Science / Medicine : ‘Rogue’ Waves : They have been blamed for upsetting oil tankers, for drowning tourists, for capsizing buoys, for almost sinking the Queen Mary.
In the popular imagination, they have the qualities of a movie behemoth--surging, Jaws-like, out of nowhere on a sunny afternoon to gulp down party boats full of fishermen out for an afternoon of sport.
They have been implicated in the demise of oil tankers. They have been blamed for drowning tourists and capsizing data buoys. They have been accused of ripping the railings off an Italian ocean liner and almost sinking the Queen Mary.
They are rogue waves.
“When people say a ‘rogue wave,’ I have this image in my mind of some guy on Mt. Olympus creating a wave and turning it loose,” said Steve Elgar, an oceanographer at Washington State University. “Clearly, that’s not what’s happening. So we try to figure it out.”
But so far, the scientists’ figurings have been far from conclusive.
Most agree that a rogue wave is a rare coincidence of many smaller waves, perhaps from different storms, moving across the ocean. They converge, but instead of canceling each other out, they form a single wave of extraordinary size.
But beyond that, there is little consensus.
Some scientists believe rogue waves travel alone. Others say they move in twos and threes. Some Say they occur in storms, outside of storms, only in deep water, only in shallows. Some say they have a distinctive shape and travel at odd angles.
A few oceanographers suggest that rogue waves are not even “roguish.” That is, there is nothing truly aberrant about them. They say if you wait long enough, one will come along--like the statistical chance of flipping a coin 10 times and coming up with 10 heads.
Others insist that they are genuine freaks. In a stormy sea, they say, statistical probability and mathematical predictions fall apart. Out on the ocean, extraordinary waves occur that no mathematician would be able to predict.
“Research on this particular phenomenon is very spotty,” said Frank Gonzalez of the National Oceanic and Atmospheric Administration. “Part of it is that in fact, it’s a very rare event. And you’re hard pressed to gather enough dependable observations.”
Yet the proliferation of commercial shipping and recreational boating has created a new demand for reliable data about rogue waves. In light of the environmental and economic consequences of, say, an oil tanker’s sinking, some scientists say more work must be done.
“Certainly, there has got to be some sort of educational program,” said Richard Seymour of Scripps Institution of Oceanography at the University of California, San Diego. “At least something that says, ‘Waves are variable, guys. Don’t relax just because you don’t see any big waves now.’ ”
First, a few facts about ocean waves:
Most ocean waves are caused by wind. The air moving against the water initially creates ripples. Then the wind begins to press against the sides of the ripples, transferring energy from the air to the water and producing waves.
Waves, rogue or not, can grow to remarkable heights. Sailors say 45-footers are common in North Atlantic storms. Others have reported 75- and 90-foot waves. In one famous account, a Navy officer crossing the Pacific in 1933 reported a wave estimated at 112 feet.
“Think about what it means for a 10-story wall of water to be coming onto your face,” marveled Robert Guza, a wave specialist at Scripps. “I mean, big waves get big, and they don’t need to be rogues.”
Nevertheless, the literature is filled with anecdotal accounts of so-called rogue waves.
In 1942, when the passenger liner Queen Mary was serving as a troop ship, she was struck broadside in a gale 700 miles off Scotland. An eyewitness was quoted as saying the ship “listed until her upper decks were awash,” then righted herself.
In 1966, accounts state that a huge solitary wave in a storm swamped the upper deck of an Italian liner 800 miles off New York. The wave reportedly smashed windows 80 feet above the water line and ripped off steel railings on the upper deck.
Earlier this year, 10 people drowned off Baja California when a San Diego sportfishing boat was suddenly swamped and sunk. The two survivors of the Feb. 5 accident on the Fish-n-Fool said the boat was capsized by a sudden 20-foot-high wave.
Oceanographers say not all rogue wave stories are true.
“Well, it’s a hell of a convenient way if you’ve been careless at sea to explain it,” said William Van Dorn, a research oceanographer emeritus at Scripps who has served as an expert witness in marine casualty cases. “Very often, you can see through the arguments, that the guy was careless or negligent and let himself get in a bad situation.”
Some reports of extreme waves are more easily explained than others.
