The Science of Ice

Tuesday, November 17, 2009
A year ago from tomorrow, the bay outside my window was being skated on. Tonight, with lows in the teen, it’s likely the bay at least will freeze over, although I don’t think I’ll be skating on anything tomorrow. By all accounts, this November’s been a mild one and while I’m vastly enjoying the absence of snow, the cooler temperatures will have to persist for a few more days before I’m trusting any ice I see.

Honestly, I’m hoping the temperatures will warm up a bit, then drop suddenly. Currently, ice is slowly forming in bits and pieces, covering the majority of the bay in a feathery puzzle of ice. It’s pretty, but it’s hardly a smooth skating surface. In scientific terms, what I want is spontaneous nucleation. What we’re getting is heterogeneous nucleation. If only this piecemeal ice would melt off so a smooth, uniform ice could replace it some night soon.

It’s the first year I’ve lived close enough to a lake that ices over for the winter to really watch the freezing process and many perplexing questions about the science of ice have surfaced as we anticipate the inevitable freeze. For example: can the lake be completely liquid one day and completely ice covered the next? We won’t get answer to that question this year since we’ve had bits of ice bobbing around for a few days now.

Here’s another: do shallower areas freeze before deeper areas of the lake because there’s a small quantity of water that needs to reach the freezing point? The resident muskrat, who takes to swimming back and forth in front of the house, may or may not be affecting the answer to that particular question.

Common sense dictates that shallower water would freeze first. After all, ice is formed by the cooling water temperature. When the top layer of water cools, the cooled water sinks, pushing up more warm water until the body of water has reached a uniform “cold” temperature and ice forms on the top of the lake. Of course, water is less dense in its frozen form which is why we can ice fish: the ice floats to the top of the lake, the little fishies keep swimming in the chilly water below. That said, there is no ice on the bay until at least fifteen feet from the shore. Are the movements of the muskrat enough to prevent ice from forming?

While I want answers to my questions, the science of ice appears to be somewhat volatile. Even the simplest ice-related question – why is ice slippery – lacks a straight forward answer. It seems the experts can’t decide whether ice is slippery when we step on it because of the heat we create from the friction of our boots or whether the molecular composition of ice alone causes the substance to be, well, slippery.

I’ll let you know when the ice gets here. We may not know how, why, and are when the ice forms, but we do know it will.

My skates are waiting for it.

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