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Intense earthquake swarm signals possible volcanic eruption in Fagradalsfjall, Iceland

reykjanes peninsula iceland earthquakes july 4 to 5 2023 f

The Icelandic Met Office (IMO) issued a special warning due to intense earthquake activity and the increased likelihood of a volcanic eruption on the Reykjanes Peninsula. IMO also warned rockfalls are possible on the Reykjanes Peninsula due to ongoing earthquake activity, particularly close to Lake Kleifarvatn.

The area between Fagradalsfjall and Keilir has been a seismic hotspot since July 4, with 2 200 earthquakes detected as of 14:29 UTC today, seven of which were over a magnitude of 4. The largest quake in the series thus far is M4.8 recorded at 08:21 UTC today.

The swarm started in a known magma upwelling area under Fagradalsfjall (near where intrusion started in July 2022) with a source at a depth of about 8 km (5 miles) which shallowed to about 4 km (2.5 miles) in about five hours after the start of the eruption. This morning, July 5, earthquakes have been measured at a depth of about 2 – 3 km (1.2 – 1.8 miles). The size of the earthquake has grown as time has passed, and there have been seven earthquakes larger than 4 this morning.

At 10:55 UTC on July 5, IMO raised the Aviation Color Code to Orange (the third level on a four-color scale).

reykjanes peninsula earthquakes 48 hours to 1725z july 5 2023
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Earthquakes near Fagradalsfjall on July 4 and 5, 2023. Credit: IMO

This trend is a recurring phenomenon for the region, echoing seismic swarms recorded in February-March and December 2021, and July-August 2022. These seismic events were caused by magmatic intrusion along the same line and resulted in eruptions in March 2021 and August 2022. The current activity bears striking similarities to the events starting on July 30, 2022, where an intrusion led to an eruption four days later, on August 3, 2022.

Given the increased seismic activity and the history of eruptions following similar trends, the IMO believes an eruption could occur in the next few hours or days. However, there remains a possibility that the activity could cease without an eruption. Nonetheless, the similarities with previous swarms, particularly those in July and August 2022, indicate an increased chance of an eruption.

In addition to the eruption threat, the IMO has warned that the deformation associated with the intrusion and seismic activity could trigger earthquakes on other cracks on the Reykjanes peninsula.

References:

1 Specialist update – IMO – July 5, 2023

2 Talið líklegt að þessi aukna virkni geti verið undanfari eldgoss – IMO – July 5, 2023

Featured image credit: IMO

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