Volcanic ash from Semeru 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 11:10 UTC on October 18, 2025. The advisory was issued by the Darwin VAAC at 11:30 UTC on the same day.

The observed ash cloud extended from the surface to flight level 140 (approximately 4 300 m or 14 100 feet) and was moving west at 28 km/h (17 mph). Satellite imagery did not clearly detect the ash cloud due to meteorological cloud cover; the assessment was based on multiple 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 experienced ongoing activity, with daily eruptive events producing white-and-gray or gray ash plumes rising 400–900 m above the summit and drifting in multiple directions. The volcano remained at Alert Level 2. The public was advised to stay at least 3 km (1.9 miles) from the summit in all directions, 8 km (5 miles) from the summit to the southeast, and to avoid drainages due to lahar and pyroclastic flow hazards.

Semeru is an active stratovolcano located in East Java, Indonesia. Known hazards include volcanic ash fall, lava flows, pyroclastic flows, and lahars, particularly affecting nearby communities such as Lumajang and surrounding villages within 20 km (12 miles) of the volcano. Ongoing monitoring and regional alerts are essential for aviation and local populations due to frequent explosive activity and associated hazards.