by George Stuteville

Since the horrors of the tsunami that brought death and destruction to the coastal nations in the Indian Ocean, even the most benign ocean waves demand a measure of respect for the power they pack with each rise and fall.

Now evidence from European Space Agency satellites that scan the oceans' waves reveals that huge, monster sea waves approaching the size of a ten-story building occur more frequently than ever thought.

And these waves may be behind the sinkings of some 200 supertankers and container ships exceeding 200 meters (700 feet) in length during the last two decades, according to the agency.

The agency reported in July 2004 that within a three-week period the satellite scans revealed more than ten separate giant waves cresting above 25 meters (82 feet) in various locations in the world's oceans. Rogue giant waves are defined as individual waves of exceptional height or abnormal shape.

Final data from a European Union study of ocean patterns is currently being incorporated into a statistical profile for a world map called WaveAtlas. The information was collected from European Space Agency satellite scans for a project called MaxWave.

The map could enable mariners to avoid encounters with rogue waves, and, at the same time, assist in the design and engineering of ships and offshore structures, such as oil rigs, to better withstand the sheer physical forces of a tower of water. Both vessels and structures are typically designed for 15-meter (49-foot) waves.

Proof of the existence of monster waves confirmed centuries of sea tales and many reports from watch stations aboard ships. It also raises questions about the causes of many cargo ship and supertanker sinkings that have been attributed to heavy weather.

In a dramatic report of a direct hit by a wave, Capt. Ronald Warwick of the Queen Elizabeth II described the 29-meter (95-foot) wave that surged over the ship at 4 a.m. on September 11, 1995, in the North Atlantic Ocean:

"…the rogue wave was sighted right ahead, looming out of the darkness from 220°, it looked as though the ship was heading straight for the white cliffs of Dover. The wave seemed to take ages to arrive but it was probably less than a minute before it broke with tremendous force over the bow. An incredible shudder went through the ship, followed a few moments later by two smaller shudders. There seemed to be two waves in succession as the ship fell into the 'hole' behind the first one. The second wave of 28-29 m [92-95 feet], whilst breaking crashed over the foredeck, carrying away the forward whistle mast."

"Yes, it is quite clear that waves well in excess of 30 meters (98 feet) in height are to be expected in parts of the Atlantic and Pacific Oceans," said Nigel Barltrop, the John Elder Chair of Naval Architecture and Ocean Engineering at the Universities of Glasgow and Strathclyde in Scotland.

Barltrop, a consultant expert in the MaxWave project, said that the study suggests monster waves occurring in the open sea are caused by wind. Those that are commonly found off the Cape of Good Hope in South Africa and Cape Horn in South America are made worse when the ocean current slows the movement of a large wave, thus compressing it and further increasing its height. In contrast, tsunamis are waves generated by underwater earthquakes or other seismic events and these, usually very low waves in deep water, only become high as they run into shallow water.

Though the study will likely reveal times and locations where rogues occur most frequently, Barltrop said that actual forecasting may prove much more difficult.

"Opposing currents off South Africa are known to cause some particularly severe conditions, but in principle rogue waves can occur anywhere," he added.

Even if technology could forecast very large, steep, or even rogue waves, Baltrop said the crucial question is whether the information could be relayed in time to vessel captains or crews on offshore sites.

"Usefully forecasting these extreme events is another matter because the wave-wave interactions that cause the large events occur over very short time scales [minutes], so forecasts would have to be very local to any particular ship, and once identified as coming, there may be insufficient time to avoid the event," Barltrop said.