Saturday, June 12, 2010

Rogue Waves

Out at sea on my sailboat, I once collided with a rogue wave that lifted the entire hull of my forty-eight-foot out of the water and suspended it in midair for a second before we crashed back into the trough. That impact had knocked a filling from my tooth, not to mention turning the cabin in the boat into a disaster area.
-- Jimmy Buffett, A Pirate Looks At Fifty
A rouge wave is not just an unexpected wave, but a very specific, and indeed very dangerous, phenomena. Two passengers were killed and six injured on the cruise ship Louis Majesty last March when three huge waves -- estimated at nearly 30 feet high -- pounded the ship as it sailed off the coast of Marseilles, France. Subsequent media reports called the waves "rogue waves." As we saw in my post on the Beaufort wind scale, waves of this height can be expected in the 60-knot winds the Louis Majesty was experiencing, but the greater-than-average height of the waves and their "Three Sisters" pattern suggest these were indeed rogue waves.

Wind waves and swells tend to behave fairly predictably, this is why forecasters can develop computer models that will predict wave height and direction sometimes days ahead of time. And just as weather forecasters can give mariners a good idea of the direction, height, and period of waves to be expected, mariners at sea can see patterns as well: sets of three or four waves a little higher or lower than average, seas that suddenly get flatter or choppier at a tide ripe, and so on. What looks like a chaos of wind and water to an untrained observer can be predicted by science and is familiar to the experienced mariner. That is not to say the forecasts are always correct or that nasty surprises don't occur. Rogue waves are one of those surprises.

Scientists believed rogue waves were a mariners' legend (or excuse) until the mid 1990s. Instruments at the Draupner oil platform in the North Sea detected the first scientifically measured rogue wave in 1995. Since then several rogue waves have been detected, including a 95-ft wave by the Queen Elizabeth 2 in 1995 during Hurricane Luis, and a 91-ft wave detected by US Navy research instruments during Hurricane Ivan in 2004. As scientists learn more about rogue waves, the phenomenon has become suspected in some previously unsolved maritime losses, including low-flying Coast Guard rescue aircraft and the famous 1975 sinking of the Great Lakes freighter Edmund Fitzgerald.

What causes rogue waves is still a bit of mystery. They are sometimes called freak waves because they are not only higher than the other waves around them, but may travel in a totally different direction from the surrounding seas. They are probably caused by tidal effects and the combining of several smaller waves together. Rogue waves are also mainly a deep water phenomena, although incidents like those of the Louis Majesty and possibly the Edmund Fitzgerald do occur.

For an amateur video shot by one of the passengers on the Louis Majesty, click here.

The film crew for the television series Deadliest Catch caught a 60-ft rogue wave slamming into the crabber Aleutian Ballad in 2006. See a clip here.

1 comment: