The study, published in the journal Nature and led by the University of Iceland, reports that the eruption was unusual because it was fed by a particularly deep magma reservoir that formed about 15 kilometers below the surface at the base of the Earth’s crust.
Their results also show that volcanoes like this one can be fed by complex piping systems where different batches of magma can mix and rise to the surface in a matter of days or weeks.
The researchers took measurements of lava and volcanic gases during the first 50 days of the eruption – giving them a near real-time report on the changing magma supply.
“I never expected the chemical composition of erupting lava to change so quickly, showing us how quickly things can change deep below volcanoes,” said Simon Matthews of the University of Iceland.
The chemical fingerprint of lava and the crystals it contains — along with the erupted volcanic gases — helped researchers decipher where the magma came from and how it got to the surface. So far, there is a lack of information about the deepest parts of magmatic systems.
The results showed that in the early stages of the eruption, lava came mostly from around the boundary between the crust and the underlying mantle — the thick, rocky layer that makes up most of the Earth’s interior. But in the weeks that followed, the composition of the lava changed, suggesting the eruption directly tapped into magma from greater depths.
“Ever since Enlightenment thinkers began writing about volcanoes, scientists have drawn cross-sections to visualize how they might function underground,” said co-author Professor Clive Oppenheimer of Cambridge’s Department of Geography. “This study brings together different strands of information from monitoring the chemistry of lava and gas emissions to describe what is happening at depths of up to 20 kilometers.”
They used indicators such as the magnesium content of the lava and the carbon dioxide content of the volcanic gases as barometers to estimate how hot and deep the magma that fed the eruption was. They suspect the eruption was channeled straight into the mantle by something like a bullet train, allowing the magma to come from 15 kilometers below the surface.
“We’ve known for some time that magma coming out of the mantle is variable,” said co-author Professor John Maclennan of the Department of Earth Sciences in Cambridge, “but we’ve had to work hard to find evidence like this.” complex mixing works that happens.”
The authors note that it has long been argued that different types of magma can mix deep within magmatic systems before an eruption. The new research shows that new magma can flow into a deep reservoir and mix with existing magma quickly, in as little as 20 days.
Scientists typically use lava erupted from ancient or extinct volcanoes to get subsurface views of volcanoes. But these samples are often too old to unravel processes that happen over the course of a few days. “I’ve looked at hundreds of samples from extinct volcanoes but have never had the opportunity to observe such a spectacular example of magma mixing in real time,” Maclennan said.
Magma mixing has been shown to be an important process in triggering volcanic eruptions, so the study results could have implications for understanding what triggered the eruption and for future monitoring of volcanic activity in Iceland and similar volcanoes.
Sæmundur A. Halldórsson et al. “Fast Displacement of a Deep Magmatic Source at Fagradalsfjall Volcano, Iceland.” Nature (2022). DOI: 10.1038/s41586-022-04981-x.