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Magma

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Magma is molten rock within Earth that consists of liquids, gases, and particles of rocks and crystals. Magma has been observed in the form of hot lava and the various rocks made from the solidification of magma. Geologists have created artificial magmas (artificial melts) in the laboratory to learn more about the physical conditions in which magma originated and its composition. Magma is the source of igneous rocks, and can intrude or force itself into surrounding rock where it cools and eventually hardens. Rocks formed by the solidification of magma beneath Earths surface are called intrusive igneous (or plutonic) rocks. If magma rises to Earths surface it will extrude (push out), flowing or erupting out at the surface as lava, forming extrusive igneous rock (also called volcanic rock). Magma and the rocks it creates have similar chemical compositions.

Magma is generated within Earths mantle, the thick layer between the crust and outer core. Rock found deep within the crust is hot, soft, and pliable, but rock does not become liquid until much deeper in the upper mantle. Pockets, or chambers of magma, can originate at various depths within Earth. The composition of the magma varies and indicates the source materials and depth from which they originated. Silicon dioxide (SiO2) is the predominant ingredient in magma. Other ingredients include aluminum oxide, iron, magnesium, calcium, sodium, potassium, titanium, manganese, phosphorus, and water.

There are three basic types of magma, each of which has a characteristic origin and composition: basaltic (the most common, originating in the lower crust/upper mantle), rhyolitic (originates in the oceanic crust), and andesitic (most originate is the continental crust). Magma is formed by rocks melting when they sink deep into the mantle at subduction zones. The chemical composition, temperature, and the amount of dissolved liquids and gases determine the viscosity of magma. The more fluid a lava mixture is, the lower the viscosity. As magma or a lava flow cools, the mixture becomes more viscous, making it move slowly. Magmas having a higher silica (SiO2) content are very viscous and move very slowly.

Magma has the tendency to rise because it weighs less than surrounding hard rock (hot liquids are less dense than their cooler solid counterparts, with the notable exception of ice) and because of the pressure caused by extreme temperature. The pressure is reduced as magma rises toward the surface. Dissolved gases come out of solution and form bubbles. The bubbles expand, making the magma even less dense, causing the magma to rise faster. The magma exerts a great deal of pressure on weak spots and fills up any cracks produced by the continual shifting of Earths crust. On its way up toward the surface, magma can melt adjacent rock, which provides a suitable environment for the development of metamorphic rocks. When magma erupts as lava, its gases are released at the surface into the atmosphere or can be trapped in the molten rock and cause air bubbles in rock. The gases can also create violent explosions capable of ejecting cubic miles of ash and other volcanic debris.

See also Volcano.

Resources

BOOKS

Blatt, H., R. Tracy, and B. Owens. Petrology: Igneous, Sedimentary, and Metamorphic. New York: Freeman, 2005.

Tarbuck, E.J., F.K. Lutgens, and D. Tasa. Earth: An Introduction to Physical Geology. Upper Saddle River, NJ: Prentice Hall, 2004.

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Magma

In geology , magma refers to molten rock deep within Earth that consists of liquids, gases, and particles of rocks and crystals. Magma has been observed in the form of hot lava and the various rocks made from the solidification of magma. Geologists have created magmas (artificial melts) in the laboratory to learn more about the physical conditions in which magma originated and its composition. Magma is the source of igneous rocks ; it can intrude or force itself into surrounding rock where it cools and eventually hardens. These rocks are called intrusive igneous rocks. If magma rises all the way to Earth's surface it will extrude (push out), flowing or erupting out at the surface as lava, forming extrusive igneous rock (also called volcanic rock). Magma and the rocks it creates have similar chemical compositions.

Magma is generated within Earth's mantle, the thick layer between Earth's crust and outer core. Rock found deep within the crust is extremely hot, soft, and pliable, but rock does not become liquid until much deeper in the upper mantle. Pockets, or chambers of magma, can originate at various depths within the earth. The composition of the magma varies and indicates the source materials and depth from which they originated. Silicon dioxide (SiO2) is the predominant ingredient in magma. Other ingredients include aluminum oxide, iron , magnesium , calcium , sodium , potassium, titanium , manganese, phosphorus , and water .

There are three basic types of magma, each having a characteristic origin and composition: basaltic (the most common, originating in the lower crust/upper mantle), rhyolitic (originates in the oceanic crust), and andesitic (most originate is the continental crust). New magma is formed by rocks melting when they sink deep into the mantle at subduction zones. The chemical composition, temperature , and the amount of dissolved liquids and gases determine the viscosity of magma. The more fluid a lava mixture is, the lower the viscosity. As magma or a lava flow cools, the mixture becomes more viscous, making it move slowly. Magmas having a higher silica (SiO2) content are very viscous and move very slowly.

Magma has the tendency to rise because it weighs less than surrounding hard rock (liquids are less dense than solids) and because of the pressure caused by extreme temperature. The pressure is reduced as magma rises toward the surface. Dissolved gases come out of solution and form bubbles. The bubbles expand, making the magma even less dense, causing the magma to rise faster. The magma exerts a great deal of pressure on weak spots and fills up any cracks produced by the continual shifting of the earth's crust. On its way up toward the surface, magma can melt adjacent rock, which provides a suitable environment for the development of metamorphic rocks. When magma erupts as lava, its gases are released at the surface into the atmosphere or can be trapped in the molten rock and cause "air bubbles" in rock. The gases can also create violent explosions, throwing debris for miles around.

See also Volcano.


Resources

books

Hamblin, W.K., and Christiansen, E.H. Earth's Dynamic Systems. 9th ed. Upper Saddle River: Prentice Hall, 2001.

