Mount Semeru Cold Lava Flood Sparks High Alert

RRI.CO.ID, Lumajang - A persistent torrential downpour over Mount Semeru in Lumajang Regency, East Java, triggered a massive cold lava flood lasting nearly four hours on February 26, 2026. This put disaster officials on high alert despite reports that the flow remained contained within river channels.

The seismic activity at Java's highest peak underscores the volatile nature of the volcano, which currently sits at Activity Level III or Alert. Consequently, authorities have intensified warnings for residents living along high-risk river corridors.

According to a written report from the Semeru Observation Post, the flooding was part of a broader surge in volcanic activity recorded during the early morning hours.

“During the observation period this Thursday from 12 a.m. to 6 a.m. Jakarta time, one flood vibration was recorded with an amplitude of 17 mm, lasting 13,304 seconds or 3 hours and 42 minutes," said observation officer, Sigit Rian Alfian, as quoted by Antara.

Beyond the flood tremors, the station logged 17 eruption earthquakes with amplitudes between 11-22 mm, alongside three landslide-induced quakes and one gust-related seismic event. Visual monitoring remained hampered by heavy fog and thick clouds, preventing clear observation of crater smoke.

The Center for Volcanology and Geological Hazard Mitigation (PVMBG) has maintained strict exclusion zones to prevent casualties from unpredictable volcanic surges. Officials have reiterated that no activities are permitted within the southeastern sector along Besuk Kobokan, extending 13 kilometers from the summit.

Additionally, a 500-meter buffer zone from riverbanks along the same route is mandatory due to the risk of expanding hot clouds and lahar flows that could reach up to 17 kilometers.

"People are also prohibited from conducting activities within a 5-kilometer radius of the crater or summit because it is prone to the danger of incandescent rock ejections," added Sigit.

While the sheer duration of the flood vibration caused concern, local disaster management authorities report that the immediate impact on residential areas has been minimal.

The Chief Executive of the Lumajang Disaster Management Agency (BPBD), Isnugroho, confirmed that while the cold lava flood occurred overnight, the situation remains under control.

"River water levels have certainly risen, so we urge the public to be cautious when crossing the Regoyo River, especially residents in Sumberlangsep Hamlet. As of Thursday morning, there has been no impact on community activities; everything is proceeding normally," explained Isnugroho.

Residents are urged to remain vigilant for potential pyroclastic flows, lava avalanches, and lahars along all river valleys originating at the summit, specifically Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat. The BPBD continues to monitor smaller tributaries as well, ensuring that the surge in volcanic material does not breach embankments or jeopardize the safety of nearby settlements. ***