Mount Semeru in East Java has once again displayed intense volcanic activity, recording four eruptions on Wednesday (7/1/2026). Based on data from the Mount Semeru Observation Post, the most significant eruption reached a height of one kilometer above the peak, while other eruptions averaged around 800 meters. Currently, the activity status of the highest volcano on the island of Java remains at Level III (Alert).
The Regional Disaster Management Agency (BPBD) of Lumajang Regency has issued a strict warning for residents to stay away from the red zone, particularly along the Besuk Kobokan riverbed and its tributaries up to a 13-kilometer radius. Although no significant impact from volcanic ash fall has been reported so far, local authorities emphasized the importance of residents adhering to the safe distance to minimize the risk of casualties.
UGM Geography lecturer, Dr. Indranova Suhendro, emphasized that the public must be more vigilant against the threat of cold lava floods rather than just eruptions. According to him, the accumulation of volcanic material such as sand and rocks on the mountain slopes is easily swept away by water currents during heavy rain at the summit area. Dangerously, these lava flows can arrive suddenly in downstream residential areas even if it is not raining at all in those locations.
Analysis of Semeru's magma characteristics shows a crystal composition reaching 50 percent, making it quite viscous and often forming a lava dome in the crater. This dome is highly vulnerable to collapse due to magma pressure from below as well as the intensity of rainfall, which then has the potential to trigger pyroclastic flows (locally known as wedhus gembel). This phenomenon requires a high level of vigilance because it is dynamic and difficult to predict.
Amid economic activity dilemmas, Dr. Indranova highlighted the issue of sand mining on the slopes of Semeru. He assessed that although this activity is a livelihood for residents, the safety risks involved are substantial. Therefore, he urged the need for stricter safety operational standards, while stressing that public understanding of volcanic characteristics is key to disaster mitigation when living alongside nature.
