The explosion at Mount Sinabung, located in North Sumatra province, shot black ash 3 kilometers (nearly 2 miles) into the air, but there were no reports of injuries or damage, said National Mitigation Agency spokesman Sutopo Purwo Nugroho.
He said villages, farms and trees around the 2,600-meter (8,530-foot) -high rumbling volcano were covered in thick gray ash, prompting authorities to evacuate more than 3,300 people. Most were from two villages within 3 kilometers (nearly 2 miles) of the mountain in Karo district.
No lava or debris spewed from the volcano, and nearby towns and villages were not in danger, but authorities warned tourists to stay away from the danger zone located 1.5 kilometers (1 mile) from the crater, Nugroho said.
Last month, more than 15,000 people were forced to flee when the volcano rumbled to life after being dormant for three years, belching ash and smoke and igniting fires on its slopes.
The volcano's last major eruption in August 2010 killed two people and forced 30,000 others to flee. It caught many scientists off guard because it had been quiet for four centuries.
Mount Sinabung is among more than 120 active volcanoes in Indonesia, which is prone to seismic upheaval due to its location on the Pacific "Ring of Fire," an arc of volcanos and fault lines encircling the Pacific Basin.
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