New Research Exposes Weird Tsunamis Caused by Gravity Waves

New Research Exposes Weird Tsunamis Caused by Gravity Waves

On April 13, 2018, a huge swell of water broke on the eastern shore of Lake Michigan. It was a tsunami, one far from any fault line typically associated with the ginormous waves. This was a meteotsunami, a wall of water forged from the air conditions above it.

On that Friday the 13th, the lakefront was still chilly and thus not heavily populated, so the tsunami caused no injuries and only minor property damage. But its occurrence gave scientists with NOAA’s Great Lake Environmental Research Laboratory a unique opportunity to study the phenomenon and better understand how to predict these waves. Their research is published in the journal Natural Hazards.

“A lot of the work of the last 10 years has been documenting how frequently they occur and looking at case studies for when these storms have hit, what happened,” said Eric Anderson, an oceanographer with the NOAA laboratory and lead author of the paper, in a phone call. “What we found here is that we’re likely able to forecast at least a certain subset of meteotsunamis, and those are the ones driven by this high-amplitude atmospheric gravity wave.”

Meteotsunamis have a history in the Great Lakes, the Gulf of Mexico, and the Mediterranean Sea. Anderson said that meteotsunamis are easier to predict than your typical thunderstorms, as there’s only one key variable at play: atmospheric pressure; more specifically, any drastic changes in it. The tsunamis occur when a sudden, drastic change in air pressure hits the water, moving it shoreward, like a rolling pin pushing dough.

When the air is moving faster or slower than the water it hits, no danger is caused — the wave peters out, lacking the thrust to keep moving. On that day in April, a rapid shift of 12 millibars in air pressure exerted an atmospheric wave that moved at the same speed as the water, acting like a jockey to the water’s horse. They moved together in a shore-bound offensive at over 97 km per hour. The swift-moving water slowed as it hit shallow water and broke, but still created a 1.83 m surge on the beach town of Ludington, Michigan.

“That meteotsunami was hands down off the chart awesome,” said Debbie Maglothin, a local resident who took photos of the event, according to an NOAA press release. “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.”

The meteotsunami fully submerged a breakwall with its 1.83 m surge. (Photo: Debbie Maglothin, Other)
The meteotsunami fully submerged a breakwall with its 1.83 m surge. (Photo: Debbie Maglothin, Other)

Maglothin’s footage of the event ended up being vital information for Anderson’s team, who were able to use the photos and clips of the water’s movement to reconstruct the storm events, modelling the situation that gave rise to the lake tsunami.

Anderson said that climate change could exacerbate the phenomenon, based on research on meteotsunamis elsewhere. They’ve been detected on all continents but Antarctica, and a recent meeting of meteotsunami experts in Croatia laid the groundwork for better understanding these unique phenomena in a global context.

“With current climate projections, the intensity is not likely to change in meteotsunamis, but the frequency at least in the summertime is likely to go up by a significant amount,” Anderson said. Especially for these areas, more convective weather patterns in the late spring and early summer are more likely to catalyze such wave events, timing that corresponds to when more humans are likely to try and enjoy time beachside. “When we get a meteotsunami in the Great Lakes in June or July, it results in injury or death.”

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