CoachIn order of increasing explosivity, among eruptions driven by the magma’s own gas:
- a Hawaiian eruption produces fountains of very fluid basaltic lava, tens to hundreds of metres high, feeding lava flows;
- a Strombolian eruption is a series of discrete bursts that throw incandescent clots of basaltic to basaltic-andesite magma up to a hundred metres or so, without a sustained column;
- a Vulcanian eruption is a short, violent explosion of gas accumulated beneath a plug of solidified lava, which shatters the plug and throws out blocks and a dark column of fine ash, typically from intermediate magma;
- a Plinian eruption is a sustained jet of gas and fragmented, usually silicic, magma that feeds a column rising into the stratosphere for hours to days and spreads a sheet of pumice and ash over thousands of square kilometres.
Where external water drives the fragmentation, a phreatomagmatic eruption ejects steam together with fragments of fresh magma, while a phreatic eruption is a steam-driven explosion of ground or surface water heated by magma or hot rock, which ejects steam and fragments of older rock but no fresh magma.