The first of two eruptions of Mount Sinabung sent volcanic ash and vapor soaring high above northwestern Sumatra on Sunday. It also pelted nearby villages with superheated volcanic debris that ignited forest fires on its slopes.
A second, less powerful, eruption on Tuesday sent ash blowing eastward into the resort town of Brastagi, according to local disaster officials.
There were no reports of injuries due to volcanic activity. The powerful eruptions came after the volcano had remained relatively quiet for three years.
Mount Sinabung surprised scientists in September 2010 by erupting suddenly for the first time in 400 years.
Two weeks of eruptions at that time forced more than 30,000 people from their homes.
Local vulcanologists failed to notice signs of rising magma, slight uplifts in land and minor volcanic tremors prior to the blasts.
Some archaeologists believe an eruption of a prehistoric volcano near Mount Sinabung nearly wiped out the human race when it erupted 69,000-77,000 years ago.