What do you do when a volcano erupts for the first time in centuries?
When Fagradalsfjall volcano erupted in 2021 after 781 years of dormancy, for many people in Iceland’s southern peninsula the answer was: take pictures. As the eruption continued over the course of six months, tourists and locals traveled closer to the volcano to take more. Red explosions flying out from a black pyramid; the tenacious creep of the flame.
But this documentary only went so far. Some scientists wanted to know what’s going on below the surface, miles deep where light can’t reach. There, the flowing rock works in a way that experts cannot yet describe. So on the first day of the eruption, a helicopter flew to the site and scooped up some lava. Some samples were distributed to laboratories, which, after testing, returned unexpected results: the lava was full of crystals.
Recently, steps have been taken to characterize the subsurface dynamics of the oceanic volcano using similar samples collected during the Fagradalsfjall eruption. In a paper published in June in the journal Nature Communications, researchers observing the chemical composition of lava crystal samples collected over a six-month period found that they contained a wide spectrum of material from different parts of the mantle and the amalgam layer between the earth’s crust and earth core. This type of variation was unexpected and painted a more vivid picture of what contributes to volcanic eruptions.
“We have a really detailed record of the different types of compositions that we can now find in the mantle, and it must be very heterogeneous and very variable,” said Frances Deegan, a volcanologist at Uppsala University in Sweden and a co-author of the paper.
The composition of the Fagradalsfjall lava was primitive, meaning that it came from a deep reservoir of magma or underground lava, not a shallow reservoir in the earth’s crust. Researchers, including Ed Marshall, a geochemist at the University of Iceland, noticed this and sprinted to collect more samples as the lava continued to pour out of the vents. “We’ve been working all this time — you’re sleeping and the volcano is still erupting and you’re like, ‘I have to get out of there,'” said Dr. Marshall. “But it’s hard to describe how rare this is.”
Fagradalsfjall exists at a confluence of fault lines along a boundary between the Eurasian and North American tectonic plates, a point where they are both pulling apart and rubbing against one another. Geological records show that the region has experienced periodic volcanic activity approximately every thousand years, and this most recent fissure was preceded by earthquakes by more than a year. Olafur Flovenz, director of the Iceland GeoSurvey, along with colleagues recently published a paper suggesting that this activity was not caused by a mass of magma accumulating in the crust, but by carbon dioxide released by deeper magma accumulations between the mantle and the crust was called Mohorovicic discontinuity or Moho region.
Normally, volcanic eruptions occur when many small flows of magma mix. “This mixing process is an important geological process, but it has never been observed directly,” said Dr. Marshall. It occurs so deep below the surface and many of the chemical signatures of individual flows are lost as the magma moves up through the crust. But when Fagradalsfjall erupted in 2021, the molten rock and crystals that shot to the surface came straight from the Moho. “For the first time we are seeing more or less an active eruption on our oceanic crust, where the lava erupts directly from the mantle source,” said Dr. florence.
Compared to other oceanic volcanoes, Fagradalsfjall’s vents were relatively easy to access, and its 2021 eruption was fairly tame. Researchers like Dr. Marshall, who did not contribute to either article but will soon publish an article on the same topic with a group of collaborators at the University of Iceland, says these studies essentially reach into the mantle, capturing otherwise hidden dynamic processes could. like lightning in a bottle.”
dr Deegan and her collaborator Ilya Bindeman, a geochemist at the University of Oregon, worked with other researchers on site at Fagradalsfjall to analyze the lava. They found that not only were the chemicals incredibly different over time, suggesting many different parts of the mantle had combined in the eruption, but also that the oxygen isotopes in these samples were virtually identical. This adds to a long-running technical investigation into the source of Iceland’s mysteriously low levels of oxygen-18, an isotope often found in volcanic rock. dr Bindeman said scientists have debated whether this was due to a lack of isotopes in the mantle for more than half a century. “We found that the exhaustion happens elsewhere,” he said.
dr Marshall and his colleagues have also used the lava samples to describe mixing and melting processes in magma reservoirs, which was not the case in the recent publication.
“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 outbreaks on this peninsula. This has been extremely interesting for the geoscientific community.”
“This is an absolutely amazing outbreak for our field,” said Dr. Marshall, “and it’s one of those things that’s going to be studied for a long time.”