In Iceland, a volcanic eruption brought researchers closer to the Earth’s core

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

For many people in Iceland’s southern peninsula, when the Vajradalsjal volcano erupted in 2021 after 781 years of dormancy, the answer was taking pictures. As the eruption continued over the course of six months, tourists and locals traveled near the volcano to take in more. red bursts flying from a black pyramid; Viscous flame creep.

But these documents are gone only so far. Some scientists wanted to know what’s going on beneath the surface, miles deep, where no light reaches. There, gushing rocks act in ways that experts still can’t describe. So on the first day of the eruption, a helicopter flew to the site and dredged a bit of lava. Some samples were distributed to laboratories, which after testing returned unexpected results: the lava was full of crystals.

Recently, with the help of similar samples collected throughout the Fagradalsfjall eruption, steps have been taken towards characterizing the dynamics below the oceanic volcano’s surface. In a research paper published in June in Nature Communications, researchers who observed the chemical composition of lava crystal samples collected over a six-month period found that they contained a wide range of material from different parts of the mantle, the fusion layer between Earth’s crust and core. This kind of contrast was unexpected, and painted a much clearer picture of what contributes to volcanic eruptions.

said Francis Degan, a volcanologist at Uppsala University in Sweden, and a co-author of the paper.

Structurally, the Fagradalsfjall lava was primitive, meaning it came from a deep reservoir of magma, or underground lava, rather than a shallow reservoir in the Earth’s crust. The researchers noticed that, including Ed Marshall, a geochemist at the University of Iceland, set out to collect more samples as lava continued to pour out of the vents. “We’ve been working all hours—you’re asleep and the volcano is still erupting and you’re like, ‘I have to go back there,'” Dr. Marshall said. “But it’s hard to describe how rare that kind of thing is.”

The Fagradalsfjall is found at the confluence of fault lines along the boundary between the Eurasian and North American tectonic plates, the point at which they separate and rub each other. Geological records show that there has been periodic volcanic activity in the area every thousand years, and this last fissure was preceded by more than a year of earthquakes. Olafur Fluvens, Director of GeoSurvey in Iceland, recently published a research paper with colleagues suggesting that this activity was caused not by a mass of magma accumulating in the crust, but from carbon dioxide emitted from a deeper pool of magma between the mantle and crust, in an area called the Mohorovic discontinuity, or moho.

Usually, volcanic eruptions occur when many small magma flows mix together. “This mixing process is an essential geologic process, but it has never been directly observed,” said Dr. Marshall. They occur at great depths below the surface and many chemical fingerprints of individual flows are lost as magma moves upward through the crust. But when Fagradalsfjall erupted in 2021, the molten rocks and crystals that rose to the surface came straight from the Moho. “For the first time, in one form or another, we are looking at an active volcanic eruption on the oceanic crust where lava is erupting directly from the mantle source,” Dr. Flovins said.

Compared to other oceanic volcanoes, the Fagradalsfjall vents were relatively easy to reach, and its 2021 eruption was rather tame. Researchers like Dr. Marshall, who did not contribute to either paper but has a forthcoming article on the same topic with a group of collaborators at the University of Iceland, say these studies can essentially reach into the mantle and capture dynamic processes otherwise hidden “like lightning in a bottle.” .

Dr. Deegan and her collaborator, Ilya Bindeman, a geologist at the University of Oregon, worked with other researchers on the ground at Fagradalsfjall to analyze the lava. They found that not only were the chemicals incredibly diverse over time, indicating that many different parts of the mantle had come together in the eruption, but also that the oxygen isotopes were nearly identical across these samples. This contributes to a long-term technical investigation into the source of Iceland’s low oxygen-18 levels, an isotope often found in igneous rocks. For more than half a century, Dr. Bendman said, scientists have been debating whether this can be attributed to a lack of isotopes in the mantle. “We found that the depletion is happening elsewhere,” he said.

Dr. Marshall and colleagues also used lava samples to describe the mixing and melting processes in magma reservoirs, which were not performed in the latest paper.

Dr. Flovens, who began studying Icelandic volcanoes in 1973, said: “These are very exciting times. I never hoped I would live to see these volcanic eruptions and eruptions on the peninsula. This has been very interesting for the Earth science community.”

“It’s a very amazing volcanic eruption in our field, and it’s one of those things that will be studied for a long time,” said Dr. Marshall.

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