Lavaflow from Geldingadalir

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Fagradalsfjall is a tuya with multiple prominences located on the Reykjanes Peninsula, around 40 kilometers from Reykjavík, Iceland. Its highest summit is Langhóll 385 meters. A volcanic eruption began on 19 March 2021 in Geldingadalir to the south of Fagradalsfjall.

The mountain Fagradalsfjall is a volcano of the Krýsuvík-Trölladyngja volcanic system on the Reykjanes Peninsula in southwest Iceland. It is situated within a zone of active rifting at the divergent boundary between the Eurasian and North American plates. The Krýsuvík volcanic system has been moderately active in the Holocene, with the second-most recent eruptive episode having occurred in the 12th century CE.

Other scientists propose that Fagradalsfjall could represent a separate volcanic system.

The unrest and eruption in Fagradalsfjall are part of a larger unrest period on Reykjanes Peninsula including unrest within several volcanic systems and among others also the unrest at Þorbjörn volcano next to Svartsengi. the Blue Lagoon during the spring of 2020.

Beginning December 2019 and into March 2021, a swarm of earthquakes, two of which reached magnitude Mw5.6, rocked the Reykjanes peninsula, sparking concerns that an eruption was imminent. Because the earthquakes were thought to have been triggered by dyke intrusions and magma movements under the peninsula. Minor damage to homes from a 4 February 2021 magnitude 5.7 earthquake was reported. In the three weeks prior to the eruption, more than 40,000 tremors were recorded by seismographs.

On 19 March 2021, an effusive eruption started at approximately 20:45 local time in Geldingadalir to the south of Fagradalsfjall, the first known eruption on the peninsula in about 800 years. Fagradalsfjall has been dormant for 6.000 years. The eruptive activity was first announced by the Icelandic Meteorological Office at 21:40. Reports state a 600–700 meter long fissure vent began ejecting lava, which covered an area of less than 1 square kilometer. Currently, the lava flows pose no threat to residents, as the area is mostly uninhabited, although there is potential for sulfur dioxide pollution.

The eruption has been called Geldingadalsgos. As of 26 March, the main eruptive vent was located at 63.8889 N, 22.2704 W, on the site of a previous eruptive mound. The eruption may be a shield volcano eruption, which may last for several years. It is visible from the suburbs of the capital city of Reykjavík and has attracted a large number of visitors. However, high levels of volcanic gases such as carbon dioxide and carbon monoxide make parts of the area inaccessible.