For more than a week now, Iceland's Reykjanes Peninsula has been continuously rocked by an intense earthquake swarm: A total of more than 20,000 tremors have been recorded since the activity started on the Reykjanes Peninsula on 24 February 24 when a magnitude 5.7 quake occurred, followed almost immediately by a magnitude 5.0 event.

In total, the Icelandic Meteorological Office (IMO) recorded 5 quakes of magnitude 5.0 or above, 51 quakes between 4.0 and 5.0 and 397 quakes between 3.0 and 4.0. Many of these quakes were felt in nearby villages and towns, but luckily, the immediate areas around the earthquake swarm are not densely inhabited and there have been no reports of significant damage.

earthquake activity may herald a new volcanic eruption

Since early on, it has been speculated whether the current seismic swarm was related to a magmatic event underground and eventually precede a new volcanic eruption.
The area is located on the active rift zone of SW Iceland, where the North American and Eurasian tectonic plates separate from each other, something that manifests itself in frequent earthquakes, underground magma intrusions and occasional fissure eruptions on the surface along SW-NE trending fissures.

This was given new evidence on 3 March, when IMO reported a sudden increase of seismic tremor in the same area, most likely sign that magma was moving underground. IMO stated that the observed burst of tremor were sourced from a region 2 km southwest of Keilir on the Reykjanes Peninsula, or a few km northeast of Fagradalsfjall, an old extinct subglacial volcano (also known as a “tuya”).
This region might be considered as part of the Krisuvik volcanic system in southwest Iceland, although it is still difficult to assign the potentially new vent area to the name of a specific volcanic system right now.

Eruptions occur on average every 800 years
According to professor of volcanology, Thorvaldur Thordarson, from the University of Iceland, volcanoes in southern Iceland experience “pulses” of activity every 800 years or so. He noted that the last eruption from this area occurred in the 11th or 13th century, so Iceland is right on time for an eruption.
However, citizens from the Reykjanes Peninsula need not worry as southwest Icelandic volcanic eruptions are very rarely explosive. “Icelandic eruption” is a specific type of effusive (not explosive) eruption where molten basaltic lava is erupted from parallel fissures in the ground, forming lava fountains and then vast lava flows.

This type of volcanic eruption is usually observed along spreading centers or mid oceanic ridges under the ocean. It was named after Iceland as this type of eruption was prominently observed occurring on-land in the country. Iceland sits on top of the Mid-Atlantic Ridge which is a spreading center where the North American and Eurasian tectonic plates are rifting apart.

In an article written by volcanologist Dave McGarvie from the Lancaster University, he noted that if there are to be any eruption in the area, it would likely not be as explosive as the 2010 Eyjafjallajökull eruption or the 2011 Grimsvötn eruption. This is due to the fact that the area is not covered by ice (which would otherwise interact explosively with the magma) and has shown fissure eruptions producing lava flows during the recorded historic past. Nevertheless, IMO has raised aviation warnings over the region.

IMO lists the most likely possible scenarios:

The ongoing seismicity reduces in the coming days and weeks.
The seismic swarm will increase in intensity, possibly with an earthquake up to magnitude 6 in size nearby Fagradalsfjall.
An earthquake up to magnitude 6.5 in size could be triggered in the Brennisteinsfjöll mountain range, over 20 km east of Fagradalsfjall.
Magma intrusions continue in the vicinity of Fagradalsfjall.
The intrusive magma movements stop and eventually solidify.
An effusive volcanic eruption could occur, resulting in lava flows that should not threaten inhabited areas of the peninsula.

The evolution of the seismicity continues to be monitored day and night, and in the event of an eruption, various contingency plans are in place.

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