Volcanic ash from Semeru volcano observed at 4 300 m (14 000 feet) a.s.l., Indonesia

Volcanic ash from Semeru in Indonesia was observed at 4 300 m (14 000 feet) above sea level at 05:10 UTC on October 17, 2025. The advisory was issued by the Darwin VAAC at 05:30 UTC.

The ash cloud, reported based on multiple ground observations and model guidance, was moving west at approximately 18.5 km/h (11.5 mph). The current Aviation Color Code is Orange. Ash was not identifiable in current satellite imagery due to meteorological cloud cover, but intermittent discrete eruptions were reported from the ground. The reported and forecast ash altitude remains at 4 300 m (14 000 feet) above sea level in all timeframes up to 18 hours after the observation.

According to the Smithsonian / USGS Weekly Volcanic Activity Report for September 24–30, 2025, daily eruptive events at Semeru were recorded, with white-and-gray or gray ash plumes rising 400–900 m (1 300–2 950 feet) above the summit and drifting in multiple directions. The public was warned to remain at least 3 km (1.9 miles) from the summit in all directions and 8 km (5 miles) from the summit to the southeast due to various volcanic hazards.

Semeru is a stratovolcano and the highest volcano on Java, Indonesia. It is known for frequent explosive activity, including ash plumes, pyroclastic flows, and lava flows. Communities near its flanks include the city of Lumajang and smaller settlements within 10–30 km (6–19 miles), which may be at risk from ashfall, pyroclastic flows, and lahars.