Theistareykjarbunga (Þeistareykjarbunga, ) is a

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...

in north-eastern

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

with two fissure vents called Þeistareykjahraun and Borgahraun , and two cones: the Stórahversmór and the , Stóravíti . They both are currently extinct, although there is evidence suggesting the potential for activity such as recent localised uplift and seismicity. The multiple vents make up the Theistareykir (Þeistareykir) volcanic system, with more recent evidence that the former classification as a shield volcano is better considered an embryonic

central volcano A central volcano is a type of volcano formed by basalts and silica-rich volcanic rocks. They contain very few or no volcanic rocks of intermediate composition, such that they are chemically bimodal volcanism, bimodal. Large silicic eruptions at c ...

with associated fissure swarm, as

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

has erupted in a limited area. The recent lava has

picrite Picrite basalt or picrobasalt is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20-50%) and black to dark brown pyroxene, mostly augite. The olivine-rich ...

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

tholeiite basalt The tholeiitic magma series () is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic ...

characteristics but before the ice age there were

basaltic andesite Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Ameri ...

and rhyolite eruptions. There is a central high temperature geothermal area with numerous steam vents and fumaroles. This has been utilised by a 90 MWe power station.

Eruptions

There have been three dated eruptions, all VEI-0: the most recent eruption was around 900 BCE and the previous eruption was in 6800 BCE. Around 9500 BCE, an eruption produced approximately 18 billion cubic metres of basaltic lava.

References

{{Reflist Shield volcanoes of Iceland North Volcanic Zone of Iceland Polygenetic shield volcanoes Volcanic systems of Iceland Calderas of Iceland Central volcanoes of Iceland

Eruptions

See also

References