INDONESIA: The enigmatic booming sound that resonated in Sumenep, Madura, East Java, has now been attributed to a fascinating natural phenomenon known as water-hammer.
This phenomenon involves the forceful interaction of water with air-filled cavities within the ground, resulting in distinctive acoustic emissions.
Earlier, the ground-shaking sound endured for approximately ten days in Dusun Tengah, Moncek Tengah Village, Lenteng District, Sumenep, prompting the evacuation of ten families.
The sound, akin to an impactful collision accompanied by vibrations, became more pronounced and tangible on Saturday (12 Aug) between 09:00 AM and 11:00 AM local time, even causing water in local wells to sway.
Over the course of several days, experts meticulously investigated the site. The culmination of their research was unveiled in a conversation with CNN Indonesia on Tuesday (22 Aug).
Tantan Hidayat, Team Leader of the Center for Groundwater and Environmental Geology (PAT GTL), explained, “What happens is that water surges into a canal and compresses entrapped air. This results from a pre-existing cavity—formed due to a fracture encountered during drilling at a depth of 30-40 meters—where air was trapped. The water’s pressure suppresses this trapped air, ultimately generating the distinct sound.”
The official statement from the Geological Agency of the Ministry of Energy and Mineral Resources (ESDM) further elaborated, “The phenomenon, based on historical records and geological insight, is likely rooted in a water-hammer process.”
“The water-hammer effect unfolds when a water stream experiences a sudden surge in pressure within a channel, subsequently compressing trapped air.”
“This cascade of high-pressure waves reverses through the channel, producing knocking or vibrational sounds. This process of pressurized water introduction likely originates from minor-scale swarm earthquakes,” expounded the expert team.
The Geological Agency stumbled upon an artesian well during their investigation
Before the revelation of the water-hammer process, the Geological Agency embarked on comprehensive monitoring encompassing diverse possibilities, including cave formations and mining activities.
Nonetheless, on-site observations eliminated these notions from the list of potential causes for the enigmatic sound.
The water-hammer hypothesis took root after Tantan and the Geological Agency research team uncovered artesian wells—natural wells that discharge water without mechanical aid—in the vicinity.
This water, it is believed, propels air cavities beneath the earth’s surface, thereby engendering the auditory phenomenon.
Tantan suggested that this water surge could be triggered by seismic activity, namely warm earthquakes or clusters of minor tremors transpiring in a short time frame within specific geographical zones.
“Typically, these earthquakes boast a modest magnitude and lack a clear principal quake as a catalyst. Swarm earthquakes manifest over concise intervals and endure from several hours to several days,” Tantan clarified.
The manifestation of the sound is further substantiated by the geological attributes of the rocks in Moncek Tengah Village, which exhibit numerous discontinuities in the form of patched zones and randomly dispersed fissures.
Not all these fissures contain water, so when water encounters increased pressure due to vibration triggers from a swarm of earthquakes, a water-hammer phenomenon is set in motion, eliciting the knocking sound.
The Geological Agency’s inquiry into this phenomenon has unearthed indications of an active fault in the vicinity, even though it might not be within the Central Moncek region.
In light of this, Tantan and his team are advising concerned parties to undertake seismic analyses and monitor potential active fault lines to preemptively mitigate their potential future ramifications.