The eruption that occurred in southwest Iceland has entered a state of equilibrium just a few hours after it began. This doesn't mean the lava will stop flowing anytime soon. Nobody knows that. But the Icelandic Meteorological Office (IMO) maintains that the intensity of the event began to decrease four hours after it began, at 10:17 p.m. on Monday, December 18, local time. Except for when it was going to occur, most of the parameters of the eruption are being as expected and everything indicates that, beyond some local problems, this time the roar of the Earth is being quiet.
Although it was not known where the eruption could occur, it was most likely that it would occur along the seismic swarm that had been taking place for almost two months. And so it has been. The lava ejection took place about 3 kilometers northeast of the coastal town of Grindavík. At the beginning of the event, more than 1,000 small earthquakes occurred in the area, as if anticipating what was to come. But, according to IMO data, since last week seismic activity had been reduced to a few hundred microseisms a day. The calm before the storm? In part yes, experts point out that the accumulation of magma had reached a limit. In fact, the deformation of the surface, one of the signs of what is to come in terms of volcanic activity, had been reducing since the weekend. Until, the earth broke.
But there has been no storm. It is the most prominent feature of the Grindavík eruption. This is not a volcano that furiously emits lava and pyroclastic material. It is like a four kilometer long wound from which lava gushes effusively. Instead of a volcanic eruption, they call it an eruptive fissure. As it occurs over several kilometers, the magma exit occurs fluidly, without the explosiveness caused by the tunnel effect of volcanoes. This configuration is very typical of Iceland. “The island is a boundary of divergent plates and, therefore, our eruptions are, above all, fissures,” says volcanologist at the University of Iceland, Ármann Höskuldsson, in an email.
The island, however, is also home to more than a hundred volcanoes. “We have more common eruptions in other parts of Iceland, that is, where the plates are not separating,” explains Höskuldsson. Of this type was the last one to erupt, Fagradalsfjall, which did so in a big way. On the occasion of the beginning of the Grindavík event, the Icelandic volcanologist already maintained that volcanism in Iceland is characterized by basaltic lava, “that means that the eruptions are mild and generate lava flows.”
In addition to it being an outpouring of lava from a fissure, two other factors help lower the alert for the eruption. One is that it occurred on land and not under the sea, which would have added explosiveness to the phenomenon. As the professor of volcanology at the University of Iceland, Thorvaldur Thordarson, explains, “if it erupted under the sea, we would have an ash-producing eruption, but its intensity would only have a local impact.”
It would be more dangerous if the eruption had occurred further north, in the frozen areas of the island. In the southwest the ice barely makes an appearance. “There is very little danger of a repeat of what happened during the Eyjafjallajökull eruption in 2010, as the volcanic activity on the Reykjanes Peninsula is of a different nature, as there are no ice sheets,” Thordarson recalls. His colleague Höskuldsson is categorical: “The rash is powerful at first and then slowly disappears, so in a maximum of 5 to 10 days, it is over.”
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