October 21, 2025 | 08:51 am
TEMPO.CO, Jakarta - Mount Semeru in Indonesia experienced consecutive eruptions this Tuesday morning, October 21, 2025. Within a span of approximately 30 minutes, three eruptions occurred. According to information from the Mount Api Observation Post (PGA) Semeru in Lumajang, East Java, eruptions occurred this morning at 05:21 AM, 05:32 AM, and 05:53 AM.
The observed height of the eruption column ranged from 600 to 700 meters above the summit. The ash column was observed as white to gray with moderate intensity, slanting towards the south. The eruption was recorded on a seismogram with a maximum amplitude of 22 mm and a temporary duration of 2 minutes and 2 seconds.
Liswanto, an officer at the PGA Semeru Post located in Mount Sawur, Sumber Wuluh Village, Senduro District, Lumajang Regency, reported that the eruption was still ongoing. However, Liswanto mentioned that the highest volcanic activity level of this volcano on Java Island remains at level II (Caution). "The status remains at level II," Liswanto stated in the report.
Meanwhile, based on seismic observations in the last 24 hours until early Tuesday morning, the PGA Semeru recorded 55 eruption earthquakes with amplitudes of 10-23 mm and durations of 64-154 seconds. There were 40 rockfall earthquakes with amplitudes of 2-10 mm and durations of 30-110 seconds.
There were also 15 blast earthquakes recorded with amplitudes of 2-7 mm and durations of 43-97 seconds. Additionally, 7 harmonic earthquakes with amplitudes of 3-6 mm and durations of 93-960 seconds were recorded. Furthermore, 6 distant tectonic earthquakes were recorded with amplitudes of 4-12 mm, S-P 12-104 seconds, and durations of 38-256 seconds.
At this Caution level, the Center for Volcanology and Geological Hazard Mitigation (PVMBG) issued several recommendations, including refraining from any activities in the southeastern sector along the Besuk Kobokan, within a distance of 8 kilometers from the summit (eruption center).
Beyond this distance, people should avoid activities within 500 meters from the edge of the river (river boundary) along Besuk Kobokan, as there is potential for being affected by the expansion of pyroclastic flows and lahars up to a distance of 13 kilometers from the summit. The public and visitors are also advised not to engage in activities within a radius of 2.5 kilometers from the crater or summit of Mount Semeru due to the risk of being hit by flying rocks (pyroclastic).
The PVMBG also urged the public to be cautious of the potential for hot clouds, lava avalanches, and lahars along the rivers or valleys originating from the summit of Mount Semeru. This admonition is particularly directed along Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat, as well as the potential for lahars in small rivers that are tributaries of Besuk Kobokan.
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