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Facts about Magma For Kids

Magma 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. 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.
  • Magma, as liquid, preferentially forms in high temperature, low pressure environments within several kilometers of the Earth’s surface.
  • 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.
  • When rocks melt they do so incrementally and gradually; most rocks are made of several minerals, all of which have different melting points, and the physical/chemical relationships controlling melting are complex.
  • Under pressure within the earth, as little as a fraction of a percent partial melting may be sufficient to cause melt to be squeezed from its source.
  • Rock types produced by small degrees of partial melting in the Earth’s mantle are typically alkaline (calcium, sodium), potassic (potassium) and/or peralkaline.
  • Typically, primitive melts of this composition form lamprophyre, lamproite, kimberlite and sometimes nepheline-bearing mafic rocks such as alkali basalts and essexite gabbros or even carbonatite.
  • Some granite-composition magmas are eutectic melts, and they may be produced by low to high degrees of partial melting of the crust, as well as by fractional crystallization.
  • Primary melts have not undergone any differentiation and represent the starting composition of a magma.
  • A parental melt is a magma composition from which the observed range of magma chemistries has been derived by the processes of igneous differentiation.
  • Magma rises toward the Earth’s surface when it is less dense than the surrounding rock and when a structural zone allows movement.
  • Magma can remain in a chamber until it cools and crystallizes forming igneous rock, it erupts as a volcano, or moves into another magma chamber.
  • There are two known processes by which magma ceases to exist: by volcanic eruption, or by crystallization within the crust or mantle to form a pluton.
  • Magma with low water content becomes increasingly viscous. Pressure builds up until the gases blast out in a violent, dangerous explosion.