Alert! Mount Slamet's Activity Increases, Geological Agency Issues Statement
Jakarta, CNBC Indonesia - The Geological Agency of the Ministry of Energy and Mineral Resources (ESDM) has reported an increase in volcanic activity at Mount Slamet as of 29 March 2026. Nevertheless, the status of this highest volcano in Central Java remains at Level II or Wary.
Mount Slamet is a stratovolcano with an elevation of approximately 3,432 metres above sea level. The mountain is located in five regencies: Pemalang, Banyumas, Brebes, Tegal, and Purbalingga.
According to records from the Geological Agency, the last eruption of Mount Slamet occurred between March and September 2014, consisting of ash eruptions accompanied by lava ejections. Then, between September and October 2023, there was an increase in seismic activity followed by a rise in tremor amplitude.
The continuous increase in tremors, accompanied by the emergence of long-duration harmonic tremors, indicates a renewed increase in volcanic activity at Mount Slamet. This condition is related to the heating of fluids and ejection activity occurring at shallow depths.
“In connection with the aforementioned conditions, effective from 19 October 2023, the activity status of Mount Slamet has been set at Level II (Wary),” the Geological Agency stated, quoted on Monday (30/3/2026).
Subsequently, in May 2024, an increase in Deep Volcanic Earthquakes was recorded, indicating magma supply towards the surface, followed by an increase in shallow earthquakes and continuous tremors until the end of 2024.
To date, the seismic activity of Mount Slamet remains fluctuating, dominated by low-frequency earthquakes and continuous tremors, without accompanying eruptions or significant visual changes.
Seismic data for the period 16-28 March 2026 recorded 541 Blast Earthquakes, 421 Low Frequency Earthquakes, 1 Deep Volcanic Earthquake, 7 Distant Tectonic Earthquakes, Continuous Tremor with 1 mm amplitude, predominantly 0.5 mm.
Low-frequency earthquakes at Mount Slamet were recorded in a fluctuating manner. Since 22 March 2026, this activity has shown an increase, with recordings becoming more pronounced and continuous since 27 March 2026 until now.
These low-frequency earthquakes are recorded regularly with relatively uniform amplitude and duration, associated with an increase in magmatic gas activity.
From deformation monitoring, distance measurements using EDM show a simultaneous elongation pattern (deflation), indicating that magma has passed the reflector and is likely at a shallow/higher position from the station location. Tiltmeter inclination monitoring shows a decrease (deflation) on the radial axis of St. Cilik and an increase (inflation) at St. Bambangan, indicating magma migration from depth (around St. Cilik) to shallower depths (towards St. Bambangan).
The results of observation and analysis of monitoring data still show an increase in pressure beneath the body of Mount Slamet, which triggers shallow earthquakes, increasing the likelihood of an eruption.
As of 29 March 2026, the activity level of Mount Slamet remains at Level II (Wary), with recommendations for the public and visitors/tourists not to be or engage in activities within a 2 km radius of the summit crater of Mount Slamet.
Intensive observations continue to anticipate further developments. For further information, contact the Center for Volcanology and Geological Hazard Mitigation, Geological Agency at (022) 7272606 in Bandung (West Java Province) or the Mount Slamet Volcano Observation Post in Gambuhan Village, Gajah Nguling, Pulosari Subdistrict, Pemalang Regency, Central Java at tel. 0823-2913-0149.
The activity level of Mount Slamet will be reviewed promptly if there are significant visual changes or seismic events.