The ice cometh: Hear it boom

Ice is slowly taking hold here on Birch Lake, near Harshaw, Wis. Actually the lake had a skin of ice over more than half its surface late last week, but that was before winds kicked up. Last night the temperature was in single digits, where it remains this mourning, yet our entire lobe of the lake – more than half the total surface – is wide open. A 20 mph winds is keeping it so. If things calm down and the weather stays cold, we are in for a very fast freeze.

As I wrote earlier, this ice is a fascinating substance. One of its properties is its expansion. Most compounds contract when they cool and expand when they warm up. At the level of chemical structure, that means the molecules pack closer together when the substance is cold and spread out when it is warm.

Water and ice break that pattern. In liquid water (H₂O), each molecule – two hydrogen atoms (H) and one oxygen atom (O) – is bonded to three or four others. In ice, each molecule is bound to four others. That means more open space between the molecules, and so an expanded – thus less dense – substance.

As kids my brother and I found our about the expansion of ice when we left a few quart bottles of pop on the enclosed but unheated porch one very cold night. In the morning the necks of the bottles were blown clean off (or parents were not amused). Actually expanding ice is a nearly irresistible force. Water that creeps into a crevice in a rock can break that rock apart when it freezes. The expansion if ice is responsible for much of the natural weathering that takes place in northern landscapes.

How much does ice expand? About 9 percent by volume. Stated another way, ice is about nine-tenths as dense as water. This is why you may hear it said that only one about one-tenth of a floating iceberg is above the water.

One of the joys of winter on your lake is the sound if ice expanding. It is an eerie sound, a bit disconcerting if you happen to be on the lake at the time. Often while skating I have heard and seen an expansion crack sizzle right past me and off into the distance. If you can take having a window open on a very cold, still night, try lying in bed and listening to the ice boom. I guess it’s winter’s version of listening to the loons call.