Iceland is threatened by a major volcanic eruption

At the Icelandic Meteorological Office (IMO), the days are recent “ all » long. “ They start with a meeting of the scientific council that analyzes the latest data and agrees on what should be made public », says Sara Barsotti, volcanic risk coordinator within the agency. Updates are published several times a day to try to inform the population, who has been living in dire uncertainty for several days, as best as possible.

On Friday evening, November 10, a state of emergency was declared on the Reykjanes Peninsula, in the southwest of the island. The next day, the 3,700 residents of Grindavik, 40 km as the crow flies from the capital Reykjavik, had to urgently evacuate the port city. They have no choice: beneath their feet, rivers of high-pressure magma cause incessant earthquakes, lifting roads and creaking buildings, warning signs of a possible major volcanic eruption. “ The current seismic activity is by far the most intense on the Reykjanes Peninsula since instrumental measurements began »admits the IMO, which has registered no fewer than 32,000 tremors since October 26, including about thirty earthquakes with a magnitude of 4.

A mistake of more than 15 kilometers long

The source of this magma is probably six kilometers deep, explains Magnus Tumi Gudmundsson, professor of geophysics at the University of Iceland. “ During the event that began Friday, ten to twelve of the Earth’s crust tore apart km long and the magma filled the hole very quickly. It went back to 800 meters from the surface. » This fault now marks the southwest of the island for about fifteen kilometers. “ On Friday, the speed of magma flowing into this rift was exceptional, hundreds of times greater than what has been observed around the Fagradalsfjall volcano in recent years. » in the neighborhood, says Sara Barsotti.

After a weekend of panic, the tremors have calmed down somewhat; but the risk of an eruption in the coming hours or days remains “ significant ». “ It is difficult to say how the situation will develop, because it is a complex process that affects a very large area and undoubtedly connects several volcanic systems. notes the IMO coordinator. You should know that we cannot see what is happening, we can only interpret data and draw the potential trajectory of the magma through models. »

Iceland, located where the Eurasian and North American tectonic plates meet, is of course not new to this: the island has no fewer than 33 active volcanic systems, and the whole world remembers the monster eruption of Eyjafjallajökull in 2010, which air traffic and led to the cancellation of 100,000 flights.

As Magnus Tumi Gudmundsson recalls, most eruptions on the island are preceded by an intense swarm of earthquakes that can last several days and correspond to the magma making its way to the surface during a certain period. “ tearing » – when the crust breaks under the influence of forces that push the North American plate away from the Eurasian plate. “ But the magma may not reach the surface, become trapped and eventually cool. the researcher suggests. In this case there would be no rash. The other possibility is that magma is seeping to the surface : we could then witness an eruption similar to those of 2021, 2022 and 2023 » in the area. The speed at which the magma has risen to the surface in recent days can also be explained by the numerous cracks caused by these previous eruptions. For him at least it would be the worst case scenario “ an eruption that created a lava field that would engulf the entire city of Grindavik » and would damage the nearby Svartsengi geothermal power plant, which produces hot water and electricity for about 30,000 people (on Tuesday, authorities were also preparing to surround it with defensive walls).

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The risk of an explosive underwater eruption

At the Icelandic Meteorological Office we note that north of Grindavik the ground has shifted vertically by more than one meter. And according to the models, the pressurized magma at this level of the crack could find a path to the surface. But “ given the degree of uncertainty », no scenario is excluded at this stage: neither that of an eruption over several kilometers along the fault line, nor that of multiple eruptions on the same line. Not even the possibility of an underwater eruption, as the rift extends up to two kilometers offshore. “ The outcome would then be explosive due to the interaction between water and magma, and its dangerousness would depend on several factors, warns Sara Barsotti. This is certainly less likely, but in this case we could expect smoke columns of more than 15 km high. » As for the apocalyptic rumors circulating on social media about an underwater eruption “ would release more carbon dioxide into the atmosphere than all humans emit in a year “, Magnus Tumi Gudmundsson reviews them “ completely absurd ». “ According to an estimate of the US Geological Surveyhuman activity (industry, aviation, agriculture, etc.) emits approximately 130 times more CO₂ that the activity of all volcanoes in the world, he remembers. Volcanic activity therefore plays a very minor role in this area. »

In Grindavik, people have had to leave their homes without knowing when – or even if – they will be able to return

Sara Barsotti, volcano risk coordinator at the Icelandic Meteorological Office

Because they are staying with relatives or in emergency centers, Grindavik residents therefore do not know where or when the eruption will occur. In the next few hours? The next few days ? Two years ago, the Fagradalsfjall explosion started a few weeks after the first ground tremors. As the IMO recalls on its site, these cycles of intense volcanic activity occur every 800 to 1000 years in the region (the last dating back to the 13th century).^e century) and that started in recent years may last decades.

“ Evacuations are not really rare in the country, but they are mainly incidental risks‘avalanches, says Sara Barsotti. In Grindavik, people have had to leave their homes without knowing when – or even if – they will be able to return. » On Monday, under strict supervision by authorities, residents of the small port town were only able to get home for a few minutes to collect their belongings. “ I was here to empty my house as much as possible and grab the necessary items. Something for the kids, Christmas presents “, Johannes Dadi Johannesson, 34, told AFP. “ We’re actually a little desperate, a little paralyzed and sad, explained Hans Wierer, another resident of Grindavik. When we think about the time and energy we put into building our home, it’s sad. »