November 20, 2025 | 06:14 am
TEMPO.CO, Jakarta - The Geological Agency has set the volcanic activity status of Mount Semeru in Lumajang, East Java, to level IV or Warning since Wednesday afternoon, November 19, 2025, at 5:00 PM local time. An hour earlier, the highest volcano activity level on the island of Java had begun to be raised from level II of Alert to level III or Watchful.
In the span of about an hour, the volcano, which stands 3,676 meters above sea level, rose two levels, from Level II to Level III to Level IV. Tempo summarizes the chronology of Mount Semeru's eruption, which spewed a giant hot cloud (pyroclastic flow), from its beginning and its end based on information from several sources in the field, reports from the Semeru Volcano Observation Post (PGA) in Lumajang, and information from the Geological Agency.
The pyroclastic flow was first reported to have occurred at 2:12 PM local time. At that time, the sliding distance had reached about 4.5 kilometers from the peak with a maximum amplitude of the earthquake vibration it produced measuring 25 mm. Less than half an hour later, around 2:35 PM, the sliding distance of the pyroclastic flow had reached 5 kilometers. Around 3:25 PM, the pyroclastic flow was reported to still be ongoing with the sliding distance increasing to 5.5 kilometers. The maximum amplitude rose to 38 mm.
At 4:00 PM, the Semeru Volcano Observation Post located in Mount Sawur, Sumberwuluh Village, Candipuro District, Lumajang Regency, reported that Mount Semeru had erupted with a eruption column height of approximately 2,000 meters above the peak. The ash column observed at that time was gray in color with a thick intensity towards the north and northwest.
Shortly thereafter, the Geological Agency immediately raised the status from Alert to Watchful. Information from the field stated that the pyroclastic flow continued to roll along with the volcanic material avalanche. The maximum amplitude of the pyroclastic flow earthquake was recorded to have reached 40 mm.
It was also reported that the sliding distance had reached up to 6.5 kilometers from the peak. Up to an hour later, the sliding distance of the pyroclastic flow had increased further to reach 10 kilometers. At approximately 5 PM, the Geological Agency announced the increase in Mount Semeru's activity level from Watchful to Warning.
Shortly thereafter, information from the field stated that the pyroclastic flow had reached the Besuk Kobokan Bridge (Gladak Perak) in Sumberwuluh Village, which had collapsed following the eruption at the end of 2021. Not more than two hours after Mount Semeru's status was raised to Warning, the Sawur Volcano Observation Post reported that the pyroclastic flow earthquake had ended at 6:11 PM.
The pyroclastic flow occurred approximately 4 hours after it was first reported to have occurred at 2:13 PM local time. The pyroclastic flow accompanying the volcanic material avalanche ended at KM 13 from the peak of Mahameru. "The pyroclastic flow that occurred was a sequential pyroclastic flow, not a singular event," said the Head of the Geological Agency, Muhammad Wafid, in an official statement.
Wafid stated that Mount Semeru's activity showed that eruption and lava avalanche activities are still occurring, but are visually observed infrequently due to weather conditions. During this period, the recorded number of earthquakes indicates that seismic activity on Mount Semeru is still high, especially in the form of eruption, avalanche, and harmonic earthquakes.
At level IV (Warning), the following recommendations are issued:
1. Do not engage in any activities in the southeast sector along Besuk Kobokan, up to 20 km from the peak (eruption center). Beyond this distance, the community should not engage in activities within 500 meters from the river edge (river boundary) along Besuk Kobokan, as there is potential for the spread of pyroclastic flow and lahar flow.
2. Do not engage in activities within a radius of 8 km from the crater/summit of Mount Semeru due to the risk of rock projectiles (piroclasts).
3. Be aware of the potential for pyroclastic flows, lava avalanches, and lava along the river/valley originating from the peak of Mount Semeru, especially along Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat, as well as the potential for lahars in small rivers that are tributaries of Besuk Kobokan.
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