Afissure vent, also known as avolcanic fissure,eruption fissure or simply a fissure, is a linearvolcanic vent through whichlava erupts, usually without anyexplosive activity. The vent is often a few metres wide and may be many kilometres long. Fissure vents can cause largeflood basalts which run first inlava channels and later inlava tubes. After some time, the eruption tends to become focused at one or morespatter cones.Volcanic cones and their craters that are aligned along a fissure form acrater row.[1] Small fissure vents may not be easily discernible from the air, but the crater rows (seeLaki) or the canyons (seeEldgjá) built up by some of them are.
Thedikes that feed fissures reach the surface from depths of a few kilometers and connect them to deepermagma reservoirs, often under volcanic centers. Fissures are usually found in or alongrifts andrift zones, such asIceland and theEast African Rift. Fissure vents are often part of the structure ofshield volcanoes.[2][3]
In Iceland, volcanic vents, which can be long fissures, often open parallel to the rift zones where theEurasian and theNorth Americanlithosphericplates are diverging, a system which is part of theMid-Atlantic Ridge.[4] Renewed eruptions generally occur from new parallel fractures offset by a few hundred to thousands of metres from the earlier fissures. This distribution of vents and sometimes voluminous eruptions of fluid basaltic lava usually builds up a thick lava plateau, rather than a single volcanic edifice. But there are also thecentral volcanoes,composite volcanoes, often withcalderas, which have been formed during thousands of years, and eruptions with one or more magma reservoirs underneath controlling their respective fissure system.[5]
TheLaki fissures, part of theGrímsvötn volcanic system, produced one of the biggesteffusive eruptions on earth in historical times, in the form of a flood basalt of 12–14 km3 of lava in 1783.[6] During theEldgjá eruption A.D. 934–40, another very big effusive fissure eruption in the volcanic system ofKatla in South Iceland, ~18 km3 (4.3 cu mi) of lava were released.[7] In September 2014, a fissure eruption was ongoing on the site of the 18th century lava field Holuhraun. The eruption is part of an eruption series in theBárðarbunga volcanic system.[8]
The radial fissure vents ofHawaiian volcanoes also produce "curtains of fire" aslava fountains erupting along a portion of a fissure. These vents build up low ramparts ofbasaltic spatter on both sides of the fissure.[9] More isolated lava fountains along the fissure produce crater rows of small spatter andcinder cones. The fragments that form aspatter cone are hot and plastic enough to weld together, while the fragments that form a cinder cone remain separate because of their lower temperature.
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