The Lake Where You Live

In spring the lake ice melts mostly from the bottom up. First some ice melts along the shore. The sun shines through and heats up the bottom sediment. That warms the water, which goes to work on the ice from underneath. The warming accelerates until, one day, the lake lies fully open.

In fall, the lake cools from the top down. That process has already started. Right now your lake’s surface temperature is probably still in the mid-fifties or so, because the days have been mostly warmer than usual.

But from here on, the temperature will drop steadily. Cold air, especially at night, persistently draws heat from the water. On some very cold mornings you might witness steam fog — tendrils of white mist rising from the surface. The relatively warm and moist air just over the water rises to meet the much colder air higher up, and that causes the moisture to condense into tiny, visible droplets. When observing steam fog, you can imagine it as the water’s warmth escaping.

Through late October and November, the temperature falls quite rapidly. By late November, the surface water is most likely at or near the freezing point of 32 degrees C. Cold wind chills the water faster. It disturbs the coldest water at the air interface and brings up slightly warmer water from below, exposing it to the freezing conditions.

Eventually, the lake takes on its winter temperature stratification. The warmest and densest water, at about 39 degrees F, lies at the bottom. The coldest and least dense water, at the freezing point, floats on top.

Now it takes a while for the ice to form. It takes 80 times as much cooling to convert that surface water to ice as it would to lower its temperature by one degree. All sorts of interesting ice formations can appear when wind sloshes that ready-to-freeze water around. Once here on Birch Lake, after a very cold and windy night, sparkling discs of ice, like coins, clung to the bulrushes along our shore, just above the water’s surface. Water left on the stalks by receding wavelets had flash-frozen in the frigid air, and the ice built up through the night.

Now the wind, which earlier made the water cool faster, actually slows down the formation of ice. That’s because the turbulence constantly shatters the tiny ice crystals as they try to form. 

Finally, as the surface water hovers at the freezing point, a very cold and very still night comes along. And in the morning, there it is, a skin of ice from shore to shore.

That ice thickens at a rate that depends on the air temperature. To give an idea how fast it happens, a full day with an average temperature of 17 degrees would add about an inch to the initial, fragile sheet. The pace of freezing slows down as the ice gets thicker, because the ice itself acts as insulation against the cold air. 

So that’s a look at what will happen as we wait for the ice to open a new and very different season of fun and adventure on our lakes. 

My ice fishing gear will be ready.

Ted Rulseh is a writer, author and lake advocate who lives on Birch Lake in Oneida County. His new book, “Ripple Effects,” has been released by UW Press. You can learn about it by visiting his website at https://thelakeguy.net.