Sometime in 1997, underwater microphones recorded a sound so puzzling and powerful that it sent ripples of excitement through the scientific community and beyond. This enigmatic underwater phenomenon, known as the Bloop, would become one of the most intriguing acoustic mysteries of the late twentieth century.
But what was it that made such a deafening underwater din? Was the Bloop sound the result of a top-secret military exercise? Was it a blue whale or a giant squid, or perhaps an unknown apex predator patrolling the Pacific? Was it something otherworldly, or was there a simpler, more logical explanation?
Such a startling event has seen the Bloop unknown sound take its place in the annals of maritime mystery. Whether the Bermuda Triangle or the Loch Ness Monster, stories of so-called ghost ships – including the MV Joyita, the Carroll A. Deering, and the SS Waratah – the oceans are packed full of enigma and the unexplained. So will the truth about the Bloop mystery come to the surface, or is it destined to stay submerged forever?
The Beginning of The Bloop

Did the noise come from a megalodon? (Credit: Racksuz via Getty Images)
First detected in 1997 by the U.S. National Oceanic and Atmospheric Administration (NOAA), the Bloop originated in the remote waters of the South Pacific Ocean, somewhere to the west of the southern tip of Chile. Hydrophones, large underwater microphones designed to monitor ice noise, mammal populations and movement, as well as submarine and seismic activity, captured an undulating, ultra-low frequency noise so loud and distinct it was picked up by sensors an astonishing 3,000 miles apart. For a noise to travel that far, it had to be loud. Very, very loud.
It was this unprecedented volume and the unique characteristics of these unidentified sounds that immediately puzzled researchers, oceanographers and cryptozoologists alike. Theories soon emerged, including that it might be biological in origin, possibly coming from an unknown sea creature of immense proportions – the call of an aquatic dinosaur or the elusive megalodon, perhaps – or from a massive underwater fissure. Yet, initially at least, the reality remained that no-one actually knew what it was.
So what exactly was the Bloop and was it ever explained? In fact, it took several years of investigation, but scientists did eventually find the answer.
What Was The Bloop? Initial Theories

Underwater tectonic plates shifting were thought to be the cause of the Bloop (Credit: Edi Gilodi via Getty Images)
When NOAA first recorded the Bloop in 1997, the unusual and extremely powerful nature of these unidentified sounds stirred up a myriad of theories.
Geological Explanations
On the more conventional end of the spectrum, many scientists initially considered geological explanations as the cause of this underwater unknown sound. Underwater volcanic activity, seismic events, or even the fracturing of massive ice shelves were proposed as likely sources. The scale and resonance of the noise, along with its relatively short duration (around a minute), fit scenarios where natural, non-living processes like ice calving or tectonic shifts could produce a loud, abrupt signal travelling great distances through water.
A Living Organism
Intrigued by the Bloop’s potential bioacoustic signature, a number of researchers and scientists suggested it might have been produced by a living organism. Some pointed out the similarity of certain aspects of the sound’s frequency to those of whale calls, yet it was far louder than any known noise made by an animal on land or in the sea. This idea inspired speculation that a marine creature larger than anything ever recorded could be lurking in the depths.
Fantastical Beasts
From there, the theories veered into the realm of the fantastical. Amateur cryptozoologists and internet forums buzzed with suggestions of colossal sea monsters, undiscovered leviathans, or even references to H. P. Lovecraft’s fictional creature Cthulhu. These imaginative leaps naturally captured the internet’s collective fascination. Tales of an ancient dinosaur or lost monster living in the darkest reaches of the South Pacific circulated widely, fuelled by a mystery for which no immediately obvious explanation had emerged.
The Bloop Mystery Explained

A tabular iceberg in the Bransfield Strait in Antarctica (Credit: Mike Hill via Getty Images)
For years the true nature of these bizarre unidentified sounds remained elusive, fueling theories ranging from secret military operations to the awakening of mythical creatures.
In an effort to solve the mystery of the Bloop sound, and to monitor seafloor earthquakes and volcanoes, the NOAA’s Pacific Marine Environmental Laboratory (PMEL) added another hydrophone array closer to Antarctica.
Between 2005 and 2010, researchers conducted acoustic surveys in the Bransfield Strait and Drake Passage, which revealed ice breaking up and cracking as a dominant source of natural sound in the Southern Ocean.
In short, the Bloop was an icequake.
What is an Icequake?

An example of a calving iceberg, confirmed as the Bloop sound (Credit: GomezDavid via Getty Images)
An icequake – known as a cryoseism – is the crack of an iceberg as it breaks away from a glacier. It’s a relatively common occurrence and most go undetected, but the ones that are recorded register similar noise signatures to that of the Bloop. The 1997 event was the result of a thunderous fracture, west of southern Chile, in the Southern Ocean.
The Bloop: Echoes From the Abyss

Glacial ice, one of the planet's most powerful forces (Credit: David Merron Photography via Getty Images)
Ultimately, while the Bloop mystery captured the world’s imagination, it was one oceanic phenomena that was eventually explained. For over a decade, the sound’s baffling attributes fuelled often frantic speculation, but in the end its origin turned out to be more terrestrial than tentacled.