An impossible recording
In 1997, deep in the South Pacific Ocean, the mysterious Bloop sound was captured by underwater sensors operated by NOAA—the U.S. agency responsible for monitoring oceans and the atmosphere. At the time, the recording drew attention due to its intensity and unknown origin. The sensors were special microphones installed in the ocean depths to detect sounds from both natural and human sources.
What impressed researchers most, however, was the nature of the sound itself. It was low-pitched, rising, and so powerful that it echoed over 3,000 miles. Those who heard the recording said it sounded like a roar emerging from the depths of the ocean. Yet no one knew what could have caused it.
The signal lasted for about a minute—and then, silence. NOAA technicians gave it a somewhat playful name. Still, behind it lay an acoustic mystery that would take years for science to unravel.
The question echoed across the seas:
What, after all, made that sound?
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The South Pacific enigma
Visual representation of the triangulation made by NOAA, suggesting that the Bloop sound originated in a remote region of the South Pacific, near Antarctica.
The sound was recorded during a routine seismic monitoring operation. In the process, a network of autonomous hydrophones submerged in the Pacific detected the anomaly from multiple locations, with enough intensity to be heard thousands of kilometers away.
Next, NOAA technicians triangulated the source and identified its approximate location: 50° south latitude, 100° west longitude—a remote area west of Chile, with no record of unusual human or animal activity.
The signal was classified as ultra-low frequency and stood out due to an unusual characteristic: it increased in pitch over the span of an entire minute—something typical of biological vocalizations, but on an unprecedented scale.
No known animal could produce a sound that powerful. Furthermore, no machine, ship, or known geological event matched the profile. At that point, the only certainty was the mystery.
The strangest—and most plausible—theories
For years, the mysterious Bloop sound remained unexplained. And as with every enigma of unknown origin, theories of all kinds began to emerge.
A colossal creature?
The first theory to gain traction was that of an animal. After all, the sound’s pattern resembled whale vocalizations—but on a much larger scale. So large, in fact, that if it were biological, the creature responsible would need to be dozens of times more massive than a blue whale.
Soon, cryptozoology websites began speculating about an undiscovered abyssal creature. The ocean’s vast unexplored areas seemed to allow room for such a possibility. However, no physical evidence or recurring phenomena supported this idea.
Secret tests or military tech?
Others proposed human causes: underwater explosions, weapons tests, or covert naval maneuvers. Among the suggested possibilities were experimental submarines or even more classified technologies. But experts quickly pointed out inconsistencies. The sound didn’t match known explosive signatures and wasn’t listed in acoustic databases used to track military activity.
Forces of nature?
What about underwater volcanoes, silent earthquakes, or tectonic shifts? Yes, those were also considered. But the spectral pattern didn’t fit any of these phenomena. The sound was too soft for seismic events and too long to be a geological burst.
With each new theory came a flaw. Until, finally, one improbable idea began to make sense.
The answer lay in the ice
The breakthrough came from an unexpected place: Antarctica.
In the mid-2000s, NOAA researchers began comparing the Bloop’s spectral pattern with other sounds captured in polar regions. And something stood out. Certain noises recorded off the Antarctic coast—when blocks of ice fractured or slid underwater—had an almost identical signature.
Indeed, the pattern was there: the rising frequency, the duration, the power. The only difference was scale. In other words, the Bloop hadn’t come from just any piece of ice—it came from something massive. A glacial collapse.
In 2012, oceanographer Robert Dziak and his team made it official: the mysterious Bloop sound had been caused by the collapse of a massive block of ice in the South Pacific, near Antarctica. An icequake.
These events occur when an iceberg breaks off or shifts abruptly, releasing enough energy to produce a sound that travels across the entire ocean—amplified by the deep-water layer known as the SOFAR Channel, which carries sound for thousands of kilometers.
That was the end of the mystery. But not the end of the story.
Listen to the Bloop sound:
The legend that ice couldn’t silence
The scientific explanation solved the mystery—but didn’t erase the fascination.
The catchy name, the remote location, the absurd reach of the sound… All of this made the Bloop something greater than a mere underwater noise. It became part of the collective imagination, like an echo from the deep. A reminder that not everything in the ocean is under our control—or within our understanding.
Coincidentally or not, the region where the Bloop originated lies near Point Nemo, the most isolated place on Earth. And according to H. P. Lovecraft’s stories, that’s where the fictional submerged city of R’lyeh would be—the resting place of the slumbering entity Cthulhu. That detail alone was enough for the internet to embrace the myth.
Even with the official explanation, the audio still circulates online in sped-up versions, making the once glacial sound resemble a living creature. As if, deep down, we still prefer to believe in monsters.
Yet perhaps the truth is even more astonishing: a single block of ice produced a sound so intense it traveled across oceans, baffled scientists, and became legend.
And that, in itself, is extraordinary.
Main references
NOAA – Icequakes (Bloop)
Official NOAA page with technical explanation about the Bloop sound, its association with icequakes, and audio/spectrogram files.
NOAA/PMEL – Acoustic Monitoring Program – Icequakes (Bloop)NOAA National Ocean Service –
What is the Bloop?
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