Six-Hour Lahar Flood Tremors Recorded at Mount Semeru in East Java, Levee Breached

The observation post for Mount Semeru in Lumajang Regency, East Java, reported a single lahar (volcanic mudflow) flood tremor lasting 21,600 seconds—approximately six hours—with an amplitude of 65mm, recorded between midnight and 6:00 AM local time on Monday following intense rainfall. Additional seismic activity included one rockfall tremor and 14 eruption-related tremors with amplitudes of 10-25mm.

According to the observation officer, the summit was obscured by fog with no visible smoke, while rain fell with weak winds blowing west and northwest, and temperatures ranged from 19-21°C.

Mount Semeru remains at Alert Level III (Siaga) as designated by Indonesia's Center for Volcanology and Geological Hazard Mitigation (PVMBG). Current restrictions include: no activity within a 5km radius of the summit/crater due to the risk of flying rocks; no activity in the southeastern sector along the Besuk Kobokan river within 13km of the peak; and no activity within 500 meters of riverbanks along Besuk Kobokan, as hot clouds and lahar flows could extend up to 17km from the summit.

Residents are also urged to remain vigilant for hot clouds, lava collapses, and lahar flows along rivers and valleys originating from the summit, including Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat.

Field reports indicate that the six hours of heavy rain around Mount Semeru caused water levels to rise in several river basins, resulting in a levee breach in Purorejo Village, Tempursari District, Lumajang Regency.

Note: This area is located in East Java around Mount Semeru and the popular Bromo Tengger Semeru National Park region. While there is no direct impact on Bali, this is relevant for foreign visitors traveling in or near East Java.