The ice cometh. Time to get to know it.

Is there any ice on your lake yet? There’s some on Birch Lake near Harshaw, Wis., where I live. It’s creeping out from the shore in ovoid shapes around the shallow inlet we call Indian Bay. I haven’t seen any ice on the main body of the lake yet, but then we haven’t seen temperatures down into the low 20s and teens, not even the overnight lows. Just give it time I guess.

Ice is a fascinating substance, and I’ll be writing about it in the next few posts. Right now the water in your lake is cooled down close to the freezing point of 32 degrees Fahrenheit (zero degrees Celsius). Or I should say, that’s the temperature at and near your lake’s the lake surface. It’s a little warmer deeper down.

Water is a peculiar compound in that it doesn’t continue getting denser as it cools. It reaches its greatest density at about 4 degrees Celsius (39 degrees Fahrenheit). And of course denser water sinks. So the water at the bottom of your lake is at around 4 degrees C, and the water at the surface is about ready to freeze. A very cold night or two will get the job done, forming a skin of ice over the surface that will thicken with more cold weather.

Here’s an interesting thought: What would happen if water and ice behaved the way most compounds do with falling temperature? That is, what if the coldest water were the densest and ice were denser still? Well, if you were to take a jar full of melted wax, and drop in a chunk of wax, that solid piece would drop to the bottom.

If water behaved that same way, ice forming at your lake’s surface from exposure to very cold air would sink. As more and more ice formed, it would continue dropping to the bottom, until after a long winter the lake most likely would be frozen solid from top to bottom. Nothing would survive the winter. In fact, deeper lakes probably would not thaw completely even through the summer.

As it is, ice floats. And the ice sheet that forms on your lake provides insulation that allows most of the water below to remain in a liquid state. So the fish, clams, turtles, frogs, snails and all sorts of macro- and microscopic life get through the winter just fine.

This anomalous density pattern is just one of many interesting properties of ice. In the next post we’ll explore why ice is slippery. You probably think you know the answer – I thought I did – but the latest scientific consensus says that answer is wrong.