Residents in the Greater Jakarta Area reported hearing strong “boom” sounds yesterday and earlier this morning, an occurrence of which have prompted responses from relevant officials, who said they may have been caused by lightning rather than volcanic activities.
Two “boom” sounds were heard across a number of areas yesterday evening, including Pasar Minggu and Pancoran in South Jakarta, Duren Sawit in East Jakarta, as well as Bekasi, West Java, and Pondok Cabe, South Tangerang between 7:30pm and 8pm.
This morning, another two loud booms were reportedly heard again at around 5.30am in the same areas.
Witnesses said the loud booms resembled the sound of a huge object dropping to the ground.
Kasbani, who heads Indonesia’s Center for Volcanology and Geological Disaster Mitigation (PVMBG), said in a statement today that the boom noises were not related to volcanic activity. In fact, the nearest volcanoes to Jakarta—namely West Java’s Mount Gede and Mount Salak and Anak Krakatoa in Sunda Strait—have not shown any signs of increased activity either visually or seismically in the past week.
“[Based on] visual observations towards the crater or the peak of Mount Salak and Mount Gede, there are no gusts of volcanic gases,” Kasbani said.
On the other hand, Anak Krakatau was observed with thin white smoke of up to 50 meters high from its peak, though there have been no eruptions in the past few days. The volcano’s status remains on level alert two or “caution”—with Kasbani saying that seismic activity of the three mountains were in “stable frequencies.”
Daryono, who heads the Earthquake and Tsunami Mitigation Division at the Meteorology, Climatology, and Geophysics Agency (BMKG), also confirmed that there were no seismic activities during the time the booms occurred last night. However, he said there were some lightning activities occurring around Mount Salak in Bogor between 7pm-9pm.
“BMKG do not wish to speculate regarding the boom sounds that were heard in South Jakarta and a part of East Jakarta. Our reference is the data from the monitoring of our equipment, which shows that there were indeed some lightning activities that occurred during the boom that the public had reported,” Daryono said in a statement yesterday.
A loud boom was previously heard in Jakarta as recently as last April, which occurred hours after the eruption of Anak Krakatoa. However, PVMBG at that time said that it couldn’t be attributed to any tectonic earthquakes triggered by the volcano.