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

Volcanic ash from Semeru in Indonesia was observed at 4 300 m (14 100 feet) above sea level at 21:40 UTC on October 22, 2025. The advisory was issued by the Darwin VAAC at 22:00 UTC on the same day.

Ash was reported up to flight level 140, which corresponds to approximately 4 300 m (14 100 feet). The ash was moving southwest at a speed of 9 km/h (6 mph). According to the advisory, the ash cloud was not identifiable in satellite imagery due to meteorological clouds, but ground reports and model guidance confirmed intermittent discrete eruptions ongoing. The current Aviation Color Code is Orange.

According to the Smithsonian / USGS Weekly Volcanic Activity Report for September 24–30, 2025, Semeru experienced 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, with warnings to avoid areas within 3 km of the summit, 8 km to the southeast, 500 m from the banks of the Kobokan drainage as far as 13 km, and other drainages due to lahar, avalanche, and pyroclastic flow hazards.

Semeru is a stratovolcano and the highest volcano on Java, Indonesia. Known hazards include ashfall, pyroclastic flows, lava flows, and lahars. The nearest population center is the town of Lumajang, located about 30 km (19 miles) southeast, and other smaller settlements are situated around its flanks, making ongoing vigilance and hazard awareness important for the surrounding communities.