Scientists at the University of Wisconsin-Madison have confirmed the phenomenon of rogue waves on Lake Superior - waves double the size of others at the same time and which have been named as a potential cause of the wreck of the Edmund Fitzgerald.

Professor Chin Wu and research assistant Josh Anderson are studying rogue waves in the Apostle Islands area where they observed waves as high as 17.7 feet when the other waves at the time averaged only 8.9 feet.

The big waves, sometimes called freak or killer waves, tend to occur unexpectedly and with huge force that makes them especially dangerous.

Although the study is still in progress, preliminary results show an increase in the probability for rogue waves near reflecting walls - such as a shoreline cliff.

Wind speed and direction and currents are likely other factors, the researchers note. And they say one rogue wave probably means another is not far behind.

"They group together during certain wave conditions," Anderson told Wisconsin Sea Grant. "You might get three or four in an hour and then you won't get one for the rest of the day."

Great Lakes mariners and others have speculated that a group of three rogue waves - the so-called "three sisters'' phenomenon - may be a factor in the sinking of the Fitzgerald in a storm near Whitefish Point, Mich., 40 years ago today.

Captain Jesse B. "Bernie" Cooper of the Arthur M. Anderson, the laker closest to the Fitzgerald at the time it sank, reported that his ship was hit by massive waves not long before he lost contact with the Fitzgerald that went down with all 29 crew members.

In the book "Shipwrecks of Lake Superior," Cooper said of the unusually large waves that "we took two of the largest seas of the trip. The first one flooded our boat deck. It had enough force to come down on the starboard lifeboat, pushing it into the saddles with a force strong enough to damage the bottom of the lifeboat. ... The second large sea put green water (the powerful center of a wave) on our bridge deck! This is 35 feet above the waterline."

Some have speculated that the rogue waves may have been the last straw for the Fitzgerald that was already taking on water and listing.

According to the National Oceanic and Atmospheric Administration, rogue waves have been part of marine folklore for centuries but have only been recently accepted as a real phenomenon by scientists. Most reports of extreme storm waves say they look like "walls of water." They are often steep-sided with unusually deep troughs.

The big waves often form because swells, while traveling across the ocean, do so at different speeds and directions. As these swells pass through one another, their crests, troughs and lengths sometimes coincide and reinforce each other. This process can form unusually large, towering waves that quickly disappear. If the swells are traveling in the same direction, these mountainous waves may last for several minutes before subsiding.

Another cause is a "focusing" of wave energy. When waves formed by a storm develop in a water current against the normal wave direction, an interaction can take place which results in a shortening of the wave frequency. This can cause the waves to dynamically join together, forming very big rogue waves.

Wu and Anderson deployed wave and current-measuring instruments throughout the Apostle Islands National Lakeshore. They examined the data for rogue wave patterns, looking at three possible causes - refraction on shoals, diffraction around islands and reflection off the sandstone bluffs so prevalent in the Lake Superior region. The largest rogue wave they observed at the sea caves area was 12.8 feet when the other waves around it were 6.1 feet.

Although the rogue waves observed in the Apostles aren't nearly as large as the offshore ones that hit the Anderson and may have doomed the Fitzgerald, "they're still dangerous to kayakers or sailboaters," said Anderson. "Waves are hazardous and we still don't know everything about them, so we're doing this research for public safety and to understand them better."

Wu and Anderson developed a computer model to calculate 35 years of waves on Lake Superior and found "the overall wave climate has been increasing on Lake Superior due to less ice cover and stronger winds in the winter, which generates larger waves," Anderson said.