Mariners have long spoken of 'walls of water' appearing from nowhere in the open seas, that is why freak waves are called freak waves.

Oceanographers have disregarded such stories and instead suggested that rogue waves - enormous surface waves that have attained a near-mythical status over the centuries - build up gradually and have relatively narrow crests, but new research says rogue (or freak) waves can emerge suddenly, being preceded by much smaller waves. At least in mathematical models published in Proceedings of the Royal Society A.

Professor Thomas Adcock, of Oxford's Department of Engineering Science, said, "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. 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.

"This happens because large waves tend to move to the front of the wave group."

The first thing you have to accept is that their mathematical model predicted non-linear physics accurately. Like freak waves themselves, that takes some suspension of disbelief. Since non-linear behavior can only be simulated as linear in really small steps, they used hundreds of simulations of random waves to analyze the differences between linear and non-linear wave dynamics.

Professor Adcock said, "These findings fit the anecdotal evidence you hear from mariners. They often describe "walls of water" coming at them in the open ocean that are impossible to steer around - an observation supported by our modeling, which shows that rogue waves tend to have a much broader crest than traditionally predicted by linear theory.

"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."