It’s hard not to feel a knot in your stomach when a mountain as massive as Semeru starts acting up again. The recent activity has grown intense, and the scale of the latest eruption has pushed many people to rethink how safe the surrounding areas really are. Travelers and hikers are being warned to stay far from the river channels around the volcano, because the 2025 eruption has spread farther than the ones in previous years.
Observers at the Semeru Monitoring Post recorded a flurry of activity on Friday morning, from 06.00 to 12.00. There were 36 eruptions in just that six-hour window. The ash column rose about 200 meters, drifting to the southeast with a mix of white and gray smoke. The mountain didn’t stop there. It also sent down four lava avalanches and released four bursts of hot clouds. Semeru remains at level 4, or the highest alert.
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When officials reviewed aerial footage of the event that happened on Wednesday, November 19, they realized the hot cloud avalanche spread much farther than the earliest estimates suggested. That eruption traveled thirteen kilometers. The hot clouds moved toward the Besuk Kobokan area on the southern side of the volcano.
The situation troubled local officials. According to Lumajang’s Regional Secretary, Agus Triyono, the eruption on Wednesday expanded beyond the paths carved by the 2020, 2021, and 2023 eruptions.
“The eruption that occurred last Wednesday headed south outside the previous eruption path,” he said on Friday. He explained that leftover volcanic deposits from past years may have contributed to the wider spread. “It could be that the remains of the 2020-2021 and 2023 eruptions have not been collected, creating a new path.”
Lumajang Regency has now declared an emergency response status for the Semeru eruption, effective until November 26. Authorities are urging residents not to carry out any activities within a 20-kilometer radius of the summit. People are also being reminded to stay alert for hot cloud avalanches and possible lahar flows along the rivers that originate on Semeru.
The warnings extend to visitors too. Officials want to make sure travelers don’t end up in dangerous situations, such as being caught in a lahar flood after heavy rainfall. With Indonesia now entering a period of extreme weather that may last until the end of the year, the risk grows even higher.
