A drone image shows the beautiful but dangerous crater known as Viti, which derives from the Icelandic word for hell. In 2021, researchers discovered that the Askja volcano had expanded rapidly, growing by 11 centimeters (4 inches) in just a few months. Askja has since grown by a further 80 centimeters.

Researchers believe Askja has grown because 44 million cubic meters of magma have accumulated under the volcano, pushing it upwards and making eruptions more likely. Michelle Parks, a volcanologist at the Icelandic Meteorological Service originally from Australia, regularly measures the temperature in the bubbling Viti. A sharp rise in temperature would indicate that an eruption could be imminent.

Nobody knows when, or even if, Askja will erupt. Parks and her team want to find out why so much magma is accumulating under the volcano. They are pursuing a hypothesis that would have consequences not only for Iceland, but for people all over the world: is the retreat of glaciers as a result of human-caused made climate change leading to an increased accumulation of magma under volcanoes?

Some courageous tourists even go swimming in the Viti crater. Researchers are investigating a basically simple theory: the enormous weight of glaciers pushes volcanoes down. When the ice retreats, the pressure on the Earth's crust and mantle lessens. This change in pressure could stimulate the dynamic forces beneath the volcanoes to produce more magma, which in turn may lead to eruptions.

"Iceland is essentially one of the best places in the world to study this … because we have both volcanism and glaciers," volcanologist Parks told the Reuters news agency. Glaciers still lie upon more than half of Iceland's 34 active volcanic systems, but they are melting rapidly due to rising global temperatures.

Mountain guide Iris Ragnarsdottir Pedersen leafs through an album with pictures of the Skeidararjokull glacier. She and her father, a volunteer glacier observer, have been watching the ice recede for years. This year, the glacier showed a retreat of 300 meters (984 feet). "It’s just devastating to see," said Ragnarsdottir Pedersen. "It’s like watching your friends disappear."

It's not just Skeidararjokull that's melting: these chunks of ice have broken away from the Fjallsjokull glacier. Over the past 130 years, Iceland's glaciers have lost around 16% of their volume, half of it in the last three decades alone. Scientists predict that around half of the remaining volume will have disappeared by the end of this century.

So far, there have been few studies on the interaction between melting ice and volcanic activity in other parts of the world. However, researchers in the US believe 245 volcanoes around the world could be affected, from the Andes to Alaska and Kamchatka in Russia. Around 160 million people live in the vicinity of one of these volcanoes; 20,000 of them in the immediate vicinity.

Volcanic gases billow over the flank of Askja. Preliminary modeling results from Parks' project have found that two to three times as much magma has formed under Iceland in the last 30 years as would have been the case without the glaciers retreating. "More magma is coming in underneath Iceland, and we just don't need it," said Parks. "We've got enough."

At the same time, Parks emphasizes it's too early to establish a causal link between climate change in the form of melting glaciers and increased volcanic activity; researchers around the world must first collect more data. One thing is certain: the small Icelandic town of Vik seen here would be flooded by melting glacier water if the nearby Katla volcano were to erupt.