Ice: is it really an insulating blanket?

OK - it's a duvet, not a blanket

OK - it's a duvet, not a blanket

Physics and thermodynamics never were my strong point, as I displayed when I wrote the other day that the ice forming on my pond was acting as an insulator.

In fact, as one of my colleagues pointed out to me, ice actually conducts heat four times faster than water – it’s not a good insulator at all.

The ice will be transferring heat to the cold air above faster than if the pond was still liquid.

Water is densest at 4 degrees C, and once it reaches this temperature it sinks to the bottom of the pond, with colder lighter water and ice floating to the top. Once the ice forms it does stop the wind from mixing the warmer, denser, water near the bottom of the pond with the colder water above it. As long as the cold weather doesn’t go on for too long (and in southern England, it usually doesn’t), this will help to slow the cooling of the pond, usually preventing it from freezing solid.

So the ice isn’t really much like the duvet above – its more like a sitting in a tent without a sleeping bag on a cold night! It’ll keep the wind off, but it’s gradually going to get colder and colder, until the sun rises the next day.

Thanks to Bob for adding to my basic grasp of the physics of ice.

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