GPS and InSAR records strongly suggest magma is migrating toward the surface between Fagradalsfjall and Keilir, Iceland

Since the onset of the seismic swarm in the Reykjanes Peninsula, on July 4, 2023, more than 8 500 earthquakes have been recorded in the area between Fagradalsfjall and Keilir. While seismic activity in this area is decreasing, deformation data strongly suggests that magma is rising toward the surface. The Aviation Color Code remains at Orange.

This activity is caused by a new dike intrusion in the area, namely between Fagradalsfjall and Keilir, and its center is believed to be between Litli-Hrútur and Litli-Keilir. A total of 17 earthquakes larger than 4 have been recorded and 50 events larger than 3. The largest earthquake detected thus far is M4.8 at 08:21 on July 5.

The largest earthquakes are felt widely in the SW-area, from Hella to the east and towards Snæfellsnes peninsula in the north.

A continuation of this activity is expected but seismic activity has decreased somewhat in the vicinity of the dike. Seismic activity has continued in the area between Keilir and Fagradalsfjall, which is interpreted to be triggered events.

In spite of decreasing seismic activity, deformation seen in GPS and InSAR records strongly suggests that magma is migrating toward the surface, the Icelandic Met Office (IMO) said.

Interferogram (InSAR) images based on satellite radar data showing deformation occurring between June 28 and July 6 confirm the results from IMO’s GPS and seismic data regarding the magmatic intrusion.

Model calculations based on the interferogram and GPS data suggest that the upper level of the dike reached a depth of 1 km (0.6 miles) on July 6, causing a fracture of a 2.8 km (1.7 miles) length between Fagradalsfjall and Keilir, with a center just north of Litli-Hrútur. These results are in good agreement with the seismic activity.

The calculations also suggest that the magma inflow rate is almost twice as fast compared to the antecedent of the eruption in August 2022, but the total volume of magma which has reached the upper part of the crust is similar, around 12 million m³ (423 million ft^³). The most recent GPS data indicates that magma is still migrating closer to the surface.

New earthquake swarm close to Eldey Island

Another earthquake swarm started close to Eldey Island on Reykjanes Ridge shortly before UTC midnight on July 6, approximately 10 km (6.2 miles) southwest off of Reykjanes Peninsula. As a result, the Aviation Color Code was raised to Yellow.

As of 10:29 UTC on July 8, around 500 earthquakes have been detected on Reykjanes Ridge. Around 20 quakes over M3 and 6 over M4 have been detected there, with the largest being M4.5 at 05:06 UTC on July 8.

Earthquake sequences in this area are not uncommon but this current activity is unusually high, IMO said. In light of that, the Aviation Color Code, for Eldey volcanic system, was raised to Yellow.

Heightened activity on the Reykjanes ridge now is potentially triggered by the dike intrusion in Fagradalsfjall, but other causes cannot be ruled out. Deformation data do not suggest that the activity is caused by magma movement, but further research and data are needed.

Updates

July 10

After 6 days of intense seismicity between Fagradalsfjall and Keilir, Reykjanes Peninsula, Iceland, a new volcanic eruption started just northwest of Litli Hrutur at around 17:00 UTC on July 10, 2023.

The announcement has been made by the Icelandic Met Office (IMO).

Volcanic eruption started just northwest of Litli Hrutur, Reykjanes Peninsula, Iceland

References:

¹ Earthquake activity in Fagradalsfjall area – IMO – July 7, 2023

Featured image credit: IMO