The Highest Mountain in Java Erupts Again, Hiking Routes Temporarily Closed

The highest mountain in Java, Mount Semeru erupted again on Wednesday (November 19, 2025), sending a massive column of ash into the sky and unleashing powerful pyroclastic flows that traveled between 15 and 16 kilometers from the summit. Authorities immediately shut down all hiking routes and warned climbers across the region to stay away from the mountain as volcanic activity remains dangerously high.

The Indonesian Center for Volcanology and Geological Hazard Mitigation (PVMBG) reported that today’s eruption was one of the strongest of the year. Seismographs recorded a maximum amplitude of 40 millimeters with nearly 17 minutes of sustained tremor, a signal typically associated with high-energy eruptions. The ash plume rose approximately 2,000 meters above the crater, indicating the release of significant volcanic material.

“Today’s pyroclastic density currents reached up to seven kilometers, and they could extend even further. We urge all climbers and local residents to maintain at least an 20 kilometer distance from the southeast sector of Semeru,” said Mukdas Sofian, an official at the Semeru Volcano Observation Post. He emphasized that pyroclastic flows—dense clouds of superheated gas and debris—are unpredictable and move too fast for anyone to outrun.

Potential Lahars in The River

Authorities also warned of secondary hazards. Heavy rainfall over the past several days has increased the likelihood of lahars, or volcanic mudflows, along rivers that originate from Semeru’s summit, including the Kobokan and Bang rivers. These flows can occur suddenly and pose extreme danger, particularly to climbers who may attempt to navigate unofficial or unmonitored trails.

“Climbing is strictly prohibited. Pyroclastic flows can accelerate to lethal speeds in seconds. This is not a situation in which risks can be justified, even by experienced mountaineers,” Sofian added. The upper sections of the official route—Kalimati, Arcopodo, and the summit ridge of Mahameru—fall directly within the danger zone, which is also exposed to ballistic ejecta such as falling rocks and incandescent debris.

Climbing The Highest Mountain in Java Rescheduled

The Bromo Tengger Semeru National Park Authority (BBTNBTS) has confirmed that all hiking permits (SIMAKSI) issued for this week will be eligible for rescheduling at no additional cost. Climbers who have already arrived in the village of Ranupani, Semeru’s main trailhead, are being instructed to return to safe areas. Officials also strongly discouraged hikers from attempting to access the mountain through informal community paths, noting that such routes are not included in the official monitoring and evacuation system.

While today’s eruption is not yet classified among the most catastrophic in Semeru’s recent history, volcanologists note that the combination of high seismic energy, long-duration tremor, and far-reaching pyroclastic flows suggests a moderate-to-major eruptive pulse. Semeru’s activity patterns in 2025 indicate a sustained phase of unrest, with the potential for continued eruptions over the coming days or weeks.

For the global mountaineering community, the situation serves as an important reminder of Semeru’s unpredictable behavior. The volcano has a long history of sudden explosive events, including deadly eruptions in 2021 and 2022 that affected nearby villages and climbing routes. Even highly experienced climbers are urged to avoid the area until PVMBG lowers the alert level and confirms that the mountain has returned to stable conditions.

International travelers and expedition planners monitoring Indonesian volcanoes are advised to follow updates from PVMBG, the Indonesian Geological Agency, the National Park Authority, and the official Volcano Observation Post in Gunung Sawur. These channels provide real-time information on seismic activity, ash emissions, and evacuation protocols.

As Indonesia is home to more than 120 active volcanoes, authorities remind all hikers visiting the country to check the status of each volcano before planning any ascent. Several other mountains in East and Central Java have shown increased volcanic activity since October, making situational awareness essential for safe expedition planning. (Wage Erlangga)