Ash cloud from Semeru volcano observed at 4 300 m (14 100 feet) a.s.l., Indonesia

Volcanic ash from Semeru in Indonesia was observed at an altitude of 4 300 m (14 100 feet) above sea level at 03:50 UTC on October 20, 2025. The advisory was issued by the Darwin VAAC at 04:10 UTC on the same day.

Ash was reported between the surface and flight level 140 (approximately 4 300 m or 14 100 feet) with movement towards the southwest at approximately 19 km/h (12 mph). The ash cloud was not identifiable in satellite imagery due to meteorological cloud cover, but intermittent discrete eruptions were expected to be ongoing according to ground reports and model guidance. The current Aviation Color Code is Orange.

According to the Smithsonian/USGS Weekly Volcanic Activity Report for September 24–30, 2025, Semeru exhibited daily eruptive events recorded by seismic networks. Ash plumes rose 400–900 m above the summit and drifted 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, and farther in certain directions due to lahar and pyroclastic flow hazards.

Semeru is a stratovolcano located in East Java, Indonesia. It is the highest volcano on the island, frequently producing ash plumes and pyroclastic flows. Hazards include ashfall, lava flows, pyroclastic flows, and lahars which can impact communities such as Lumajang and Malang located within 35 km (22 miles) of the edifice.