Definitions

A'a: Hawaiian term for lava with a blocky structure.

Active volcano: A volcano that is currently erupting, or has erupted during recorded history.

Aerosol: Fine liquid or solid particles suspended in the atmosphere. Aerosols resulting from volcanic eruptions are tiny droplets of sulphuric acid - sulphur dioxide that has picked up oxygen and water.

Ash: Fragments, less than 2 millimeters in diameter, of lava or rock blasted into the air by volcanic explosions.

Ashfall: Rain of airborne volcanic ash from an eruption cloud.

Basalt: Dark coloured, fine grained volcanic rock.

Breach: Lava may break through the cone wall, leaving a hole in the structure.

Crater: The circular depression containing a volcanic vent.

Crust: The Earth's outermost layer.

Dormant volcano: An active volcano that is in repose (quiescence) but is expected to erupt in the future.

Earthquake: Sudden motion of trembling in the earth caused by the abrupt release of strain that is built up over time.

Explosion crater: As magma rises it comes into contact with surface water which causes violent steam explosions that throw ash and shattered rock high into the air. These violent explosions leave an explosion crater.

Extinct volcano: A volcano that is not expected to erupt again.

Fire fountaining: The rhythmic eruption of molten lava (normally basaltic) from a volcanic vent (eg, a lava fountain).

Fissure: Long narrow crack or vent along which an eruption takes place.

Fossil lava forest: An ancient forest that has been preserved in the form of lava moulds.These lava moulds formed as lava flowed through the former forest, and solidified around the trees. The burnt trees disintegrated over time, leaving only hollow lava moulds as evidence of their presence.

Hot spot: An area in the middle of the lithospheric plate where magma rises from the mantle and erupts at the Earth's surface. Volcanoes sometimes occur above a hot spot.

Lava fields: A broad area of lava flows, commonly surrounding a volcanic cone.

Lava flows: Fluid rock, erupted from a volcano or fissure on the Earth's surface that flows away from the source.

Lava: The term used for magma once it has erupted onto the Earth's surface.

Maar: A low-relief, vertical walled volcanic crater that has been cut (largely by collapse) into pre-existing rock and surrounded by a low rim of ejecta.

Magma: Molten rock containing liquids, crystals, and dissolved gases that forms within the upper part of the Earth's mantle and crust. When erupted onto the Earth's surface, it is called lava.

Mantle: A zone in the Earth's interior between the crust and the core that is 2900 kilometres thick.

Monogenetic: Resulting from one process of formation developing at one place and time.

Pahoehoe: Hawaiian term for lava having a ropey surface structure.

Pits: Depressions of varying sizes that are the remains of semi-subterranean and roofed structures used for storage of crops.

Platforms: Leveled areas on ridges or hilltops.

Prevailing winds: The direction from which winds most frequently blow at a specific geographic location.

Scoria cone: A volcanic cone composed of coarse grained rock containing empty cavities.

Scoria: Coarse grained rock containing empty cavities.

Seismic/seismicity: Pertaining to earthquakes.

Seismograph: A scientific instrument that detects and records vibrations (seismic waves) produced by earthquakes.

Seismometer: The sensor part of a seismograph. A seismograph is a device for recording seismic waves (produced by earthquakes).

Tephra: Solid material of all sizes explosively ejected from a volcano into the atmosphere.

Terraces: Artificially leveled areas on slopes.

Topographic map: A map that uses contour lines to represent the three-dimensional features of a landscape on a two-dimensional surface.

Tuff cone: A cone with smaller crater and higher rim than a tuff ring, with steeply dipping beds produced by the deposition of ejecta close to the vent.

Tuff ring: A prominent rim of consolidated ash and shattered rock encircling an explosion crater.

Tuff: Ash and other ejecta which has consolidated into a rock deposit.

Vent: The opening at the Earth's surface through which volcanic materials (lava, tephra, and gases) erupt. Vents can be at a volcano's summit or on its slopes they can be circular (craters) or linear (fissures).

Volcanic field: A broad area containing a number of volcanoes.

Volcano: A vent (opening) in the Earth's surface through which magma erupts it is also the landform that is constructed by the eruptive material.