MOUNT MERAPI, Indonesia – Clouds of gray ash rumbled down the slopes of Indonesia’s most volatile volcano Saturday in its most powerful eruption of a deadly week, prompting soldiers to force reluctant villagers to evacuate amid fears of a larger blast.

On the other side of the archipelago, storms again prevented aid deliveries to increasingly desperate survivors of a tsunami — including a teenage girl with an open chest wound — that killed 413 people in the Mentawai islands. Relief workers found some comfort, however, when the number of missing dropped by half to 163 as searchers discovered more survivors and villagers who had fled to the hills returned home.

The simultaneous catastrophes have severely tested the emergency response network. Indonesia lies in the Pacific “Ring of Fire,” a cluster of fault lines prone to earthquakes and volcanic activity.

Mount Merapi, which sprang back to life early last week, unleashed a terrifying 21-minute eruption early Saturday, followed by more than 350 volcanic tremors and 33 ash bursts, said Surono, chief of the Center for Volcanology and Geological Hazard Mitigation.

The latest spewing of the notoriously unpredictable volcano forced the temporary closure of an airport and claimed another life, bringing the death toll this week to 36.

At least 47,000 people have fled the mountain’s wrath, according to the National Disaster Management Agency. Government camps well away from the base were overflowing with refugees, including most of the 11,000 people who live on the mountain’s fertile slopes. They were told Saturday, with signs the danger level was climbing, that they should expect to stay for three more weeks.

Despite such warnings, many people have returned to their land to check on precious crops and livestock. The new eruption triggered a chaotic pre-dawn exit, killing a 44-year-old woman who was fleeing by motorcycle, said Rusdiyanto, head of disaster management office in the main city of Yogyakarta.

For the first time Saturday, more than 2,000 troops were called in to help keep villagers clear of the mountain.

The villagers may be later allowed to go back for a few hours a day if the volcano appears to be calm, said Djarot Nugroho, head of the Central Java disaster management agency, adding that they must return to the camps immediately if a new alarm is raised.

“Once the sirens go off, no excuse, everyone has to get back to the camps,” he said.

The eruption temporarily forced the closure of the airport in Yogyakarta, 12 miles south of the volcano, because of poor visibility and heavy ash on the south of the runway, said Naelendra, an airport official.

Despite earlier hopes that Merapi’s activity might be waning, scientists warned Saturday the worst may be yet to come.

High-pressure gas appeared to be building up behind a newly formed thick magna dome in the crater, “setting the stage, potentially, for a more explosive eruption,” said Subandrio, who heads the nearby volcanology center.

“It’s a bad sign,” he said.