Iceland declared a state of emergency after a series of earthquakes sparked fears of a volcanic eruption.
The authorities ordered thousands of people living in the southwestern town of Grindavik to evacuate as a precaution.
The Icelandic Meteorological Office (IMO) says it is concerned that large amounts of magma – molten rock – are spreading underground and could appear there.
Thousands of tremors have been recorded around the nearby Fagradalsfjall volcano in recent weeks.
It was centered on Iceland’s Reykjanes Peninsula, which had been dormant for volcanic activity for 800 years before the 2021 eruption.
The Icelandic Civil Protection Agency said that the decision to evacuate came after the International Maritime Organization did not rule out that “the magma tunnel currently forming could reach Grindavik.”
In a statement issued on Friday, the agency said people should leave the city, but also stressed that it was not an “emergency evacuation” – calling on them to “remain calm, as we have a significant amount of time to respond.”
She added: “There is no imminent immediate danger. The evacuation is primarily preventive with the safety of all Grindavik residents as the main goal.”
All roads leading to the town, which has a population of about 4,000 people, were closed except in emergency cases, to ensure that traffic could enter and exit.
The International Maritime Organization said in a statement on Friday that “significant changes have occurred in seismic activity,” with tremors moving towards Grindavik throughout the day.
She added that it was possible that magma had extended beneath the town and that “it is not possible to determine exactly” whether or where it could have appeared.
“The amount of magma present is much greater than observed in the largest magma intrusions associated with the Vagradalsfjall eruption,” the IMO said.
Iceland is one of the most geographically active regions in the world, with about 30 active volcanic sites.
Volcanic eruptions occur when magma, which is lighter than the surrounding solid rock, rises to the Earth’s surface from deep within.
In July, the Little Ram volcano erupted in the Fagradalsfjall region, attracting tourists to the site of “the world’s newest mini-volcano”.
The site lay dormant for eight centuries until eruptions in 2021, 2022 and 2023.
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