Volcanic ash up to 4.6 km (15 000 feet) a.s.l. at Semeru volcano, Indonesia

An eruption at Semeru volcano in Indonesia produced volcanic ash reaching up to 4.6 km (15 000 feet) above sea level as observed at 21:50 UTC on August 6, 2025. According to the Darwin VAAC, the ash cloud was moving toward the northwest at 5 knots at this time.

The eruption was monitored using Himawari-9 satellite imagery and ground reports, though ash was not currently visible in satellite images due to meteorological cloud cover. The reported ash height was based on model guidance and observational data. The current Aviation Color Code is Orange. Forecasts indicate possible ash persistence at the same altitude and movement for the next 18 hours. No ash cloud was detected in satellite imagery at the time of the report.

According to the latest Smithsonian / USGS Weekly Volcanic Activity Report, eruptive activity at Semeru continued during July 30–August 5, 2025, with daily eruptive events producing plumes rising between 400 and 900 m above the summit and drifting to the south and southwest. The alert level remained at 2, and public access restrictions were maintained in zones closest to the summit and certain drainages.

Semeru is a large stratovolcano, the highest volcano on the island of Java. It poses hazards that include ashfall, pyroclastic flows, and lahars. Settlements such as the town of Lumajang are within reach of volcanic hazards, and the southern and southeastern flanks are particularly vulnerable to ashfall and lahars affecting local populations.