The bodies of 11 hikers were found on the slopes of Mount Marapi on the Indonesian island of Sumatra after a volcanic eruption sent ash plumes cascading down the mountain Sunday, the local search and rescue agency said today.

Dozens of climbers were on the active volcano in West Sumatra province when it began spewing a column of ash nearly 3,000 meters, about 10,000 feet, high, according to Indonesia’s National Disaster Mitigation Agency. Volcanic ash rained on nearby towns, and residents were advised not to leave their homes, the agency said.

The local search and rescue team based in the city of Padang said that 12 climbers were still missing. Efforts to find them have been stalled by periodic volcanic activity, the team leader, Abdul Malik, said in a statement. As of this morning, eight eruptions had been recorded.

Indonesia, the world’s largest archipelago nation, is sprawled across the so-called Ring of Fire, where the meeting of tectonic plates catalyzes earthquakes and volcanic eruptions. Marapi has erupted several times in recent years. During an eruption in January, the disaster mitigation agency said climbers were still camping on the volcano despite warnings not to ascend.

Seismologists said the eruption Sunday came without the preamble that often precedes such activity. On Saturday and Sunday, 75 hikers were cleared to climb the mountain, according to the West Sumatra Natural Resources Conservation Agency, which issues permits to access Marapi.

Lingga Duta Andrefa, a university student, was trekking with two friends when they heard a roar like an airplane flying overhead.

Climbers who were ahead of them on the mountain yelled down that the volcano was erupting. Rocks, some as large as a human head, rained down like a hailstorm, Lingga said. Ash plumes coursed down the mountain. Smoke choked those trying to escape. The eruption sent molten sand, ash and rocks hurtling, spanning a nearly 2-mile radius.

Lingga and his friends sheltered beneath an overhang, seeking protection from the airborne debris, before running down to safety. They narrowly missed a landslide, triggered by crashing boulders. Some of the climbers who were not far from them did not make it out alive, he said.

“I am still traumatized,” he said. “Thank God all three of us are safe.”

As of today, 49 climbers had descended the mountain and another three had survived the eruption but had not been evacuated yet, the conservation agency said. Of the 49 people, nine suffered burns and were being treated at a hospital in Padang.

Dian Indriati, the head of the conservation agency, said that she and her team had received no indications that Marapi was in danger. Otherwise, climbers would not have been allowed up its slopes, she said.

“This is a full natural disaster, because there were no signs of increased activity,” she said.

The local area depends on tourism revenue from hikers, and the mountain park reopened in July, after being closed because of the January eruption. Previous volcanic activity has shuttered the park for months and even years, most recently in 2019 and 2011.

This article originally appeared in The New York Times.