November 19, 2025 | 06:02 pm
TEMPO.CO, Jakarta - A pyroclastic flow descended from the summit of Mount Semeru in Lumajang, East Java, on Wednesday afternoon, November 19, 2025, ahead of a later eruption. As of publication, the hot avalanche of volcanic material had traveled up to 8 kilometers from the crater.
According to information compiled by Tempo, the pyroclastic flow became visible at 02:12 PM local time from Indonesia’s tallest volcano, which stands 3,676 meters above sea level.
Initial seismic readings showed the flow reaching about 4.5 kilometers from the summit with a maximum amplitude of 25 mm. Within less than 30 minutes, it advanced to 5 kilometers.
By 03:25 PM, officials monitoring the volcano reported the flow reaching 5.5 kilometers, with its seismic amplitude increasing from 35 mm to 38 mm, and later recorded at 40 mm.
Lumajang’s Acting Disaster Management Agency Chief, Isnugroho, confirmed the activity. “Yes, there is a pyroclastic flow,” he told Tempo.
Nearly two hours after the first appearance of the flow, Mount Semeru erupted, sending an ash column rising 2,000 meters above the crater. Mukdas Sofian, an officer at the Semeru Volcano Observatory, said the 04:00 PM ash plume was thick and gray, drifting toward the north and northwest.
“The eruption is still ongoing as this report is being made,” he noted in an official update.
Lahar flood of Mount Semeru overflowing from Regoyo River in Gondoruso Village, Pasirian District, Lumajang, East Java, November 5, 2025. Antara/Irfan Sumanjaya
Despite the escalation in activity, authorities have not raised the volcano’s alert level. Mount Semeru remains at Level II (Alert), the second tier on Indonesia’s four-level scale.
At this level, the Center for Volcanology and Geological Hazard Mitigation (PVMBG) urges residents and visitors to avoid the southeast sector along the Besuk Kobokan channel for up to 8 kilometers from the crater.
Outside the main danger zone, people are also advised to stay at least 500 meters away from the edges of Besuk Kobokan due to the possibility of pyroclastic flow expansion. Authorities warn of potential lahar, volcanic mudflow, traveling as far as 13 kilometers from the summit.
“The public is urged to remain cautious of possible pyroclastic flows, lava flows, and lahar along rivers and valleys that originate from the summit of Mount Semeru,” Mukdas said. Areas of concern include the riverbanks of Besuk Bang, Besuk Kembar, and Besuk Sat.
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