Uncovering ‘Holes in the Ocean’ : Science: Giant waves could be to blame for the mysterious disappearance of several ships. What causes the sea to swell into towering walls of water?
They roar up suddenly out of the sea, giant waves up to six stories tall that can smash oil tankers, swallow ocean liners or sweep across the decks of aircraft carriers.
Now, a Johns Hopkins University scientist and his former student have begun to describe the shapes these waves can take, work that ship designers may one day use to anticipate the worst the sea can toss at them. The researchers have also discovered a way that forecasters may, someday, use to predict the shape that a given storm will generate.
Until recently, little was known about giant waves, also called freak or rogue waves, because they are so rare and because witnesses are seldom in a position to study them.
“When they hit a ship, people are looking after their skins,” said Owen M. Phillips, a Johns Hopkins professor of earth and planetary science, who has been studying the physics of waves since the 1950s. “People characteristically say they came out of nowhere. And they can be very large. There are reports of green water coming over the deck of aircraft carriers.”
They occur infrequently: The U.S. Navy usually reports one or two giant waves hitting its ships each year, Phillips said. But they can be devastating and strike with little warning.
“Our (studies) show there’s not a whole train of them, there’s just one or two,” he said. “Say you’re on a ship in the rough seas, then suddenly one comes along that’s bigger than all the others. Then, whammo.”
The Navy’s interest in giant waves intensified after one hit the carrier Dwight D. Eisenhower on Halloween, 1989.
The ship was cruising 90 miles southeast of Cape Hatteras off the North Carolina coast when a towering wave struck the ship, catching a group of sailors on an open elevator between the flight and carrier decks.
Three sailors were washed overboard along with 38 Sparrow and Sidewinder missiles, weighing many tons. Two of the crew members were rescued, but the third was lost.
Beginning in October, 1990, the Navy and the National Aeronautics and Space Administration conducted what they called the Surface Wave Dynamics Experiment, a six-month study using buoys and highly sensitive radar to study the ocean’s surface off Wallops Island, Va.
Giant waves sometimes appear amid Atlantic storms moving south, opposite the flow of the Gulf Stream, off the Eastern Seaboard. One may have been triggered last July 3 at Daytona Beach, Fla., when a wall of water estimated at 18 feet high and 27 miles long loomed out of calm seas and crashed on about 100 cars on the sand.
Vehicles were sent tumbling, and some were sucked out to sea in the backwash. Seventy-five people were treated for minor injuries. Scientists later theorized that the wave was triggered by a squall heading south off the coast of Georgia that evening.
Off South Africa’s treacherous southeastern or Transkei coast, giant waves are known locally as “holes in the ocean.” The appear where the Agulhas current, moving southwest, slams into storm winds and Antarctic currents heading in other directions.
Between 80 and 100 ships have been wrecked in this area, where giant waves from 25 to 30 feet high can roll behind troughs between 25 and 30 feet deep. The Greek cruise ship Oceanos sank off the Transkei in August, 1991, after wallowing in 24-foot waves while storm winds gusted up to 88 m.p.h.
South African sea captain C.J. Harris, in a 1991 interview, described his encounter with a giant wave years earlier: “It was a Sunday afternoon and I was in my bunk when the ship just dropped into a hole. It was like going down in a lift (elevator) and then this huge wave crashed down on the ship and stripped all the lifeboats away.”
In 1909, witnesses on shore said the British passenger liner Waratah was engulfed in a single wave and disappeared, in what the London Times has called “one of the mysteries of this century.” All 211 people on board were lost. The wreckage of the Waratah, now believed to be the victim of a giant wave, was located on the seabed in 1990.
Giant waves are suspected as the culprits in the mysterious disappearance of several ships, Phillips said. “If you hit one of these things, there’s no time to send a message,” he said.
Unlike tidal waves or tsunamis, giant waves are not triggered by earthquakes. They appear to swell up when two strong ocean currents collide or when the winds from a storm blow opposite the direction of a current. The ocean stores the energy until a certain critical point, when the sea swells into towering walls of water.
Researchers think that giant waves might be spawned by the accidental alignment of natural forces. At most times, the sloshing of waves in a stormy sea appears random, coming in different frequencies from different directions, Huang said.
But once in a while, those choppy seas may align in such a way that the dispersed power of many small waves is concentrated into a few huge waves. “If all the components come together at a certain place and all reinforce each other, you have a big wave,” he said.
Scientists say that it is possible to design ships to better withstand giant waves and to identify those sea surface conditions likely to spawn them. But, they add, weather forecasters will probably never be able to predict precisely where and when they will occur.
“It’s like a tornado,” Phillips said. “You can’t tell exactly where a tornado will touch down. You can’t tell where exactly these waves are going to appear.”
