A rare photograph of a giant wave, taken by seaman
Philippe Lijour off the coast of South Africa in 1980.

Vessel Measures Record Ocean Swells

By Markus Becker

March 31, 2006

A British research team has observed some of the biggest sea swells ever measured. A whole series of giant waves hammered into their ship that were so big, according to computer models used to set safety standards for ships and oil rigs, they shouldn't even exist.

When the RRS Discovery set out to sea, the crew was expecting stormy weather. Meteorologists had predicted a violent storm, and the scientists -- a team from Britain's National Oceanography Center -- wanted to observe it from up close. What they ended up experiencing went far beyond anything they could have imagined -- and could have cost them their lives.

Near the island of Rockall, 250 kilometers (155 miles) west of Scotland, enormous waves came racing toward the vessel. When they checked their measuring instruments later, the scientists discovered that the tallest of these monster waves had hit nearly 30 meters (98 feet) at wind force 9. And it didn't come alone. "We were shaken up these waves for 12 hours," said Naomi Holliday, the leader of the expedition. Entire sets of giant waves hammered the ship.

After the adrenaline levels of the scientists had fallen somewhat, astonishment spread among the crew. The standard computer programs had predicted stormy weather for February 8, 2000, but not such a tempest. Even more astonishing, the giant waves had not appeared individually, but in a group. Previously waves of such size were assumed to only appeared alone.

What Holliday characterized as a "dangerous situation" has turned out to be a spate of luck. The Discovery's crew witnessed the largest waves ever measured by a scientific instrument on the open sea, according to an article the scientists have only now published in the journal Geophysical Research Letters.

Biggest waves ever measured

With a height of up to 29.1 meters (95 feet) from trough to crest, the single waves are the highest ever measured. In terms of so-called significant wave height, they established a new record, according to the scientists: 18.5 meters (61 feet). Significant wave height is the median height of a wave's upper third. It corresponds roughly to the sea swell that experienced sailors can estimate with the naked eye.

More important than the record, however, is how the waves were born. "They were not caused by very strong winds," Holliday told SPIEGEL ONLINE. The strongest phase of the storm had already been over for a day when the largest water masses hit the RRS Discovery.

The scientists think a so-called resonance effect was responsible for the monstrous waves: waves and wind travelled across the Atlantic at practically the same speed. The storm was able to pump energy into the waves efficiently for a long time, building them up to giant size. According to the article published by Holliday and her team, the rapid increase in wave height at the beginning of the event supports this hypothesis.

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