Nature Notes – Lakes have frozen over, or will soon
Hilks Lake and Goose Lake near the western edge of Waconia, and Swede Lake near Watertown all froze over Nov. 24 and have kept their ice covers. Some other area lakes froze over in late November and opened up again a few days later, and some are freezing-up for the first time this week.
Freezing and the formation of ice covers on lakes or other waters is a process controlled in large part by a unique characteristic of water. Most materials, for example mercury in a thermometer, shrink as they cool. Water also shrinks as it cools from summer temperatures to 39 degrees F. As the cool water sinks it mixes with the rising warmer water until the lake becomes a uniform 39 degrees. However, as water drops below 39 degrees it begins to swell.
For this reason, water cooler than 39 degrees is lighter than water at 39 degrees and will float on the surface. Ice forms at 32 degrees, so on the first calm, freezing day or night after the lakes and ponds reach 39 degrees throughout, ice covers will form. The temperature of the water just in contact with the ice sheet in winter is 32 degrees, but a few feet below the ice the temperature is 35 to 38 degrees, and 39 degrees on the bottom.
If water cooler than 39 degrees continued to shrink and to become more dense and sink, ice would form from the bottom of a pond, lake or stream, rather than the top. Just think, our lakes and other bodies of water could have permanent ice covered by a layer of water in the summer.
Always remember, it takes at least 4 inches of new solid ice in contact with stationary freshwater for safe walking, skating and ice fishing. A snowmobile takes 6 inches of ice, 8 to 12 inches are needed for a car or small truck, and 12 to 15 inches for a medium-size pickup. You don’t want to fall through the ice as cold water saps body heat 25 times faster than air of the same temperature. In 32 degree water, you have about 15 minutes before going unconscious.
What’s happening outdoors now?
Pairs of great horned owls can be heard duet hooting, probably establishing nesting territories or at least keeping in touch. American tree sparrows, dark-eyed juncos and northern cardinals are the first and last birds at feeding stations each day. They begin coming to feeders about 25 minutes before sunrise and continue to come until about 25 minutes after sunset. All three species like to eat on the ground.
Red squirrels are active all winter. They prefer evergreen forests, which explains why they’re far less abundant in southern Minnesota than in the north. Flying squirrels come nightly to a good number of wildlife feeding stations. They typically arrive about 5 p.m. to dine on sunflower seeds, peanut butter and suet. Floodlights don’t scare these squirrels, nor does the presence of someone sitting quietly outside watching them.
On Dec. 13 a year ago
We had a cloudy, foggy day with a low temperature of 35 and a high of 38 degrees. Just traces of snow remained. Some oaks, like swamp white and northern red, continued holding a good share of their brown leaves. Lake Waconia had been frozen over since Dec. 6, and Burandt Lake since Dec. 2.