Earth is its own frontier of intrigue and unexplainable phenomena. From mysterious bloops to baffling sonic booms and puzzling hums, our planet rings with unexplained sounds. Here are just a few that continue to confound scientists.
Upsweep is an unidentified sound that’s existed at least since the Pacific Marine Environmental Laboratory began recording SOSUS—an underwater sound surveillance system with listening stations around the world—in 1991. The sound “consists of a long train of narrow-band upsweeping sounds of several seconds duration each,” the laboratory reports. The source location is difficult to identify, but it’s in the Pacific, around the halfway point between Australia and South America. Upsweep changes with the seasons, becoming loudest in spring and autumn, though it isn’t clear why. The leading theory is that it’s related to volcanic activity.
2. The Whistle
The Whistle was recorded on July 7, 1997, and only one hydrophone—the underwater microphones used by the National Oceanic and Atmospheric Administration (NOAA)—picked it up. The location is unknown and limited information has made it difficult to speculate on the source.
Bloop is the big kahuna in unexplained sounds. In 1997 (a big year for auditory ocean mysteries), an extremely powerful, ultra-low-frequency sound was detected at various listening stations thousands of miles apart and traced to somewhere west of the southern tip of South America. The sound only lasted about a minute and and was heard repeatedly over the summer, but not since. Bloop is generally believed to be the sound of a massive icequake, but scientists haven’t totally ruled out the possibility that the sound originated from something “organic.”
That’s where things get eerie. If an animal was the source of Bloop, it would have to be larger than a blue whale. The most fanciful of all theories stems from the fact that Bloop’s location is somewhat close to author H.P. Lovecraft’s fictional sunken city of R’lyeh, where the creature known as Cthulhu lies “dead but dreaming.” Cthulhu can best be described as part man, dragon, and octopus, which seems as likely a source as any for the ocean’s greatest aural anomaly.
Julia was recorded on March 1, 1999, lasted for roughly 15 seconds, and was loud enough to be heard by the entire Equatorial Pacific Ocean hydrophone array. An Antarctic iceberg run aground is the leading suspect for its source.