How does magma form and get stored underground?

Magma is a mixture of molten or semi-molten rock, suspended crystals, and gas bubbles that forms through the melting of the Earth's mantle or crust. It is generated in diverse tectonic settings such as subduction zones, continental rifts, mid-ocean ridges, and hotspots. Once formed, melts migrate upward through the crust and are stored in magma chambers or crystal-rich mush zones before either erupting as lava or solidifying into underground intrusions.

What we know

• Magma is produced by the melting of the mantle or the crust in various tectonic settings including subduction zones, continental rift zones, mid-ocean ridges, and hotspots. [2]
• Besides molten rock, magma may also contain suspended crystals and gas bubbles. [2]
• Mantle and crustal melts migrate upwards through the crust where they are thought to be stored in magma chambers or trans-crustal crystal-rich mush zones. [2]
• Magma chambers are pools of liquid rock typically located close to the surface between 1 km and 10 km down, where buoyant forces drive the less dense molten rock upward. [3]

Still open

• Magma chambers deep within the Earth are hard to detect, leaving most known chambers restricted to those close to the surface between 1 km and 10 km down.

Where to go next

• what followedWhat happens when magma erupts onto the surface?
• what caused itHow do tectonic settings influence melting?
• the bigger pictureWhat are magma oceans on early planets?
• a case in pointHow has magma been encountered during drilling?
• how it workedWhat intrusive rocks form when magma cools underground?
• an unexpected connectionHow does planetary accretion relate to magma oceans?Early magma oceans were sustained not just by impacts, but initially by the radioactive decay of aluminium-26 in small planetesimals.

Sources

• [1]magma (Wikidata Q42278) · CC0 1.0
• [2]Magma · CC BY-SA 4.0
• [3]Magma chamber · CC BY-SA 4.0
• [4]Magma ocean · CC BY-SA 4.0
• [5]Oceanic crust · CC BY-SA 4.0