Definition of magma in US English:



  • Hot fluid or semifluid material below or within the earth's crust from which lava and other igneous rock is formed on cooling.

    ‘when red-hot magma comes into contact with seawater, an explosion results’
    count noun ‘basaltic magmas are normally expelled at the surface in a very hot and fluid state’
    • ‘Melts form at the highest temperatures and lowest pressures resulting in large volumes of tholeiitic magma that form shield volcanoes such as Mauna Loa.’
    • ‘An aircraft will soon fly over the lava dome to test for the presence of carbon dioxide and sulfur dioxide, signs that magma might be building up.’
    • ‘The continuing uplift of the caldera rim can be explained by the restricted size of the magma's exit route.’
    • ‘Magmas concentrate metals, and magma fluids traveling into the surrounding wall rock plant the seeds for mineral growth.’
    • ‘This magma is rich in carbon dioxide gas, which produces explosive eruptions.’
    • ‘Until the rocks crystallized, uranium atoms could move freely through the molten magma from which they formed, and decayed uranium could be replenished.’
    • ‘Injections of new batches of mafic magma have been important for triggering dacitic eruptions.’
    • ‘Normally magma would fill the crack and the adjacent plates would inch away by just that amount.’
    • ‘Crystals of the mineral were then carried in suspension by the upward-moving magma and forced toward the center of the flowing slurry.’
    • ‘Massive sulfide deposits may also form in other settings where water circulates in rocks near cooling magma.’
    • ‘From beneath the dome, the magma could combine with pressurized gases and steam to trigger an eruption, Pierson said.’
    • ‘In other words, the magma is squeezed upwards as thin sheets through long, narrow fractures.’
    • ‘Vulcanites, such as basalt and fire opal, will be formed within erupted magma where cooling is rapid and only tiny crystals have the chance to form.’
    • ‘As old oceanic crust was consumed in the trenches, new magma rose and erupted along the spreading ridges to form new crust.’
    • ‘What they do know is that a ‘slow rise’ of magma is driving lava to the surface, which has created a new lava dome in the mountain's crater.’
    • ‘Prior to any volcanic eruption, magma wells up through the earth's crust via any weaknesses in the rock structure.’
    • ‘Scientists believe that diamonds ascend to the earth's surface in rare molten rock, or magma that originates at great depths.’
    • ‘Two years ago the magma was close enough to the crown of the volcano to be seen clearly from the air.’
    • ‘Dolerite is basaltic magma that solidifies rapidly in sills and dikes near the surface.’
    • ‘Igneous rocks are those that have formed from molten magma.’


Late Middle English (in the sense ‘residue of dregs after evaporation or pressing of a semiliquid substance’): via Latin from Greek magma (from massein ‘knead’).