The mechanism by which lakes freeze from the top down

Question

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.

In: 23

Answer 1

Two other points to add. First, the freezing temperature of water changes with pressure. Water lower in a pind is under pressure from the water above it so it freezes at lower temperatures than the surface water.

Second water at the surface is exposed to the air. Wind cooling makes it freeze first.