Local topography is known to affect wave height in shallower water, said Richard Seymour, head of the ocean engineering research group at Scripps. If a wave encounters a sudden shoal or a current, it may suddenly rise to an unusual height.
For example, a wave rounding a headland and encountering a current flowing against it can suddenly get very steep, Seymour said. Similarly, a reef or a change in the bottom contour can “focus” waves, forcing them to increase in height and break, as if on a beach.
Along the Northern California coast, Coast Guard officials say, shoals exert that effect. As a result, a National Oceanic guide to Bodega and Tomales bays warns boat operators of sudden “sneaker waves” during ebb tide and advises them to leave the area before the tide turns.
Perhaps the best known of such places lies off the Cape of Good Hope, where the Agulhas current races down Africa’s east coast. Huge waves generated in the Antarctic Ocean come around the cape and meet the current, becoming suddenly higher and steeper.
In recent decades, that wild coast has been a prime location for reports of rogue wave sightings. At least half a dozen tankers, taking advantage of a ride on the Agulhas current, have been damaged or destroyed in that area.
Other reports of rogue waves are less easily explained.
Most oceanographers say a true rogue wave is the sum of multiple waves traversing the ocean in different “wave trains.” On rare occasions, they converge to form a larger rogue or freak wave--or a “rogue hole,” as the trough before such a wave is called.
“Extreme coincidence, that’s all it is,” said Reinhard Flick of the California Department of Boating and Waterways. “It’s just a very, very, very rare coincidence--that all those wave trains that happen to be present happen to end up in that spot.”
Oceanographers have even calculated the probability of large single waves. By one theory, one wave in 23 is over twice the average height; one in 1,175 is over three times the average height, and one in 300,000 exceeds four times the average height.
Assuming that waves are arriving at 10-second intervals, Robert Guza of Scripps concludes, “what this says is if you wait 800 hours--and that’s a pretty long time, it’s like weeks--you’ll see one that’s four times the average.”
To Guza, that probability suggests the term “rogue” may be misplaced.
“You see what I’m starting to get to?” he said one morning recently in La Jolla, waves slapping the beach beyond his window. “Some of what’s called rogue waves is wrong place, wrong time. You were there for the one in 300,000 probability--and you ate it.
“Probability distribution happens all the time. Surfers know about it. They’ll sit out there and wait and wait. What are they waiting for? We call it a rogue. They call it a ‘bitchin’ tube on the horizon,’ or something.”
But the statistics are based on theory, not observation. So oceanographers who have studied case reports of extreme waves say they are convinced that rogue waves are not merely statistical flukes but are qualitatively different from other waves.
Gonzalez, an expert in ocean waves with National Oceanic’s Pacific Marine Environmental Laboratory in Seattle, said case reports suggest that freak waves appear to move at an odd angle, about 30 to 60 degrees of the prevailing direction of the other waves.
They also appear to have unusually long crests and occasionally move with one or two others, he said. Gonzalez said they may also be associated with a type of storm called a “bomb,” which intensifies dramatically in a short period of time.
“It’s not just a case of the waves being just like other ocean waves, except they’re bigger,” Gonzalez said. “The evidence is spotty and sketchy, but if I was a betting man, I would say it really looks like a distinct phenomenon.
“I think that the real answer, of course, is to do some serious research on the problem.”
Gonzalez noted that he has received little encouragement. “It’s a question of priorities on the part of agencies like the Coast Guard, the Navy and National Oceanic,” he said.
“The interesting thing about people who drive boats is that they have been doing it for 3,000 years but they still spend half their time wondering about it,” mused Van Dorn of Scripps. “Nobody knows all the answers, and they don’t seem to study it really, either. They just go on telling stories.”
THE BUILD UP OF ‘ROGUE WAVES’
1. Most waves are caused by wind, which creates ripples. As wind presses against the ripples, more energy is transferred to the water, producing waves which can grow to remarkable height.
2. Waves move in parallel rows called “wave trains.” When two or more such trains meet, their energies add up or subtract, depending on the “phase” of the waves.
3. If the converging wave trains are unsynchronized--out of phase--they tend to cancel each other out.
4. If the trains are synchronized--in phase--their combined energy may produce sudden “rogue” waves, of much greater height and force.
