Magma
Magma is a mixture of molten rock and gases below the surface of the Earth that may erupt from a volcano as lava. It may also cool and solidify below the surface.
The rocks that form from magma are crystalline and fit into a general category called igneous rocks. Examples of common types of igneous rock include granite and basalt.
One way to learn how different types of igneous rock form is to compare the relative sizes of their mineral crystals. Igneous rocks with larger mineral crystals (for example, granite) cool slowly below the surface. Basalt, with its fine mineral structure, cools relatively quickly after it erupts as lava from a volcano.
Image: 3D model of hot magma plumes (light orange) rising from the Earth's core (dark orange, centre), cooling, and sinking back down (credit: Shuxia Zhang/Shuo Wang/SPL)
Introduction
Magma
TV clips (3)
play
Inside our planet
Liz Bonnin uses a plum to explain what's happening inside the Earth.
Reporting from Eyjafjallajokull volcano in Iceland, Liz Bonnin explains the Earth's inner structure using a plum to show the different layers inside our planet. She explains why hot bits of the mantle that are rising melt to form magma.
play
Musical volcanoes
Geophysicist Bernard Chouet explains what notes from an organ can tell us about volcanoes.
Geophysicist Bernard Chouet explains how notes from an organ and a volcano about to erupt give off similar resonant signals. As magma enters cracks below the Earth's surface, it resonates and gives off signals known as long period events. These signals help scientists predict eruptions.
play
Yellowstone's super magma chamber
How big is the magma chamber at Yellowstone?
Seismologists study how earthquake waves travel through the Earth to map the huge magma chamber below Yellowstone National Park.
Magma
Magma (from Greek μάγμα "mixture") is a mixture of molten or semi-molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals, dissolved gas and sometimes gas bubbles. Magma often collects in magma chambers that may feed a volcano or turn into a pluton. Magma is capable of intrusion into adjacent rocks, extrusion onto the surface as lava, and explosive ejection as tephra to form pyroclastic rock.
Magma is a complex high-temperature fluid substance. Temperatures of most magmas are in the range 700 °C to 1300 °C (or 1300 °F to 2400 °F), but very rare carbonatite melts may be as cool as 600 °C, and komatiite melts may have been as hot as 1600 °C. Most are silicate mixtures.
Environments of magma formation and compositions are commonly correlated. Environments include subduction zones, continental rift zones,mid-ocean ridges and hot spots. Despite being found in such widespread locales, the bulk of the Earth's crust and mantle is not molten. Rather, most of the Earth takes the form of a rheid, a form of solid that can move or deform under pressure. Magma, as liquid, preferentially forms in high temperature, low pressure environments within several kilometers of the Earth's surface.
Magma compositions may evolve after formation by fractional crystallization, contamination, and magma mixing. By definition rock formed of solidified magma is called igneous rock.
While the study of magma has historically relied on observing magma in the form of lava outflows, magma has been encountered in situ three times during drilling projects—twice in Iceland, and once in Hawaii.
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