Geology Agency: Bandung booms came from acoustic waves produced by Anak Krakatau

The mysterious booms that startled residents across Greater Bandung have been traced by Indonesia’s Geology Agency to acoustic waves from Anak Krakatau’s eruption in the Sunda Strait.

Geology Agency chief Lana Saria said the timing of the eruption matched wave data recorded at monitoring stations in West Java. Reports from Sept. 4-5 described booming sounds and vibrations affecting windows and doors in several parts of the province.

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The match between the timing of the volcanic eruption and the signals at monitoring stations in West Java strongly supports that this phenomenon came from acoustic waves produced by the eruption.

Saria said the phenomenon involved low-frequency sound waves, or infrasound, that can travel long distances under particular atmospheric conditions. They may be felt as booms or vibrations, she said, but the agency confirmed that the air-borne waves posed no danger to building structures.

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These low-frequency acoustic waves can travel far under certain atmospheric conditions and are felt as booms or vibrations.

She added that similar long-distance sounds have been recorded during other volcanic eruptions in Indonesia, including Mount Kelud, whose eruption was heard as far away as Central Java, and Mount Lewotobi Laki-Laki, whose activity was heard in Maumere and on Alor Island.

The explanation conflicts with an assessment from the Bandung office of the Meteorology, Climatology and Geophysical Agency. Its chief, Suaidi Ahadi, said the distance made it unlikely that residents of Bandung City had heard the Krakatau eruption. He said the booms could instead have resulted from earthquake swarms, activity in karst areas or collapses, noting that similar sounds had been heard in Cianjur, including during the 2025 earthquake.

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But in Bandung City, in my view, it is too far to hear activity from the Krakatau eruption that occurred as it did yesterday.