Numerous Minnesota lakes freeze over toward the end of November, with those already ice-covered adding new inches of ice.
Freeze-up dates for Minnesota lakes in 2020 include Sibley Lake at Pequot Lakes on Nov. 15; Caribou Lake near Lutsen on Nov. 18; Lake Hendricks on the South Dakota border in Lincoln County and Lake Bemidji on Nov. 30; and Lake Vermilion at Tower and Lake of the Woods on Dec. 1.
Lake Mille Lacs iced over Dec. 3, and Lake Minnetonka finally froze over Dec. 24. The freeze-up date recorded is when at least 90% of a lake is ice-covered and stays that way.
During the fall season, as the angle of the sun drops, lake water cools. As it cools it shrinks, becoming more dense. Once the water drops below 39 degrees, however, the water begins to swell. This cooler water, having become less dense as it swells, naturally rises to the surface. Ice forms at 32 degrees. On the first calm, freezing day or night after a particular pond or lake reaches 39 degrees in all parts, an ice cover will form. The temperature of the water in contact with the ice sheet is 32 degrees, but a few feet below the ice the temperature remains above freezing, reaching 39 degrees on the bottom.
It takes at least 4 inches of new solid ice in contact with stationary water for safe walking, skating and ice fishing. A snowmobile requires 6 inches of ice, with 8 to 12 inches needed for a car and 12 to 15 inches for a medium-size pickup.
Some other observations:
- Flocks of Canada geese are gleaning corn in combined fields.
- With fresh snow animal tracking is interesting.
- Pairs of great horned owls are hooting in duet, possibly setting up territories, or maybe just keeping in touch.
- I've seen muskrats up on the ice of ponds eating water plants they have gathered from below.
- As long as most days remain above 27 degrees, raccoons will be active about the landscape.
- Across central and northern Minnesota, black bears are sleeping, not hibernating. They go into torpor, a reduced state of activity and metabolism from which they easily awaken
Jim Gilbert has taught and worked as a naturalist for more than 50 years.
