High seas

Natural History, Oct, 2004 by Jordan Paul Amadio

Sailors' tales of braving bad weather and choppy waters have been standard fare for centuries. But even the crustiest old salt has nightmares about facing a rogue wave, the ultimate in mountainous seas. Just ask the crews of the Bremen or the Caledonian Star. Early in 2001, both ships, with hundreds of tourists onboard, were nearly sunk by ten-story-high waves in the South Atlantic.

Until recently, definitive sightings of rogue waves have been rare, but now a team of investigators headed by Susanne Lehner, a marine physicist at the University of Miami in Florida, has not only confirmed their existence, but also discovered that they're disturbingly common. The team recently procured three weeks' worth of radar images of the world's oceans, supplied by European Space Agency satellites, and found more than ten waves whose height from trough to crest was greater than eighty feet.

What causes supersize waves? According to the investigators, currents at the boundary of an ocean gyre--such as the dangerous Agulhas Current at the western edge of the South Indian Ocean, or the Gulf Stream in the North Atlantic--can concentrate and magnify the energy of ordinary waves. By contrast, in regions of open ocean where currents are not a dominant force, prolonged storms, fast-moving fronts, or crossing seas might pump up run-of-the-mill waves to gargantuan proportions. (www.esa.int/esaCP/SEMOKQL26 WD_index_0.html)