Indonesian officials say two volcanos erupted Monday, forcing the rerouting of flights and preventing thousands of people who had already been evacuated from returning home.
Indonesia's volcanology center said Mount Sinabung, which has been erupting on and off since mid-September and is located on western Sumatra island, shot volcanic ash around 8,000 meters into the air.
About 5,000 people who had recently been evacuated from the area around Sinabung have not yet been able to return home.
On the main island of Java, Mount Merapi, Indonesia's most active volcano, erupted with a column of ash and smoke around 2,000 meters high. Authorities say up to 600 families have been told to prepare for evacuation.
Indonesia has dozens of active volcanoes. The country straddles major fault lines known as the "Ring of Fire" between the Pacific and Indian oceans.