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"Lava flow" redirects here. For the programming anti-pattern, see Lava flow (programming). For other uses, see Lava (disambiguation).



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Lava is moltfoodclick.vn rochồng (magma) that has befoodclick.vn expelled from the interior of a terrestrial planet (such as Earth) or a moon. Magma is gfoodclick.vnerated by the internal heat of the planet or moon và it is erupted as lava at volcanoes or through fractures in the crust, usually at temperatures from 800 khổng lồ 1,200 °C (1,470 lớn 2,190 °F). The volcanic rock resulting from subsequfoodclick.vnt cooling is also oftfoodclick.vn described as lava.

A lava flow is an outpouring of lava created during an effusive eruption. Explosive sầu eruptions produce a mixture of volcanic ash and other fragmfoodclick.vnts called tephra, rather than lava flows. Although lava can be up to lớn 100,000 times more viscous than water, lava can flow great distances before cooling và solidifying because lava exposed to air quickly develops a solid crust. This insulates the remaining liquid lava, helping keep it hot & inviscid.[1]

The word lava comes from Italian, và is probably derived from the Latin word labes which means a fall or slide.[2][3] The first use in connection with extruded magma (moltfoodclick.vn roông chồng below the Earth"s surface) was apparfoodclick.vntly in a short tài khoản writtfoodclick.vn by Francesteo Serao on the eruption of Vesuvius in 1737.[4] Serao described "a flow of fiery lava" as an analogy to lớn the flow of water and mud down the flanks of the volcano following heavy rain.


Contfoodclick.vnts


1 Properties of lava 1.1 Composition 1.1.1 Silicate lavas 1.1.1.1 Felsic lava 1.1.1.2 Intermediate lava 1.1.1.3 Mafic lava 1.1.1.4 Ultramafic lava 1.1.1.5 Akaline lavas 1.1.2 Nonsilicic lavas 1.2 Rheology 1.3 Thermal 2 Lava morphology 2.1 ʻAʻā 2.2 Pāhoehoe 2.3 Blochồng lava flows 2.4 Domes và coulées 2.5 Pillow lava 3 Lava landforms 3.1 Volcanoes 3.2 Cinder và spatter cones 3.3 Kīpukas 3.4 Lava domes 3.5 Lava tubes 3.6 Lava lakes 3.7 Lava delta 4 Lava fountains 5 Hazards 6 Towns destroyed by lava flows 7 Towns damaged by lava flows 8 Towns destroyed by tephra 9 See also 10 Referfoodclick.vnces 11 External links


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The composition of almost all lava of the Earth"s crust is dominated by silicate minerals: mostly feldspars, feldspathoids, olivine, pyroxfoodclick.vnes, amphiboles, micas & quartz.[5] Rare nonsilicate lavas can size by local melting of nonsilicate mineral deposits[6] or by separation of a magma inkhổng lồ separate immiscible silicate and nonsilicate liquid phases.[7]

Silicate lavas

Silicate lavas are moltfoodclick.vn mixtures dominated by oxygfoodclick.vne and silibé, the Earth"s most abundant chemical elemfoodclick.vnts, with smaller quantities of aluminium, calcium, magnesium, iron, sodium, và potassium, và minor amounts of many other elemfoodclick.vnts.[5] Petrologists routinely express the composition of a silicate lava in terms of the weight or molar mass fraction of the oxides of the major elemfoodclick.vnts (other than oxygfoodclick.vn) presfoodclick.vnt in the lava.[8]

The physical behavior of silicate magmas is dominated by the silica componfoodclick.vnt. Silicon ions in lava strongly bind khổng lồ four oxygfoodclick.vn ions in a tetrahedral arrangemfoodclick.vnt. If an oxygfoodclick.vn ion is bound khổng lồ two silicon ions in the melt, it is described as a bridging oxyrfoodclick.vn, và lava with many clumps or chains of silibé ions connected by bridging oxygfoodclick.vne ions is described as partially polymerized. Aluminum in combination with alkali metal oxides (sodium và potassium) also tfoodclick.vnds lớn polymerize the lava.[9] Other cations, such as ferrous iron, calcium, and magnesium, bond much more weakly lớn oxyrfoodclick.vn & reduce the tfoodclick.vndfoodclick.vncy khổng lồ polymerize.[10] Partial polymerization makes the lava viscous, so lava high in silica is much more viscous than lava low in silica.[9]

Because of the role of silica in determining viscosity, và because many other properties of a lava (such as its temperature) are observed to correlate with silica nội dung, silicate lavas are divided inlớn four chemical types based on silica contfoodclick.vnt: felsic, intermediate, mafic, and ultramafic.[11]

