Rogue waves
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In December 1978, the MS München set sail from a port in northern Germany.

The giant freight container ship was one of the biggest ships of its time. It was nearly 900 feet long, about the length of three football fields, and carried thousands of tons of cargo. The Munchen started on its way across the northern Atlantic, the same journey it had made dozens of times before. On the Atlantic, the weather got worse and worse, buffeting the ship with hurricane-force winds

It was a bad storm, but the Moonchin was considered to be practically unsinkable. But a few hours later, just after 3 a.m., a nearby freighter received a very weak, very garbled SOS signal from the Moonchin. And then, the Moonchin disappeared.

During the next few weeks, over a hundred ships and planes combed the area, desperately trying to find out what happened to the Moonjin in one of the largest search and rescue operations in shipping history. They only found a couple clues. A few life jackets scattered among the waves. A raft that looked like it had been violently sheared off the side of the ship, even though it had been hung over 60 feet above the waterline.

Ultimately, the sinking of the MS Munchen was declared impossible to explain. Something extraordinary must have destroyed the ship. There were theories among the search and rescue teams that the Munchen had run into a mythical rogue wave. Rogue waves are waves that tower above the rest of the ocean. They are at least twice the size as the biggest waves surrounding them and seem to come out of nowhere.

In stormy seas, rogue waves can become monster swallows of water, looming 60, 80, sometimes over 100 feet high. But the problem was that rogue waves were the stuff of legends. Maritime tales akin to mermaids or leviathans, krakens in the deep, they weren't real. Sure, sailors had stories. Over the centuries, there were tall tales of sightings from ships,

But anyone that had possibly witnessed these legends firsthand probably wasn't alive to tell the tale. And even in modern times, every few years, there were mysterious disappearances of ships like the Munchen all around the world.

Rogue waves were so out of the realm of possibility from everything that scientists knew about the physics of waves that these stories were dismissed and any recordings were written off as equipment failures. And so rogue waves were a myth until New Year's Day 1995, when the legend became real.

The Drapner Deep Sea Oil Platform is a lonely place out in the North Sea, nearly 100 miles off the coast of Norway. And on January 1st, 1995, the platform had been weathering a miserable storm for hours. Its support pillars were continually battered by 40-foot waves. The Drapner was designed to put up with this sort of punishment. It was 80 feet above the ocean surface.

But then, suddenly, an 85-foot wave rose out of the sea. This wave was impossibly steep, a nearly vertical wall of water as tall as a seven-story building. It was so high that it racked the underbelly of the elevated platform. No one was outside to see the giant, but the whole thing was caught by a detector measuring the height of the waves below the platform.

The first rogue wave to ever be recorded. In the years since the Drapner wave, scientists have captured more rogues on camera, documented them with buoy sensors, and picked them out of satellite imagery. Scientists now believe that dozens of ships and hundreds of lives have been lost to rogue waves in the last few decades alone. Ships like the MS Munchen that disappeared with no explanation until rogue waves became real.

But there are still big scientific mysteries that remain. The physics of these waves are confounding. Now that scientists know that rogue waves exist, they really want to understand how. How do giant walls of water spring out of the ocean seemingly out of nowhere? ♪

Rogue waves should have been nearly impossible, based on how scientists ordinarily thought about waves. Anything out of the ordinary deserves a scientist's attention. And quite literally, what we're trying to do here is we're trying to look things that are way from the ordinary. Tom van der Berne is an associate professor of environmental fluid mechanics. He studies the behavior of waves, how they grow, how they move across the ocean. Trying to understand...

basically how large a wave can become. And to understand that, you have to understand how a wave forms in the first place. Let's first talk about how it begins. How it begins is by wind. Waves are energy traveling across the surface of the ocean. The wind starts blowing.

the wind starts creating smaller ripples and then these smaller ripples, if the wind keeps blowing, they become bigger and bigger and bigger until we have a proper wave. The harder the wind blows, the longer it blows. The more energy the wind gives to the ocean and the bigger the waves will be. But rogue waves aren't just any big wave. Take for example tsunamis.

