Waves crashing
Large, rogue waves can appear at any time in the deep ocean Johnnorth/iStock

Large, rogue waves can appear out of nowhere in the open ocean, say researchers. The new study shows that these huge waves are followed by a group of smaller waves.

The researchers, from the University of Oxford, aimed to show that old fishermen tales of giant 'walls of water' appearing out of nowhere may not actually be a myth. The study, published in Proceedings of the Royal Society A, used mathematical modelling to compare differences in linear and non-linear wave dynamics.

"The waves we're dealing with here occur in deep water in the open ocean – very different from the waves you'll see if you go to the beach, which is what most people are familiar with," said Thomas Adcock, researcher on the study. "In deep water, where waves are much less regular, you expect a larger wave from time to time. Our paper shows that, in contrast to what was previously thought, if you're the observer on a ship, rather than seeing a gradual build-up of waves, the rogue wave will come seemingly out of nowhere."

Oceanographers had previously believed that while rogue waves do exist, they didn't just form from nothing. They believed smaller waves would build up gradually, forming one giant. However, the study showed that larger waves tend to move to the front of the wave group, so that was impossible. Therefore, the conclusion was that one giant wave is then followed by smaller waves.

Adcock said: "These findings fit the anecdotal evidence you hear from mariners. All of this means that in a very rough storm, you can't simply assume you'll get a warning before a freak wave hits. Seafarers need to be aware that a large wave may appear out of nowhere."

In August 2009, a young girl, 7, was killed by a rogue wave whilst wave-watching, following Hurricane Bill. The wave, which hit a viewing platform in Acadia National Park in Maine, also hospitalised nine people.