Mount Semeru: Dozens of Eruption Tremors Recorded

Mount Semeru, the highest volcano on Java Island, erupted multiple times on Thursday morning, September 10, 2026. The tremors were recorded by seismographs at the Mount Semeru observation post on Mount Sawur in Lumajang, East Java. However, the eruption was not visible due to thick fog surrounding the volcano, which was also cloudy with rain. Yadi Yuliandi, who was observing the volcano, noted that the fog prevented the smoke from the crater from being seen.

Seismic observations revealed that 29 eruption earthquakes were recorded between early morning and around 12 p.m. local time. These earthquakes had magnitudes ranging from 10 to 22 mm and lasted between 73 to 162 seconds. Additionally, 11 avalanche earthquakes and two gusts were also recorded during this period. At around 12 p.m., another 29 eruption earthquakes were detected, with similar magnitudes and durations.

Yadi Yuliandi warned that the ongoing rainy and cloudy weather might cause rain-induced lava flows to enter river basins on the slopes and below Mount Semeru. Head of the Regional Disaster Management Agency (BPBD) of Lumajang Regency, Isnugroho, cautioned that heavy rain has not occurred yet, but there is a potential risk of such flows.

The Center for Volcanology and Geological Hazard Mitigation (PVMBG) advised the public to stay away from the southeastern sector along the Kobokan River, which is 13 kilometers away from the summit. PVMBG also suggested avoiding activities within a 500-meter radius of the riverbank along the Kobokan River and up to 17 kilometers from the summit due to the risk of expanding pyroclastic and lava flows.

Furthermore, the public is advised to stay clear of a five-kilometer radius around the Mount Semeru crater due to the risk of incandescent rocks. Mount Semeru's volcanic activity status remained at alert level III.