May 27, 2012 was an unusually hot and sticky spring day. A severe thunderstorm rumbled over London and south across Lake Erie toward Ohio just after 1 p.m.

The mercury topped out at 31C and skies quickly cleared. Beaches near Cleveland came alive with sun-seekers and swimmers. It was the Memorial Day long weekend.

But by late afternoon the weather office was fielding urgent telephone calls from alarmed citizens.

“People saw three seven-foot waves, out of nowhere,” says Eric Anderson, an oceanographer with the U.S. National Oceanic and Atmospheric Administration in Ann Arbor, Mich.

A trio of swimmers in Madison, 40 minutes east of Cleveland, was swept almost a kilometre into the lake and later rescued. A marina was swamped.

These were no ordinary waves. They were a type of tsunami known as a meteotsunami.

Anderson was one of 25 experts who met this week at the University of Michigan Co-operative for Great Lakes Research to devise an early-warning system for the planet’s largest fresh water system, which has 16,000 kilometres of coastline.

“The risk is always higher if you have not prepared for anything,” says Chin Wu, an engineering professor at the University of Wisconsin.

“It’s not a big problem in the deep part of the lake, until you reach the shore where the water will be shallower, and it will always pump up the tsunamis.”

Unlike regular tsunamis caused by earthquakes, such as the 2011 wave that devastated parts of Japan, meteotsunamis are caused by meteorological conditions, specifically, fast-moving convective storms with enough power to push water down and ahead of them akin to a tidal surge.

In a research paper published last year, Anderson, Wu and several co-authors warn “meteotsunamis may become even more frequent under a changing climate” with fiercer storms.

“Generally, they’re not as destructive as earthquake tsunamis, but they can surprise you,” says Anderson, a Pennsylvania native who grew up going to Lake Erie beaches. He works at NOAA’s Great Lakes Environmental Research Laboratory.

The term meteotsunami, coined about a decade ago, is not widely known.

But the phenomenon is not new. Records suggest at least six major events since 1929, Wu says.

On June 26, 1954, what is now considered a meteotsunami washed eight people fishing off a pier in Chicago. They drowned in Lake Michigan.

A storm had passed, and they thought it was safe to approach the lake when a wall of water more than two metres high hit unexpectedly.

On Sept. 4, 2014, a storm-driven surge of water from Lake Superior overflowed the locks at Sault Ste. Marie and flooded homes on the Canadian side.

“There was a five-foot fluctuation in a couple of hours,” recalls Keith Kompoltowicz, chief of watershed hydrology for the U.S. Army Corps of Engineers in Detroit.

In the examples from Chicago and the Cleveland-area, lake water driven by storms bounded from one side of the lake to the other, building momentum before striking with dramatic force.

In the Ohio case, the water driven by the storm first hit the Ohio shore with little fanfare, bounced north to the Canadian side of Lake Erie around Port Stanley and returned south to give unsuspecting beachgoers and boaters the fright of their lives.

It took hours for the three big waves to build. They hit five minutes apart, bringing with them swift outflows often confused with rip currents that pull swimmers into deeper water without mercy.

“All of us have the intuition when it’s rough water to stay out of the lake. But with a meteotsunami, any of us could be out there and (get) caught in a tough spot,” says Anderson.

That’s why an early warning system, based on information from lake buoys and other nautical and meteorological tracking devices, is considered important for public safety.

“The more lead time we can give somebody, the better,” adds Anderson.

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“We have a lot of infrastructure that can detect this stuff. But the meteotsunamis can be a little hard. We may have to find ways to dig into the data and to set up new measurements.”

Wu, who attended the Ann Arbor meeting, says he hopes a warning system can be in place within a couple of years as various government agencies combine efforts.

“This is our passion. We want to see how we integrate it and build on existing infrastructure and technology and messaging through the media.”

Experts estimate, based on the data they have compiled, that there are about 100 meteotsunamis on the Great Lakes every year. Most are small or hit in areas that are sparsely populated and go mostly unnoticed, however.

Lake Erie, which is relatively shallow and aligned with west-to-east thunderstorm patterns, and the southern half of Lake Michigan appear most prone to the meteotsunami phenomenon which also occurs in fresh water areas in other parts of the world.

The shallower the water, the less energy a thunderstorm needs to cause a meteotsunami.

Because many storms coming from the west dissipate enough force by the time they get to the GTA, Lake Ontario is less prone, but not immune, says Wu, who is based at the campus in Madison, Wis.

Anderson calls meteotsunamis a “distinctly different” type of wave.

On one end of the spectrum are wind-driven waves, such as those that cause whitecaps and crash on shore. A wind wave is also blamed for swamping and sinking the Detroit-bound freighter Edmund Fitzgerald, taking all 29 hands down, in Lake Superior in 1975.

A longer type of wave called a seiche (pronounced saysh) is at the other end of the spectrum and is best compared to water sloshing from end-to-end in a bathtub.

“We’ve seen 15-foot differences from Toledo (Ohio) to Buffalo,” says Klompoltowicz. “There are boats in Toledo in marinas sitting on the bottom while there’s not enough line for boats at marinas in Buffalo, and they break free.”

Until the phenomenon of meteotsunamis was better understood, some coastal tragedies were blamed at first on seiches, research by Wu and colleagues at the University of Wisconsin shows.

They include a six-metre wave that hit Grand Haven State Park in Michigan, on the eastern shore of Lake Michigan, killing 10 on July 4, 1929.

A three-metre wave drowned five at Holland State Park in Michigan on July 13, 1938.

On the same date in 1995, large waves were reported on Lakes Superior, Huron and Erie, but no deaths were reported.

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