THE ERUPTION OF THE FAGRADALSFJALL VOLCANO

IMMINENT PUTS ICELAND ON ALERT STATE

An intense series of earthquakes shook the Reykjanes Peninsula in southwest Iceland, starting on Friday, November 10, 2023. Hundreds of earthquakes were detected by regional seismometer networks and several were strong enough to be felt in Reykjavik, 50 kilometers away. A civil protection alert was triggered warning of the risk of a volcanic eruption – it would be the fourth since 2021.

Iceland straddling a collapsing ditch

Iceland sits majestically on the Mid-Atlantic Ridge, a place where the North American and Eurasian plates are gradually moving away from each other, at a rate of about 2 centimeters per year. In the depths of the Earth's mantle, where the rocks adopt the consistency of extremely rigid caramels, the plates agree to deform in an uninterrupted manner.

However, as they approach the surface, the rocks of the earth's crust reveal their cold and brittle nature: their extension only occurs at the cost of their rupture. The Reykjanes Peninsula forms the southwest tip of Iceland, where the Mid-Atlantic Rift emerges from the ocean. There, the Earth's crust responds to relentless tectonic forces by cracking every few centuries, giving rise to a collapse gap, commonly called a rift.

The last sequence of crustal rupture and eruptions dates back more than 800 years. Since then, the plates should have moved apart by about sixteen meters. Currently, Iceland is experiencing a new phase of rupture, marked by hundreds, if not thousands, of earthquakes, many strong enough to be felt in the southwest of the island. All these phenomena are caused by the intrusion of magma close to the surface.

Each earthquake and eruption releases some of the energy stored in these tectonic plates, and eventually, when all of this tension is completely released, the eruptions will end. Crustal ruptures are facilitated by the presence of magma, acting as a lubricant, a feature shared with other ocean ridges. Magma forms continuously at depth, and its density means it will rise.

Within the rigid and brittle crust, magma can only make its way by following existing fractures, if any. However, once it begins its ascent, it traces its path towards increasingly shallow areas, thus intensifying the risk of eruption.

In early November 2023, the Icelandic government declared a state of emergency in the area surrounding the Fagradalsfjall volcano, following a series of earthquakes, often warning indicators of a volcanic eruption.

On November 11, 2023, preventive measures were announced to mitigate the possible devastating effects of an impending eruption. The response plan by the authorities and the tourism industry was activated in response to recent developments, including the numerous earthquakes recorded in Reykjanes, as reported on the government website in English.

As part of these measures, the town of Grindavík, home to 4,000 inhabitants, was evacuated to ensure the safety of residents. The Icelandic Meteorological Office (IMO) expresses serious concerns about the possibility of large quantities of magma spreading underground, which could erupt in the region. Scientists are carefully monitoring the region's seismic activity.

“Since midnight on November 11, approximately 800 earthquakes have been recorded in the area where the magma intrusion is occurring. Although seismic activity has decreased slightly in recent hours, it remains high.

Most of the recent earthquakes occurred near Grindavík, where the southwest end of the magmatic dike intrusion is estimated to be present," the IMO said. At midday on November 11, the Office meteorologist published on Twitter a map of ground deformations in the region, described as "much higher than normal".

With around 30 active volcanoes over 100,000 square kilometers, Iceland strives to best manage the anticipation of volcano-related risks. In the case of Fagradalsfjall, the threat comes from underground magma that could soon emerge.

An imminent eruption with the release of magma

The possibility of an imminent eruption with the emergence of magma now concerns observers. Signs of this threat are manifested by a progressive deformation of the Earth's surface, signaling the intrusion of fresh magma into the crust. Over the past weekend, the situation has evolved dynamically. Parameters such as the size, number and location of earthquakes clearly indicate the filling of a crustal fracture with magma, at a depth of about 5 kilometers.

The magma persists in its intrusion, widening the ends of the fracture and creating a passage through the crust, thus forming a "dike" - a vein of rock infiltrated into a fissure - about 15 kilometers long. Although the magma has not yet reached the surface, ground movements and computer models suggest that a magma reservoir has built up within a kilometer of the surface.

Anticipation of an imminent eruption remains high, but monitoring teams will only be able to determine the precise time and location when they detect specific signals indicating magma movement. These signs could include a repetitive "buzzing" of volcanic tremors, announcing a possible eruption in the coming hours, or an increase in earthquakes at very shallow depths.

The results

Currently, the dike appears to extend directly beneath the town of Grindavik, a fishing community in southwest Iceland. If a surface eruption occurs, it could resemble those of 2021-2023 at Fagradalsfjall, with a fissure opening onto the earth, fountains of hot red molten rock, and lava flowing down the hillside from the site of the rash.

The potential threat will depend on the exact location of the start of the eruption and how far the lava has traveled. Fumes emanating from erupting magma, combined with the burning of peat and vegetation, could also create toxic air, depending on the speed of the eruptions and the direction of the winds.

In the event of an eruption in Grindavik, the consequences could be comparable to those of the Eldfell eruption in 1973, which buried part of the town of Heimaey.

This is why a preventive evacuation of the town, the nearby Svartsengi geothermal power plant, and the Blue Lagoon, one of Iceland's most popular tourist attractions, is currently underway.