A swarm of earthquakes shakes Iceland. Are volcanic eruptions next?

For the past 800 years, the picturesque Reykjanes Peninsula in Iceland’s southwestern corner has been relatively quiet. But 15 months ago, there was an awakening. What started as a series of murmurs gave way to a dramatic crescendo that culminated in more than 17,000 earthquakes in the past week alone.

Scientists have now seen part of the land changing shape, and they have detected the seismic whispers of magma moving toward the surface. The question on everyone’s mind: Is there going to be an eruption?

A few days ago, the answer looked to be an emphatic yes. The most plausible scenario involved spectacular lava fountains and rivers of molten rock that would not endanger any population centers. Nor would such an eruption threaten airplanes zipping through the skies above, which is what happened during the ash-laden 2010 eruption of the Eyjafjallajökull volcano in another part of the country.

But the volcanic system in Reykjanes is now acting in a surprising way, such that it’s impossible to say if an eruption is likely in the coming days or weeks. “People started wondering, what the hell is going on here?” says Dave McGarvie, a volcanologist at Lancaster University in England.

Past cycles of volcanic activity in the region suggest that this tectonic turbulence may mark the start of a succession of eruptions that could persist for a century. If this transpires, the Reykjanes Peninsula could be bathed in the glow of a thousand volcanic fires that ignite, disappear, and then reappear intermittently for an entire human lifetime.

To those outside of Iceland, this uncertainty may sound distressing, but such geologic hyperactivity is par for the course for Icelanders. “You live in a country that’s very active, and it’s just something people have to deal with,” says Thorbjörg Ágústsdóttir, a seismologist at Iceland GeoSurvey.

Molten rock churning below

The country’s Reykjanes Peninsula, situated 17 miles southwest of the capital city of Reykjavik, is volcanic like everywhere else on the island and is closely monitored. On March 3, seismometers detected acoustic signals linked to the movement of magma through the crust close to the peninsula’s Fagradalsfjall flat-topped mountain and the Krýsuvík-Trölladyngja volcanic system, a series of fissures streaking through the ground. The ground here also deformed, confirming the migration of molten rock.

Volcanologists and civil authorities began to suspect an eruption was on its way. “This looks like the turmoil we would expect in the run-up to the eruption,” Kristín Jónsdóttir of the Icelandic Meteorological Office told local media that same day. The flowing magma below the surface suggested an eruption could occur in a matter of hours.

At volcanoes elsewhere in the country, those sorts of signals would herald emergence of lava, McGarvie says. But then nothing happened.

“That’s something new. We didn’t expect that,” McGarvie says. “There are always surprises. You can’t predict anything.”

At the time of writing, the tremors signifying magma movement have died down. They could reappear, but they may not return. “We’ll just have to wait and see,” says Bergrún Arna Óladóttir, a volcanologist with the Icelandic Meteorological Office. “Prepare for the worst and hope for the best.”

When you have an intrusion of magma, as in this case, it’s always possible that it will get stuck, cool, solidify, and simply remain underground, Ágústsdóttir says.

“For me, the most likely scenario is that this slowly declines and stops,” says Sigurjón Jónsson, a geophysicist at the King Abdullah University of Science and Technology in Saudi Arabia.

The challenge is that all volcanoes are idiosyncratic. Several volcanoes may share the same eruption precursors, but that doesn’t mean all of them do. The last major eruption on the Reykjanes Peninsula happened eight centuries ago—not long after people first settled in Iceland. Back then the science of volcanology essentially didn’t exist, and without records of the region’s specific seismic data, no one knows exactly what the volcanoes in this corner of Iceland will do immediately prior to erupting.

But taking a closer look at what we do know about the geologic history of the region could reveal clues about the recent spate of tremblors, and hint at what the future may bring.

