Signs continue to accumulate that the Reykjanes Peninsula in southwestern Iceland is on the brink of a second eruption. The area has not stopped shaking after the explosion of the first volcano on December 18, accumulating more than 800 earthquakes in one week—the vast majority imperceptible. Ground deformations have also returned, unequivocal indications of a new entry of magma at depth, at a rate similar to that measured before the first eruption.
“The probability of an eruption increases day by day,” reported the Icelandic Meteorological Office (IMO), the entity in charge of monitoring seismic and volcanic activity in the country. Predicting the exact moment in which the event will take place is impossible, but the experience of December 18 suggests that, if it occurs, the eruption will take place in a few weeks. This is how long it will take, if everything goes as it was then, for the system to accumulate underground the more than 10 million cubic meters of magma that it needed to open a fissure in the Earth's crust ten days ago.
“It may also take longer, or take less,” warns Rubén López, volcanologist at the National Geographic Institute (IGN), in conversation with La Vanguardia. Past scenarios “serve to give us an idea,” he continues, because “if the deformation and seismicity are similar, we can think that both eruptions may take a similar time.” However, “a new eruption does not have to do the same as the previous one,” he concludes.
The current preeruptive signals began while the December 18 event was still underway, and have intensified in recent days. In fact, these indicators "made us think that there could be new mouths" within the same eruptive process, explains López. However, the eruption stopped after two and a half days, something "not many people expected," because the most recent precedents suggested an episode that would last weeks or months.
"It is true that in Iceland the last eruptions had not been like this, but it is quite common for a volcano to have an eruption, sometimes lasting less than a day, and then have other eruptions in the following days or weeks," summarizes the expert.
The same uncertainty that prevents us from answering precisely when the eruption will occur makes it difficult to determine the location where it will take place. It is most likely that a fissure will open in the same area as during the first eruption, but the IMO does not rule out that the eruptive mouths could open in the fishing town of Grindavík, or even in the sea, beyond the limits of the island. After all, the magma that began to accumulate underground on November 10 spread over more than 15 kilometers, including the underground bowels of the small urban center.
It is impossible to predict what exact point the magma will find to break through the Earth's crust and emerge outside. Although the scenario is, for now, very similar to that before the eruption on the 18th, the resolution may be very different. “Depending on whether [the magma] goes further north or further south, or east or west, it can reach Grindavík or the geothermal power plant” of Svartsengi, which supplies energy to the entire country, says López, of the IGN. The municipality has asked the Icelandic government to start building defenses north of the town as soon as possible.
Another possible scenario, although less likely, is that the entry of magma at depth stops, the deformation stops and there is no eruption. “If the deformation stops, the only thing it will cause will be a thickening of the crust, the island will have become a little larger and that's it,” summarizes the expert.
In the last five days, the IMO has also detected more than 140 tremors, practically all of magnitude less than 1, on the western slope of Fagradalsfjall, a volcanic system very close to that of Svartsengi (the one that is starring in the current episode), where There were separate eruptions in 2021, 2022 and 2023.
The IGN volcanologist rules out, for now, that this signal suggests that the eruption will move towards that area, because both the number of earthquakes and their magnitude are small. “Wherever the seismicity is, the magma will come out,” he points out, and this, for now, points to the Svartsengi system.
