Breaking more than seven months of calm, western Iceland’s Reykjanes Peninsula once again burst into volcanic flames this past summer. After a swarm of earthquakes in late July and early August rocked the area, lava burst forth from the Fagradalsfjall volcano into the Meradalir valleys—close to the barely cooled lava from the same volcano’s 2021 eruption—treating tourists and researchers to the vibrant red-orange glow of fresh molten rock just 20 miles from the capital city of Reykjavk.
Such striking volcanic displays are not uncommon in Iceland, one of the world’s geologically youngest landmasses. The whole country is the product of millions of years of eruptions and is perfectly placed for ongoing volcanic activity—and scientists say the recent series of eruptions may signal the reawakening of a powerful volcanic system after 800 years.
The summer eruption gave researchers a valuable chance to collect data on the developing system and subterranean magma movement. Measurements at this uniquely accessible site will also help scientists better predict when and why volcanic eruptions occur, says geophysicist Sigrun Hreinsdóttir: “We don’t have a lot of [view-obscuring] vegetation in Iceland, so we are getting a wealth of satellite imagery that really helps us understand what’s going on. The entire image is quite astonishing for one of these events.”
Iceland straddles the boundary between two of Earth’s tectonic plates, enormous crust fragments that fit together like puzzle pieces to form our planet’s rocky outer shell. The North American and Eurasian plates are pulling away from each other at a rate of one to two inches a year, gradually unzipping the Atlantic Ocean’s floor to form a chain of submarine volcanoes known as a mid-ocean ridge. As the plates pull apart, new material rises from Earth’s mantle: a layer of hot, viscous rock sandwiched between the crust and our planet’s metal core.
This material partially melts as it rises, supplying Iceland’s volcanoes with magma. But it isn’t the only source of molten rock in the region. Iceland, like Hawaii, is perched above a “hotspot,” a column of heated rock that rises through the mantle, driven by its own buoyancy. This adds yet more fuel to Iceland’s volcanic fires.
On the island, this combination of magma sources expresses itself as several different kinds of volcanoes. Hekla’s towering cone in the south is closer to the mantle hotspot, whereas the strings of small craters and fissures now forming in Reykjanes’s volcanic system are where the plate boundary comes onshore.
“The kind of volcanic eruptions that take place in this area [Reykjanes] are not originating from the typical cone-shaped mountain but more through openings in the crust,” says Sara Barsotti, coordinator for volcanic hazards at the Icelandic Meteorological Office (IMO). These openings occur because the area is located along a kink in the mid-ocean ridge, and the cracks form as a result of the two plates moving apart at an odd angle. Some of these cracks fill with magma, which can eventually erupt; others let chunks of crust slide past one another, leading to earthquakes. Magma moving through the crust can also cause seismic activity as new cracks form or widen to accommodate the molten rock.
As the mid-ocean ridge widens over millennia, Reykjanes cycles through quiet periods that typically last 800 to 1,000 years before two or three centuries of spectacular eruptions—a period that scientists studying Iceland suspect is starting now. During the 1990s Hreinsdóttir (now at the New Zealand geoscience research and consulting company GNS Science, Te Pū Ao) set up GPS stations throughout the peninsula to monitor the land’s slow shifting, bending and buckling, accompanied by small earthquakes. At the time, there were no active eruptions.
Looking back, though, Hreinsdóttir says, these measurements may have captured the first signs of new volcanic action in the region. “There was a lot of activity in [the mountain] Hengill, at the edge of Reykjanes Peninsula—lots of earthquakes,” she explains. All the action led scientists to suspect a magma chamber was filling up deep below the surface, and “we were wondering if that was kind of the first sign that Reykjanes might be close to coming alive.”
Now it seems clear that the peninsula is waking up. Since the late 2000s magma gathering beneath the surface has caused the whole area to periodically inflate and deflate, bulging to accommodate the movements of molten rock underground.
Barsotti and her colleagues at IMO track the locations of these bulges, combining this information with data from earthquake sensors, GPS and satellite imagery to try to anticipate which parts of Reykjanes are most primed for future eruptions.
Just before the first fissures opened in the 2021 eruption, the final warning sign was a cluster of large earthquakes that shook western Iceland. After longing to see an eruption since she began her fieldwork on the peninsula around 30 years ago, Hreinsdóttir could only watch her dream come true from afar in 2021, when the COVID pandemic kept her home in New Zealand. This past August, she says, she went on a pilgrimage to lay her hands on the cooled lava from last year—and her six-year-old son was knocked off his feet by a magnitude 4.5 earthquake.
That quake, on August 2, turned out to be a warning for an eruption the very next day that would prove to be even bigger and more spectacular than the one she had missed, although it wouldn’t last as long. “It was quite a nice feeling for me,” she says. “It felt like Fagradalsfjall was just saying, ‘Hello!’”
On the day of the eruption, Hreinsdóttir hiked to Meradalir with her colleagues from the University of Iceland, with which she was previously affiliated, and some 1,800 other visitors. All watched the fluorescent orange glow of lava fountaining up from between the rocks of Hreinsdóttir’s former study area.
The area stayed active for weeks and proved a hotspot for hikers and photographers. The eruption was just an hour’s drive from Reykjavík, so IMO’s volcanologists used data and models to assess current and future risks to infrastructure, water quality and human health caused by the lava and gases emanating from the new fissure.
Hreinsdóttir is looking forward to new data on the geochemistry and the speed of the magma coming up, as well as on how the eruption affects the magma of neighboring volcanic systems. And eruptions may occur as often as every few years now that Reykjanes has apparently awakened from its eight-century slumber, offering even more glimpses into the system’s inner workings.
“I just wish I could become two to three hundred years old,” Hreinsdóttir says, “so that I could watch it for a while.”
Editor’s Note (10/5/22): A version of this article with the title “Volcanic Awakening” was adapted for inclusion in the November 2022 issue of Scientific American. This text reflects that version, with the addition of some material that was abridged for print.