Slowly pulling apart the peninsula

After a series of major eruptions between the 10th and 13th centuries, the Reykjanes Peninsula been pretty calm. That changed at the end of 2019, when the peninsula started quaking more frequently and violently. A magnitude-5.7 quake in February of this year shook the region, and this week quakes were coming thick and fast.

“It is the most intensive earthquake sequence in this area for almost a hundred years,” Jónsson says.

Key to this tectonic bedlam is the fact that Iceland sits on the northern part of the Mid-Atlantic Ridge, a split in the seafloor that stretches down the length of the world. Here, lava erupts and cools to make new oceanic crust on either side of the rift. The North American and Eurasian tectonic plates sit to the west and east of it, respectively, and they are pushed away from each other at roughly the same speed as your fingernails grow.

Most of the Mid-Atlantic Ridge is underwater, but the Reykjanes Peninsula sits on the northern part of the ridge, so it’s gradually being pulled apart all the time. For reasons unknown, once every 800 years or so, the rifting suddenly escalates, causing a major uptick in tectonic earthquakes, as is happening now. Ancient lava flows studied by geologists and historical accounts from Iceland’s early settlement note that when you get a serious spike in quakes here, magma follows.

“It’s not understood why there are these turbulent periods of lots of earthquakes accompanied by magma moving into the crust. But the two are clearly interlinked,” McGarvie says.

It’s possible that as the peninsula is being pulled apart, it creates new pathways for the magma to take to the surface, but scientists aren’t sure. It is clear, however, that three past episodes all followed this pattern of quakes followed by eruptions, “and this appears to be the latest episode,” McGarvie says.

The start of something spectacular

If the seismic storm on the peninsula does lead to an eruption, it will be quite different from some of the more explosive and expansive events that have rocked other parts of the island country.

For instance, the infamous 2010 eruption of Eyjafjallajökull created a sustained, towering column of hot ash. Fears that the glassy volcanic matter would enter and damage jet engines caused the most extensive shutdown of European airspace since World War II. But the molten rock beneath Reykjanes Peninsula is a somewhat different concoction, a runny and not-too-gassy recipe similar to the stuff coming out of Hawaii’s Kīlauea volcano right now.

This magma struggles to build up enough pressure as it rises to the surface to create big, ashy explosions. The relative lack of ice cover here also starves the magma of a dangerous fuel, water, which in small amounts is vaporized so violently by molten rock that it triggers ash-producing blasts.

There’s also no sign that an eruption in Reykjanes would involve the same volume of magma as the prolific outpourings of the Laki eruption between 1783 and 1784. That event produced enough lava to bury a city the size of Boston in 200 feet of molten rock.

Instead, one plausible scenario is that lava erupts out of a fissure or series of fissures in the area, says McGarvie. The eruption may last for a few weeks or so, producing spectacular fountains of lava shooting skyward as little cones build up around them and lava flows head toward lower ground. Such flows would not hit any population centers but might overrun a road or knock over a couple power lines.

Magma could rise into an aquifer—or even into the Blue Lagoon tourist attraction, triggering explosive activity. But “that’s considered a very unlikely scenario,” McGarvie says, and no matter what, seismic signals would allow scientists to track the magma’s movement beforehand and warn people to stay away.

There is also some concern that Grindavík, a town on the peninsula’s southern coast that has been shaken by the barrage of earthquakes, could be imperiled if lava emerges close by, Jónsson says. But if there is an eruption, in all likelihood, “people will be enjoying it, watching the lava flow with the northern lights behind them,” McGarvie says.

And it may just be the beginning of something far greater. Past work on the peninsula has revealed that when a new cycle of volcanism begins, it doesn’t involve one eruption, but many. Seismic signals and ground deformation data from the past year show that magma has been gathering at not one, but three different spots beneath two of the peninsula’s volcanic systems, McGarvie says.

It’s too early to call, but this week’s activity could herald the start of another hundred years of intermittent volcanic fires along the southwestern peninsula of Iceland. According to McGarvie, “people are waking up to the fact that this could be a long-term thing.”