Some witnesses at the foot of Mount Sinabung reported seeing an orange glow — presumably magma — in cracks along the volcano's slopes for the first time.
"It was really terrifying," said Anissa Siregar, 30, as she and her two children arrived by truck at an emergency shelter near the base, adding the mountain shook violently for at least three minutes. "It just keeps getting worse." Mount Sinabung's first eruption last week caught many scientists off guard. With more than 129 active volcanoes to watch, local vulcanologists had failed to monitor the long-quiet mountain for rising magma, slight uplifts in land and other signs of seismic activity.
There are fears that current activity could foreshadow a much more destructive explosion in the coming weeks or months, though it is possible, too, that Singabung will go back to sleep after letting off steam.
More than 30,000 people living along the volcano's fertile slopes have been relocated to cramped refugee camps, mosques and churches in nearby villages.
But some — such as Siregar, the mother who fled with her children — have insisted on returning to the danger zone to check on their homes and their dust-covered crops.
The government sent dozens of trucks to the mountain to help carry them back before Tuesday's eruption, which sent ash and debris shooting 3 miles (5,000 meters) into the air, said Surono, who heads the nation's volcano alert center.
Local media said ash had reached as far as Berastagi, a district 15 miles (25 kilometers) from the base of the mountain.
Surono said activity was definitely on the rise: There were more than 80 volcanic earthquakes in the 24-hour lead up to the blast, compared to 50 on Friday, when ash and debris shot nearly 2 miles (3,000 meters).
The eruption early Tuesday occurred just after midnight during a torrential downpour. Witnesses said volcanic ash and mud oozed down the mountain's slopes, flooding into abandoned homes. Others said saw bursts of fire and hot ash.
The force of the explosion could be felt 5 miles (8 kilometers) away.
Indonesia is a seismically charged region because of its location on the so-called "Ring of Fire" — a series of fault lines stretching from the Western Hemisphere through Japan and Southeast Asia.
It has recorded some of the largest eruptions in history.
The 1815 explosion of Mount Tambora buried the inhabitants of Sumbawa Island under searing ash, gas and rock, killing an estimated 88,000 people.
The 1883 eruption of Krakatoa could be heard 2,000 miles (3,200 kilometers) away and blackened skies region-wide for months. At least 36,000 people were killed in the blast and the tsunami that followed.
