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 09:40 UTC on October 21, 2025. The advisory was issued by the Darwin VAAC at 10:00 UTC.

According to the VAAC advisory, ash was observed at the surface up to flight level 140, which is approximately 4 300 m (14 100 feet). Ash movement was reported toward the west at approximately 19 km/h (12 mph). The Aviation Color Code is currently Orange. Due to meteorological cloud cover, volcanic ash could not be identified on satellite imagery. Ground reports as of 22:56 UTC on October 20, 2025, estimated ash up to flight level 130 (about 4 000 m or 13 100 feet), and intermittent eruptions were noted to be ongoing. Ash height and forecast were derived from ground reports and model guidance.

According to the Smithsonian / USGS Weekly Volcanic Activity Report for September 24-30, 2025, activity at Semeru continued with daily eruptive events detected by the seismic network. Daily white-and-gray or gray ash plumes rose 400–900 m above the summit and drifted in multiple directions. The public was advised to remain at least 3 km away from the summit in all directions, with extended distances in certain sectors due to lahar, avalanche, and pyroclastic flow hazards.

Semeru is a large stratovolcano located in East Java, Indonesia, and is the highest volcano on the island. It poses significant hazards including ashfall, pyroclastic flows, lava flows, and lahars. Populations in nearby settlements such as Lumajang and surrounding villages are at potential risk, especially within a 10–13 km (6–8 miles) radius from the summit in certain directions during periods of heightened activity.