Semeru on High Alert After 45 Eruptive Quakes, Residents Urged to Stay Clear

Lumajang: Mount Semeru, which straddles the Lumajang and Malang Regencies in East Java, recorded a surge in volcanic activity early Friday, November 21, 2025. Over a six-hour span—from midnight until 6:00 a.m. WIB—monitoring instruments detected 45 eruption-related earthquakes.

“Between 00:00 and 06:00, our seismic equipment registered 45 eruption quakes with amplitudes ranging from 10 to 22 millimeters, lasting between 58 and 184 seconds,” said Rudra Wibowo, an officer at the Mount Semeru Observation Post, as reported by Antara.

In addition to the eruptive tremors, six avalanche quakes were detected, along with eight gust quakes and five distant tectonic quakes. The amplitudes ranged between 2 and 8 millimeters, with varying durations and S–P intervals.

Rudra added that visual observations showed intermittent fog covering the peak, with no crater smoke visible. Weather conditions during the monitoring period were cloudy to rainy with light winds blowing from the southeast.

Semeru remains at Alert Level IV (Warning) — the highest status. In response, the Center for Volcanology and Geological Hazard Mitigation (PVMBG) has imposed expanded exclusion zones. Residents are strictly prohibited from any activities within 20 kilometers of the southeastern sector along Besuk Kobokan, the primary channel for pyroclastic flows.

Outside the 20-kilometer radius, the public is also advised to avoid areas within 500 meters of riverbanks along Besuk Kobokan due to the potential expansion of hot clouds and lava flow paths. Activities within an 8-kilometer radius of the crater are also banned due to the threat of incandescent rock ejections.

Authorities further warn communities to remain alert for pyroclastic surges, lava flows, and potential lahars along rivers and valleys originating from the summit — especially Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat.