Title: Iceland Rifting Today

Speaker: Haraldur Sigurdsson, Emeritus Professor of Oceanography, URI GSO

Abstract: As an exposed segment of the Mid-Atlantic Ridge, Iceland is a valuable and accessible laboratory for detailed geophysical and geochemical studies in this type of environment. The Reykjanes Peninsula in south-west Iceland is the on-shore continuation of the active and submarine Reykjanes Ridge. However, the peninsula has been volcanically dormant for about 800 years, with the last eruption in 1226 AD. Rifting has however continued, at a lower level. The peninsula is a leaky transform, with six rift segments arranged en echelon. In 2020 a rifting episode began, ending the 800 year dormant period. It began in the Fagradalsfjall volcanic system, with a small eruption in 2021, 2022 and summer 2023. Then the next rift segment to the west showed signs of unrest, with ground deformation, updoming, fissuring and finally an eruption on 11. November 2023. As this lava flow directly threatened the fishing town of Grindavík, it has been focus of much study. Fortunately the lava from the 3.7 km long erupting fissure has not yet reached the town but the fissure has rifted the town down the middle. A third rift segment, further to the west is known as Krísuvík, and also shows unrest. This is of even greater concern as fissures from this volcanic system extend to the east and intersect southern suburbs of Reykjavík, Iceland´s capital. The crisis has just begun, after 800 years of dormancy, and Iceland may be in for an extended period of tectonic and volcanic activity in the backyard of the capital. Ultimately, this is due to the slow but steady westward motion of the North American plate, but this is now opening up pathways for magma that resides in horizontal sills at the crust-mantle interface. It is likely that each of the six volcanic systems that make up the en echelon zone will experience rifting and volcanism in succession. There are four more to go.