The blast Wednesday afternoon followed a morning eruption that sent searing gas clouds down the volcano's scorched flanks. The volcano started erupting Oct. 26 and most of the 38 deaths occurred the first day. No new casualties were immediately reported from Wednesday's activity.
The government widened the danger zone to 9 miles from 6 miles. The massive blast endangered places that had not been not evacuated as well as refugee camps within that distance.
The volcano and tsunami that hit another part of the country last week have claimed nearly 470 lives and sent tens of thousands crowding into emergency shelters. They were settling in for the long haul Wednesday, with relief operations expected to take weeks, possibly months.
Mount Merapi's morning blast spewed hot ash and fiery rocks three miles down the mountain's largely evacuated slopes at 8:11 a.m. The multiple eruptions may be helping ease pressure inside the volcano's crater, Safari Dwiyono, a state volcanologist, said.
The government has ordered airlines to circumvent Merapi for safety reasons and two international carriers briefly canceled flights altogether to nearby airports.
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.
More than 800 miles west of the volcano, helicopters and boats were delivering aid to the most distant Mentawai islands, where an Oct. 25 tsunami swept entire villages to sea.
The death toll was lowered by three Wednesday to 428, said Ade Edward, a disaster official, with 75 others still missing. The figures were revised after compiling and comparing data from various private and government search and rescue teams, health workers and security forces, he said.
There has been talk in recent days, meanwhile, about relocating villagers away from vulnerable coastlines. Refugees who already fled when the mountain started eruption last week were among those being moved hastily to safer areas.
"I'm all for it," said Regen, who lives on Pagai Utara island and goes by one name. "We're all terrified now, especially at night, and wouldn't mind moving further inland."