NOAA: Pressure-formed meteotsunami documented, could help forecasters with warnings

Apr. 17—LUDINGTON — Large waves on Lake Michigan aren't unusual, but the one that crashed ashore on April 13 three years ago was a real whopper.

A large wave surged out of the lake and onto the shoreline in Ludington, flooding infrastructure and damaging homes and docks. And somebody with a smartphone happened to be there when it did.

Scientists for the National Oceanic and Atmospheric Administration used those photographs and videos to reconstruct the event in computer models, and determined it to be the first documented meteotsunami in the Great Lakes caused by an atmospheric inertia-gravity wave.

"We figured they were out there in the Great Lakes, but we had never documented one before," said Eric Anderson, physical scientist and oceanographer for NOAA's Great Lakes Environmental Research Laboratory.

Meteotsunamis are just like tsunamis, he said, but they are generated by weather instead of being caused by an earthquake. Then there are two types of meteotsunamis — those caused by thunderstorms and those caused solely by atmospheric pressure changes, he said.

The latter is the sort a Ludington resident recorded on her mobile phone that spring day three years ago.

"That meteotsunami was hands down off the chart awesome," said Debbie Maglothin, of Ludington.

She was standing in sight of popular tourist attraction Ludington Breakwater Lighthouse when the natural phenomenon happened, she said.

"The water in between the breakwaters didn't go down like the water on the outside of them, so it created waterfalls that cascaded over the breakwaters. Had this event occurred during summer it could have washed people right off the breakwaters," Maglothin said.

But meteotsunamis caused by air pressure changes will now be easier to forecast because she was there that day to record the event for later forensic analysis, Anderson said.

An atmospheric inertia-gravity wave is a wave of air between 6 and 60 miles long created when a mass of stable air is displaced by an air mass with significantly different pressure. This leads to a wave of air with rising and falling pressure that can influence the water below, synchronizing with water movement on the lake's surface.

"These pressure waves are generally easier to predict than thunderstorm-driven meteotsunamis," Anderson said.

Meteorologists now know what "ingredients" to watch for in weather conditions, he said, "so it's not like a forecast, but an alertness for these conditions."

NOAA scientists used data from weather records, water level gauges, and the photos and videos Maglothin recorded to create both an atmospheric model and a lake model, Anderson said, then built a system to monitor those two things together.

He said most Great Lakes meteotsunamis are caused by thunderstorms, which are difficult to predict to the level of detail needed to forecast when they may cause these large, shoreline-jumping waves.

But now the less common sort of meteotsunamis are easier to predict, perhaps minutes to hours in advance.

"At least we have the capability in hand to predict at least a fraction of the meteotsunamis we see in the Great Lakes," Anderson said. "Our short-range weather models can pick up these atmospheric pressure waves, whereas predicting thunderstorms is more difficult."

The research was recently published in a special edition of the journal Natural Hazards about meteotsunamis.

NOAA scientists said meteotsunamis occur around the world, and in the U.S. mostly in the Great Lakes and along the East and Gulf of Mexico coasts. These events in the Great Lakes can be particularly insidious because they can bounce off the shoreline and return when the skies are clear, they said.

The largest such waves are typically between 3 and 6 feet and occur only about once a decade, record show.

Anderson said predicting these waves in advance could give communities possibly life-saving warnings and allow residents and property owners to take protective measures.

In Ludington, the meteotsunami three years ago caused property damage but no injuries. Had it happened during the height of the summer tourism season, people may have been harmed like during the meteotsunami that killed seven people in Chicago in June 1954, NOAA officials said.