Tsunamis are big waves, but they're not rogue. They get their massive energy from earthquakes instead of wind. And scientists know how that energy travels across the water and crashes into land. There's a clear explanation. Rogue waves, on the other hand, can't be explained by a source like earthquakes. They are outliers, statistical anomalies that seem to spring up out of nowhere.

If you think about waves, right, there are lots of them. They occur all the time, right? And one occurs after the other, and one might be a little bit bigger, the other might be a little bit smaller. But then, there's suddenly a wave that's at least twice the size of the biggest wave surrounding it. That, by definition, is Rogue.

So if you're in the middle of a hurricane, the wind is whipping by, stoking up the ocean with tons of energy. You're getting tossed around by 20-foot waves, and then a 45-foot wave crashes down on you. That's rogue. But if it's a calm day on the sea, a light breeze blowing, one-foot waves gently rocking your boat, and you feel a little bump as you ride over a three-foot wave, that is also rogue.

It's exactly that. So it doesn't matter. A rogue wave could still be small, but it's just big relative to the surrounding population. So if the height of normal waves is the result of wind pushing on the water, then shouldn't all the waves in one area, all the waves experiencing the same wind, be around the same height? How do these rogues get so much extra energy?

One factor playing a role is that rogue waves are actually just big piles of smaller waves. This is something scientists see in all kinds of waves. A small wave coming from the right and a little wave coming from the left can come together in the middle and combine to become a big wave before continuing on in the directions they were originally going as if nothing had happened.

Essentially, when waves meet, they add up. You have a one-meter wave and another one-meter wave. They add up to a two-meter wave. One plus one equals two.

And out on the open ocean, all the waves that you see are actually made up of piles of smaller waves. Exactly. They're just stacking up. And this can play out on a grand scale, spanning thousands and thousands of miles, so that it's possible for a storm in Japan to contribute to a rogue wave off the sunny coast of Peru. So let's start in the storm. The wind here is howling and generating all sorts of waves.

There are high frequency waves, waves bobbing up and down really quickly. Choppy stuff. You can imagine these high frequency waves like the high notes in a song. The hurricane winds are also making long, low frequency waves. In the storm, you might not even notice these long, undulating swells, the low notes in our song.

The high frequency waves spend a lot of energy moving up and down, so they don't travel very fast or very far from the storm. High frequency waves, they won't get far. But the low frequency waves, they can go far. These really long waves, really long, really low, they travel really long distances. So the next time you're on a beach, you can read the waves like listening to a song. High notes from any local storms in the area

and you get all the low frequencies from the rest of the world. So the ocean is full of different waves traveling at different speeds. And if a fast-moving wave catches up to a slower one,

Then they're at the same place at the same time, and the waves add together to become one big wave. If you wait for long enough, you'll have lots of waves coming from different directions, and they might just superimpose to something really tall. Some scientists think that this is what's behind rogue waves. A lot of little waves, sometimes traveling for thousands of miles, all coming together by total random chance at the same time in the same place to

to create a massive rogue. But other scientists aren't so sure that this simple wave addition can explain everything. There's just too much chance. If this was the only mechanism at play, then rogue waves would be really, really rare. And that doesn't line up with what scientists see out in the ocean. It's possible that something much weirder is going on here as well.

Sometimes, if the conditions are just right, when a wave is traveling close to, and the key here is close to, not on top of, if it's traveling close to another wave, energy from the first wave can kind of leak sideways into the nearby wave, bending and concentrating, so that the resulting combination is more than the sum of its parts. Scientists call this effect nonlinear focusing.

There are certain conditions under which if I have two waves, one is one meter, another is another meter, that they don't add up to two meters, but they might add up to two and a half meters or maybe three meters. So this is like a one plus one equals three situation? Yeah, exactly. Exactly. That's why we call it nonlinear because it doesn't add up in the normal way. Right. And it's to do with an instability in the waves.

I still have trouble wrapping my head around this. How can one plus one equal three? The math holds up. Scientists use equations that combine simple linear addition with weird non-linear focusing to describe the behavior of waves that they see in the world. There has been some debate about how these mechanisms could interact to create rogue waves.

