Some of the Earth's deepest secrets brought to light. Iceland eruption in 2021 proves to have originated below the planet's solid crust.

What do you do when a volcano erupts for the first time in centuries? For many people in the southern peninsula in Iceland, when the Fagradalsfjali volcano erupted in 2021 after 781 years of dormancy, the answer was to take pictures.

Fagradalsfjall exists at a confluence of fault lines along the boundary between the Eurasian and North American tectonic plates, a point where the plates are both pulling apart and rubbing against each other.

Geological records show that there has been periodic volcanic activity in the region about every thousand years, and the most recent fissure was preceded by more than a year of earthquakes.

Olafur Flovenz, director of the Iceland Geosurvey, recently published a paper with colleagues that suggests this a activity was not caused by the accumulation of a body of magma in the crust but by carbon dioxide released by deeper magma pooling between the mantle and the crust, in a region called the Mohorovovicic discontinuity or moho.

Usually. volcanic eruptions occur when lots of small magma flows mix together. ''This mixing process is an essential geologic process, but it's never been directly observed,'' said Dr. Marshall.

It occurs so deep under the surface and many of the chemical signatures of individual flows are lost as the magma moves up through the crust. But when Fagradalsfjll erupted in 2021, the molten rock and crystals that shot up to the surface came directly from the moho.

''For the first time, more or less, we are looking at an active eruption on our oceanic crust where the lava is directly erupting from the mantle source,'' Dr. Flovenz said.

Compared with other oceanic volcanoes, Fagradalalsfjall's vents were relatively easy to reach, and its 2021 eruption was fairly tame.

Researchers like Dr. Marshall, who did not contribute to either paper but has a forthcoming article on the same subject with a group of collaborators at the University of Iceland, say these studies could essentially reach right into the mantle and capture otherwise hidden dynamic processes ''like lightning in a bottle.''

Dr. Deegan and her collaborator, IIlya Blindeman, a geochemist at the University Of Oregon, worked with other researchers on the ground at Fagradaisfjall to analyze the lava.

They found that not only were the chemicals incredibly varied over time, suggesting that many different parts of the mantle had combined in the eruption, but also that oxygen isotopes were virtually identical in all these samples.

This contributes to a longstanding technical inquiry into the source of Iceland's mysteriously low levels oxygen-18, an isotope often found in volcanic rock.

Dr. Bindeman said that scientists have been debating for more than half a century whether this can be attributed to lack of the isotope in the mantle.

Dr. Marshall and his colleagues have also been using the lava samples to describe mixing and melting processes in magma reservoirs.

''These are very exciting times,'' said Dr. Flovenz, who started studying Icelandic volcanoes in 1973. ''I had never had the hope that I would live to see this unrest and eruptions on this peninsula. This has been extremely interesting for the geosciences community.''

''It's an absolutely amazing eruption for our field,'' said Dr. Marshall, ''and it's one of those things that will be de studied for a long time.''

The Publishing continues. World Students Society thanks author Oliver Whang.


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