This Tuesday at 9:12 p.m., a magnitude 4.2 earthquake shook the Gindavik region in southwest Iceland. More than an hour later, large lava fountains appeared near the Sundahnúkur crater, a formation that dates back 2,350 years.
The magma came from a 4 kilometer long fissure. It is not the classic cone with which the word volcano is associated, but a fracture in the ground from which lava flows: the flows have flowed rapidly outwards, forming shallow layers around it.
Seismic activity around the eruption decreased in the following hours, a situation that for now excludes scenarios for the cancellation of flights internationally. But this was also influenced by the type of eruption, which was exuberant: “These are eruptions in which the lava is very fluid and moves easily.” Normally, the amount of ash is very small,” explains the geologist and popularizer. Nahum Mendez Chazarra to this newspaper.
In the three hours before the eruption, data from the United Nations' International Maritime Organization suggests that at least 258 earthquakes were recorded. There have been at least 450 in the last 24 hours.
But authorities were already on alert and had evicted Grindavik's nearly 4,000 residents last month (the nearby Blue Lagoon tourist resort was closed). They knew an eruption was likely because of the seismic movement that had been recorded for nearly two months.
On several days last month, the earth shook much more strongly than on this Tuesday: for example, at least 1,071 earthquakes were recorded between November 10th and 11th. Then why wasn't there an outbreak? “We will only know after some time, when scientists have collected all the data and can examine it in detail,” argues Méndez Chazarra. “In addition, although the system appeared calm, deformation continued and seismic swarms still occurred, prompting authorities to maintain alert levels in certain areas due to the possibility of an eruption.”
A crucial factor in monitoring earthquakes is the depth at which they occur. “It tells us where the magma is moving and where it could accumulate, as well as the area where it would have the greatest chance of breaking on the surface,” explains Méndez Chazarra. In the two hours before Tuesday's eruption, half a dozen tremors were recorded within 100 meters of the surface.
A good sign is that this eruption in southwest Iceland has reached a state of equilibrium just a few hours after it began. It would have been more dangerous if it had happened further north, in the frozen areas of the island (there is hardly any ice in the south). There, the Eyjafjallajökull volcano paralyzed European air traffic in 2010: it was a different type of eruption, not exuberant but explosive, in which the lava emerging from the volcano can be transformed into large quantities and volcanic ash distributed everywhere B. in the atmosphere, can lead to the closure of the airspace.
The Icelandic authorities claim that the intensity of the event began to decrease four hours after it began: with the exception of the time at which it was supposed to take place, most of the parameters of the eruption are in line with expectations. Of course: It is possible that new magma outlets will open along the original fissure, warns the Icelandic Meteorological Institute.
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