why frozen lakes seem to unfreeze from the bottom up. I know the top freezes over first because of density but why does the I’ve seem to simply get thinner while it unfreezes rather than having a pool of water over the ice. Go easy if it sounds like a dumb question.
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Lake ice doesn’t thaw just from the bottom. It thaws from the top, the inside, and the bottom.
Thawing on the top is driven mostly by warm air. If the weather suddenly turns warm and windy, there can be enough thawing on the surface to form a pool of water on top of the ice while the ice remains thick and impenetrable. I’ve seen that a few times.
Thawing inside the ice is driven mostly by sunlight that penetrates the ice. This weakens the ice and forms cracks and channels throughout. But ice floats on water, so if the melt water is able to go anywhere through the cracks, it’s down, not up.
The lake water beneath the ice is above the freezing point, of course, because it is not frozen. That water melts the ice from below if the ice isn’t cold enough to stay frozen. Water currents will accelerate thawing from below, which is why lake ice tends to thaw more quickly near an inlet or outlet.
How much of each kind of melting you get depends on the composition of the ice, the temperature of the ice, the temperature of the air, how windy it is, how sunny it is, the temperature of the water, and the currents in the water.
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