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Welcome to the first birthday of The Nature of Phenology where we share the cycles and seasons of the outdoors. As we cruise into our second year, we welcome your nature questions or input about future topics! You can find our contact information on our blog which you can get to via archives.weru.org. I’m your host, Hazel Stark, and this episode was written by Joe Horn.
The cold weather over the past couple of months has slammed us from the arctic north and has only broken a few times as warm moist storms have pushed in from the south. This repeated cycle of gentle thaws paired with deep freezes has sent us skittering into winter like so many shards of ice across a frozen pond. “Frozen” is the operative term that can be applied to our neck of the woods for the coming months, though it is easy to keep warm and stave off the cabin nasties when shuffling across the frosty world on a pair of skates, skis, or snowshoes. Now that we are in the depths of winter, folks will be taking advantage of the peculiar physical properties of water as it freezes into the subject of today’s topic: ice.
In past years, the droughts that persisted from mid-summer straight through to winter meant that my local river’s flow was at a record low. This calm water followed by a deep freeze yielded some of the most extraordinary ice skating I have ever experienced for miles up and down the river. This year’s summer drought, however, was matched by weekly torrential rain storms which made the waters of the river swell and the prospects of good skating unlikely. But despite the high water, the cold of late fall built up a thick layer of black ice over the river by mid-December. What could be more incredible than skating? The simple fact that water behaves in such an odd way as to allow for skating.
Most substances expand when they get warm and contract when they get cool. If they get warm enough, they expand sufficiently to go through a phase change from a solid to a liquid or from a liquid to a gas. If they then cool, gasses will turn to liquid, and liquids will become solid. These are basic trends one can observe in a variety of settings: goldsmiths casting rings of molten gold or glassblowers melting sand in a kiln and then, after much work, cooling the molten glass into a vase. But what is especially odd about water is what happens when it freezes.
If you were to take a bar of iron and toss it into a vat of molten iron it would instantly sink to the bottom. This is because the hotter the iron, the more spread out the molecules become, making it less dense. When first tossed in, the iron bar is much colder, and therefore denser, so it will easily sink out of sight. If you were to try that same experiment by tossing a frozen block of ice into a lake, it would float—seemingly defying physics! This is because the density increases as water cools, but when it finally freezes all the molecules align in such a way that the water expands as it freezes to form a crystal. This unusual tendency for ice to float allows for life as we know it in our northern lakes, ponds, and rivers.
When the weather turns cold enough for our northern water bodies to begin to freeze, ice forms across the surface of the water, allowing the liquid water to remain protected from the elements below. If ice were instead more dense than water, as the surface of the water began to freeze, sheets of ice would begin to descend the water column crushing the life beneath. Instead, we get to skate across the ice or auger through it while fish swim beneath.
So this weekend, you too could experience the joy of this icy world. If the ice happens to be safe in your area, you could go for a ski or skate across the frozen surface or you could even try your hand at ice fishing (assuming you have a license). If your ice happens to be unsafe or if you don’t want to brave the cold, you could just go fetch a tall glass of iced coffee so you can poke playfully at the physical marvel that is ice.
You can find a link to the full transcript of this show as well as references, contact information, and accompanying photos by visiting archives.weru.org. You can also listen to or download our features or subscribe to podcasts. Theme music was by a pileated woodpecker, made available by the US Fish and Wildlife Service. Thanks for listening and please join us next week for another dive into The Nature of Phenology.
Marchand, P. J. (1996). Life in the cold: An introduction to winter ecology. Hanover, NH: University Press of New England.