The strong earthquake swarm that started yesterday near Grindavik on Iceland’s Reykjanes peninsula is probably caused by magma forming a dike – a vertical fissure-shaped intrusion at shallow depth, which allows the magma to rise and get closer to an eruption. The earthquakes have subsided compared to the peak yesterday, but remain very frequent.
Nearby GPS stations registered a dramatic jump in ground deformation yesterday: within a few hours, a NW-SE oriented ground expansion of up to more than one meter (120 cm at maximum, see image). This fits into the picture of the formation of a vertical dike or underground fissure oriented perpendicular to it (NE-SW).
The Icelandic Met Office (IMO) believes that the magma volume involved is much bigger than during the build-ups of the previous eruptions in 2021, 2022, and 2023 at Fagradalsfjall to the east. IMO considers it possible that the magma-filled dike extends even underneath Grindavik town. In this case, it could be a possibility that an eruptive fissure forms right there, threatening one of Iceland’s most important harbors and towns along the southern coast.
Civil Protection declared emergency Level and residents of Grindavík were told to evacuate.
The latest update of IMO reads:
„Significant changes have occurred in the seismic activity measured near Sundhnjúkagígar north of Grindavík and deformation observed in the Reykjanes Peninsula this afternoon. The seismic activity has moved south towards Grindavík. Based on how the seismic activity has evolved since 6 PM today, along with results from GPS measurements, there is a likelihood that a magma intrusion has extended beneath Grindavík.
In light of this outcome, the police chief in Suðurnes, in cooperation with the Civil Protection Authorities, has decided to evacuate Grindavík. An emergency level of civil protection is now in effect. This is not an emergency evacuation. Residents of Grindavík are advised to proceed with caution.
„At this stage, it is not possible to determine exactly whether and where magma might reach the surface. There are indications that a considerable amount of magma is moving in an area extending from Sundhnjúkagígum in the north towards Grindavík. The amount of magma involved is significantly more than what was observed in the largest magma intrusions associated with the eruptions at Fagradalsfjall. Further data is being collected to calculate models that provide a more accurate picture of the magma intrusion. It is currently not possible to say when this work will be completed.“
