A
fissure vent, also known as a
volcanic fissure or simply
fissure, is a linear
volcanic vent through which
lava erupts, usually without any
explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large
flood basalts and
lava channels. This type of volcano is usually hard to recognize from the ground and from
outer space because it has no central
caldera and the surface is mostly flat. The volcano can usually be seen as a crack in the ground or on the
ocean floor. Narrow fissures can be filled in with lava that hardens.
 |
| A volcanic fissure and lava channel |
As
erosion removes its surroundings, the lava mass could stand above the surface as a
dyke. The dykes that feed fissures reach the surface from depths of a few kilometers. Fissures are usually found in or along
rifts and
rift zones, such as
Iceland and the
Great Rift Valley in
Africa. Fissure vents are often found in
shield volcanoes.
 |
| Mauna Loa with different lava flows and fissure vent |
In Iceland, volcanic vents are often long fissures parallel to the rift zone where
lithospheric plates are diverging. 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 voluminous eruptions of fluid basaltic lava usually build up a thick lava plateau rather than a single volcanic edifice. The
Laki fissure system produced the biggest eruption on earth in historical times, in the form of a flood basalt, during the
Eldgjá eruption A.D. 934, which released 19.6 km³ (4.7 mi³) of lava. The radial fissure vents of
Hawaiian volcanoes produce “curtains of fire” as
lava fountains erupt along a portion of a fissure. These vents produce low ramparts of
basaltic spatter on both sides of the fissure. More isolated lava fountains along the fissure produce crater rows of small spatter and
cinder cones. The fragments that form a spatter cone are hot and plastic enough to weld together, while the fragments that form a cinder cone remain separate because of their lower temperature.
 |
| Lava Channel of Hawaii |
