New seismic tremor on Reykjanes Peninsula, more than 22 000 earthquakes since February 24, Iceland

A new seismic tremor similar to the one measured on March 3 started on Reykjanes Peninsula at 00:22 UTC on March 7, 2021.

Today's tremor was much shorter than the one on March 3 — it lasted 20 minutes vs. several hours four days ago.

Seismicity increased following the tremor with earthquakes larger than M4.

In total, around 1 300 earthquakes were detected from 00:00 to 12:25 UTC. Nearly 40 had magnitude above 3 and five above 4.

The largest was M5.0 at 02:02 UTC, about 3 km (1.8 miles) WSW of Fagradalsfjall. It was felt widely in the SW-part of Iceland.

Civil Protection and IMO experts met with the Police in Suðurnes and a representative of Grindavík at 03:30 UTC.

It is the opinion of experts based on the available data, that the earthquakes that were detected last night and this morning in Grindavík are not due to a displacement of magma and are therefore not considered as a short-term predictor of an eruption.

Similar bursts of tremor have been observed ahead of previous volcanic eruptions in Iceland. 

Magma movements are a likely cause for the ongoing signal, and it is possible that an effusive (lava-producing) eruption could occur close to Keilir, IMO said on March 3.

As a precaution for domestic and international air travel, the volcanic Aviation Color Code for the Reykjanes Peninsula has been elevated from Yellow (elevated unrest) to Orange (heightened unrest) on March 3.

Orange alert represents the third-highest level, with red reserved for an imminent or ongoing volcanic eruption.

Experts have made several possible scenarios involving magma intrusion under Fagradalsfjall:

• The seismic activity reduces in the next few days or weeks.
• Seismicity increases with larger quakes, up to M6 in the vicinity of Fagradalsfjall.
• An earthquake of magnitude up to 6.5 will have its source in the Sulfur Mountains.
• Magma intrusions continue in the vicinity of Fagradalsfjall: (1) Magma intrusion activity decreases and magma solidifies; (2) The activity leads to a lava flow that will probably not threaten settlements.

It is difficult to predict the exact development and whether one scenario is more likely than another, IMO said.

Since February 24 when an intense earthquake swarm started on the peninsula, IMO has detected more than 22 000 earthquakes in the area.​

Geological summary

The Reykjanes volcanic system at the SW tip of the Reykjanes Peninsula, where the Mid-Atlantic Ridge rises above sea level, comprises a broad area of postglacial basaltic crater rows and small shield volcanoes.

The submarine Reykjaneshryggur volcanic system is contiguous with and is considered part of the Reykjanes volcanic system, which is the westernmost of a series of four closely-spaced en-echelon fissure systems that extend diagonally across the Reykjanes Peninsula.

Most of the subaerial part of the volcanic system (also known as the Reykjanes/Svartsengi volcanic system) is covered by Holocene lavas.

Subaerial eruptions have occurred in historical time during the 13^th century at several locations on the NE-SW-trending fissure system, and numerous submarine eruptions at Reykjaneshryggur dating back to the 12^th century have been observed during historical time, some of which have formed ephemeral islands.

Basaltic rocks of probable Holocene age have been recovered during dredging operations, and tephra deposits from earlier Holocene eruptions are preserved on the nearby Reykjanes Peninsula. (GVP)

Featured image credit: IMO