'Freak' ocean waves hit without warning, new research shows

Date:: December 16, 2015
Source:: University of Oxford
Summary:: Rogue waves in deep oceans emerge suddenly and have long crests, backing up anecdotal evidence from mariners who speak of 'walls of water', new research demonstrates.

Graphic showing linear vs non-linear wave groups.

Credit: Thomas Adcock

Mariners have long spoken of 'walls of water' appearing from nowhere in the open seas. But oceanographers have generally disregarded such stories and 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.

New research from the University of Oxford in collaboration with the University of Western Australia, however, shows that the anecdotal evidence may not be so far from the truth. Rather than coming at the end of a series of increasingly large waves, rogue (or freak) waves emerge suddenly, being preceded by much smaller waves.

The mathematical modelling also demonstrates that the crests of these rogue waves are longer than the smaller waves that surround them.

The research is published in the journal 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 research made use of mathematical modelling based on non-linear physics. The investigators 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 modelling, 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.'

Story Source:

The above post is reprinted from materials provided by University of Oxford. Note: Materials may be edited for content and length.

Journal Reference:

Thomas A. A. Adcock, Paul H. Taylor, Scott Draper. Nonlinear dynamics of wave-groups in random seas: unexpected walls of water in the open ocean. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, 2015; 471 (2184): 20150660 DOI: 10.1098/rspa.2015.0660

University of Oxford. "'Freak' ocean waves hit without warning, new research shows." ScienceDaily. ScienceDaily, 16 December 2015. <www.sciencedaily.com/releases/2015/12/151216082200.htm>.