Gargantuan waves, which appear unexpectedly even under calm conditions in the open ocean, have damaged and sunk numerous ships over the years. Now, researchers have identified a plausible mechanism that may account for the occurrence of these rogue waves. Using a mathematical model, they demonstrate that ocean currents or large fields of random eddies and vortices can sporadically concentrate a steady ocean swell to create unusually large waves. The current or eddy field acts like an optical lens to focus the wave action, says applied mathematician Bengt Fornberg of the University of Colorado at Boulder. Fornberg and Benjamin S. White of Exxon Research and Engineering Co. in Annandale, N.J., describe their model in a report submitted to the Journal of Fluid Mechanics.
Rogue waves can arise in all oceans.
However, their frequency and size are particularly notable off the southeastern coast of South Africa. Every year, a few supertankers and other major vessels suffer severe structural damage while traveling southward along a standard route from the Middle East to the United States or Europe. The vessels boost their speed by taking advantage of the strong, south-flowing Agulhas Current, which skirts the South African continental shelf. Depending on the prevailing winds, this current often meets a steady incoming wave swell nearly head-on. The interaction of wave and current reduces the spacing between the waves and changes their direction.