Sound Mysteries“Sound Mysteries” is a Gizmodo series in which we explore weird or unexplained sonic phenomena.  

In 1997, scientists with the U.S. National Oceanic and Atmospheric Administration were recording the sounds of underwater volcanic activity when they picked up a noise that was so incredibly loud—louder than any underwater sound ever detected—that they initially thought it must be an equipment malfunction. But then another underwater microphone picked up the same noise... over 3,000 kilometers away.

What could have created such a sound? No living animal—at least, no known creature—could have produced it. The U.S. Navy denied any doing testing in the area. When a sped-up recording of the sound went public, it soon became known as “the bloop,” and conspiracy theories abounded. Years later, scientists finally did discover the true nature of the massive noise. In the second episode of our new series “Sound Mysteries,” we look into the case of the mysterious underwater bloop.

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Correction: A previous version of this blog incorrectly referred to “National Oceanic and Atmospheric Association” instead of the National Oceanic and Atmospheric Administration. We regret the error.