [[sv:Lava]] [[ta:லாவா]] [[te:లావా]] [[th:หินหลอมเหลว]] [[tr:Lav]] [[uk:Лава]] [[zh:熔岩]]'
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