Many Icelanders have been on edge in recent weeks, as magma moving underground in the country’s southwest threatens to breach the surface and begin flowing across the landscape. If it does, the volcanic eruption could threaten the coastal community of Grindavík, home to more than 3,000 people, as well as a geothermal power plant that supplies energy to tens of thousands of houses.

Scientists are tracking every aspect of the geological unrest, helping Icelandic officials to prepare for whatever might be coming next. “It’s so close to a populated area,” says Evgenia Ilyinskaya, a volcanologist at the University of Leeds, UK. “I really feel for the people there.”

Regardless of whether this particular batch of magma starts an eruption or not, many researchers now think that this region of Iceland is entering a new phase of volcanic activity that could last for decades or centuries. In the past three years, three small eruptions have taken place in this area, the Reykjanes peninsula. The last time this part of the country was volcanically active — roughly between the years ad 800 and ad 1240 — lava flowed into what is now the suburbs of Reykjavík¹, Iceland’s capital city.

Unrest begins

The latest unrest kicked off on 25 October, when thousands of small earthquakes began occurring north of Grindavík. In the following days, Global Positioning System and satellite radar measurements showed that parts of the ground had risen 7 centimetres — a startlingly large rate of uplift. Volcanologists at the Icelandic Meteorological Office (IMO) in Reykjavík and elsewhere concluded that molten rock had injected itself into a 15-kilometre-long crack in the Earth’s crust, known as a dike, less than 5 kilometres beneath the surface.

Since then, earthquakes have continued to rattle the area, and some roads have cracked as the ground subsides around Grindavík as the magma moves. On 10 November, another earthquake swarm prompted authorities to evacuate the town, fearing that an eruption was imminent. Workers have been building earthen barriers around the nearby power plant, in the hope of diverting any lava flows. The Blue Lagoon geothermal spa, one of Iceland’s largest tourist attractions, is closed until at least the end of November.

A 20 November update from the IMO reported that the ground in the area around the power plant continues to uplift rapidly as magma accumulates beneath it.

The activity is the latest in several years of volcanic action on the Reykjanes peninsula — and the most hazardous, because it is happening so close to where people live and work. The three most recent eruptions — in 2021, 2022 and July 2023 — sent lava flowing into uninhabited valleys about 10 kilometres east of the current activity. “What is different now is that the dike is larger and things happened much faster,” says Freysteinn Sigmundsson, a volcanologist at the University of Iceland in Reykjavík.

Magma began pooling underground at Reykjanes as far back as January 2020, says Andy Hooper, a geophysicist at the University of Leeds. It then began travelling in separate injections towards the surface for each eruption. This time, the magma has flowed upwards much more rapidly than it did in the lead-up to the three most recent eruptions. “That means, if it erupts, the effusion rate is likely to be higher,” Hooper says. (The effusion rate is the rate at which magma flows out onto the surface and becomes lava.)

An eruption is not certain. In December 2021, magma rose in a dike beneath Reykjanes but did not erupt onto the surface.

Iceland is volcanically active because it sits atop a plume of molten rock coming from deep inside the Earth, as well as at the boundary between the North American and Eurasian tectonic plates. As the plates pull apart, magma wells up from the depths and out onto the surface. If the current activity leads to an eruption, scientists do not expect it to be as widely devastating as the 2010 eruption of the volcano Eyjafjallajökull, which sent ash across European airspace and grounded planes for days. The magma beneath the Reykjanes peninsula is relatively low in viscosity, which allows gas bubbles to escape and reduces the chance of an explosive eruption. And the activity is not taking place beneath glacial ice, which increases the chance of explosions.

Tracking the changes

Icelandic volcanologists are monitoring the situation with a variety of instruments to measure changes in the ground as magma shifts beneath it. They have even repurposed a fibre-optic communications cable to detect earthquakes in real time. IMO scientists have also deployed gas sensors to detect sulfur dioxide and other gases wafting up from the magma.

Working with IMO and other researchers, Laura Wainman at the University of Leeds has also collected samples of volcanic gas from a 2-kilometre-deep borehole at the geothermal power plant. It is a rare opportunity to sample gas that is probably coming directly off magma at depth, rather than after it has erupted and its chemistry starts to change, Wainman says. Studies of the three recent eruptions show that the magma that fuelled them seems to have come from perhaps as far down as 20 kilometres^2,3.

Scientists are also using lava-flow models to understand how lava, if it erupts, would move across the landscape, and how it might cool down or remain hot depending on whether it spreads out across the ground or is confined to narrow channels. That information can determine where officials might need to construct barriers.

Whether and when it might erupt remains anyone’s guess. Before the 2021 and 2022 eruptions, the number of earthquakes and the amount of ground deformation dropped in the days before the eruption^4,5. That’s because much of the tectonic stress had already been relieved, meaning there were fewer indicators that an eruption was about to start. Something similar happened at Nyiragongo volcano in the Democratic Republic of the Congo in 2021, Sigmundsson notes. A fissure opened in that volcano essentially without warning⁶ and sent deadly lava flows into the city of Goma, killing dozens of people and displacing hundreds of thousands more.