On the morning of June 21, residents watched from the shoreline as Lake Superior appeared to drain like a bathtub. But no plug had been pulled. Instead, the Great Lake was experiencing a confluence of severe weather events.
Between 6 a.m. and 10 a.m. that morning a thunderstorm rolled across Lake Superior moving west to east. With it, the storm brought a strong low-pressure system. Air pressure from this system began to press unevenly on the lake’s surface generating large waves known as meteotsunami.
“We don’t get events of this magnitude as frequently as some of the southern Great Lakes,” said Ketzel Levens, a meteorologist with the National Weather Service in Duluth, Min., in a statement.
While far less damaging than a tsunami, meteotsunamis have been known to reach nearly two metres in height. This particular meteotsunami crashed against the eastern shore of Lake Superior near Sault Ste. Marie, Ont., around 8 a.m., causing the water level in the area to rise by approximately 48 centimetres.
Strong gusts of wind, however, reaching up to 64 kilometres per hour, began blowing out of the south and southeast, pushing the water back across the lake. This caused a 109-centimetre drop in water levels around Sault Ste. Marie starting at 9:48 a.m. This was the draining bathtub effect many residents saw.
By pushing the water back to the western side of Lake Superior, the winds caused a seiche. This is when water oscillates back and forth across the lake, like water sloshing in a bathtub.
At 11:24 a.m. the lake’s surface rebounded to the eastern shore in the Sault Ste. Marie area causing the water level to rise by 114 centimetres. This was the highest water level surge ever observed in this section of Lake Superior. The seiche calmed slightly after this with the water oscillating east to west every eight hours or so.
Seiche’s have been known to cause water to oscillate back and forth for hours if not days. This one persisted until June 25.
Seiches have also been known to cause significant damage. In the winter of 1844, a seiche caused a 6.7 metre swell on Lake Erie that breached a sea wall killing 78 people and damming enough ice to cause Niagara Falls to temporarily stop flowing.
While no injuries were reported during the June 21 event, the fluctuation in water levels left many boats stranded on the lakebed, it damaged docks, resulted in minor flooding along the Wisconsin coast, and caused chaotic waves near the Duluth Harbor Canal in Minnesota. Researchers clocked the Duluth Harbor Canal’s current moving at two metres per second.
The Great Lakes Environmental Research Laboratory (GLERL) monitors for severe weather events on Lake Superior, but according to the organization, the storm was moving too fast for its models to forecast. “Fast moving squall lines, such as those that move across the lake to produce meteotsunami, often evolve too quickly to be fully represented in the hourly data generated by these models,” the GLERL said in a statement.
Moving forward, researchers at the GLERL plan to study how the water moved around the lake that day, while also improving its forecast models.
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