Hancock P.L., and Skinner B.J., eds. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.

Woodhead, James A. Geology. Boston: Salem Press, 1999.

periodicals

Petford, N., Cruden, A., McCaffrey, K., and Vigneresse, J-L. "Granite Magma Formation, Transport and Emplacement in the Earth's Crust." Nature (December 2000): 669-673.

views updated

Magma

In geology , magma refers to molten rock deep within Earth that consists of liquids, gases, and particles of rocks and crystals . Magma has been observed in the form of hot lava and the various rocks made from the solidification of magma. Geologists have created magmas (artificial melts) in the laboratory to learn more about the physical conditions in which magma originated and its composition. Magma is the source of igneous rocks ; it can intrude or force itself into surrounding rock where it cools and eventually hardens. These rocks are called intrusive igneous rocks. If magma rises all the way to Earth's surface it will extrude (push out), flowing or erupting out at the surface as lava, forming extrusive igneous rock (also called volcanic rock). Magma and the rocks it creates have similar chemical compositions.

Magma is generated within Earth's mantle, the thick layer between Earth's crust and outer core. Rock found deep within the crust is extremely hot, soft, and pliable, but rock does not become liquid until much deeper in the upper mantle. Pockets, or chambers of magma, can originate at various depths within the earth. The composition of the magma varies and indicates the source materials and depth from which they originated. Silicon dioxide (SiO2) is the predominant ingredient

in magma. Other ingredients include aluminum oxide, iron , magnesium, calcium, sodium, potassium, titanium, manganese, phosphorus, and water .

There are three basic types of magma, each having a characteristic origin and composition: basaltic (the most common, originating in the lower crust/upper mantle), rhyolitic (originates in the oceanic crust), and andesitic (most originate in the continental crust). New magma is formed by rocks melting when they sink deep into the mantle at subduction zones. The chemical composition, temperature , and the amount of dissolved liquids and gases determine the viscosity of magma. The more fluid a lava mixture is, the lower the viscosity. As magma or a lava flow cools, the mixture becomes more viscous, making it move slowly. Magmas having a higher silica (SiO2) content are very viscous and move very slowly.

Magma has the tendency to rise because it weighs less than surrounding hard rock (liquids are less dense than solids) and because of the pressure caused by extreme temperature. The pressure is reduced as magma rises toward the surface. Dissolved gases come out of solution and form bubbles. The bubbles expand, making the magma even less dense, causing the magma to rise faster. The magma exerts a great deal of pressure on weak spots and fills up any cracks produced by the continual shifting of the earth's crust. On its way up toward the surface, magma can melt adjacent rock, which provides a suitable environment for the development of metamorphic rocks. When magma erupts as lava, its gases are released at the surface into the atmosphere or can be trapped in the molten rock and cause "air bubbles" in rock. The gases can also create violent explosions, throwing debris for miles around.

See also Volcanic eruptions; Volcanic vent

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magma A hot, silicate, carbonate, or sulphide melt containing dissolved volatiles and suspended crystals, which is generated by partial melting of the Earth's crust or mantle and is the raw material for all igneous processes. The melt component of silicate magmas, by far the most common magma type, comprises a disordered mixture of single Si—O tetrahedra and chains, branching chains, and rings of Si—O tetrahedra, between which are located randomly positioned cations (e.g. Ca2+, Mg2+, Fe2+, and Na+) and anions (e.g. OH, F, Cl, and S) loosely co-ordinated with the oxygens in the silicate tetrahedra. The greater the silica content of the magma, the more chains and rings of silicate tetrahedra there are to impede each other and hence increase the viscosity of the magma. The pressure regime and composition of the magma control which minerals nucleate and crystallize from a magma when it cools.

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magmaAlabama, clamour (US clamor), crammer, gamma, glamour (US glamor), gnamma, grammar, hammer, jammer, lamber, mamma, rammer, shammer, slammer, stammer, yammer •Padma • magma • drachma •Alma, halma, Palma •Cranmer • asthma • mahatma •miasma, plasma •jackhammer • sledgehammer •yellowhammer • windjammer •flimflammer • programmer •amah, armour (US armor), Atacama, Brahma, Bramah, charmer, cyclorama, dharma, diorama, disarmer, drama, embalmer, farmer, Kama, karma, lama, llama, Matsuyama, panorama, Parma, pranayama, Rama, Samar, Surinamer, Vasco da Gama, Yama, Yokohama •snake-charmer • docudrama •melodrama •contemner, dilemma, Emma, emmer, Jemma, lemma, maremma, stemma, tremor •Elmer, Selma, Thelma, Velma •Mesmer •claimer, defamer, framer, proclaimer, Shema, tamer

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mag·ma / ˈmagmə/ • n. hot fluid or semifluid material below or within the earth's crust from which lava and other igneous rock is formed by cooling. ∎  dated a fluid medicinal suspension of a solid. DERIVATIVES: mag·mat·ic / magˈmatik/ adj.

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magma Molten rock, silicate, carbonate, or sulphide in composition and containing dissolved volatiles and suspended crystals, which is generated by partial melting of the Earth's crust or mantle and is the raw material for all igneous processes.

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magma Molten material that is the source of all igneous rocks. Magma refers to this material while it is still under the Earth's crust. In addition to its complex silicate composition, magma contains gases and water vapour.

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magma †dregs of a semi-liquid substance XV; thin pasty mixture of substances XVII; (geol.) stratum of fluid matter XIX. — L. — Gr. mágma thick unguent, f. base *mag- of mássein knead.

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magma (măg´mə): see lava.