RRI.CO.ID, Lumajang - Mount Semeru in Lumajang and Malang Regency, East Java, the highest peak on Java Island standing at 3,676 meters above sea level (mdpl), experienced a significant eruption on Monday morning, May 4, 2026. The eruption was accompanied by hot cloud avalanches (APG) that reached approximately 2 kilometers from the summit.

An officer at the Mount Semeru Observation Post, Sigit Rian Alfian, reported that the main eruption occurred at 07.44 local time. "An eruption of Mount Semeru has occurred... with an observed volcanic ash column height of approximately 1,200 meters above the peak," Sigit said in a written report, as quoted by Antara.

The eruption produced a prominent ash column observed in white to gray hues with thick intensity, which drifted steadily toward the southwest.

According to seismic data, the volcanic event was recorded with a maximum amplitude of 12 mm and lasted for approximately 3 minutes and 10 seconds. Regarding the trajectory of the eruption, the hot cloud avalanches moved toward the southeast, specifically targeting the Besuk Kobokan area.

Volcanology and Geological Mitigation Center (PVMBG) has established several safety mandates to protect the public, starting with a strict prohibition of activities in the southeastern sector along Besuk Kobokan up to 13 km from the summit.

Additionally, a 500-meter buffer zone must be maintained from the riverbanks of Besuk Kobokan to safeguard against the potential expansion of hot clouds and lava flows, which could extend up to 17 km from the peak. There is a total ban on all activities within a 5 km summit radius of the crater due to the high risk of being struck by ejected incandescent rocks.

Residents are urged to remain vigilant regarding potential secondary hazards, including lava flows and lahars (volcanic mudflows) along river valleys originating from the summit. Key areas under watch include Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat, as well as smaller tributaries. ***