Lava

10-metre-high (33 ft) fountain of pāhoehoe lava, Hawaii, United States
Lava flow during a rift eruption at Krafla, Iceland in 1984

Lava is molten rock generated by geothermal energy and expelled through fractures in planetary crust or in an eruption, usually at temperatures from 700 to 1,200 °C (1,292 to 2,192 °F). The structures resulting from subsequent solidification and cooling are also sometimes described as lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites, though such material located below the crust is referred to by other terms.

A lava flow is a moving outpouring of lava 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. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic and shear thinning properties.[1][2]

Explosive eruptions 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.[3][4] 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 in 1737.[5] 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.

Lava composition

Pāhoehoe and ʻaʻā lava flows side by side in Hawaii, September 2007

The composition of almost all lava of the Earth's crust is dominated by silicate minerals: mostly feldspars, olivine, pyroxenes, amphiboles, micas and quartz.

Silicate lavas

Silicate lavas can be classified into three chemical types: felsic, intermediate, and mafic (four if one includes the super-heated ultramafic). These classes are primarily chemical; however, the chemistry of lava also tends to correlate with the magma temperature, viscosity and mode of eruption.

Felsic lava

Felsic or silicic lavas such as rhyolite and dacite typically form lava spines, lava domes or "coulees" (which are thick, short lava flows) and are associated with pyroclastic (fragmental) deposits. Most silicic 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 polymerized liquid rich in feldspar and quartz, and thus has a higher viscosity than other magma types. Felsic magmas can erupt at temperatures as low as 650 to 750 °C (1,202 to 1,382 °F). Unusually hot (>950 °C; >1,740 °F) 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 lava

Intermediate or 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 °C (1,380 to 1,740 °F)), 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 phenocrysts.

Mafic lava

Mafic or basaltic lavas are typified by their high ferromagnesian content, and generally erupt at temperatures in excess of 950 °C (1,740 °F). 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 higher 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 volcanoes 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 ʻAʻā or pāhoehoe types, rather than block lavas. Underwater, they can form pillow lavas, which are rather similar to entrail-type pahoehoe lavas on land.

Ultramafic lava

Ultramafic lavas such as komatiite and highly magnesian magmas that 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 1,600 °C (2,910 °F). At this temperature there is no polymerization of the mineral compounds, creating a highly mobile liquid.[6] 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.

Unusual lavas

Some lavas of unusual composition have erupted onto the surface of the Earth. These include:

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.[11] (See cryovolcanism).

Other Languages
Afrikaans: Lawa
العربية: حمم
Avañe'ẽ: Tata hyku
azərbaycanca: Lava
বাংলা: লাভা
Bân-lâm-gú: Iûⁿ-gâm
беларуская: Лава вулканічная
беларуская (тарашкевіца)‎: Лява
भोजपुरी: लावा
български: Лава
català: Lava
čeština: Láva
corsu: Lava
Cymraeg: Lafa
dansk: Lava
Deutsch: Lava
eesti: Laava
Ελληνικά: Λάβα
español: Lava
Esperanto: Lafo
euskara: Laba
فارسی: گدازه
français: Lave
Frysk: Lava
furlan: Lave
Gaeilge: Laibhe
galego: Lava
한국어: 용암
հայերեն: Լավա
हिन्दी: लावा
hrvatski: Lava
Ido: Lavao
Bahasa Indonesia: Lava
íslenska: Hraun
italiano: Lava
עברית: לבה
Jawa: Lava
ಕನ್ನಡ: ಲಾವ ರಸ
ქართული: ლავა
қазақша: Лава
Kiswahili: Lava (volkeno)
Kreyòl ayisyen: Lav
Кыргызча: Лава
Latina: Lava
latviešu: Lava
Lëtzebuergesch: Lava
lietuvių: Lava
Limburgs: Lava
lumbaart: Lava
magyar: Láva
македонски: Лава
മലയാളം: ലാവ
Malti: Lava
मराठी: शिलारस
მარგალური: ლავა
Bahasa Melayu: Lava
Nederlands: Lava
Nedersaksies: Lava
日本語: 溶岩
norsk: Lava
norsk nynorsk: Lava
occitan: Lava
oʻzbekcha/ўзбекча: Lava
ਪੰਜਾਬੀ: ਲਾਵਾ
پنجابی: لاوا
Picard: Lave
Plattdüütsch: Lava
polski: Lawa
português: Lava
română: Lavă
Runa Simi: Ratata
русский: Лава
Scots: Lava
sicilianu: Lava
Simple English: Lava
slovenčina: Láva
slovenščina: Lava
српски / srpski: Лава
srpskohrvatski / српскохрватски: Lava
suomi: Laava
svenska: Lava
తెలుగు: లావా
Türkçe: Lav
українська: Лава
اردو: لاوا
Tiếng Việt: Dung nham
Volapük: Lavat
Winaray: Lava
吴语: 熔岩
粵語: 熔岩
žemaitėška: Lava
中文: 熔岩