A Mysterious Sound Echoed Across the Pacific — Its Source Took 8 Years to Find

In 1997, underwater microphones operated by the US National Oceanic and Atmospheric Administration detected an extraordinarily powerful low-frequency sound in the southern Pacific. The signal was heard by hydrophones positioned thousands of kilometres apart and seemed to rise rapidly in frequency, earning it the memorable nickname “the Bloop.”

Its unusual acoustic shape initially left room for theories involving secret machinery, whales, giant squid, or an unknown creature larger than anything known to science. NOAA researchers suspected a geological explanation, but it took eight years of Antarctic recordings before they could confidently identify what had produced it.