A fiery beast has awoken from centuries of slumber. The past three years have seen it create cracks in Earth’s crust on the southwestern tip of Iceland and belch fountains of lava up through them.
It’s captivated people worldwide and inspired a mix of awe and fear. Experts say that after 800 years of quiet, this beast – the Icelandic fault line – has entered a new period of activity that could last decades.
Located in the North Atlantic Ocean, Iceland is a hotspot of volcanic activity, with over 30 active volcanoes distributed across the 100,000km2 (38,600-mile2) island.
On average, an eruption occurs here once every three to five years, although they’re not evenly distributed over time and tend to come in clusters of activity, punctuated by periods of relative calm.
Over the last 500 years, Iceland’s volcanoes have ejected one-third of all the lava that has flowed across Earth’s surface. Its volatile temperament is a product of the island’s geological context.
Iceland lies on the Mid-Atlantic Ridge, a rift between the North American and Eurasian tectonic plates, which are slowly moving apart at about 1cm (0.3in) each year, creating a growing crack in Earth’s crust. Iceland is also situated directly above an upwelling of molten rock, known as a mantle plume.
“Iceland is very volcanically active because there’s a [tectonic] plate boundary, the Mid-Atlantic Ridge, and there’s a mantle plume that comes from deep [below it],” explains Magnús Tumi Guðmundsson, professor of geophysics at the University of Iceland.
The plume is thought to originate in the lower part of Earth’s mantle, more than 2,000km (1,240 miles) below the surface. “It’s one of the only places [on Earth] where you have the Mid-Atlantic Ridge and a mantle plume,” says Guðmundsson.
This unusual convergence of geological features has built Iceland, he adds.
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Fire and ice
This is an island of contrasts. As well as being an area of volcanic activity, its location at the edge of the Arctic Ocean means Iceland definitely lives up to its name. Around 11 per cent of the land area is covered by ice.
Many of the country’s volcanoes lie directly beneath glaciers and ice sheets, which makes for a tumultuous combination.
The island’s most infamous recent volcanic event was the eruption of the Eyjafjallajökull volcano in southern Iceland in 2010. When lava meets ice – as it did during this eruption – it reacts violently, creating a plume of ash.
The tiny particles it released into the atmosphere caused huge disruption around the globe. Tourists everywhere were stranded as over 100,000 flights were cancelled over safety concerns.
The recent eruptions on the Reykjanes Peninsula haven’t produced ash plumes like this because they’re not ejecting magma under an ice sheet.
Another ice-covered volcano that has gained global notoriety is Katla, one of the largest volcanoes in Iceland, which lies under a glacier hundreds of metres thick. A major eruption of Katla would melt huge quantities of ice and cause potentially devastating floods.
Katla’s last major eruption occurred in 1918 and the area is closely monitored for any new activity.
The Reykjanes Peninsula sits directly above the Mid-Atlantic Ridge that cuts across Iceland. The area is home to four volcanic systems, which each go through periods of activity, usually with an interlude of around 800 to 1,000 years.
“The activity is episodic, meaning that there are periods of volcanic activity… that may last four to five centuries, with eruptions every 20 to 30 years on average,” says Guðmundsson.
Before 2020, the last eruptions on the Reykjanes Peninsula took place during the 12th century. Known as the Reykjanes Fires, volcanism occurred on the peninsula every few years between 1211 and 1240 AD.
Both the Reykjanes and the Eldvörp-Svartsengi volcanic systems were active during this episode, ejecting large amounts of magma and producing vast lava fields.
This series of eruptions marked the end of a sustained period of volcanic activity on
the peninsula, which is thought to have started around 800 AD.
After 1240 AD, activity on the peninsula ceased. “Reykjanes Peninsula was quiet for 800 years,” says Guðmundsson. Until now.
When the current period of activity on the Reykjanes Peninsula began in early 2020, scientists measured earthquakes and uplifting land near Mount Þorbjörn, around 40km (25 miles) south of the country’s capital, Reykjavík.
Experts speculated that this could be the beginning of a new phase of volcanic unrest in the region. These suspicions were strengthened by the dramatic eruption of the Fagradalsfjall volcano in March 2021.
After weeks of intense earthquake activity, a 500m (1,640ft) fissure opened up in the mountain, ejecting fountains of molten rock and creating a spectacle that went on for nearly six months.
Then followed a brief period of calm, before Fagradalsfjall erupted again in August 2022. In the summer of 2023, a 900m (2,950ft) fissure opened on the mountain of Litli-Hrútur, north of Fagradalsfjall, spewing rivers of lava across the countryside.
Early warning signs
Following the Litli-Hrútur eruption last summer, activity on the peninsula resumed in late October. Magma rising towards the surface near another mountain, Þorbjörn, created enough pressure to lift the land by 6cm (2in) in a matter of just 12 days.
In early November, a swarm of thousands of small earthquakes near the fishing town of Grindavík signalled that another eruption might be imminent. Icelandic authorities declared a state of emergency, and the town’s 3,800 inhabitants were evacuated.
Weeks of uncertainty followed, as locals anxiously waited to discover the town’s fate. On 18 December, a 4km (2.5-mile) fissure opened to the north of Grindavík, forming lava fountains that ejected hundreds of cubic metres of lava per second.
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Infrastructure at risk
Although the recent Reykjanes eruptions have been relatively small (by Icelandic standards), they’ve raised major concerns because of their proximity to towns and key infrastructure, including the Svartsengi geothermal power station, which supplies electricity and hot water to the peninsula.
“It’s serious because it’s so close to where people live and lots of infrastructure, not because of its sheer magnitude,” says Guðmundsson.
