Why Iceland's latest eruption may be the most dangerous in recent history

It was perhaps only a matter of time before Iceland’s Reykjanes Peninsula ran out of luck.

During the night of December 18, the peninsula exploded in a volcanic outburst—its fourth in under three years, and a decidedly dangerous entry in the nation’s volcanic saga.

Just two hours after a swarm of earthquakes warned of the impending eruption, it was firing out 10 times more lava per second than any of the past three at their peaks, all while the fissure itself expanded to an astonishing 2.5 miles in length in a matter of minutes.

After nearly a millennium of dormancy, this southwesterly strip of land entered a new volcanic era in March 2021. The past three eruptions—in 2021, 2022, and earlier this summer—were nothing less than scientific and aesthetic spectacles. The last time there was a period of multiple eruptions on the peninsula was in the early 13^th century. That it is undergoing another similar span of lava-oozing eruptions is one reason the world has been watching so closely.

(Iceland has entered a new volcanic era.)

But this fourth eruption has caught the attention of the international media for another three reasons: the ramp up to the main event was unusual compared to the last three; the location, combined with its vigorous opening salvo of molten rock, threatens to destroy a town; and its overall behavior created an uncomfortable amount of uncertainty as to what may happen next.

“Just in context of the past three years on the Reykjanes Peninsula, it is pretty mind-blowing,” says Tom Winder, a volcano seismologist at the University of Iceland.

As of the afternoon of December 19, just a third of the fissure remains volcanically active, and the eruption’s output has greatly diminished. Things could still change for the worse, but hopefully it continues to fizzle.

Regardless, this volcanic pyre has already cemented its reputation as one of the most consequential and scientifically beguiling Icelandic eruptions of the last few decades—which is why scientists from across the world are on the case gathering clues to its origins.

A chaotic prelude

Although most people understandably think of volcanic eruptions as coming from a volcano, all four of the most recent eruptions have actually been fissure-style: when lava forces its way out of Earth’s crust through a newly formed thin crevasse, often at location that cannot be identified prior to the paroxysm. Unpredictable fissure eruptions happen around the world, including on Hawai‘i, but they aren’t as well known.

But this latest eruption is especially notable because it did something the 2021, 2022, and mid-2023 events didn’t. Instead of materializing once again in a secluded spot near the volcanic mountain of Fagradalsfjall, it made its underground way to Svartsengi—home to a region-critical geothermal power plant, the tourism hotspot Blue Lagoon spa, and the 3,500 people living in the coastal town of Grindavík.

(Startling volcanic activity has town in Iceland bracing for crisis.)

And it made quite an entrance: On November 10, the magma suddenly rose to within a few hundred feet of the surface, before pausing—all to the tune of a cacophony of rock-breaking quakes.

“This shift in the system reopening was honestly quite surprising. But it was the scale of the earthquake activity that took most people by surprise,” says Samuel Mitchell, a volcanologist at the University of Bristol. A pause between magma’s ascent and the onset of the eruption is not uncommon for fissure events, but this eruption’s prelude was especially intense and hasty.

By mid-November, it seemed very likely that an eruption along a 10-mile surface ‘corridor’ was going to happen in the coming days or weeks—a corridor that included Grindavík.

Location, location, location

For the international eruption watchers, thoughts of another colossal, persistent, flight-grounding ash cloud—as was seen during Iceland’s 2010 Eyjafjallajökull eruption—attracted concern. Fortunately, as magma isn’t being directly injected into the underbelly of an ice sheet this time around, prolific ash-generating explosivity is extremely unlikely.

You May Also Like

SCIENCE

Iceland's latest eruption is quieting down—but the explosive upheaval isn't over yet

SCIENCE

Startling volcanic activity has town in Iceland bracing for crisis

SCIENCE

Mysteries lurk below Iceland's restless volcanoes

But its location did indicate that, unlike the past three events, this eruption could cause some serious damage

It was a good thing the molten rock’s prelude wasn’t subtle: It handily convinced authorities to swiftly evacuate Grindavík that same day in November, keeping residents far from any potential harm, while giving officials time to erect lava-deflecting walls around the power plant.

Still the eruption had an element of surprise: Lava began to spew just about two hours after an earthquake swarm just north of the town signaled the impending eruption—an astonishingly short interlude. That “underlines how close we were to an eruption soon after the initial evacuations last month, and the reason they were essential to ensure people's safety,” says Winder.

That the magma ultimately found a skylight near a series of ancient craters a couple of miles to the town’s northeast was briefly relieving. But the intensity of the eruption and the shocking growth of the fissure quickly made clear that the town to the south, and the power plant to the west, were in jeopardy.

For now, however, the grimmest of eventualities may have been avoided—all thanks to a mixture of luck and Icelandic proactivity.

The fuzzy future

That very little about the eruption is known with certainty also bolsters its intrigue.

Just a day into its paroxysm, the eruption noticeably calmed down, and it seemed possible that it would die out in a matter of days. Alternatively, experts say, this behavior might indicate that it will continue pumping out lava at that modest rate for months.

“If the magma stored at Svartsengi is still being renewed from depth, then the eruption could reach equilibrium at a lower intensity, and continue for quite some time,” says Winder. “It looks like there has been near-continuous magma supply there since late October, so it certainly seems realistic that it might continue for another two months into the future.”

(Volcanoes don’t just erupt on schedule—but they have been in Iceland.)

That the region’s subsurface volcanic plumbing is a largely unresolved puzzle only exacerbates the uncertainty of this crisis. It simply isn’t clear why Svartsengi was the magma’s target this time round. Did it migrate from Fagradalsfjall, or did it come from another subsurface store? And why has the ground around Svartsengi inflated before without producing an eruption, whereas this time it succeeded?

In less than 24 hours after it began, researchers managed to sample some of the new eruption’s lava and compare it to the past three on the peninsula. And according to Ed Marshall, a geoscientist at the University of Iceland, they all have broadly similar chemistry. That implies there is some sort of magmatic connection between Svartsengi and Fagradalsfjall—but the nature of that connection is very fuzzy at present.

What volcanologists want to know, above all else, is what happened between the seismic dramatics of early November and this week’s eruption. Could they have been able to forecast exactly when and where the magma would find its way to the surface with the data they obtained in the weeks leading up to the outburst? “This is a great and intriguing question, which is at the core of what many people will be looking at in the coming months,” says Mike Burton, a volcanologist at the University of Manchester.

For now, all scientists can do is monitor the infernal proceedings—and hope that their observations will, eventually, reveal the secrets behind this novel show of volcanic force.