January 12, 2026 | 07:23 am
TEMPO.CO, Jakarta - Mount Slamet in Central Java, Indonesia, is reported to be experiencing an increase in activity through an increase in volcanic earthquakes associated with an increase in magmatic gas. However, the level of volcanic activity has not been declared to have changed and remains at level II or Alert.
"Residents and visitors or tourists are advised not to be within and around a 2-kilometer radius from the crater," said Acting Head of the Geological Agency, Lana Satrianya, through a written statement on Sunday, January 11, 2026.
Based on seismic data from January 1-11, 2026, until 6 AM, there were recorded 321 volcanic earthquakes, 993 low-frequency earthquakes, and one distant tectonic earthquake. According to Lana, the increase in volcanic earthquakes has been recorded since Saturday, January 10, 2026, at 21:37.
The volcanic earthquakes from the 3,432-meter-high mountain above sea level have been regularly recorded with relatively uniform amplitude and duration. "The results of observation and data analysis still indicate an increase in pressure beneath Mount Slamet, triggering shallow earthquakes and increasing the likelihood of eruption," Lana said.
Meanwhile, deformation monitoring shows relatively stable conditions. Mount Slamet is a conical stratovolcano. Administratively, the mountain is located in the regencies of Pemalang, Banyumas, Brebes, Tegal, and Purbalingga, in the province of Central Java.
The last eruption of Mount Slamet occurred during the period of March-September 2014, characterized by ash eruptions accompanied by lava bursts. In September-October 2023, there was a previous increase in seismic activity followed by an increase in tremor amplitude.
"The sustained increase in tremors and the appearance of long-duration harmonic tremors mark the resurgence of volcanic activity at Mount Slamet, which is related to the heating of fluids and shallow-depth gaseous activity," the statement read.
Since then, as of October 19, 2023, the Geological Agency has designated Mount Slamet's activity status at level II or Alert. Around May 2024, an increase in volcanic earthquakes was recorded, indicating magma supply towards the surface, followed by increased shallow earthquakes and continuous tremors until the end of 2024.
"Up to this point, seismic activity at Mount Slamet is still fluctuating, dominated by low-frequency earthquakes and continuous tremors without eruption or significant visual changes," Lana said.
Read: Geological Agency: Indonesia Saw 41 Destructive Earthquakes in 2025
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