Saturday and Sunday Eruptions

Mount Semeru on the border of Lumajang and Malang regencies in East Java erupted again on Sunday (18/10/2026) at 00.39 WIB. When the activity report was published, the eruption was still ongoing, while the eruption column height could not be visually observed. Instrumental monitoring continued to record seismic events as part of volcanic activity surveillance.

Seismograph observations over a six-hour window recorded 29 eruption quakes, three rockfall quakes, and three emission quakes, with amplitudes of 12–25 millimeters and durations of 0.6–160 seconds. The data shows eruptive activity continued throughout the monitoring period.

On Saturday (17/10/2026), Semeru had already erupted three times in succession. The first eruption occurred at 04.52 WIB with an ash column about 700 meters above the summit, followed by a second eruption at 06.35 WIB reaching about 800 meters, and a third at 10.42 WIB that hurled ash up to 1,000 meters above the summit, according to Semeru observation post officer Agastya Rajendra.

Alert Status, Hazard Zones Reinforced

Indonesia's Center for Volcanology and Geological Disaster Mitigation (PVMBG) maintains Semeru's volcanic activity at Level III, or Alert. Residents are prohibited from any activity within a 5-kilometer radius of the crater or summit due to the danger of flying hot rocks.

In the southeastern sector, residents are barred from activity along the Besuk Kobokan stream up to 13 kilometers from the summit. Beyond that distance, activity is prohibited within 500 meters of riverbanks due to the potential spread of pyroclastic flows and lava up to 17 kilometers from the summit.

PVMBG also urged residents to remain alert to potential pyroclastic flows, lava falls, and lahar along rivers originating from Semeru's summit, especially Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat.