Mount Semeru registers 583 eruptive earthquakes in late May

Mount Semeru in Indonesia has registered a significant surge in seismic activity, with the Geological Agency recording 583 eruptive earthquakes between May 23 and May 31, 2026. Lana Saria, Acting Head of the Geological Agency, highlighted the volcano's high seismic activity during this period. The agency's instrumental observations also logged numerous rockfall, deep volcanic, gas explosion, and tectonic earthquakes, alongside harmonic tremors. Visual monitoring revealed a white-to-gray eruptive column extending up to 1,500 meters above the summit, with white and gray crater smoke rising between 100 and 300 meters. Lava avalanches were observed traveling up to 1,000 meters southeast, and pyroclastic flows extended as far as 2,500 meters in the same direction. Saria clarified that the pyroclastic flows stem from unstable surface material, not active magmatic processes, and that deformation monitoring shows no pressure buildup. Despite the activity, Mount Semeru remains at Alert Level III, or 'Watch'. Residents and visitors are warned of potential pyroclastic flows, lava collapses, and cold lava mudflows, particularly along the Besuk Kobokan riverbed within a 13-kilometer radius of the eruption center. The hazard zone for airborne volcanic debris is within 5 kilometers of the crater.

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And they are not due to active magmatic processes.