As more cruise liners and commercial ships sail the world's oceans, encounters with freakishly large waves — such as the 70-foot one that damaged the Norwegian Dawn cruise ship during a Bahamas cruise last weekend — are becoming more common.

For centuries, reports of a monster wave — a freestanding wall of water that can reach 100 feet and is much taller than the surrounding ocean waves — were believed to be sailors' tall tales. But in recent decades, scientists have used satellite imagery to track and observe what are called rogue or freak waves and, although researchers don't fully understand what causes them, they're believed to be responsible for sinking many vessels, from ancient sailing ships to today's super-tankers.

In one three-week period in 2001, 10 rogue waves welled up, according to research by a German scientific group called Max Wave that examined 30,000 worldwide satellite photos taken by the European Space Agency in that year.

"They're more common than we thought," Mark Donelan, professor of marine physics at the University of Miami, told the South Florida Sun-Sentinel. "On any given day this sort of thing is happening. You don't notice them unless somebody is there with a ship or an oil rig."

Cruise ship slammed

Most recently, the Norwegian Dawn, a 3-year-old cruise ship carrying more than 2,200 passengers and heading back to New York from the Bahamas, was pounded by a freak wave during a storm last Saturday off the South Carolina coast. The wave reached the 10th deck of the towering ship, shattering two windows, flooding 62 cabins (and damaging some public areas) and injuring four people, according to the cruise line. The freak wave was estimated at 70 feet, far taller than surrounding waves.

Some passengers in affected cabins were badly frightened by water sloshing about on the floor of their staterooms. But the ship had no structural damage and departed Monday for another weeklong Bahamas cruise.

Studying the waves

Scientists are trying to decipher the complex forces that cause such rogue waves (they are not tsunamis, the waves that are caused by quakes).

Rogue waves, far bigger than any surrounding them, can occur during storms or calmer seas, and almost anywhere, although it appears they occur more frequently where there are strong currents, such as the Gulf Stream off the eastern coast of North America.

The European Space Agency, which provided satellite images on which much rogue-wave research has been based, says, "Severe weather has sunk more than 200 supertankers and container ships exceeding 200 meters in length during the last two decades. Rogue waves are believed to be the major cause in many such cases."

Cruise-ship damage is rare, but in recent years some cruise liners have been hit hard by rogue waves, including:

• The Explorer, on a "semester-at-sea" sailing in the North Pacific, was damaged in January when the ship, carrying almost 700 American college students, was struck by a wave estimated at 55 feet tall about 650 miles south of the Aleutian Islands. The wall of water smashed into the bridge of the 591-foot ship, knocking out windows and damaging the ship's controls and power. There were some injuries; the ship diverted to Honolulu for repairs.

• The Caledonian Star, sailing in the South Atlantic in 2001, was hit by a rogue wave estimated at 100 feet; it caused extensive damage and flooding to the bridge and navigation controls as it swept over the ship. The cruise ship limped back to port in southern Argentina; no serious injuries were reported.

• A smaller expedition cruise ship, the Bremen, was hit by a similar-sized rogue wave in the South Atlantic in 2001. The wall of water damaged the ship and knocked out power. No major injuries were reported; the crew was able to restart engines.

• The Queen Elizabeth II was struck by a rogue wave estimated at about 90 feet — about eye level with the ship's bridge — in 1995 in the North Atlantic. The large, well-built ship suffered little damage, and few injuries were reported.

Kristin Jackson: 206-464-2271 or kjackson@seattletimes.com