A volcano in southwestern Iceland began erupting on Tuesday, prompting the closure of the popular Blue Lagoon tourist destination and threatening the town of Grindavik, about 25 miles southwest of the capital, Reykjavik.

The country’s meteorological office said that the length of the magma intrusion — about seven miles — was the longest measured since November 2023, when the authorities ordered Grindavik’s approximately 4,000 residents to evacuate.

The eruption began at 9:45 a.m., and within 30 minutes a fissure in the Earth’s surface appeared to be about half a mile long, according to the meteorological office.

By 11 a.m., the office said, the first fissure had grown and another had opened a few hundred yards from the protective barriers near Grindavik.

This is a developing story. Check back for updates.