By Kevin Roeten:
What are meteotsunamis, and why are they occurring on the Great Lakes?
It turns out it is quite feasible for a major wave to develop in the Great Lakes, other than what may form in the open seas such as the Atlantic Ocean, or even the Pacific. Evidently, massive rogue waves aren’t as rare as previously thought. University of Miami marine scientist Mark Donelan captured new information about an extreme wave. He witnessed one of the steepest waves ever recorded when it passed by the North Sea Ekofisk platforms in the early morning hours of November 9, 2007.
In the first hour of the day, it was detected an Andrea wave passed by several ocean sensors designed to measure the wavelength, direction, amplitude and frequency of waves at the ocean surface. Having information from a wave set of a total of 13,535 individual waves, was quite helpful. This was accomplished and collected by a system installed on a bridge between two offshore platforms out in the vast expanse of water. Researchers took the wave apart to examine how the components came together to produce this steep “rogue” wave.
This 100-meter wide “wall of water” moving at 40 mph proved Andrea reached a height greater than the height of 49 feet above mean sea level that was recorded. They also realized rogue waves can be more frequent, and occur roughly twice daily at any given location in a storm. Findings showed the steeper the waves are less frequent in their occurrence. This occurs about every three weeks at any location for the steepest rogues. The Andrea crest height was 1.63 times the average height of the one third highest waves. Optimal focusing of the Andrea wave showed the crest could have been even higher and limited by breaking at 1.7 times the significant height. This establishes the greatest height rogues can reach for any given significant height.
“Rogue waves are known to have caused loss of life as well as damage to ships and offshore structures,” said Donelan, professor emeritus of Ocean Sciences at University of Michigan. “Our results, while representing the worst-case rogue wave forecast, are new knowledge important for the design and safe operations for ships and platforms at sea.”
What’s Happening in the Great Lakes?
Are there tsunamis in the Great Lakes? Tsunamis have been on the news lately with a wave system hitting Japan in November 2016. A November 22 tsunami hit the island country after a magnitude 7.4 earthquake occurred in the ocean offshore of Japan. Have there been tsunamis in the Great Lakes? The answer is actually yes, but the Great Lakes region is an area of low seismic activity. Incredibly, new research published has found tsunamis have occurred in all five of the Great Lakes, but none formed from earthquake activity. Actually, the tsunamis in the Great Lakes are caused by large groups of thunderstorms.
Check this latest outlook in Nature.com, November, 2016 Great Lakes meteotsunamis.
Tsunamis in the Great Lakes are technically called meteotsunamis, or tsunamis caused by weather conditions. A meteotsunami is a rapidly moving wave generated by quickly changing air pressure, high wind speeds, or a combination. While these meteotsunami waves are not as large as those generated by seismic tsunamis, NOAA reports a wave was actually measured off Chicago in 1954 at 10 feet high, several people were torn off a pier, and seven drowned.
There has been some notable meteotsunamis in the Great Lakes recently. In 2014 a Lake Superior meteotsunami overtopped the Soo Locks, impacted shipping operations and caused evacuation of some homes in Sault Ste. Marie, Ontario. And the NOAA report documented another one in 2012 off Cleveland, Ohio, knocking people on the beach off their feet and swamping boats in harbors.
Great Lake Thunderstorms
What does it take for thunderstorms to form meteotsunamis in the Great Lakes? Usually, situations which cause these tsunamis are a long line formation of thunderstorms or an organized grouping of long-lasting thunderstorms. The highest probability of occurrence of these convective events is during the late-spring to mid-summer timeframe, with April and May being the highest probability months.
Researchers used the NOAA water level gauges in the Great Lakes to analyze causes and frequency by detailed analysis of these long-term water level records. Results indicated an overall average of 106 meteotsunami events per year throughout the entire Great Lakes basin with Calumet Harbor, Ill., on Lake Michigan (29 per year) followed by Buffalo, New York, on Lake Erie (17 per year) and Alpena, Mich., on Lake Huron (14 per year). Of the 5 Great Lakes, Lake Michigan had the highest frequency of meteotsunamis at 51 per year, followed by Lake Erie (27/year); Huron (17/year), Superior (6/year) and Ontario (5 /year).
While water level changes are dealt with by coastal communities, this research found waves generated by meteotsunamis are not considered design along the Great Lakes coasts. It seems this research has also shown the value and need for continued monitoring of existing Great Lakes water level gauges. Coastal communities possibly impacted need to understand what meteotsunamis actually are.
The majority of the observed meteotsunamis happen from late-spring to mid-summer and are associated primarily with convective storms. Meteotsunami events of potentially dangerous magnitude (height > 0.3 m) occur an average of 106 times per year throughout the region. These results reveal that meteotsunamis are much more frequent than follow from historic anecdotal reports.
In Michigan, most meteosunamis occur from late spring to early summer, occurring on average 106 times/yr. Results reveal meteosunamis are more frequent than follow from historic anecdotal reports. To date, meteosunamis in the Great Lakes have been an overlooked hazard.
The Laurentian Great Lakes, which form the Earth’s largest freshwater system and include over 10,000 miles of coastline, show an example of a region with low seismic activity but a long history of impactful meteotsunami events.
Kevin Roeten can be reached at roetenks@CHARTER.NET.
© Copyright by Kevin Roeten, 2017. All rights reserved.