Mount Semeru, on the border of Lumajang and Malang in East Java, erupted again on Saturday morning (December 20, 2025) with an ash column reaching 1,000 meters above the peak. This marks the 11th eruption since early morning, accompanied by intense seismic activity. PVMBG maintains Alert Level III status and urges residents to avoid hazardous areas.
Mount Semeru, Java's highest peak, experienced a significant eruption on Saturday, December 20, 2025. According to Sigit Rian Alfian, officer at the Mount Semeru Observation Post, the eruption occurred at 07:30 WIB with an ash column height of about 1,000 meters above the summit, or 4,676 meters above sea level (mdpl). The ash column was white to gray with thick intensity drifting east, recorded on seismographs with a maximum amplitude of 18 mm and duration of 130 seconds.
From 00:22 WIB to 07:30 WIB, the volcano recorded 11 eruptions with plume heights varying between 700 and 1,100 meters above the peak. The tallest eruption happened at 05:35 WIB, reaching 1,100 meters with ash drifting northeast. Seismic monitoring from 00:00 to 06:00 WIB showed 50 eruption earthquakes with amplitudes of 13-22 mm and durations of 68-141 seconds, plus 7 avalanche earthquakes with amplitudes of 4-7 mm and durations of 41-76 seconds.
Visually, the mountain was clearly visible under clear weather with light winds from the north and northeast, though no crater smoke was observed. Semeru's status remains at Level III or alert, as explained by Sigit. PVMBG recommends no activities in the southeastern sector along Besuk Kobokan up to 13 km from the summit. Beyond that radius, residents should stay 500 meters from the riverbanks of Besuk Kobokan due to potential hot ash clouds and lahars extending up to 17 km.
Additionally, activities are prohibited within a 5 km radius of the crater due to risks of projectile rocks. The public is advised to be wary of hot ash avalanches (APG), lava flows, and lahars in rivers such as Besuk Kobokan, Besuk Bang, Besuk Kembar, Besuk Sat, and their tributaries. The eruption was ongoing at the time of reporting, underscoring the need for continued vigilance.
