Mount Lokon, located on northern Sulawesi island, has been dormant for years but rumbled back to life late last week.
A series of overnight blasts Thursday and Friday claimed one life — a woman who suffered a heart attack as she fled.
But Surono, a government volcanologist who uses only one name, said Sunday's 10:35 a.m. eruption released the greatest amount of energy so far, shooting soot and debris 11,400 feet (3,500 meters) into the sky.
"We're hoping this helped ease pressure building up behind the magma dome and that we'll now start seeing a reduction in activity," he said. "But it's too early to know."
More than 33,000 people live along the slopes of Mount Lokon, taking advantage of fertile soil to grow cloves and coffee. About 5,000 of them with homes nearest to the crater have been relocated in recent days to schools, mosques and other makeshift shelters near the base.
Despite warnings that the mountain was still not safe, some had returned early Sunday to tend to their crops and their livestock.
The powerful explosion sent them racing back down the slopes, some jumping into cars and motorcycles, others rounded up by soldiers and police and escorted down in trucks.
"It was huge," said Henny Lalawi, who works as a picker for a coffee plantation. "It sounded like a bomb and then I saw the crater burst, sending ash high into the air. It was pretty awesome, really."
She said she'll have to go back when things settle down.
"It's only ash, after all, and I need the work."
Sutopo Purwo Nugroho from the National Disaster Management Agency said there were no reports of injuries or new deaths Sunday.
Airlines traveling within six miles (10 kilometers) of the peak were told to reroute their flights, but none have been canceled so far.
The nearby international airport in Manado also was operating normally, said Lucky Pondaag, an airport spokesman.
Mount Lokon is one of about 129 active volcanoes in Indonesia. Its last major eruption in 1991 killed a Swiss hiker and forced thousands of people to flee their homes.
Indonesia, a vast archipelago of 240 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.