Volcanic ash from Semeru volcano detected 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 15:40 UTC on October 9, 2025. The advisory was issued by the Darwin VAAC at 16:00 UTC on the same day.

According to the advisory, ground reports confirmed intermittent eruptions with volcanic ash identified up to flight level 140 (approximately 4 300 m or 14 100 feet). The ash cloud was moving southwest at a speed of 9 km/h (5.6 mph). Ash was not identifiable in recent satellite imagery due to meteorological cloud cover, but ash height and movement were determined from ground observations and model guidance. The current Aviation Color Code is Orange.

The Smithsonian / USGS Weekly Volcanic Activity Report for September 24–30, 2025, noted that daily eruptive events were recorded at Semeru, producing 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 and 8 km from the summit to the southeast, with additional restrictions for drainages due to lahar and pyroclastic flow hazards.

Semeru is a large stratovolcano located in East Java, Indonesia. It is the highest mountain on Java and is known for frequent explosive eruptions, pyroclastic flows, lava domes, and lahars. The volcano poses risks to nearby populations, including the town of Lumajang, approximately 20 km (12 miles) to the southeast. Hazards include ashfall, lava flows, pyroclastic flows, and lahars, especially along river valleys leading from the volcano.