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Geography 5
B Glossary of Geography Unit Volcanoes

Key Vocabulary

active volcano* a volcano that is in a state of regular eruptions and might erupt at any time.
ash the grey powder that remains after something has burnt.
blast an explosion; the sudden loud sound caused by the violent explosion of an erupting
volcano (Geography).
caldera a basin-shaped volcanic depression, sometimes containing a lake, caused by the
collapse of the top of a volcanic cone after an eruption.
conduit (of a volcano) the channel through which magma flows.
crater the round hole at the top of a volcano from which volcanic material erupts.
dormant volcano a volcano that is active, but erupts very rarely, so it’s considered “sleeping”.
earthquake a sudden shaking of the ground caused by movements occurring along plate
boundaries, within the Earth’s crust.
eruption (of a volcano) the action of ejecting lava, rock fragments, ash, gases.
extinct volcano a volcano that is no longer active and, it is thought, will never erupt again.
fissure a long deep crack on the surface of a rift zone through which an eruption can occur.
lava hot molten rock flowing out of a volcano.
layer any of the distinct strata which make up the inner structure of the Earth (Geology).
magma hot molten rock inside the Earth.
magma chamber a deep cavity within the Earth’s crust where magma gathers, especially
below a volcano.
plate each of the separate rigid slabs which together make up the Earth’s surface (Geology).
pyroclastic material the material ejected during a volcanic eruption (for example ash, obsidian,
pumice, rock fragments).
tectonic referring to the structure of the Earth’s crust and the way it is formed.
vent an opening at the Earth’s surface from which volcanic material is emitted (Geology).
viscosity the state of being thick, sticky and semi-fluid in consistency, commonly perceived
as resistance to pouring (example given: magmas with high viscosity flow with great difficulty
compared to magmas with low viscosity).
volcanism any of volcanic activity or phenomenon associated with the superficial emission
of molten rock, pyroclastic material, gas, hot water, and steam.

* Currently, there is no consensus among scientists about what constitutes “active”: the Global
Volcanism Program claims that an active volcano is one that has erupted since the last ice age
(10 000 years), but the most general definition is the one given above.