November 25, 2025 | 05:24 pm
TEMPO.CO, Jakarta - Heruningtyas, Head of the Volcano Disaster Mitigation Team at Indonesia’s Geological Agency under the Ministry of Energy and Mineral Resources, has highlighted the ongoing risk of secondary eruptions following the recent acivity of Indonesia's Mount Semeru.
Secondary eruptions often occur away from the volcano’s central crater, such as along the Kobokan River, which currently contains deposits of high-temperature pyroclastic material.
“When it rains, it’s like pouring water into a furnace, which could trigger an explosive eruption,” she explained in a phone interview with Tempo on Tuesday, November 25, 2025.
Smoke from these secondary eruptions can be as dense as the primary pyroclastic flows, posing dangers not only to nearby areas but also disrupting visual monitoring efforts by the observation teams.
Pyroclastic flow of Mount Semeru in Sumberwuluh Village, Candipuro, Lumajang, East Java, November 19, 2025. Due to high volcanic activity, the status of the highest mountain on the island of Java was raised from Level III (Alert) to Level IV (Danger) at 5:00 PM WIB. Antara/Irfan Sumanjaya
Mount Semeru’s pyroclastic flow was observed in Lumajang, East Java, on November 19, 2025. In response to heightened volcanic activity, authorities raised the volcano’s alert status from Level III (Alert) to Level IV (Danger) at 05:00 PM local time.
The Geological Agency has prohibited residents and visitors from approaching within a 500-meter radius of the Kobokan River for at least 20 kilometers.
Heruningtyas explained that the riverbanks remain particularly vulnerable to pyroclastic flows due to the high temperatures and recent heavy rainfall, which has generated multiple smoke plumes in the area.
Damaged electricity transmission poles due to the eruption of Mount Semeru in Supiturang Village, Pronojiwo District, Lumajang, East Java, November 23, 2025. Antara/Irfan Sumanjaya
Recent observations indicate that while the November 19 eruption was significant, it was less intense than the 2021 eruption, which could be predicted five months in advance.
In contrast, this year’s increase in volcanic activity was detected only three weeks before the eruption.
“The energy of this eruption is much lower than four years ago,” said Heruningtyas. She noted that in 2021, pyroclastic flows reached Galadak Perak and damaged several bridges, whereas this time, the flows did not affect that area.
Images from the eruption show damaged electricity transmission poles in Supiturang Village, Pronojiwo District, Lumajang, East Java, as authorities continue to monitor the volcano and assess risks to surrounding communities.
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