Since 2023, many volcanic eruptions have taken place near the town of Grindavik in Iceland. Photos of these eerily beautiful occurrences are proving popular – like this one from 2024. | Photo: Veðurstofa Íslands

For several weeks back in early 2021, the fishing village of Grindavik in Iceland was subjected to dull rumblings, as dozens of earthquakes of up to magnitude 5.6 caused its buildings to shake. The geologist Joël Ruch and three colleagues from the University of Geneva happened to be staying in a nearby house by the sea. Suddenly, things went quiet, and stayed that way for two days. “I knew then that an eruption was very likely”, he says. And on 19 March 2021, that’s what happened. “The night sky was suddenly glowing red. It was incredible”.

Lava began shooting out of a fissure on the Reykjanes Peninsula near the capital Reykjavik – the first such eruption for 800 years. “It was a stroke of luck for us researchers”, says Ruch. He and his team had actually travelled to Iceland because of a series of earthquakes that was taking place. “Now we had to be quick”, he says, because they wanted to document this surprising eruption in real time. Using drones, satellite radar interferometry and local GPS measurements, they scanned the region with inch-perfect precision and created 3D maps of the changes being wreaked upon it. Since then, there have been 12 more eruptions on the Reykjanes Peninsula.

Observing volcanoes better

In Italy, seismic tremors have also been increasing again in the Campi Flegrei volcanic caldera, next to the city of Naples, since summer 2025. Over the past decades, the nearby town of Pozzuoli has experienced a bell-shaped, four-metre ground uplift in the Earth’s surface over an area of several square kilometres. But these tremors and this bulge are nothing out-of-the-ordinary for volcano researchers. “We’re observing normal activity after long periods of dormancy”, says Olivier Bachmann, a volcanologist at ETH Zurich. “Our monitoring options are now more comprehensive than ever. News also spreads quicker than ever before, so people get the impression that volcanic activity overall is intensifying. In reality, we are only getting more efficient at observing it”.

Researchers can now register minimal shifts and assess whether these are harbingers of a catastrophe, or just everyday happenings. A series of earthquakes is like the pulse of a fire-breathing system. When the Earth’s surface expands, it’s an indication of increased pressure in a magma chamber beneath it. When gases such as CO₂, methane or sulphur compounds rise up from the depths, this can also tell us whether something’s happening underground. But as Bachmann insists, “Every volcano is different”.

Iceland is an ideal place for researchers like him. It has many active systems, because it’s situated directly where the North American and Eurasian continental plates are moving away from each other at a rate of two centimetres every year. A rift zone runs right across the surface of the country. The drift causes tension at the edges of the plates. If this tension is released, earthquakes occur that create cracks in the Earth’s crust. In extreme cases, glowing lava can penetrate through them and reach the surface.

‘Basaltic lava’ is what geologists call the liquid rock that emerges here in Iceland. It can’t build up enough pressure to cause very large eruptions on its own. Volcanoes like the one on Reykjanes are called ‘effusive eruptions’ and tend to remain dangerous only on a local basis. “But the speed of the magma that rose up there was unprecedented since science first started monitoring basalt eruptions”, says Ruch. It took just a few days for it to rise to the surface from a depth of 20 kilometres. “The warning time was extremely short and was mainly dependent on the local seismic network”.

Tsunamis and super eruptions

Teams like Ruch’s are working with the Icelandic authorities to make constant surveys of new fissures and cracks, taking samples to determine the composition and gas content of the magma that emerges. They often spend up to 16 hours out in the rugged landscape. “Excursions like these are also valuable for our students”, says Ruch. And they also provide new knowledge – such as when fresh cracks appear in the ground before new eruptions. After three eruptions on Reykjanes in 2023, seismic activity shifted to the west. As a result, the town of Grindavik – population 3,500 – had to be evacuated.

Ruch is also monitoring the Askja caldera on Iceland. Its crater has a lake 220 metres deep and it’s a tourist magnet. But there are warning signs there, too. In July 2014, millions of cubic metres of rubble slid into the water, triggering a tsunami that was 80 metres high. Luckily, the rockslide happened at night. But the danger isn’t over. The centre of the crater under the lake recently rose by 90 cm. “In 2022, Askja was one of the fastest deforming volcanoes on Earth”, says Ruch.

Despite continuous monitoring, it’s still difficult to predict new eruptions. This is why researchers are also keen to learn from history by investigating earlier events. For example, Bachmann is analysing the Kos-Nisyros-Yali volcanic field in the Aegean Sea off Greece, where the dry climate has helped to keep volcanic rocks well preserved. It’s like an archive. By analysing the composition of solidified lava, researchers can deduce its former density, viscosity and the gas content in its magma chamber. “These properties are decisive in determining whether an eruption is explosive or effusive”, says Bachmann.

Predictions remain dubious

Ruch’s colleague Luca Caricchi at the University of Geneva is also trying to learn from history. He’s working on the Campi Flegrei, which is probably the most dangerous volcanic area in Europe, although it’s also the best monitored. The earthquakes there last summer made the civil defence authorities nervous. A new research project has been taking a more detailed look at the nature of the seismic waves that occurred. There were unusual vibration modes and patterns. “They seem to indicate that relatively large fractures are forming above the magma reservoir”, says Caricchi. He suspects that fractures of this kind could cause the molten rock to move upwards. The temperature of it is about 1,000 degrees. If it continues to ascend, and if there is sufficient pressure in the second chamber that is deeper and bigger, the magma will at some point reach the surface. But will this happen any time soon? “We don’t know”, says Caricchi. “We can only interpret the indications we’ve got and prepare for different scenarios”.

Large volcanic caldera such as Campi Flegrei pose a challenge to research, because their life cycle spans 200,000 years. As a result, their behaviour is highly variable. Their structures that lie several kilometres beneath the Earth’s crust are especially difficult to study. Although measuring the Earth’s magnetic field can localise electrically conductive areas such as magma chambers, they often only provide rough values. What’s more, it’s impossible to determine the precise location and size of the channel connecting the two magma reservoirs under the town of Pozzuoli – and that would be crucial for predicting what might happen next.

The researchers know that it would need big quantities of magma to rise from the large chamber – which is located at a depth of 10 to 12 km – for it to be sufficient to fuel a so-called super eruption such as those that last took place here 39,000 and 15,000 years ago. But as Caricchi says, their models also show that “The narrower the connection between the two magma reservoirs, the more explosive the eruption will be”.

Their models also incorporate geological signals from past eruptions. The researchers can do this as the structure of certain crystals in the cooled lava is dependent on pressure. Caricchi was able to determine that the lava from the last violent eruption – which took place in 1538 – came almost exclusively from the upper, smaller magma chamber. But things look different with samples from the two earlier super eruptions. “We find crystals here from both the upper and lower chambers”, says Caricchi. This provides him with another piece of the jigsaw puzzle: “Their ratio enables us to determine how much magma flowed from the lower chamber to feed the eruption”. It seems that super eruptions will only occur if magma rises quickly from the depths.

Ensuring enough time to evacuate

So the research team is cautiously feeling its way ahead. They’re now also using AI analysis tools to process data for their models and to improve their forecasting ability. “We want to create plausible scenarios that would enable the necessary preparations for evacuating the city of Naples”, says Caricchi. According to their plan, they would need at least 72 hours. In Reykjanes, the authorities are aiming for similar times. The eruptions there behave in a kind of cyclical manner and always begin with ground uplift. This is why the authorities in Iceland have defined a threshold value for an eruption that would leave them with a few days’ grace. But as Ruch points out, the area of seismic activity can also shift again, just as it did in 2023, when Grindavik was suddenly affected directly.