The facts behind the booming sounds that startled Bandung

Mysterious booming sounds unsettled residents across Greater Bandung from Friday night into the early hours of Saturday. The Bandung station of Indonesia's Meteorology, Climatology and Geophysics Agency, or BMKG, investigated the phenomenon by reviewing seismic, lightning, weather and geomagnetic data.

The agency classified the event as a skyquake, a term used for a booming sound whose main cause remains unexplained. BMKG said the data showed no local earthquake activity between 11 p.m. and 5 a.m. in the Lembang Fault, the Cimandiri Fault or other active faults. Weather conditions in Greater Bandung were relatively clear.

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Based on BMKG seismic data, no seismic activity was detected in the area.

Researchers also recorded magnetic anomalies and concentrated thunderstorm activity around Mount Anak Krakatau while a volcanic eruption was taking place. But the connection to the sounds in Bandung remains a major scientific puzzle. Teguh Suadi noted that residents in Banten, Jakarta and Bogor, which are closer to Krakatau, had not reported or discussed similar booms.

BMKG raised another possibility from scientific literature: methane escaping from the floor of the basin of the ancient Bandung Lake. The hypothesis fits the geological setting of Greater Bandung, which lies above the former lake area, but officials stressed that it has not been confirmed. BMKG plans to study it with the Geological Agency and the Center for Volcanology and Geological Hazard Mitigation.

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Volcanic activity occurred at Krakatau, but residents in Banten, Jakarta and Bogor did not report or discuss it, even though they are closer. This booming phenomenon occurred only in Bandung and its surroundings.