Inp.polri.go.id - Lumajang. A volcanic tremor from volcanic mudflow activity on Mount Semeru lasted more than five hours Friday night, following intense rainfall at the summit, authorities reported Saturday.

“One lahar tremor was recorded with an amplitude of 20 mm and a duration of 19,800 seconds, or approximately 5.5 hours,” said Mukdas Sofian, the Semeru Volcano Monitoring Post officer, on Saturday (28/6/2025), as quoted by antaranews.com.

Throughout Friday, 36 eruption tremors and multiple emissions, harmonic, and tectonic quakes were also detected. Mount Semeru remains on Alert Level II. 

The Geological Agency has advised against any activity within 8 km of the southeast sector along Besuk Kobokan and urges a 500-meter buffer from riverbanks due to potential pyroclastic flows and lahars.

Communities are also warned against entering a 3-km radius of the summit due to rockfall hazards and should stay alert for lava avalanches and lahars in rivers stemming from the peak.

(mg/inp/pr/rs)