Volcanic ash from Semeru volcano observed at 4 000 m (13 100 feet) a.s.l., Indonesia

Volcanic ash from Semeru volcano in Indonesia was observed at 4 000 m (13 100 feet) above sea level at 21:30 UTC on October 21, 2025. The advisory was issued by the Darwin VAAC at 22:00 UTC on October 21, 2025.

According to the VAAC advisory, volcanic ash was reported to flight level 140 (approximately 4 000 m or 13 100 feet) based on a ground report at 18:18 UTC on October 21, 2025, with movement towards the west at 9 km/h (6 mph). The current Aviation Color Code is Orange. Ash was not identifiable in satellite imagery due to meteorological cloud cover. Forecasts indicated continued ash presence up to 4 000 m (13 100 feet) for at least 18 hours after the report time.

According to the Smithsonian / USGS Weekly Volcanic Activity Report for September 24–30, 2025, Semeru exhibited daily eruptive events with white-and-gray or gray ash plumes rising 400–900 m above the summit and drifting in multiple directions. The Alert Level remained at 2, and the public was advised to stay at least 3 km away from the summit in all directions, with further distance required in some sectors due to lahar, avalanche, and pyroclastic flow hazards.

Semeru is a stratovolcano located in East Java, Indonesia, and is the highest volcano on the island. It is prone to producing ash plumes, pyroclastic flows, and lava flows. Settlements near the volcano, such as the town of Lumajang, can be at risk from volcanic hazards including ashfall and lahars, particularly along river valleys extending from the summit. Residents should follow official guidance and maintain safe distances from hazardous areas.