The Fagradalsfjall and Sundhnúkur Fires of 2021–2024: A single magma reservoir under the Reykjanes Peninsula, Iceland?

Abstract

The Reykjanes Peninsula (RP) hosts several volcanic lineaments that have been periodically active over the last 4000 years. Since 2021, following a ca. 800-year quiescence, eight eruptions have occurred on the RP, with more expected in the future. To better understand the origins of this renewed volcanism and help forecast future eruptions, we examine (i) if the ongoing volcanism is fed from a single or multiple magma storage zone(s) or from several smaller reservoirs and; (ii) where the zone(s) are located (i.e. mantle or lower or upper crustal depths). Using major and trace element geochemistry, oxygen isotopes, and seismic tomography we rule out a single, RP-scale, deep-seated magma storage zone. Instead we propose the presence of a ca. 10-km-wide region of crustal-level (9–12 km) magma accumulation beneath the Fagradalsfjall volcanic lineament that fed both the 2021–23 eruptions of the Fagradalsfjall Fires and the 2023–24 eruptions of the Sundhnúkur Fires.