TRAVERSE CITY — Don’t underestimate waves on the Great Lakes.
A wind storm last week created waves so strong it blew the ice lid off much of Lake Michigan. In a matter of days, ice coverage shrank from about 60 percent of the lake to 30 percent.
Wind creates waves in the open water, which crash into the ice and break it up. The tumult also churns the water, which in turn mixes warmer deep water with the surface water and heats it to just above freezing.
“The ice is getting shoved under the main ice pack so you get melting and compacting of the ice, so you’re opening up even more water,” said Nick Schwartz, a meteorologist at the National Weather Service in Gaylord. “It’s not overly complicated, but it’s a bit of a snowball effect that goes on.”
Ice cover on the lake peaked at 82 percent around Feb. 13. Winds broke it down to 60 percent over several days, but the wind storm Friday to Saturday did the most damage, with gusts up to 50 miles per hour and waves of 10 feet or more.
Other lakes also lost ice coverage, though not such a large percentage.
“Lake Michigan took the biggest hit because of existing open water,” Schwartz said. “Once you had a decent stretch of open water, it lent itself to a decrease in open water ice coverage.”
Ice over deep water is much less stable than the ice that forms over inland lakes and bays.
“It’s very prone to fracturing and winds,” Schwartz said.
Rain and warm temperatures last week also made it hard for the water to refreeze, said George Leshkevich, a physical scientist at the Great Lakes Environmental Research Laboratory of the National Oceanic and Atmospheric Administration.
Lake Michigan hasn’t frozen to such an extent since 1994, when it was about 90 percent covered, Leshkevich said.