Major Changes in What We Know About How Volcanoes Work

Iceland’s Fagradalsfjall volcano erupts at night.

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

It’s not very often that we learn something that fundamentally changes how we perceive the world. But for University of California, Santa Barbara Earth scientist Matthew Jackson and thousands of volcanologists around the world, such a revelation just happened.

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

“Just when we think we’re getting closer to understanding how these volcanoes work, we get a big surprise,” he said.

Geologists’ findings were published in the journal on September 14 Nature.

10,000 years per month

Thanks to rest, the pandemic, and 780 years of underground rock melting, Jackson was in the right place and time to witness the birth of a fissure called Fagradalsfjall in the plains of southwest Iceland that split and exploded with magma in March 2021. at that time everyone on the Reykjanes peninsula said they were ready for some sort of eruption.

“The earthquake was very strong,” he said of the nearly 50,000 magnitude-4 and higher earthquakes that shook the ground for weeks and left most of Iceland’s population stranded.

However, the sleep deprivation was worth it, and as the lava bubbled up from a hole in the ground of the relatively empty Geldingadalur region, the allure quickly turned to admiration. Scientists and visitors alike have flocked to the site to see the newest part of the Earth’s crust form. Because of the slow flow of lava and the extensive winds that blow away noxious gases, they were able to get close enough to take a continuous sample of the lava from the very beginning.

Volcanic eruption at Fagradalsfyal mountain in Iceland.

Geologists led by Sæmundur Halldorsson at the University of Iceland were “trying to find out how deep in the mantle the magma originated, how long it was stored below the surface before it erupted, and what happened in the reservoir both before and during the eruption. Although such questions are fundamental, they are actually one of the biggest challenges for those who study volcanoes. This is due to the unpredictability, danger and extreme conditions of eruptions, and the remoteness and inaccessibility of many active areas.

“It was assumed that the magma chamber filled slowly over time and that the magma was well mixed,” Jackson explained. “And then it dries up during the eruption.” As a result of this well-defined two-step process, he added, researchers of volcanic eruptions do not expect to see significant changes in the chemical composition of magma as it flows from the ground.

“This is what we saw on Mount Kīlauea in Hawaii,” I said. “There will be eruptions that last for years and there will be small changes over time.

“However, Iceland had a much higher rate of change of more than 1,000 for key chemical indicators,” Jackson said. “In one month, the eruption of Fagradalsfjall showed more compositional variability than Kilauea eruptions have shown in decades. The total range of chemical compositions sampled during this eruption during the first month covers the entire spectrum of eruptions in southwestern Iceland over the past 10,000 years.

A night view of the volcanic eruption at Fagradalsfjall mountain in Iceland.

According to scientists, this variability is the result of subsequent batches of magma flowing into the chamber from deep within the mantle.

“Imagine a lava lamp in your mind,” Jackson said. “You have a hot bulb underneath, it heats a drop and the drop rises, cools and then sinks. We can think of the Earth’s mantle—from above the core to below the tectonic plates—functioning like a lava lamp. He further explained that when heat causes regions of the mantle to rise and plumes form and float toward the surface, molten rock from these plumes collects and crystallizes in chambers, gases escape the crust and rise until pressure builds. the magma finds a way to escape.

As described in the article, it was the expected “depleted” type of magma that erupted during the first few weeks that accumulated.g in a reservoir about 10 miles (16 km) below the surface. However, by April, evidence showed that the chamber was filling with deeper, “enriched”-type melts of a different composition. These originated from a different region of the upwelling mantle plume beneath Iceland. This new magma had a less altered chemical composition, containing higher magnesium and a higher proportion of carbon dioxide. This indicated that less gas was released from this deeper magma. By May, the magma that dominated the flow was a deeper, enriched type. These rapid, extreme changes in magma composition at a plume-fed hotspot “have never before been observed in near real time,” they say.

But Jackson said these compositional changes may not be so rare. Simply, opportunities to sample eruptions at such an early stage are not common. For example, before the Fagradalsfjall eruption in 2021, Iceland’s Reykjanes Peninsula last erupted eight centuries ago. I suspect that this new activity marks the beginning of a new, possibly centuries-long volcanic period in southwest Iceland.

“We often don’t have information about the first stages of eruptions because they are buried by lava flows from later stages,” he said. According to the researchers, this project allowed them to see for the first time a phenomenon that was thought to be possible but had never been directly witnessed.

For scientists, the result provides a “key constraint” on how to build models of volcanoes around the world. However, it is not yet clear to what extent this phenomenon is representative of other volcanoes or what role it played in initiating the eruption. For Jackson, it’s a reminder that Earth still has secrets to reveal.

“So when I go out to sample an old lava flow, or when I read or write articles in the future, I’ll always have this in mind: This may not be the full story of the eruption.”

Reference: Sæmundur A. Halldorsson, Edward W. Marshall, Alberto Caracciolo, Simon Matthews, Enikő Bali, Maja B. Rasmussen, Eemu Ranta, Johandur Hunnarsson, Johann Hunnarsson, Rapid displacement of a deep magmatic source at Fagradalsfjall volcano in Iceland Gudfinnsson, Olgeir Sigmarsson, John Maclennan , Matthew G. Jackson, Martin J. Whitehouse, Heejin Jeon, Quinten HA van der Meer, Geoffrey K. Mibei, Maarit H. Kalliokoski, Maria M. Repczynska, Rebekka Hlín G. Rúnarsdóttirson, Rúnarsdóttirson Anne Pfeffer, Samuel W. Scott, Ríkey Kjartansdóttir, Barbara I. Kleine, Clive Oppenheimer, Alessandro Aiuppa, Evgenia Ilyinskaya, Marcello Bitetto, Gaetano Giudice and Andri Stefansson, 14 September 2022, Nature.
DOI: 10.1038/s41586-022-04981-x