For centuries, sailors spoke of two maritime nightmares — gaping holes that swallow water, and walls of waves rising from nowhere. These were tales of terror, not science, and naturalists regarded them with skepticism. It just didn’t seem likely that the ocean could just open beneath your feet or smash down from above.

That all started to change in modern times. Scientists realized that these so-called “rogue waves” were not myths. They are real and increasingly observable. But “rogue holes,” the opposite of rogue waves, were still unconfirmed and unobserved.

Then, in 2012, researchers at the Australian National University proved the existence of “rogue wave holes.” Rogue holes are transient, abnormally deep depressions on the ocean surface that mirror the dramatic height of rogue waves — essentially, they are like an inverted rogue wave.

The sailors of yore have their vindication. But why haven’t we seen any rogue holes yet?

We still don’t understand the ocean

Over 80 percent of the ocean is still unmapped and unseen. Of the seafloor, less than 0.001% has been directly visualized. To imagine what that means, picture Rhode Island. That’s what we know. Now imagine that everything else — every trench, crack, cavern, and abyss — is still foggy on our planetary map.

Sailors in the past likely observed the sea more closely than sailors today. They had to rely heavily on their observations of the sea, sky, and any natural phenomena, as they had no GPS or advanced tools. They certainly wrote about lots of curious phenomena. But it’s hard to say how many of the things they were reporting were actually real.

Rogue waves — also known as freak waves, monster waves, or extreme storm waves — are immense, spontaneous swells that seem to defy the laws of physics. They’re not tsunamis, and they’re not triggered by any geological phenomena. Instead, they result from the interactions of other waves, focusing their energy and making them unpredictable and exceptionally powerful. For ships and offshore structures, they can be extremely dangerous.

Rogue holes are sort of the opposite of that. According to the 2012 study that proved their existence, a rogue hole would appear on the ocean surface as a sudden, localized depression — a deep trough flanked symmetrically by two large crests. It looks like a sharp, hollow dip in the water, the inverted mirror image of a towering rogue wave.

The only problem is we’ve never seen one. We’ve seen rogue waves, just not rogue holes.

From Columbus to documented 30-meter waves

In August 1498, during the third voyage of Christopher Columbus, crew members heard a tremendous roar. They observed a wave approaching from astern that was “as tall as the ships’ masts”. Columbus described the wave as lifting his ships higher than anything he had ever experienced before, after which the ships dropped into a huge trough.

Several other high-profile sailors reported such waves. But perhaps the most striking example happened in 1861, on the coast of West Ireland. It smashed some of the lamps down the stairs and damaged the upper part of a light house. In order to reach that height, water had to surmount a seaside cliff measuring 40 m (130 ft) in height and a further 26 m (85 ft) of lighthouse structure.

But it wasn’t until 1995 that the first rogue wave was measured. The Draupner wave struck an offshore gas pipeline in the North Sea, off the coast of Norway. It hit on the 31st of December and measured 25.6 m (84 ft) in height. That one measurement changed oceanography. Suddenly, rogue waves were real. But they were still considered exceedingly rare.

Then, in 2000, the European Space Agency (ESA)’s MaxWave project confirmed the widespread existence of rogue waves. MaxWave used radar data from ESA’s ERS satellites to analyze global ocean surface patterns. The project identified numerous waves exceeding 25 meters in height, demonstrating that rogue waves, once considered rare, are a common occurrence. The largest confirmed such wave was 30 meters (98 feet) in Newfoundland.

Rogue waves are indeed very rare: less than one in 100,000 waves. But they clearly exist.

What about rogue holes?

The MaxWave project did not explicitly confirm or report the detection of rogue holes as distinct phenomena. The project did, however, mention the occurrence of deep troughs accompanying large wave crests. This implied that rogue holes might have been implicitly observed or suggested in the data analyzed by MaxWave but stopped short of claiming their existence. So Amin Chabchoub, currently at Kyoto University, decided to study this idea in a tank.

In a 15-meter-long wave tank, researchers reproduced the ocean under controlled conditions. By adjusting the conditions, they generated both elevated rogue waves and rogue holes. The latter appeared as symmetric troughs, deeper than the surrounding wave field and bordered by equally dramatic crests. The results matched theoretical predictions with striking accuracy.

The 2012 study found that rogue holes and rogue waves are actually caused by the same underlying process — they’re just different phases of it. Imagine a wave pattern moving through the ocean with a big “energy envelope” riding along. If that envelope lines up with a high point (a crest), you get a huge rogue wave. But, if it lines up with a low point (a trough), you get a rogue hole instead. So they’re two sides of the same wave event — one rises up, the other sinks down.

This provided evidence that rogue holes should exist. Then, in 2016, another study provided strong evidence that rogue wave holes are not limited to laboratory conditions — they can and do occur in real oceanic environments. This study employed a mathematical framework and compared it with real data. It found that wave groups resembling both rogue crests and rogue holes have been observed at sea.

Unlike the idealized symmetric shapes seen in wave tanks, the study highlights that actual rogue events often appear asymmetrical — with steeper leading or trailing edges — yet still match the structure of exact breather solutions when adjusted for asymmetry. This also confirmed the idea that rogue holes and rogue waves are part of the same larger process.

From sailing myths to infrastructure safety

For centuries, sailors reported these waves. Their accounts were dismissed as exaggeration — until one struck an oil platform in the North Sea in 1995. Then, even as rogue waves were confirmed, rogue holes were still dismissed. It took a lot of real data and a lot of math to finally confirm them.

But this is more than just confirming an old myth. These events pose real threats to maritime safety. A ship caught in a rogue hole could suffer structural stress from sudden changes in buoyancy, especially if a towering rogue wave follows. We have more and more offshore infrastructure, so understanding how the ocean behaves (even isolated, rare events) can save millions or even billions of dollars. More importantly, it can also save human lives.

The study also opens up cross-disciplinary possibilities. The same wave equations used to model rogue holes in water have analogs in optics, plasma physics, and even finance. As the authors note, understanding rogue holes may have implications well beyond oceanography.