Some scientists think nonlinear focusing can only really play a role when waves are all moving in the same direction. It's possible that in the wide open ocean, waves disperse and spread out before their energy can bend and concentrate. To complicate things further, not all rogue waves are alike. The answer of how they get their energy to grow to monstrous heights could vary from wave to wave. And as the height of these rogues start to mount,

So do the mysteries, because their very shape seems to defy gravity. Normally, as a wave absorbs energy, it grows and grows, and the top of the wave starts moving faster than the bottom. Eventually, the wave gets so big that it sort of trips over its own feet and topples over.

It falls over. It becomes too steep. And there's a well-understood maximum steepness. So simply, if it gets any taller than that, it will fall over and that's it. You can't go taller. But rogue waves can get much taller and steeper than a normal wave before breaking. So what is going on? To dive into this mystery, Tom set out to create a rogue of his own. That's after the break. This episode is brought to you by Shopify. Whether you're selling a little or a lot...

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Go get Dropnir. Dropnir? But we need it. Those aren't mountaineers. They're waves. So how do waves go rogue? Before the break, we heard a few theories for how rogue waves might accumulate enough energy to become massive walls of water, towering high above the other surrounding waves.

But Ton van de Brenne is grappling with another rogue mystery. How do they get so tall and so steep without collapsing? We can understand, we can predict really well how those waves evolve, but not when they break, our predictive models they break down. Of course, rogue waves do break eventually, but not until they climb much higher and get much steeper than an ordinary wave ever could.

So what does it mean for a wave to break? So wave breaking we know, right? Because we go to the beach and we see wave breaking. The wave basically falls over, there's a lot of white water, and the wave stops becoming taller and it breaks, quite literally. Think of a wave as roughly triangle-shaped. A fat bottom triangle with a wide base.

As the wave gets more energy, the height of the triangle increases. Eventually, the triangle gets so tall that the top of the wave starts moving faster than the bottom. So instead of growing upwards, it starts curling forwards until the whole thing crashes down. Whether the wave is 8 feet tall or 80 feet tall, what matters here is the steepness of the slope.

A wave typically breaks when the height of the triangle is about one-seventh the width of the base. So still a fat bottom triangle, kind of like the gable on the roof of a house. At the beach, the rising ocean floor squeezes the base of the wave, so it reaches this threshold sooner.

But waves can break out in the open ocean too. So if you look out of an airplane, you look down, you see white capping, you see white streaks. And that is basically waves losing energy. So essentially there's a physical limit to how steep a wave can get before it topples over. Once it reaches that limit, the wave breaks and the energy it's been accumulating dissipates back into the ocean water.

But some rogue waves go way past this limit. They just keep absorbing energy, growing taller and getting steeper and steeper. Tan wants to find out why.

But studying the mechanisms of wave breaking gets really complicated, really fast. There's so many scales involved. By scales, he means that there are just so many measurements to make a wave. There's the kilometer scale of a wave rolling in along an entire beach.

There's the meter scale of the wave's height, the centimeter scale of the top of the wave, even down to the submillimeter scale of the tippity top curling over. Then this fluid falls over and that creates more scales, that starts to mix, that creates more scales. And each of these scales has an effect on the behavior of the wave. That level of complexity means it's very hard to build equations and computer models to understand wave breaking.

And that's not even taking into account the influence of winds, currents, or the ocean floor. Wave breaking is one of the processes, even for state-of-the-art computer models and the biggest computers out there, we're only beginning to learn. We're beginning to have the computers large enough so we can understand wave breaking. And studying wave breaking in real life presents its own challenges.

It's very difficult to study waves in the real ocean because everything's large and everything is very uncontrolled. So we go to the lab.

And basically what we have are swimming pools. A swimming pool strikes a balance between the abstraction of computer models and the uncontrolled chaos of the open ocean. These scientific swimming pools are in laboratories all over the world. But Tom went to a unique pool called Flow Wave at the University of Edinburgh. And it's unique because it's a round swimming pool. So it's 25 meters in diameter.

and each section of the wall is a wave maker. These wave makers built into the wall of the pool are like giant bellows. Imagine a door and you normally have the hinges on the side, right? So the door opens to the side. You can put the hinges on the bottom and then you can open it by slamming the door down. Motors push open the doors and the doors push the water in the pool.

