Enjoying EarthSky? Subscribe.

121,138 subscribers and counting ...

By in
| Earth on Oct 13, 2012

What are rogue waves?

Rogue waves are gigantic ocean waves that can be over 100 feet high that seem to appear out of nowhere.

Rogue waves are gigantic ocean waves that can be over 100 feet high. Rogue waves are not tsunamis, said Tulane University physicist Lev Kaplan. Tsunamis are caused by undersea earthquakes. Rogue waves seem to appear out of nowhere, he said.

Image Credit: sub_lime79

Let’s take an example. Imagine you’re in a storm where the average wave is 20 feet tall, right? Then, all of a sudden, one wave appears, or maybe two or three waves appear, that are 70 feet tall. Now, that would be an example of a rogue wave. But they can also appear in completely calm seas, so in that sense they’re quite unpredictable.

Image Credit: Philippe Lijour

Which is why rogue waves can be dangerous to fishermen and rig workers, or even cruise ships. Dr. Kaplan explained that, while rogue waves are still not well understood, two factors are thought to contribute to their formation. The first is the force of ocean currents. The second is the collision of several individual waves, which can combine their power. He explained:

This is a little like light being focused or concentrated in a microscope, or in a telescope. Sometimes you get focusing and increased wave heights.

Scientists will never be able to predict exactly when and where a rogue wave will show up, Kaplan said, because the sea is too chaotic a system. But, today, computer modeling techniques are being developed to help forecast the probability that a rogue wave will occur in certain place at a certain time.

A ship damaged by a rogue wave. Image Credit: H.Gunther and W.Rosenthal

What we certainly hope is to be able to forecast risk, so we might be able, for example, by looking at the ocean in real time and measuring sea conditions, we might be able to say, over the next 24 hours, in this particular area of ocean, the risk of a wave occurring is 100 times greater than average.

Ocean movement is so complex, he said, that it could be 20 years before such a system is usable.

Dr. Kaplan explained that he devised his mathematical models not by looking at ocean waves, but by looking at electrons – tiny subatomic particles that have wavelike movement. He said:

The way that we got into this research is that several years ago we were trying to understand electron transport in nano structures, which are systems on a very, very, very small scale. And if you look at electrons, they actually behave like waves. What we decided to do was to take some of the mathematical tools that we used to understand how electrons move, and apply them to understand the behavior of waves in the ocean.

He explained in greater detail how the math behind his rogue wave computer model works:

If you take a random incoming sea and you assume that the currents that are bending the waves left and right are also completely random, then sometimes you get focusing and increased wave heights, and sometimes you can get de-focusing and decreased wave heights. But you can show, mathematically, when the probability of seeing an extremely tall waves goes up. And further, you can calculate how often rogue waves will occur if you know how fast the currents are, and how fast the waves are traveling.

Dr. Kaplan described a recent occurrence of a freak wave that caused fatalities:

There was a rogue wave that occurred in the Mediterranean last year, and happened to encounter a cruise ship. Two people died on account of that incident. The wave in the Mediterranean was only 26 feet tall, but it fits the description of rogue wave, in the sense that it came out of nowhere and is much much taller than the surrounding sea. Another well-known incident: 2001, in the south Atlantic ocean, it was a wave almost 100 feet tall that hit two cruise ships, that year.

He underscored that the research he’s doing right now on rogue waves is very basic. It will be several decades before a good rogue wave forecasting system is in place, he said.