Monster waves of mysterious origin prowl the oceans, surprising ship captains as they appear on the horizon like great walls before crashing across the bow, or worse.
Windows of luxury liners get broken. Supertankers are disabled and left vulnerable to the whim of the next wave. Many ships disappear.
"Two large ships sink every week on average, but the cause is never studied to the same detail as an air crash," says Wolfgang Rosenthal of the GKSS Forschungszentrum GmbH research center in Germany. "It simply gets put down to bad weather."
A significant handful of these sunken ships -- about 200 over the past two decades -- are supertankers or large container ships, according to a statement explaining Rosenthal's new research.
The cause for most of the mishaps is a mystery, but so-called rogue waves as tall as 10-story buildings are believed to be the major culprit in many cases. Yet until recent years, scientists doubted such strangely huge waves occurred so frequently.
A new study based on satellite data and lab experiments reveals the rogues are fairly common and helps explain how they form.
The Queen Elizabeth II was struck by a 95-foot (29-meter) rogue wave in February 1995. Captain Ronald Warwick said "a great wall of water" appeared. "It looked as if we were going into the White Cliffs of Dover.
On Jan. 1 1995 an oil rig in the North Sea was hit by an 85-foot (26-meter) wave. The waves around it were less than half as tall.
In one week during early 2001, two tourist vessels, the Bremen and the Caledonian Star, were smacked by separate 98-foot (30-meter) waves in the South Atlantic while the ships were 620 miles (1,000 kilometers) apart. Windows on the bridge of each ship were broken and the Bremen was disabled and left adrift for about two hours.
Rosenthal, an expert on rogue waves, and his colleagues obtained satellite data taken during the time of the mishaps with the two cruise ships. The data were collected by the European Space Agency's twin spacecraft ERS-1 and 2, which employ a technique called synthetic aperture radar to measure wave height.
In the three weeks of satellite data, researchers found 10 waves in various parts of the world that were more than 82 feet (25 meters) high. That added a global perspective to information collected from various oil platforms. (A radar device on the North Sea's Goma oilfield counted 466 rogue waves over 12 years.)
The giants often form where normal waves meet strong ocean currents or eddies, the new analysis shows. A current can concentrate wave energy, causing a wave to grow. Also, a series of fast waves can catch a set of slower-moving waves and merge into a single beast.
Rogues also develop from weather fronts and low-pressure systems. Winds blowing in one direction for long periods of time -- more than 12 hours -- can create unusually large waves. Scientists already know that, and anyone living along the southeast coast of the United States has seen large waves arrive days in advance of an approaching hurricane.
The new research found that some waves travel in sync with the wind, setting up superb growth conditions. Quicker waves move ahead of the storm and slower waves fall behind, in both cases causing them to dissipate somewhat.
More needs to be learned, including whether the deadly waves can be predicted.
"We know some of the reasons for the rogue waves, but we do not know them all," Rosenthal said.
© 2013 Space.com. All rights reserved. More from Space.com.