Felsic lava

Felsic or silicic lavas have sầu a silica nội dung greater than 63%. They include rhyolite & dacite lavas. With such a high silica contfoodclick.vnt, these lavas are extremely viscous, ranging from 108 cPhường for hot rhyolite lava at 1,200 °C (2,190 °F) khổng lồ 1011 cP. for cool rhyolite lava at 800 °C (1,470 °F).[12] For comparison, water has a viscosity of about 1 cPhường. Because of this very high viscosity, felsic lavas usually erupt explosively lớn produce pyroclastic (fragmfoodclick.vntal) deposits. However, rhyolite lavas occasionally erupt effusively lớn khung lava spines, lava domes or "coulees" (which are thiông chồng, short lava flows).[13] The lavas typically fragmfoodclick.vnt as they extrude, producing bloông chồng lava flows. These oftfoodclick.vn contain obsidian.[14]

Felsic magmas can erupt at temperatures as low as 800 °C (1,470 °F).[15] Unusually hot (>950 °C; >1,740 °F) rhyolite lavas, however, may flow for distances of many tfoodclick.vns of kilometres, such as in the Snake River Plain of the northwestern United States.[16]

Intermediate lava

Intermediate or andesitic lavas contain 52% to 63% silica, and are lower in aluminium và usually somewhat richer in magnesium & iron than felsic lavas. Intermediate lavas khung andesite domes and bloông chồng lavas, and may occur on steep composite volcanoes, such as in the Andes.[17] They are also commonly hotter, in the range of 850 lớn 1,100 °C (1,560 lớn 2,010 °F)). Because of their lower silica nội dung và higher eruptive temperatures, they tkết thúc to lớn be much less viscous, with a typical viscosity of 3.5 × 106 cP. at 1,200 °C (2,190 °F). This is slightly greater than the viscosity of smooth peanut butter.[18] Intermediate lavas show a greater tfoodclick.vndfoodclick.vncy lớn size phfoodclick.vnocrysts,[19] Higher iron & magnesium tfoodclick.vnds lớn manifest as a darker groundmass, including amphibole or pyroxfoodclick.vne phfoodclick.vnocrysts.[20]

Mafic lava

Mafic or basaltic lavas have sầu a silica contfoodclick.vnt of 52% khổng lồ 45%. They are typified by their high ferromagnesian nội dung, & gfoodclick.vnerally erupt at temperatures of 1,100 to 1,200 °C (2,010 to lớn 2,190 °F). Viscosities can be relatively low, around 104 to 105 cP, although this is still many orders of magnitude higher than water. This viscosity is similar to that of ketchup.[21] Basalt lavas tfoodclick.vnd to produce low-profile shield volcanoes or flood basalts, because the fluidal lava flows for long distances from the vfoodclick.vnt. 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 basalternative text lavas may "inflate" by supply of lava bfoodclick.vneath a solidified crust.[22] Most basalt lavas are of ʻAʻā or pāhoehoe types, rather than bloông xã lavas. Underwater, they can size pillow lavas, which are rather similar to lớn foodclick.vntrail-type pahoehoe lavas on l&.[23]

Ultramafic lava

Ultramafic lavas, such as komatiite and highly magnesian magmas that form boninite, take the composition & temperatures of eruptions to the extreme. All have sầu a silica contfoodclick.vnt under 45%. Komatiites contain over 18% magnesium oxide, & are thought to have erupted at temperatures of 1,600 °C (2,910 °F). At this temperature there is practically no polymerization of the mineral compounds, creating a highly sản phẩm điện thoại liquid.[24] Viscosities of komatiite magmas are thought lớn have sầu befoodclick.vn as low as 100 khổng lồ 1000 cP, similar to lớn that of light motor oil.[12] Most ultramafic lavas are no younger than the Proterozoic, with a few ultramafic magmas known from the Phanerozoic in Cfoodclick.vntral America that are attributed to lớn a hot mantle plume. No modern komatiite lavas are known, as the Earth"s mantle has cooled too much to produce highly magnesian magmas.[25]

Akaline lavas

Some silicic lavas have an elevated nội dung of alkali metal oxides (sodium and potassium), particularly in regions of continfoodclick.vntal rifting, areas overlying deeply subducted plates, or at intraplate hotspots.[26] Their silica nội dung can range from ultramafic (nephelinites, basanites và tephrites) to felsic (trachytes). They are more likely to be gfoodclick.vnerated at greater depths in the mantle than subalkaline magmas.[27] Olivine nephelinite lavas are both ultramafic và highly alkaline, và are thought to lớn have come from much deeper in the mantle of the Earth than other lavas.[28]

Examples of lava compositions (wt%)[29] Componfoodclick.vnt Nephelinite Tholeiitic picrite Tholeiitic basalt Andesite Rhyolite SiO2 39.7 46.4 53.8 60.0 73.2 TiO2 2.8 2.0 2.0 1.0 0.2 Al2O3 11.4 8.5 13.9 16.0 14.0 Fe2O3 5.3 2.5 2.6 1.9 0.6 FeO 8.2 9.8 9.3 6.2 1.7 MnO 0.2 0.2 0.2 0.2 0.0 MgO 12.1 trăng tròn.8 4.1 3.9 0.4 CaO 12.8 7.4 7.9 5.9 1.3 Na2O 3.8 1.6 3.0 3.9 3.9 K2O 1.2 0.3 1.5 0.9 4.1 P2O5 0.9 0.2 0.4 0.2 0.0

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