Volcanic materials are seen spewing from Mount Sinabung in North Sumatra Province, Indonesia, Aug. 31, 2026. Mount Sinabung in Indonesia's North Sumatra province erupted Monday morning, sending volcanic ash over the nearby city of Berastagi, a local monitoring official said. (Photo by Adiva Niki/Xinhua)

Mount Sinabung in Indonesia's North Sumatra province erupted Monday morning, sending volcanic ash over the nearby city of Berastagi, a local monitoring official said.

Armen Putra, head of the Sinabung Volcano Observation Post, said a thick, dark ash column rose about 3,500 meters above the summit and drifted east and southeast.

The eruption was recorded on a seismogram with a maximum amplitude of 120 millimeters and lasted about one hour. Volcanic ash blanketed roads and vehicles in Berastagi, reducing visibility in the area.

Authorities urged residents to wear masks and remain vigilant, while schools in affected areas advised students and teachers to wear masks when outdoors.

Mount Sinabung remains at Level II, or Alert status. Activities are prohibited within a three-kilometer radius of the summit and within 4.5 kilometers in the southeast sector. Residents near rivers originating from the volcano have also been warned of potential lahar flows.

Volcanic materials are seen spewing from Mount Sinabung in North Sumatra Province, Indonesia, Aug. 31, 2026. Mount Sinabung in Indonesia's North Sumatra province erupted Monday morning, sending volcanic ash over the nearby city of Berastagi, a local monitoring official said. (Photo by Adiva Niki/Xinhua)

Volcanic materials are seen spewing from Mount Sinabung in North Sumatra Province, Indonesia, Aug. 31, 2026. Mount Sinabung in Indonesia's North Sumatra province erupted Monday morning, sending volcanic ash over the nearby city of Berastagi, a local monitoring official said. (Photo by Sarianto/Xinhua)