Editing Magma (section)

== Migration and solidification ==
Magma develops within the [[Mantle (geology)|mantle]] or [[Crust (geology)|crust]] where the temperature and pressure conditions favor the molten state. After its formation, magma buoyantly rises toward the Earth's surface, due to its lower density than the source rock.{{sfn|Philpotts|Ague|2009|p=80}} As it migrates through the crust, magma may collect and reside in [[magma chamber]]s (though recent work suggests that magma may be stored in trans-crustal crystal-rich mush zones rather than dominantly liquid magma chambers <ref name="Sparks 2017 35–40"/>). Magma can remain in a chamber until it either cools and crystallizes to form [[intrusive rock]], it erupts as a [[volcano]], or it moves into another magma chamber.{{citation needed|date=October 2021}}

=== Plutonism ===
When magma cools it begins to form solid mineral phases. Some of these settle at the bottom of the magma chamber forming [[Cumulate rock|cumulates]] that might form mafic [[layered intrusion]]s. Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as [[gabbro]], [[diorite]] and [[granite]], depending upon the composition of the magma. Alternatively, if the magma is erupted it forms [[volcanic rock]]s such as [[basalt]], [[andesite]] and [[rhyolite]] (the extrusive equivalents of gabbro, diorite and granite, respectively).{{citation needed|date=October 2021}}

=== Volcanism ===
{{Main|Volcanism}}
Magma that is extruded onto the surface during a volcanic eruption is called [[lava]]. Lava cools and solidifies relatively quickly compared to underground bodies of magma. This fast cooling does not allow crystals to grow large, and a part of the melt does not crystallize at all, becoming glass. Rocks largely composed of volcanic glass include [[obsidian]], [[scoria]] and [[pumice]].

Before and during volcanic eruptions, [[Volatility (chemistry)|volatiles]] such as CO<sub>2</sub> and H<sub>2</sub>O partially leave the melt through a process known as [[exsolution]]. Magma with low water content becomes increasingly [[Viscosity|viscous]]. If massive exsolution occurs when magma heads upwards during a volcanic eruption, the resulting eruption is usually explosive.<ref>{{cite journal |last1=Allison |first1=Chelsea M. |last2=Roggensack |first2=Kurt |last3=Clarke |first3=Amanda B. |title=Highly explosive basaltic eruptions driven by CO2 exsolution |journal=Nature Communications |date=December 2021 |volume=12 |issue=1 |pages=217 |doi=10.1038/s41467-020-20354-2|pmid=33431860 |pmc=7801484 }}</ref>