People living near ponds and lakes have the good fortune of being able to directly observe the ice-out phenomenon. Although some believe that ice sinks when it goes out, that is not the case because ice is lighter than water.
The process starts with ice retreating from the shore, creating a belt of open water around the lake with a temperature of about 45 degrees. A wide band of ice beyond the open water then becomes soft and rotten while the rest of the ice cover turns dark. At this point, turtles and leopard frogs begin to break their winter hibernation in water near shore, emerging from the bottom sediments.
The main ice sheet weakens and begins to fracture in large sections when winds become strong enough to move it. This is followed by rapid melting of ice crystals on the edges of the floating sections as they come in contact with warmer water. Eventually wind will sweep the last ice sheets from the lake. As the ice sheets are pushed ashore, the remaining ice is generally in chunks up to 7 inches thick and honeycomb-shaped.
Some loose ice along a shore doesn’t mean the ice is still in, because a boat can easily be pushed through. I consider ice-out to have occurred when at least 90 percent of the lake is free of ice.
Ice-out is an exciting time. Common loons arrive on many lakes just as the ice is leaving. Soon fishing boats and sailboats will appear and docks will go in, as we are off and running into summer. During the early spring of 2012, the ice went out of Lake Minnetonka on March 21 and Lake Mille Lacs on March 26. 2013 was considered to be a late spring, and ice-out on Lake Minnetonka was May 2 and for Lake Mille Lacs was May 16.
Jim Gilbert’s Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.