It is my understanding that within a given medium warmer substances tend to rise and cooler substances fall, i.e. warmer air above cooler.
Assuming the same is true with water then in a lake the cooler water should fall to the bottom while warmer water rises to the top, correct? If so, I would expect that lakes would freeze from the bottom up. Can you please explain why this isn’t the case?
Thanks for your explanation.
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The ELI5 version is that the whole lake has to get to 0C first before any ice can form at all (with the top water getting cooler, falling down, warmer water rising, cooling, falling down, etc), then once the entire lake is sufficiently cold, ice crystals will start to form and rise to the top as they are less dense (and the cold air/wind at the top help to wick away heat).
For a really cool book about this topic that explains it in a ELI18-ish way, check out [Lakes: Their Birth, Life, and Death](https://www.amazon.com/Lakes-Their-Birth-Life-Death/dp/1643260480)
Edit: and the reason the whole lake doesn’t freeze is that the top layer of ice provides an insulating effect
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