A type of lava flow with a rough, blocky surface.
A type of volcanic rock. Andesite is intermediate in composition between basalt and dacite, and contains about 60 percent silica. Andesite is common in volcanoes above subduction zones.
Any rock particle or crystals thrown out by volcanoes that are less than 2mm in size.
The most abundant volcanic rock on Earth. Basalt contains about 50 percent silica. Most basalt erupts to form black lava flows. Block and ash flow – one type of pyroclastic flow where the fragments carried by the flow are mostly dense blocks of lava.
A large volcanic crater, usually formed by collapse of the volcano during large eruptions. Calderas can be kilometers or tens of kilometers across with steep cliffs up to a kilometer high.
Cinder cone (or scoria cone)
A steep conical hill formed during fire-fountaining, and usually made of frozen droplets (‘cinders’ or ‘scoriae’ of basalt or andesite).
The pipe, crack or fracture through which magma flows.
The outermost layer of the Earth. The crust is between thirty and seventy kilometers thick on the continents, and six to eight kilometers thick under the oceans. Crust is usually cool and cold.
A common volcanic rock that forms pumice, or glassy lava. Dacite contains about 65% silica. Dacite lava is very sticky, and often forms domes or stubby flows.
A steep-sided pile of lava formed by the eruption of sticky lava.
A steep fracture filled with magma. Most magma rises thorough the outer layers of the Earth through dykes.
A white or colourless mineral that is found in many types of volcanic rock.
An incandescent spray of red-hot droplets of melt. Fire fountains can reach several hundred metres high on Earth, and can stretch for kilometers along erupting fissures. Fire-fountaining is common at basaltic volcanoes.
A slowly cooled, light-coloured crystalline rock made up mainly of crystals of feldspar and quartz. Granite is the coarsegrained equivalent of volcanic rocks like dacite or rhyolite.
Hot spot volcano
An isolated volcano or group of volcanoes that forms above hot, upwelling part of the Earth’s interior. Hot spot volcanoes need not lie near to the boundary between two tectonic plates.
A pumice-rich deposit formed by a pyroclastic flow.
An Icelandic term for a sudden burst of water that escapes from a glacier.
A rare volcanic rock-type that usually fills narrow, deep vents in areas of very old crust. Some kimberlites contain small amounts of diamond.
A rare form of basalt that contains about 40 percent silica. Komatiite was only common more tan two billion years ago. Komatiite lava is hotter and more fluid than basalt.
A volcanic ‘mudflow’. Lahars are mixtures of ash and rock fragments in water that flow with the consistency of wet cement and may be hot.
Molten rock that flows over the surface of a volcano as a very dense fluid and solidifies to form a hard, dense rock.
The rigid outer shell of the earth. The lithosphere includes the crust and the coolest upper parts of the mantle.
A form of volcanic crater. Maars are often a few hundred metres wide, up to a hundred metres deep, and filled with water.
A general term that describes molten rock below the surface. Magma erupts either to form lava, or pyroclastic rock when it reaches the surface.
The interior of the Earth tat extends from the base of the crust to a depth of 2900 km. below the lithosphere, the mantle is hot enough to flow.
A flowing slurry of water, rock and mud.
Literally a ‘glowing cloud’; a form of pyroclastic flow.
A black volcanic glass of rhyolite or dacite composition.
A green mineral commonly found in basalt lava.
A type of lava flow with a smooth but ropy surface.
Steam-driven explosion of ash and rock.
An explosive eruption that forms a vertical column of ash and pumice, which rises several tens of kilometers into the atmosphere.
A volcanic rock that is so full of gas bubbles that it has a very low density. Pumice fragments can often float on water.
A black coloured mineral common in basalt and andesite.
A hot avalanche of ash, rock and gas. Flows often have a thick, dense lower part underneath a billowing, more dilute cloud of ash and hot air
A general term for any volcanic material that is ejected as broken solidified fragments of rock.
A type of volcanic rock that commonly erupts as pumice. Rhyolite typically contains about 75 percent silica and the stickiest lava known.
A type of long sinuous channel, found on the Moon.
The fracture system that forms where two tectonic plates pull apart (like the oceanic ridges) or where a single plate is being pulled apart (like the East African rift).
Dark-coloured droplets or fragments of basalt or andesite, typically formed during fire-fountaining.
A volcanic cone built up of both pyroclastic deposits and lavas during more than one eruption. Statocones are usually quite steep, and may be several kilometers high
The place on Earth’s surface where two tectonic plates converge, and one plate plunges into the mantle.
Pyroclastic surges, sometimes called ‘base surges’ move as ground-hugging dilute ash and gas flows. They are often wet or damp, and may be caused by eruptions through water.
The rigid, outer layer of the Earth is divided into several tectonic plates, each of which s about 100km thick. Tectonic plates move apart at rifts, and converge at subduction zones.
A general term used to describe any type of pyroclastic rock.
A sea wave produced by an underwater earthquake or volcanic explosion.
The opening at the Earth’s surface through which materials erupts.
A measure of liquid’s resistance to flow, or its ‘stickiness’. The most fluid basalt has a viscosity similar to chick engine oil. Andesite lava can be several thousand times stickier than basalt; rhyolite is at least a million time more viscous.