Glossary

VEI ranks the size of an eruption from 0 to 8. The scale is logarithmic — each step up is roughly ten times more erupted material than the one below. It was proposed by Newhall and Self in 1982, and the Global Volcanism Program assigns a value where the record allows. Where this site shows VEI ?, no value has been assigned, usually because the eruption is known only from its deposits.

The volume counts fragmented material — ash, pumice, blocks — and not lava flows. That is why Kilauea, which erupts a great deal of lava, sits at VEI 0. This catalogue covers the Holocene, the last 11,700 years, and contains no VEI 8 eruption; the most recent one was far older.

Most eruption records carry the method used to date it. This site sorts those methods into four grades and shows the grade as a badge beside each eruption.

Observed

Someone or something recorded the eruption as it happened — an eyewitness account, a seismometer, a hydrophone, a satellite. These dates are the most precise.

Historical

Known from written accounts rather than direct scientific observation. The year is usually reliable; the month and day often are not.

Geological estimate

Dated from deposits — radiocarbon, tephra layers, tree rings, ice cores, annual lake sediments. Expect an uncertainty of years to centuries.

Method not stated

The Global Volcanism Program records no dating method for this eruption, or marks the dating uncertain. The date is in the catalogue, but nothing says how it was arrived at — read it as an estimate.

Most volcanoes sit near the edge of a tectonic plate. The map can draw those edges from the Bird (2003) PB2002 dataset, coloured and dashed by class.

Convergent (subduction / collision)

Two plates move toward each other and one is forced beneath the other. Water carried down with it lowers the melting point of the mantle above, and the arc of volcanoes that results is usually explosive. The Pacific Ring of Fire follows these boundaries.

Divergent (ridge / rift)

Two plates pull apart and mantle rises into the gap. Eruptions here are mostly fluid basalt. Almost all of it happens on the ocean floor; Iceland is the rare stretch that stands above sea level.

Transform

Two plates slide past each other. Little melt is produced, so volcanoes are uncommon along these boundaries.

GVP's primary volcano type describes the shape of the edifice — how the volcano is built — rather than what it erupts.

Stratovolcano

A steep cone built up in layers of lava and fragments by repeated eruptions at one vent. The most common type in this catalogue.

Volcanic field

An area scattered with small vents rather than one central mountain. Each vent usually erupts only once.

Shield volcano

A broad, gently sloping dome built by fluid lava that travels a long way before it cools.

Caldera

A large basin left when the ground collapses into a magma chamber emptied by an eruption. Often far wider than the cone that stood there before.

Complex volcano

Two or more vents or cones of different kinds treated as a single volcano.

Compound volcano

A single edifice carrying several summits or cones.

Fissure vent

A crack that erupts along its length instead of from one opening.

Pyroclastic cone

A small, steep cone of loose fragments piled around a vent. Also called a cinder or scoria cone.

Lava dome

A mound of lava too stiff to flow away, piled over its own vent. Domes can collapse and send pyroclastic flows down the slope.

Lava cone

A cone built from lava viscous enough to stack up near the vent.

Maar

A broad, shallow crater cut below the surrounding ground by steam explosions where magma met groundwater. Often holds a lake.

Tuff cone

A steep cone of ash built by wet, steam-driven eruptions.

Tuff ring

A low, wide ring of ash from the same wet eruptions as a tuff cone, thrown out on a flatter arc.

Crater rows

A line of craters along a fissure.

Explosion crater

A crater blasted out with little or no cone around it.

Cone

A cone-shaped edifice that GVP has not classified more precisely.

Unknown

GVP records no type for this volcano.