MOUNT MERAPI, Indonesia >> One by one the bodies of dozens killed by Indonesia’s most volatile volcano — some too charred to ever be identified — were placed into a mass grave Sunday, as people terrified that another eruption was coming fled the city at the foot of Mount Merapi.

As relatives wept and men recited traditional Islamic prayers, villagers and policemen unloaded the corpses — some in plain wooden coffins, others still in the morgue’s yellow body bags — from ambulances. They were placed into a massive trench, dug into a large green field in the shadow of the volcano, which has claimed 138 lives in the past two weeks.

The notoriously unpredictable mountain unleashed its most powerful eruption in a century Friday, sending hot clouds of gas, rocks and debris avalanching down its slopes at highway speeds, smothering entire villages and leaving a trail of charred corpses in its path.

Concerns over the ash it spewed prompted international airlines to cancel flights to the capital of Jakarta just days before President Barack Obama’s planned trip to Indonesia — his second stop in a 10-day Asian tour.

With more than 90 killed, Friday was the deadliest day at Merapi since 1930.

Islam mandates that the dead be buried quickly, so authorities gave relatives three days to identify their loved ones. To speed up the process, most families chose to have their relatives interred in a mass grave — a common practice in Indonesia following a disaster. About 30 bodies were taken by relatives to be buried elsewhere.

Those that were identified were put in plain wooden coffins and slipped into the ground. Those that were not claimed were buried in their body bags.

Merapi, meanwhile, showed no signs of tiring Sunday, sending out thunderous claps as it shot ash up to four miles into the air, dusting windshields and rooftops hundreds of miles away. The ash hung so thickly in the air that breathing became painful and clothes stunk of smoke after any time spent outdoors.

The Indonesian government has put Yogyakarta, a city of 400,000 people 20 miles from Merapi, on high alert.

Though there have been no orders to evacuate, panicked residents crammed onto trains and buses to seek temporary refuge with family and friends elsewhere. With the closest airport closed since Friday, Malaysia’s air force sent three C-130 transport planes to Solo, a city 20 miles from the volcano, to pick up more than 600 citizens, many of them university students.

“My parents have been calling since Friday, saying ‘You have to get out of there! You have to come home!”‘ said Linda Ervana, a 21-year-old history student from Indonesian Borneo who was waiting in a train station with three friends from her Yogyakarta university.

After failing to get tickets, they finally decided Sunday to rent a minibus with some other classmates. Their classes have been canceled for at least a week.

“It feels like that movie ‘2012,”‘ said Ervana’s 22-year-old friend, Paulina Setin. “Like a disaster in a movie.”

Others in Yogyakarta hopped onto motorbikes and into cars with their families. “What choice do we have?” asked Sukirno, 37, as he sped away with his wife and their 8-year-old daughter, saying he worried about the effect of the ash on their health.

An employee at the Novotel said so many staff had left town that the hotel was planning on closing most of its rooms. He said other hotels in the Accor group would do the same. He spoke on condition of anonymity because he was not authorized to speak to the media. No one answered the phones at Accor’s office in Jakarta on Sunday.

The biggest threat to the city, experts say, is not searing gas clouds, but the Code River, which flows right into the city’s heart from the 9,700-foot mountain.

It could act as a conduit for deadly volcanic mudflows that form in heavy rains. A thick, black volcanic sludge has already inundated one city neighborhood that starts at the river bank and climbs a hillside.

In Romomangun, the mud burst the banks and poured into buildings. It has filled a path that runs along the river — which is usually about three feet below a retaining wall but is now even with it. The sludge also rushed into a small, one-room building on the bank that houses a public bathroom. The top of the entry door is now at waist level.

Romomangun’s residents — along with others who live along the Code — have been urged by the government to evacuate, but Ariyanto, a neighborhood leader, says they have decided to stay. For now, they think they can manage to escape fast enough up the hillside if another surge comes.

Racing at speeds of 60 mph, the molten lava, rocks and other debris can destroy everything in their path.

The ash spewed, meanwhile, can clog airplane engines, and concerns over that Saturday prompted airlines to cancel nearly all international flights in and out of Jakarta — 280 miles to the west of the volcano. Airlines slowly started resuming operations Sunday, though Lufthansa, EVA Air, Philippine Air and others were still on the ground.

Paul Belmont, a U.S. Embassy spokesman, said there was no talk yet of changing Obama’s schedule.

“But certainly, if the situation evolves into something like what we saw in Europe not long ago (when the eruption of Iceland’s Eyjafjallajokul closed airports for a week) it’s something we’d have to take seriously,” he told The Associated Press on Sunday.

Merapi’s latest round of eruptions began Oct. 26, followed by more than a dozen other powerful blasts and thousands of tremors. More than 200,000 people — many of whom normally live on the fertile slopes of the volcano — have since jammed into emergency shelters.

With muddy floors and flies landing on the faces of sleeping refugees, many complained of poor sanitation, saying there were not enough toilets or clean drinking water.

Indonesia, a vast archipelago of 235 million people, is prone to earthquakes and volcanoes because it sits along the Pacific “Ring of Fire,” a horseshoe-shaped string of faults that lines the Pacific Ocean.