Magma chamber
A reservoir of molten and partially molten rock within the crust, from which intrusions and volcanic eruptions are supplied.
Crystal fractionation: Dense crystals settling out of cooling magma, changing the residual melt's composition step by step. The main process by which a chamber's melt evolves away from its original composition.
Axial Seamount: A submarine volcano on the Juan de Fuca Ridge with a well-imaged melt lens and documented eruptions. A directly observed magma chamber under a spreading center, matching the ridge context.
Mush zone: A mostly solid crystal framework containing small amounts of interstitial melt, rather than an open body of liquid. Seismic imaging suggests many reservoirs are crystal-rich mushes, not liquid vats.
Melt lens (seismic reflection): A bright reflector under ridge axes interpreted as a thin sill of melt, imaged since the 1980s. The key observational constraint: it shows thin melt sheets, not big liquid tanks.
Wager and Brown: Lawrence Wager, who mapped Skaergaard and established layered intrusion petrology. His fieldwork turned the fossil intrusion into evidence for chamber dynamics.
Dike (geology): A sheet of magma that cuts across older rock, carrying melt out of the reservoir into its surroundings. The principal way melt leaves the chamber to feed fissure eruptions and crustal intrusions.
Long Valley Caldera: A large rhyolitic caldera in California whose collapse followed evacuation of a silicic reservoir. Caldera collapse is the most dramatic way a chamber can be emptied.
Magma ocean: A planet-scale body of molten rock, as existed on early Earth before the mantle solidified. An extreme counterpart showing what melt storage means at a very different scale.
Volcano seismology: The use of earthquakes, tremor and deformation to map magma storage and movement. The main live method for tracking where melt actually resides and moves.
Ocean Drilling Program: An international scientific drilling effort that sampled the oceanic crust from 1985 onward. Drilling and seismic work under ridges reshaped views of crustal chambers.