| Theistareykjarbunga | |
| Listing: | List of volcanoes in Iceland |
| Map: | Iceland |
| Elevation M: | 564 |
| Label Position: | left |
| Coordinates: | 65.8833°N -66°W |
| Type: | Shield volcano |
| Last Eruption: | 900 BCE ± 100 years |
Theistareykjarbunga (Þeistareykjarbunga, pronounced as /is/) is a shield volcano in north-eastern Iceland with two fissure vents called Þeistareykjahraun in Icelandic pronounced as /ˈθeiːstaˌreiːcaˌr̥œyːn/ and Borgahraun in Icelandic pronounced as /ˈpɔrkaˌr̥œyːn/, and two cones: the Stórahversmór in Icelandic pronounced as /ˈstouːraˌkʰvɛr̥sˌmouːr̥/ and the, Stóravíti in Icelandic pronounced as /ˈstouːraˌviːtɪ/. They both are currently extinct,[1] although there is evidence suggesting the potential for activity such as recent localised uplift and seismicity.[2] 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 with associated fissure swarm, as rhyolite has erupted in a limited area.[3] The recent lava has picrite, olivine tholeiite basalt characteristics but before the ice age there were basaltic andesite and rhyolite eruptions.[3] There is a central high temperature geothermal area with numerous steam vents and fumaroles.[3] This has been utilised by a 90 MWe power station.[2]
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.[1]