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

Volcanic ash from Semeru volcano in Indonesia was observed at 4 300 m (14 100 feet) above sea level at 08:40 UTC on October 15, 2025. The advisory was issued by the Darwin VAAC at 09:00 UTC.

The ash cloud was reported at surface to flight level 140 (approximately 4 300 m or 14 100 feet) and was moving southwest at approximately 19 km/h (12 mph), based on Himawari-8 satellite imagery and model guidance. The current Aviation Color Code is Orange. Ash was not identifiable in satellite imagery due to meteorological clouds, but intermittent discrete eruptions were expected to continue according to the advisory.

According to the Smithsonian / USGS Weekly Volcanic Activity Report for September 24–30, 2025, Semeru’s activity included daily eruptive events recorded by the seismic network. White-and-gray or gray ash plumes frequently rose 400–900 m above the summit and drifted in multiple directions. The Alert Level for Semeru remained at 2, and the public was advised to maintain distances of at least 3 km from the summit in all directions and 8 km to the southeast 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 known for frequent explosive eruptions producing ash plumes, lava flows, and pyroclastic flows. Communities near Semeru at risk include those in the Lumajang region, particularly villages along rivers that drain the volcano. Hazards include ashfall, pyroclastic flows, lava flows, and lahar (volcanic mudflows), with the potential to affect areas up to several kilometers from the summit.