Status of Mount Semeru on Alert, Geological Agency: Volcanic Activity Still High

JAKARTA - Acting Head of the Geological Agency Lana Saria said the volcanic activity of Mount Semeru, which is at Level III or Alert, is still high.

"This is marked by the repeated occurrence of falling hot clouds, especially towards the southeast sector with a glide distance of 5,000 meters from the peak towards Besuk Kobokan," Lana said in a written statement received in Lumajang, Thursday, quoted by Antara.

Based on visual and instrumental monitoring results, he continued, on Wednesday, January 14, two hot cloud events were observed with a glide distance of about 5,000 meters from the peak to the southeast.

"In addition, during the period of 7-14 January 2026, hot cloud discharge was also observed several times with similar glide distances, accompanied by material discharge activity," he said.

According to him, the seismic activity of Mount Semeru is dominated by eruption earthquakes, subsidence earthquakes, eruption earthquakes and harmonic tremors.

"The recorded earthquakes indicate that there is still a supply from below the surface of Mount Semeru along with the release of material to the surface through eruptions and gusts," he said.

"The parameter of seismic velocity variation (dv/v) fluctuates with a large value of strain," he said, indicating that the volcanic system is in a relaxation phase and is not experiencing pressurization, but is still very vulnerable to increased pressure.

He explained that monitoring deformation showed a relatively stable pattern, interpreted that there was no increase in pressure inside the body of Mount Semeru.

"Based on the results of analysis and evaluation, the level of activity of Mount Semeru remains at Level III (Alert) with the main recommendation that the public, visitors, and climbers are prohibited from carrying out activities within a radius of five kilometers from the Jonggring Seloko Crater," he said.

He appealed to the public not to enter the southeast sector as far as 13 kilometers from the peak in the southeast direction, which can extend up to 17 kilometers along the Besuk Kobokan stream.

The public is also asked to be aware of the potential for hot clouds, lava discharge, and lahar along the river/valley flows upstream of the summit of Mount Semeru, especially along Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat, as well as the potential for lahar in small rivers which are tributaries of Besuk Kobokan.

Based on monitoring by the Semeru Mountain Observation Post officers on Thursday at 06.00-12.00 WIB, it was recorded that the activity of Mount Semeru was still dominated by 35 times of eruption/erupting earthquakes, one subsidence earthquake, one eruption earthquake, and one volcanic earthquake.