Wave Interactions May Explain Why Some Tsunamis Are So Powerful

Lawrence LeBlond for redOrbit.com – Your Universe Online

Ocean waves are a source of calming for meditation, and a source of enjoyment for thrill-seeking surfers. These waves are also a source of wonder for researchers trying to explain the power of the tsunami.

Two applied mathematicians from University of Colorado Boulder have taken a closer look at these waves, discovering X- and Y-shaped ocean waves that could help explain why some tsunamis become as powerful as they do.

Professor Mark Ablowitz and doctoral student Douglas Baldwin observed these wave interactions in shallow water at two different coastal locations: Nuevo Vallarta, Mexico, and Venice Beach, California. Their observations showed wave interactions that were previously believed to be rare occurrences actually happen every day near low tide.

During these low tide events, the duo observed single, straight waves interacting with each other to form X and Y-shaped waves and other even more complex wave patterns, all of which were predicted by mathematical equations, said Ablowitz.

Baldwin added that when these ocean waves collide, the “interaction height” is the sum of the incoming wave heights. “But the wave heights that we saw from such interactions were much taller, indicating that they are what we call nonlinear.”

Satellite observations during the March 2011 Japan tsunami indicate there was an X-shaped wave created by the merger of two large waves.

“This significantly increased the destructive power of the event,” said Ablowitz. “If the interaction had happened at a much greater distance from shore, the devastation could have been even worse as the amplitude could have been even larger. Not every tsunami is strengthened by interacting waves, but when they do intersect there can be a powerful multiplier because of the nonlinearity.”

These wave interactions were first noticed by Ablowitz in 2009 while visiting Nuevo Vallarta with his family. He took hundreds of photographs and videos of the nonlinear waves over the following several years.

“Unlike most new physics, you can see these interactions without expensive equipment or years of training,” said Ablowitz. “A person just needs to go to a flat beach, preferably near a jetty, within a few hours of low tide and know what to look for.”

To see if these wave interactions existed elsewhere, Ablowitz’s research partner, Baldwin, drove from Colorado to Los Angeles to observe wave interactions on the Pacific Coast. He found what he was looking for at Venice Beach, California.

“I don’t think there is anything more enjoyable in science than discovering something by chance, predicting something you haven’t seen, and then actually seeing what you predicted,” said Baldwin.

The research is published this month in the journal Physical Review E.

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