The Bloop: an ocean sound with a natural explanation

In 1997, hydrophones in the Pacific detected an exceptionally powerful, low-frequency sound nicknamed the Bloop. Its apparent loudness and the fact that it was first unfamiliar prompted speculation, including the playful idea of an enormous unknown animal. NOAA later compared the sound with recordings of icequakes and concluded that the Bloop’s characteristics were consistent with a large icequake, such as ice cracking or fracturing.

The case is a useful reminder that “unidentified” can describe the state of knowledge at one moment, rather than a permanent mystery. Underwater sounds travel over long distances, and their source is not always obvious from a recording alone. A compelling name and an unusual signal do not establish a biological or extraordinary origin.

NOAA’s explanation is grounded in comparison with known natural events; it does not mean every ocean sound has the same cause. The Bloop is best remembered as a striking acoustic observation whose mystery diminished as reference data improved. [1]

Editorial note: This feature summarises the published sources listed below; it is not a new archive investigation. The accompanying image is AI-generated illustration, not an archival photograph or evidence of the event.