Mount Agung has been hurling clouds of white and dark gray ash about 3,000 meters (9,800 feet) into the atmosphere since the weekend and lava is welling up in the crater, sometimes reflected as a reddish-yellow glow in the ash plumes. Its explosions can be heard about 12 kilometers (7.5 miles) away.
Videos released by the National Disaster Mitigation Agency showed a mudflow of volcanic debris and water known as a lahar moving down the volcano’s slopes. It said lahars could increase because it’s rainy season and warned people to stay away from rivers.
The agency raised the volcano’s alert to the highest level early Monday and expanded the danger zone to 10 kilometers (6 miles) in places from the previous 7.5 kilometers. It said that a larger eruption is possible.
Spokesman Sutopo Purwo Nugroho told a news conference in Jakarta that the extension of the danger zone affects 22 villages and about 90,000 to 100,000 people. He said about 40,000 people have evacuated but others have not left because they feel safe or don’t want to abandon their livestock.
“Authorities will comb the area to persuade them,” he said. “If needed we will forcibly evacuate them.” About 25,000 people were already living in evacuation centers after an increase in tremors from the mountain in September sparked an evacuation.
Lava rising in the crater “will certainly spill over to the slopes,” Sutopo said.
The volcano’s last major eruption in 1963 killed about 1,100 people.
Villager Putu Sulasmi said she fled Monday with her husband and other family members to a sports center that’s serving as an evacuation center.
“We came here on motorcycles. We had to evacuate because our house is just 3 miles from the mountain. We were so scared with the thundering sound and red light from the peak,” she said.
The family had stayed at the same sports center in September and October when the volcano’s alert was at the highest level for several weeks but didn’t erupt. They had returned to their village about a week ago.
“If it has to erupt let it erupt now rather than leaving us in uncertainty. I’ll just accept it if our house is destroyed,” she said.
Bali’s airport was closed early Monday after ash, which can pose a deadly threat to aircraft, reached its airspace.
Flight information boards showed rows of cancelations as tourists arrived at the busy airport expecting to catch flights home.
Airport spokesman Air Ahsanurrohim said 445 flights were canceled, stranding about 59,000 travelers. The closure is in effect until Tuesday morning though officials said the situation will be reviewed every six hours.
Bali is Indonesia’s top tourist destination, with its gentle Hindu culture, surf beaches and lush green interior attracting about 5 million visitors a year.
Some flights to and from Bali were canceled on Saturday and Sunday but most had continued to operate normally as the towering ash clouds were moving east toward the neighboring island of Lombok.