Intense earthquake swarm near Fagradalsfjall volcano, Iceland

An intense earthquake swarm started north of Grindavik and near Fagradalsfjall volcano, Iceland’s Reykjanes Peninsula early on October 25, 2023, prompting the Civil Protection Service to declare an uncertainty phase due to the seismic swarm.

• The earthquake swarm follows a similar seismic event in July 2023 that led to a volcanic eruption within six days.

Starting at midnight UTC on October 25, the area north of Grindavík became a seismic hotspot with more than 700 earthquakes detected in less than 24 hours. The two largest quakes were measured at magnitudes of M3.9 at 05:35 UTC and M4.5 at 08:18 UTC. These seismic activities were felt both in the Rekjanes Peninsula and the Capital Region of Iceland.

Civil Protections have escalated their alert level to an uncertainty phase as a response to the ongoing seismic activity. This move comes as authorities recognize the potential for earthquakes of similar magnitude to occur again, based on the current data.

The most recent occurrence of a seismic event of comparable magnitude in the Rekjanes Peninsula was recorded in July 2023, making this the second significant seismic event in the region this year.

The earthquake swarm in July 2023 started on July 4 and was followed by a volcanic eruption just six days later, on July 10.

The seismic swarm continues to be closely monitored as earthquakes of magnitudes similar to the largest ones recorded this morning could potentially occur again.

On October 14, the Icelandic Meteorological Office (IMO) issued warnings of a potential volcanic eruption in the Reykjanes Peninsula, following significant changes in land elevation near the Fagradalsfjall volcano.

Data indicates the formation of a new magma chamber, leading experts to predict that a volcanic eruption could occur in the coming weeks or months.

Kristín Jónsdóttir, the head of natural hazards at the IMO, stated that the current tension levels in the area are similar to those measured prior to the last eruption, adding that another magma intrusion is anticipated.

Given the region’s history of earthquake swarms preceding volcanic activity, and powerful tremors being a significant feature before the last eruption, heightened caution is advised, especially for those planning outdoor activities in the area.

Updates

15:37 UTC, October 26

About 3300 earthquakes were detected since midnight UTC on October 25 and the swarm is still ongoing, IMO said at 10:23 UTC today.

A total of 10 earthquakes over M3 have been detected there, and one M4.5 — at 08:18 UTC on October 25. The earthquakes originate at a depth of around 5 km (3.1 miles).

In light of the data currently available, this seismicity is interpreted to be likely triggered by the stress changes related to previous intrusive activity on the peninsula. There are currently no indications of magma migration beneath the Þorbjörn/Grindavík area, but the situation might change anytime, and it might evolve over a short time from hours to days.

As reported in September a magmatic intrusion is currently ongoing beneath Fagradalsfjall.

References:

¹ Specialist remark – IMO – 12:02 UTC on October 25, 2023

² Officials warn of potential volcanic eruption near Fagradalsfjall before Christmas, Iceland – The Watchers – October 17, 2023

Featured image credit: IMO