Mystery Wave Strikes Maine Harbor

This rare photo of a rogue wave was taken by first mate Philippe Lijour aboard the supertanker Esso Languedoc, during a storm off Durban in South Africa in 1980. The wave approached the ship from behind before breaking over the deck, but in this case caused only minor damage. The wave was between 16 and 33 feet (5-10 meters) tall. Credit: Philippe Lijour via ESA

A giant wave in the Bay of Biscayne, in an image published in Fall 1993 issue of Mariner's Weather Log. Credit: NOAA

How tsunamis work.

A series of large, unexpected tsunami-like waves as high as 12 feet struck Maine's Boothbay Harbor on Oct. 28, and there's still no explanation for what caused them.

From the Boston Globe: "The waves could have been caused by a powerful storm squall or the slumping of mountains of sediment from a steep canyon in the ocean — a sort of mini tsunami. The last time such rogue waves appeared in Maine was at Bass Harbor in 1926."

Damage estimates range from $10,000 to $20,000.

Rogue waves on the open ocean are known to come out of the blue and sink ships. They soar up to 100 feet and have long been thought of as myths, in part because they typically leave no survivors. But an 80-foot rogue wave was measured by instruments on a North Sea oil platform in 1995. A study earlier this year found that tiny waves can concentrate together to become huge rogues very quickly in rare circumstances.

Tsunamis can be caused by undersea earthquake, as was the case with the 2004 Indian Ocean catastrophe. But seafloor "landslides" can do the trick, too. The thing about a tsunami: it can be just inches tall on the open ocean — practically unnoticeable — but when it nears shore, the shallower seafloor forces the wave up. A tsunami is not one wave, but a series — much like what was desribed in Maine, where a witness said the water rose, receded, and rose again 15 minutes later, then once more.

• Gallery: Monster Waves