magma
This term describes the subterranean state of molten rock, distinguishing it from lava, which is the same material once it breaches the surface. It carries a connotation of immense pressure and hidden power, evoking images of deep crustal heat and geological instability. While typically treated as an uncountable mass noun in general descriptions, the word is used as a countable noun in geological and petrological contexts to refer to distinct types or batches of molten rock, such as when discussing different magmas originating from separate sources.
Used exclusively as a mass noun to describe the molten material, such as saying there is a large volume of magma beneath the crust.
Meanings
Molten rock stored beneath the Earth's surface.
"The volcano erupted when the magma chamber overflowed."
Examples
The volcano erupted when the magma chamber overflowed.