These motors we can control. So we basically, we create the waves that we want. And Ton and his team wanted to recreate the first rogue wave ever recorded, the legendary Drapner wave. They studied the sensor data from the Drapner recording in 1995 and saw the shape of the wave that they wanted to recreate.

And it's important here to talk about scale, right? So the real Dreibner wave had a height of about 25 meters, and ours was more like a few tens of centimeters. Had you been stood there looking at our basin, you wouldn't have been terribly excited. It wouldn't have looked enormous. So not a full-sized rogue, a roguen miniature. But Tom wasn't too interested in height anyways. And what's helpful here is to...

Think about what matters. What matters is not the height of the wave, but the steepness, the slope. - Tan wanted to unlock the secrets of the shape of the Draupner wave, that almost vertical wall of water. He believes that this is the key to understanding how it got so steep without tripping over its own feet and breaking like a normal wave. At first, Tan and his team at the Flow Wave Pool tried to recreate their mini-rogue by adding up a bunch of waves traveling in the same direction.

But this didn't give them the dramatic, steep slope of the Dropner wave. The waves broke just before we could reach the steepness that we want. So they tried something else. They started two sets of wave makers going at the same time, at about 11 and 3 o'clock along the pool's circular walls.

When the two sets of waves crashed into each other in the middle of the pool, they combined but also pushed each other higher, kind of like a chest bump. They actually splash upwards. That allowed for a wave to become much bigger before it actually broke. And it worked. Tan and his team matched the shape of the dropner.

And so they think the Drapner rogue was able to grow to such steep heights without breaking because it was created by two sets of waves crossing at a wide angle. And now, they're using other wave breaking experiments to tease apart the mystery of rogue waves' extraordinary slope beyond the Drapner. So what we've done is we've taken a lot of measurements of breaking waves and we've given all of the data to our computer

And we've told it to learn. You go away and learn. Tan and his team are inching closer to a better understanding of wave breaking through a mixture of real-life observation, pool experiments, and machine learning. But it's still an incomplete picture.

The ultimate goal here is to understand the mechanics of rogue waves so well that scientists could predict them, kind of like the weather, and possibly warn ships to change course if they're headed into a rogue-prone area. Hopefully in the future, this kind of technology could save lives, like the 28 souls aboard the MS Moonchin. The moment the drop-ner wave was recorded in 1995, everything changed.

the legend of rogue waves became a reality, a scientific phenomenon to be measured and studied. And in the decades since, chasing rogue waves has revolutionized our understanding of energy in the ocean. But waves aren't just in the ocean. They aren't just in the water. Our whole universe is made of waves, and we interact with them every day. There are light waves, electromagnetic waves, sound waves,

All these waves, they follow the same kinds of equations. They have a sort of shared fundamental nature. And so wherever there are waves, there might also be rogues. One physicist told me that when you listen to a choir, there are rogue sound waves hitting your ears. And these rogue notes, they might sound a little harsh or a little loud, but it's all part of what we hear as the beauty of the song.

There are also much stranger waves out there in the universe. Quantum waves, gravity waves, dark matter waves. And there are rogues here as well. So understanding the nature of rogue waves, whether in the deepest ocean or at the quantum edges of reality, could give us a better understanding of our universe and of our world. This episode was reported and produced by Meredith Hodnot, who also manages our team.

Editing from Brian Resnick, with help from me, Noam Hassenfeld. Christian Ayala mixed the episode. Christian Meredith and I all worked together on scoring and sound design. Serena Solon checked the facts. And Manding Nguyen has some amazing things in store. Bird Pinkerton was confused. She turned to the Doctopus. "The birds? They were trying to find you? What's going on?" "This is just the latest tragedy of the Great Octopus-Bird War," the Doctopus explained.

Let me tell you the whole story. Special thanks to Charlie Wood, whose article, The Grand Unified Theory of Rogue Waves in Quantum Magazine, inspired this episode. Thanks to Alvisa Benitazo and Rick Heller for their time and expertise as well. If you have thoughts about this episode or ideas for the show, please email us. We're at unexplainable at vox.com. And as always, we'd love it if you'd write us a review or a rating.

This podcast and all of Vox is free in part because of gifts from our readers. You can go to vox.com slash give to give today. Unexplainable is part of the Vox Media Podcast Network, and we'll be back next week.