Volcano Glossary

A cloud of ash formed by volcanic eruptions. The ash consists of small pieces of pulverized rock, minerals, and volcanic glass.

A dark, fine-grained volcanic rock rich in iron and magnesium, formed from the rapid cooling of low-viscosity lava.

A large mass of intrusive igneous rock that forms from cooled magma deep in the Earth's crust.

A large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption.

A steep, conical hill of volcanic fragments that accumulate around and downwind from a volcanic vent.

A sheet-like body of igneous rock that cuts across the layers of older surrounding rock.

An opening in or near a volcano through which hot gases and vapors emerge.

A rare kind of hot spring that is under pressure and erupts, sending jets of water and steam into the air.

A volcanic area that forms over a relatively stationary and unusually hot part of the Earth's mantle.

A destructive mudflow on the slopes of a volcano.

Magma that has reached the Earth's surface through a volcanic vent.

A large volume of molten lava contained within a volcanic vent or crater.

Molten or semi-molten natural material found beneath the surface of the Earth, consisting of melt, suspended crystals, and dissolved gases.

A large pool of liquid rock beneath the Earth's surface.

A naturally occurring volcanic glass formed as an extrusive igneous rock.

An explosive eruption driven by steam, occurring when magma heats groundwater or surface water, causing it to flash-boil instantaneously.

An extremely explosive eruption type characterized by a towering column of gas and ash extending into the stratosphere.

A highly vesicular, low-density volcanic rock formed when gas-rich frothy lava cools rapidly.

A fast-moving current of hot gas and volcanic matter that flows along the ground away from a volcano at high speeds.

A highly vesicular, dark-colored volcanic rock that may or may not contain crystals.

A broad, domed volcano with gently sloping sides, characteristic of the eruption of fluid, basaltic lava.

A tabular sheet of igneous rock intruded between and parallel to existing strata of sedimentary rock or volcanic beds.

A tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash.

A tectonic boundary where one plate sinks (subducts) beneath another, creating deep ocean trenches and explosive volcanic arcs.

A massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.

A general term for all fragmented material ejected from a volcano during an eruption.

A type of rock made of volcanic ash and skeletal remains of organisms ejected from a vent during a volcanic eruption.

A logarithmic scale (0-8) used to measure the explosive magnitude of a volcanic eruption, similar to the Richter scale for earthquakes.

A continuous seismic signal indicating the movement of magma or gas beneath a volcano.

A reduction in global temperatures caused by volcanic ash and droplets of sulfuric acid obscuring the Sun.