Fundamental changes to what we know about how volcanoes work

Fagradalsfjall volcano in Iceland erupts at night.

Recent discoveries from the Fagradalsfjall eruptions in Iceland are changing what we know about how volcanoes work.

Learning something that radically changes how we understand our world doesn’t happen very often. But for Earth scientist Matthew Jackson at the University of California, Santa Barbara, and thousands of volcanologists around the world, this discovery has just happened.

While sampling magma from the Fagradalsfjall volcano in Iceland, Jackson and his colleagues discovered a much more dynamic process than anyone in the two centuries had assumed scientists had been studying volcanoes.

“It’s just when I think we’re close to figuring out how these volcanoes work that we get a big surprise,” he said.

The geoscientists’ findings were published on September 14 in the journal temper nature.

10000 years per month

Thanks to leave, a plague, and 780 years of plutonic rock melt, Jackson was in the right place and time to witness the birth of Fagradalsfjall, a fissure in the lowlands in southwest Iceland that split and erupted with magma in March 2021. By then, everyone was at The Rikjan Peninsula is ready for some kind of volcanic eruption.

“The earthquake swarm was intense,” he said of the 50,000 or so earthquakes—magnitude 4 or higher—that shook the ground for weeks and kept most of Iceland’s population on edge.

However, the sleep deprivation was worth it, and weirdness quickly turned to magic as lava spurted and splattered from the hole in the ground in the relatively empty Geldingadalur. Scientists and visitors alike flock to the area to see the newest part of what the Earth’s crust is like. From the start, they were able to get close enough to continuously sample lava, due to the slow flow of lava and gale-force winds that blew noxious gases away.

The volcanic eruption of Mount Fagradalsfjall in Iceland.

Led by Simundur Halldorsson at the University of Iceland, geologists have been trying to figure out “the origination depth of magma in the mantle, how much was stored below the surface before the eruption, and what was going on in the reservoir before and during the eruption.” Questions like this, though basic, However, they are actually some of the biggest challenges for those who study volcanoes. This is due to the unpredictability of eruptions, the danger and extreme conditions, the remoteness and inaccessibility of many active sites.

“The assumption was that the magma chamber fills slowly over time, and that the magma mixes well,” Jackson explained. “Then it dries up over the course of the eruption.” As a result of this well-defined, two-step process, he added, those who study volcanic eruptions do not expect to see significant changes in the chemical composition of magma as it flows out of the Earth.

“This is what we see at Mount Kolawea in Hawaii,” he said. “You’re going to have a volcanic eruption that lasts for years, and there will be subtle changes over time.

“But in Iceland, there were more than 1,000 factors with higher rates of change for key chemical indicators,” Jackson continued. “Within a month, the Fagradalsfjall eruption showed more compositional variance than the Kīlauea eruption has shown in decades. The total range of chemical compositions sampled in this first month eruption spans the entire range that has erupted in southwestern Iceland in the last 10,000 years.”

Night view of a volcanic eruption at Mount Fagradalsfjall in Iceland.

This asymmetry is caused by subsequent batches of magma flowing into the chamber from deeper in the mantle, according to scientists.

“Imagine a lava lamp in your mind,” Jackson said. “You have a hot lamp at the bottom, a bubble heats up and the point rises and cools and then sinks. We can think of the Earth’s mantle—from the top of the core to the bottom of the tectonic plates—working a lot like a lava lamp.” He went on to explain that as the heat causes the mantle regions to rise and form plumes and move forcefully upward toward the surface, the molten rock from these plumes accumulates in chambers and crystallizes, gases exit through the crust, and pressure builds up until the magma finds a way to escape.

As shown in the paper, what erupted in the first few weeks was the expected “spent” type of magma that was accumulatingg in the reservoir, which lies about 10 miles (16 km) below the surface. However, by April, evidence showed that the chamber was being recharged with a deeper “enriched” type that dissolved with a different composition. Obtained from a different region of the rising mantle plume under Iceland. This new magma has a less modified chemical composition, with a higher magnesium content and a higher percentage of carbon dioxide. This indicates that fewer gases escaped from this deep magma. By May, the magma that controlled the flow was of the deepest and richest type. These rapid and extreme changes in magma composition at a plume-feeding hotspot have, they say, “never been observed before in near real time.”

However, Jackson said these changes in makeup may not be so rare. It’s just that chances of sampling eruptions at such an early stage are not uncommon. For example, before the 2021 Fagradalsfjall eruption, the most recent eruptions occurred on the Reykjanes Peninsula in Iceland eight centuries ago. He suspects that this new activity signals the beginning of a new, centuries-old volcanic cycle in southwestern Iceland.

“We often don’t have a record of the early stages of most volcanic eruptions because they are buried by later-stage lava flows,” he said. This project allowed them, according to the researchers, to see a phenomenon that was thought to be possible but that was not seen directly.

For scientists, this finding represents a “major limitation” in how we build models of volcanoes around the world. However, it is not yet clear how representative this phenomenon is for other volcanoes, or what role it plays in causing an eruption. For Jackson, this is a reminder that Earth still has secrets to lose.

“So when I go out to sample ancient lava flows, or when I read or write papers in the future, it will always be on my mind: This may not be the whole story of the eruption,” he said.

Reference: “Rapid transformation of a deep magmatic source at Vagradalsvilla Volcano, Iceland” by Somundur A. Halldorsson, Edward W. Marshall, Alberto Carracciolo, Simon Matthews, Eniko Bali, and Maja B. . Guðfinnsson, Olgeir Sigmarsson, John Maclennan, Matthew G. Jackson, Martin J. Whitehouse, Heejin Jeon, Quinten H. A. van der Meer, Geoffrey K. Mibei, Maarit H. Kalliokoski, Maria M. Melissa Ann Pfeffer, Samuel W. Scott, Ricky Kiertensdottir , Barbara I. Klein, Clive Oppenheimer, Alessandro Ayuba, Evgenia Ilyinskaya, Marcelo Pettito, Gaetano Giudice and Andrei Stefansson, September 14, 2022, temper nature.
DOI: 10.1038 / s41586-022-04981-x