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The 2021-23 Fagradalsfjall and 2023-? Sundhnúkur Fires, Reykjanes Peninsula, Iceland

Thor Thordarson1; Ármann Höskuldsson1, Ingibjörg Jónsdóttir1 William M. Moreland1,2; Valentin R. Troll3; Frances M. Deegan3.

  • Affiliations:  1Faculty of Earth Sciences, University of Iceland, IS101 Reykjavík, Iceland 2Iceland Meteorological Office, IS105 Reykjavík, Iceland 3Uppsala University, Uppsala, Sweden   

  • Presentation type: Talk

  • Presentation time: Tuesday 11:15 - 11:30, Room R380

  • Programme No: 1.6.4

  • Theme 1 > Session 6

Abstract

In the early morning on 19 March 2021, when an eruption began on a 180-m-long linear vent system at the Fagradalsfjall volcanic complex, the Reykjanes Peninsula, Iceland, entered into its 4th Eruption Period in the last 4000 yrs after 781 years of quiescence. This also marks the onset of the 2021-23 Fagradalsfjall Fires, featuring 3 effusive eruptions: the 19.03-18.09.2021 Geldingadalir, 03-21.08.2022 Meradalir, and 10.07-05.08.2023 Stóri-Hrútur events. Collectively they erupted 135106m3 (DRE) of olivine tholeiite lava (8-8.5wt% MgO) that was extracted from a ~553 km magma storage zone situated at 9-12 km depth beneath Fagradalsfjall and containing an estimated ~15-25 km3 of melt. Late in 2023 the unrest shifted from the Fagradalsfjall volcanic lineament and onto the Sundhnúkur volcanic lineament that stretches across the Reykjanes Peninsula between the towns of Grindavík and Vogar. To date (i.e. January 2025) the 2023-ongoing Sundhnúkur Fires have featured 7 effusive eruptions. Collectively, they have produced ~170106 m3 (DRE) of olivine tholeiite lava (6.0-6.8wt% MgO) erupted from a 41.50.004 km magma storage situated at ~5 km depth beneath Svartsengi. This storage is supplied by the Fagradalsfjall magma storage described above. An intriguing aspect of the Sundhnúkur data set is that in the first 3 events the volume of magma accumulated in the Svartsengi magma storage prior to eruption was roughly equal to volume of erupted lava. In the 4 events that followed the volume of erupted lava is factor 1.5-2 greater than the accumulated magma volume, indicating direct additional contribution from the deeper Fagradalsfjall magma storage.