How Do 'Rogue Waves' Work?

Workers clean up broken windows on the cruise ship Louis Majesty, anchored at the port in Barcelona

Manu Fernandez / AP

It was like something out of a Hollywood disaster movie. On March 3, a sudden wall of water hit a cruise ship sailing in the Mediterranean Sea off the northeastern coast of Spain, killing two people, injuring 14 and causing severe damage to the vessel.

According to Louis Cruise Lines, the owner of the vessel, the Louis Majesty was hit by three "abnormally high" waves, each more than 33 ft. (10 m) high, striking in clear weather and without warning. "We heard a loud noise, and it was the wave that hit us," Claudine Armand, a passenger from France, told the Associated Press Television News. "When we came out of [our room], we saw the wave had flooded everything." (See the top 10 scientific discoveries of 2009.)

The Louis Majesty wasn't hit by a sudden storm or any of the other expected dangers of maritime travel. Rather, it may have been the victim of rogue waves. For centuries mariners have told stories about sudden waves that would emerge out of the open ocean without warning, strong enough to topple even large ships. The S.S. Waratah, which vanished on a journey to Cape Town; the M.S. München, lost en route to Savannah, Ga.; even the S.S. Edmund Fitzgerald, "the good ship and true" of the Gordon Lightfoot song, which disappeared on Lake Superior — all were rumored to have been sunk by rogue waves.

Until recently, however, marine scientists dismissed the idea of rogue waves as little more than a sailors' fantasy, with reason — there was little evidence to back it up. But in 1995, an oil rig in the North Sea recorded an 84-ft.-high (25.6 m) wave that appeared out of nowhere, and in 2000, a British oceanographic vessel recorded a 95-ft.-high (29 m) wave off the coast of Scotland. In 2004, scientists from the European Space Agency (ESA), as part of the MaxWave project, used satellite data to show that freak waves higher than 10 stories were rare but did occur on the oceans. (Comment on this story.)

Scientists still don't know exactly how rogue waves occur, nor do they know how to predict them. Open ocean waves, possibly including rogue waves, form when wind produces distortion over the surface of the sea — the stronger the wind, the higher the wave, which is why hurricanes can create such destructive walls of water. Tsunamis, on the other hand, like the one produced by the 8.8-magnitude earthquake in coastal Chile on Feb. 27, don't create rogue waves; tsunamis barely make a ripple on the open ocean and gather in size only when they reach shallow land near a coastline. (See TIME's special report on the environment.)

Rogue waves generally occur out in the open ocean. They may be the result of a number of factors coming together — strong winds and fast currents coinciding, for instance — or of a focusing effect, in which several smaller waves join together to form one big wave. There may even be a nonlinear effect at work, in which just a small change in wind speed multiplies to form a big wave. And certain areas of the ocean, like the strong waters off Africa's coast, may be more vulnerable to rogue waves than others. Read more..