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Below are definitions of important volcano terms.

• active volcano: a volcano erupting or liable to erupt
• caldera: a large, more or less circular, more-than-a-mile-in-diameter depression formed either by collapse or by explosion, usually at the summit of a volcano
• continental drift: the breakup of the earth’s original single landmass into continents that then separated; they are still drifting apart today
• cinders: nut-sized pieces of red or black lava containing bubble-like cavities known as vesicles
• crust: the outside solid part of the earth’s surface
• dormant: when a volcano remains inactive for a long time
• eruption: the sudden emergence of hot material from the earth’s interior
• extinct volcano: volcanoes no longer liable to erupt
• fire fountain: a jet of magma spouting from a narrow volcanic vent
• fissure volcano: a long crack in the Earth’s crust through which magma erupts
• lahars: volcanic mudflows and debris flows
• lava: liquid, molten rock
• magma: hot molten rock created by the partial melting of the crust and mantle at high temperatures far below the ground
• magma chamber: a cavity beneath a volcano where magma collects
• plug: a tower of hard rock left by a volcano
• pyroclastics: volcanic solids like rock, cooled lava, etc.
• scoria: bubble-filled stones ejected from a volcano
• subduction zones: areas where the crustal layer descends into the mantle
• tectonic plates: 70-mile-thick blocks of the earth’s crust on which the continents ride
• tephra: fragments thrown into the air by a volcanic eruption
• vent: the single hole from which magma erupts
• volcanic cone: a conical mountain built up by volcanic eruptions
• volcanic crater: a steep-walled depression at the top or on the flank of a volcanic cone, out of which the volcanic materials are ejected
• volcanic sunset: a colorful sunset following a volcanic eruption
• volcano: a gap in the earth’s crust where molten rock and other materials escape onto the Earth’s surface

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