6 December 2012

Surprising Source of Tsunamis

Posted by kramsayer

A wave surge from a storm in October 2001, along the same coast in South Bass Island State Park, Ohio, affected by the meteotsunami. (Credit: Ohio Sea Grant)

No one knew what happened when a 7-foot wave hit Lake Erie’s shoreline, sweeping holiday weekend beach-goers off of their feet and swamping boats in their harbors on May 27 of this year.

News reporters jokingly called it a tsunami, but explained it was just another wave surge in the wake of windy weather coming from the Canadian border.

But it was a tsunami, said Eric Anderson, a physical scientist at the Great Lakes Environmental Research Laboratory, Ann Arbor, Mich. during the Tuesday afternoon poster session on natural hazards at the American Geophysical Union’s Fall Meeting. And the storm clouds stirred it up. A squall that was hauling across Lake Erie added speed and a spike of pressure to turn the water into a solid wave.

These weather-driven walls of water, called meteotsunamis, are different from the low-pressure storm surges and the seiches—those large sloshes of water often mistaken for high tides after storms, Anderson said. It takes three specific conditions to make a meteotsunami, he said. First, it takes a burst of pressure to get the process started. Then, the storm has be moving as fast as the water, so it can “feed” more energy into the waves. Finally, the waves have to hit shallow terrain that causes them to slow down but grow in size.

The 7-foot tsunami on Lake Erie was a surprise with significant consequences. As a result, Anderson focused his research on real-time forecasting systems. He studied the effects of storm speed, pressure changes, and wind on waves that wash onshore, with the gauge network already in place around the Great Lakes. The results of his experimental models may lead to better meteotsunami predictions, he showed in his poster presentation.

“With our current system, we never would have known about this wave unless it affected people,” said Anderson.

Other scientists studying these interactions between weather and waves are finding meteotsunamis are more frequent than previously thought. Scientists thought they only occurred in specific areas, such as the Mediterranean and China seas, said Dave Tappin, a marine geologist for the British Geological Survey, in Nottingham, United Kingdom. There they have special names: it’s an “abiki” in Japan, a “marrobbio” in Italy, and a “rissaga” in Spain.

But then one struck Great Britian unexpectedly. Tappin started studying meteotsunamis after one struck the southwest coast and then surged up the English Channel in June, 2011. The 20- to 40-centimeter wave was reportedly the result of a submarine landslide. Yet wave anomalies were also tracked along the eastern European coast, from Calais to Spain. So Tappin searched for another cause.

With data gathered from tidal gauges, weather buoys, satellite images, and a YouTube video, Tappin and his collaborators tied the unexpected waves to a series of storm cells traveling through the area, he said during a talk at the natural hazards session on Tuesday morning.

“It’s the first time a meteotsunami has been identified in England,” said Tappin.

Now that scientists know how weather can trigger meteotsunamis, the next step is to investigate more of them, said Tappin.

Although the meteorological tsunamis don’t typically generate waves as big as those caused by earthquakes, they still be very dangerous. Some of the most destructive waves on the Adriatic Sea coast caused more than $5 million of damage.

-Elizabeth Devitt is a science communication graduate student at UC Santa Cruz