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Icelandic volcanic eruption brings researchers closer to Earth’s core

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What to do when a volcano erupts for the first time in centuries?

For many in Iceland’s southern peninsula, when the Fagradalsfjall volcano erupted after 781 years of inactivity in 2021, photography was the answer. As the eruption continued for six months, tourists and locals drove closer to the volcano to take on more. Red splashes fly out of the black pyramid; viscous creeping flame.

But this documentation has gone so far. Some scientists wanted to know what was going on under the surface, miles down where no light could penetrate. There, the flowing rock works in a way that experts still cannot describe. So on the first day of the eruption, a helicopter flew to the site and scooped up some lava. Some of the samples were sent to laboratories, which, after testing, returned unexpected results: the lava was full of crystals.

Recently, using similar samples collected during the Fagradalsfjall eruption, steps have been taken to characterize the dynamics beneath the surface of an oceanic volcano. In a paper published in June in the journal Nature Communications, researchers studying the chemical composition of lava crystal samples collected over a six-month period found that they contain a wide range of material from different parts of the mantle, the amalgam layer between Earth’s crust and core. This variation was unexpected and painted a brighter picture of what drives volcanic eruptions.

“We have really detailed records of the different types of composition that we can find in the mantle now, and it must be very heterogeneous, very variable,” said Frances Deegan, a volcanologist at Uppsala University in Sweden and co-author. paper.

The composition of the Fagradalsfjall lava was primitive, meaning it originated from a deep reservoir of magma or underground lava rather than from a shallow reservoir in the earth’s crust. Noticing this, researchers, including Ed Marshall, a geochemist at the University of Iceland, rushed to collect new samples as lava continued to erupt from the vents. “We’ve been working all hours – you’re sleeping and the volcano is still erupting and you’re thinking, ‘I need to get back there,'” Dr. Marshall said. “But it’s hard to describe how rare these things are.”

Fagradalsfjall is located at the confluence of fault lines along the border between the Eurasian and North American tectonic plates, at the point where they both pull apart and rub against each other. Geological records show that periodic volcanic activity in the region occurred about once every thousand years, and this last fissure was preceded by more than a year of earthquakes. Olafur Flovenz, director of the Icelandic Geosurvey, recently published a paper with colleagues suggesting that this activity was caused not by a body of magma accumulating in the Earth’s crust, but by carbon dioxide released by deeper magma accumulating between the mantle and the Earth’s crust. an area called the Mohorovichic gap, or moho.

Typically, volcanic eruptions occur when many small magma flows mix with each other. “This mixing process is an important geological process, but it has never been directly observed,” Dr. Marshall said. It lies so deep below the surface that many of the chemical signatures of individual flows are lost as the magma moves through the crust. But when Fagradalsfjall erupted in 2021, molten rock and crystals erupted to the surface came straight from the moho. “For the first time, more or less, we are seeing an active eruption on our oceanic crust, where lava is erupting directly from a mantle source,” Dr. Flowenz said.

Compared to other oceanic volcanoes, Fagradalsfjall’s vents were relatively easy to access, and its 2021 eruption was fairly quiet. Researchers such as Dr. Marshall, who has not contributed to any of the papers but is preparing a paper on the same topic with a group of collaborators from the University of Iceland, say these studies can get right into the mantle and capture hidden dynamic processes.” like lightning in a bottle.”

Dr. Deegan and her collaborator Ilya Bindeman, a geochemist at the University of Oregon, worked with other researchers on the ground at Fagradalsfjall to analyze the lava. They found that not only did the chemicals change incredibly over time, suggesting that many different parts of the mantle came together during the eruption, but also that the oxygen isotopes in these samples were virtually identical. This contributes to a long-standing technical investigation into the source of Iceland’s mysteriously low levels of oxygen-18, an isotope often found in volcanic rocks. Dr. Bindemann said that for more than half a century scientists have been arguing about whether this can be explained by the absence of an isotope in the mantle. “We found that the depletion is happening somewhere else,” he said.

Dr. Marshall and his colleagues also used lava samples to describe mixing and melting processes in magma reservoirs, which was not done in the last paper.

“These are very exciting times,” said Dr. Flovenz, who began studying Icelandic volcanoes in 1973. “I never had any hope that I would live to see these riots and eruptions on this peninsula. It was extremely interesting for the geoscience community.”

“This is an absolutely amazing eruption for our area,” Dr. Marshall said, “and it’s one of those things that will be studied for a long time.”

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