Iceland lies on a mid-ocean ridge (where two tectonic plates are moving apart) and is also associated with a hot spot (a rising plume of hot rock within the mantle) that feeds its volcanic activity. An intense period of seismic (earthquake) activity begun on Friday 10th November, associated with land displacement, that indicated the presence of magma moving within the subsurface under the Reykjanes peninsula. Scientists have been monitoring the activity through GPS, seismic, and satellite data (amongst others) and have noted a 15 km long region of magma that is vertically extending within the Earth’s crust (like a vertical sheet of paper) with the shallowest point thought to be around 800 m below the surface. This close proximity to the surface, in combination with the seismic activity, suggests that an eruption in the area is likely.

The town of Grindavik lies above this magma region and has experienced severe seismic activity that prompted the evacuation of the town late on Friday 10th November and has damaged much of the infrastructure within the town. However, seismic activity has reduced in intensity somewhat over the previous two days, and so the Icelandic Civil Protection allowed residents to temporarily re-enter the town in controlled conditions to retrieve personal belongings and pets on 13th November. Note that the reduction in seismic activity does not necessarily mean a reduction in the volcanic risk.

An eruption in this region would likely look like that in the previous three years (2021, 2022, and 2023) – a fissure system with lava fountains and lava flows, although the extent of the 15 km magma region is larger than noted in previous years. Due to the challenging and evolving conditions, it is very difficult to predict when/where this would occur along the magma region, and it is still possible that magma will stabilise in the subsurface and cool to form an intrusion, rather than move upwards to erupt. If it were to erupt, it is very unlikely that this would result in the formation of a large ash plume like that in the 2010 Eyjafjallajökull eruption as the volcanic system is very different. However, if the magma were to move up to the surface and erupt under the sea, the eruption would be more explosive due to the water-magma interaction and would likely produce some ash (like that seen in the Surtsey eruption, in the 1960s).