Iceland’s international airport, Keflavík, is also on the Reykjanes Peninsula, although experts say it’s not at direct risk from the lava flows, hence it has remained open during the recent activity.
One of the country’s most popular tourist attractions, the Blue Lagoon, is also situated on the Reykjanes Peninsula, close to the recent eruptions. But, unlike the airport, this has been closed throughout much of the latest activity due to safety concerns.
Just a few kilometres northeast of the peninsula is the capital, Reykjavík, which around a third of Iceland’s population call home. Like Keflavík airport, it lies outside the current danger zone, but its proximity to the eruptions has helped tourists and volcano enthusiasts access the sites with relative ease, resulting in some truly spectacular imagery.
Tourist-friendly eruptions
In Iceland, where people have lived alongside explosive volcanic power for millennia, volcanic eruptions that are relatively low volume, predictable and easy to access are often referred to as ‘tourist eruptions’.
When faced with an erupting volcano, many people would feel compelled to travel in the opposite direction as quickly as possible, but in Iceland, these events can be a major tourist draw.
The 2021 and 2022 Fagradalsfjall eruptions were considered to be tourist-friendly eruptions – in addition to being easy to access and fairly safe to watch, they went on for weeks or months at a time, giving tourists plenty of notice to organise a trip.
Hundreds of thousands of people flocked to the region to witness the mesmerising lava flows.
In contrast, the eruptions this winter have been more explosive and much shorter, and experts have largely advised tourists to stay away. The eruption that occurred on 18 December was “a very different beast,” says Guðmundsson.
As concerns about an imminent eruption grew in November last year, the authorities began taking precautionary measures to protect key infrastructure, starting with a defensive barrier to safeguard the geothermal power plant.
The barrier wall was completed in December, after which attention switched to protecting Grindavík. At the start of this year, construction began on a 2km (1.2-mile) barrier north of the town, which it was hoped could deflect and redirect lava flows away from homes and businesses.
The barrier was still under construction when the next eruption hit. After a cluster of over 200 small earthquakes on 14 January, two new fissures opened to the north of Grindavík town. The fissures formed further south than expected, catching experts and locals by surprise.
The first fissure encroached on the new barrier wall, but the second, smaller fissure emerged to the south of the barrier, leaving the town exposed to an unstoppable lava flow. One official described the events as the “worst-case scenario” for Grindavík.
Three houses were destroyed by the lava flow, while shifting land damaged hot and cold-water pipes and knocked out power cables, leaving the community of Grindavík in shock.
Fortunately, the barrier was able to deflect the majority of the lava, which flowed from the larger, more northerly fissure, and it protected the western part of the town from destruction.
Predicting eruptions
Scientists use sophisticated technology to help them monitor activity in volcanic hotspots, such as the Reykjanes Peninsula. Nevertheless, predicting exactly where and when an eruption will occur is extremely difficult.
The most recent volcanic events in Reykjanes have been fissure eruptions, which occur when lava breaks through the crust, forming a long, thin crevasse.
The location of fissure eruptions are much harder to predict than eruptions from the more ‘traditional’ conical mountain vent volcanoes often depicted in popular culture.
By estimating the movement of magma beneath the crust – often signalled through a rising of the land above and by earthquakes propagating through the area – it’s possible to identify areas at higher risk of an imminent eruption.
This is what happened in the area around Grindavík in November and led to the town’s evacuation. This predictive science doubtlessly saved lives. But the precise location and timing of an eruption can’t be predicted with any certainty.
After a magma intrusion is detected, it’s impossible to say whether an eruption will occur in a matter of days, weeks, months or not at all.
Scientists in Iceland use various types of equipment to try and predict future eruptions. Seismometers are one of the most important types, which scientists use to measure earthquake swarms that can indicate the location of magma flowing under the ground.
Earthquakes often give advance warning hours, days or even weeks before an impending eruption.
Further clues are obtained via a network of GPS stations, which allows scientists to detect uplifting land caused by magma movements beneath the crust. Ground-level GPS stations “show where magma is accumulating underground,” says Guðmundsson.
Satellite imagery can also reveal regions where the land is rising as a result of magma flowing and accumulating underneath it.
Despite this sophisticated technology, what the future holds for Grindavík, and the Reykjanes Peninsula, is difficult to predict.
About one per cent of the population of Iceland has been displaced by the recent eruptions. Although some Grindavík residents had started to return to the town, they were forced to evacuate again when volcanic activity resumed in early January, with no clear idea of if, or when, they may be able to return.
For Icelanders, this is a difficult and sometimes devastating feature of life in a volcanic hotspot, where towns and cities are built on top of ancient lava fields. “The town of Grindavík is partly built on the lava flow that formed about 2,000 years ago,” says Guðmundsson.
What seems clear is that Reykjanes has entered a new period of activity after an 800-year dormancy. The Icelandic Met Office says that seismic activity on the Reykjanes Peninsula over the past four years has been more intense than anything measured in the region since scientists began recording.
But predicting exactly what this period of volcanism holds for Icelanders in general, and for Grindavík residents in particular, is impossible. “We may see several events in the coming months or years,” says Guðmundsson.
Experts expect that the intense period of activity we have witnessed over the last few years will eventually calm, once magma close to the surface has been exhausted.
But, if history is anything to go by, the reawakening of the Reykjanes fault line could last several decades or longer, with alternating periods of volcanic activity and earthquake swarms, before the beast finally returns to its rest once more. No one can say for sure.
About our expert:
Magnús Tumi Guðmundsson is an Icelandic geologist and professor of geophysics in the Faculty of Earth Sciences at the University of Iceland. His research has been published in prestigious journals such as the Geological Society of America Bulletin, the Journal of Geophysical Research and the Bulletin of Volcanology.
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