Below 4° Celsius, water i do not care less thick as it it s okay colder, causing water around to freeze to float come the top. Public Domain Image, source: Christopher S. Baird. Data source: CRC Handbook the Chemistry and also Physics.

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Warm water usually gets much more dense as it gets colder, and also therefore sinks. This reality may command you to think that ice cream should kind on the bottom the a lake first. However a funny point happens to water as it gets even colder. Colder than 4° Celsius (39° Fahrenheit), water begins expanding and also becomes less thick as it gets colder. As a result, close to freezing, chillier water floats to the top and also the warmer water sinks to the bottom. The thickness of water as a function of temperature have the right to be seen in the plot top top the right. Eventually, the coldest water, which has floated to the height of the lake in wintry conditions, freezes to kind a great of ice. Right as soon as the water freezes come ice, the ice becomes substantially less thick than the water and also continues to float ~ above the lake"s surface.

Ice is less thick than water since of the means it develops a hexagonal crystalline structure. Each water molecule consists of two hydrogen atoms bonded come the bottom of an oxygen atom. Once ice forms, the hydrogen atom of one water molecule type weak hydrogen bonds v the top of the oxygen atom of two other water molecules. Lining up the water molecule in this pattern takes up much more space than having them jumbled randomly together (as is the case in fluid water). And also because the very same mass of molecules takes up much more space as soon as frozen, ice cream is less dense than liquid water. Because that this same reason, water listed below 4° Celsius becomes increasingly less thick as it gets colder. Nearby to freeze temperatures, the molecule in the fluid water start to heat up right into the space-filling hexagonal structure.


In the winter, temperatures in a lake acquire close enough to freezing that the cooler water is much less dense and also floats to the top. Public domain image, source: Christopher S. Baird.

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The textbook River and Lake Ice engineering by George D. Ashton states, "As a lake cools from over 4° C, the surface ar water loses heat, becomes an ext dense and sinks. This process continues till all the water in the lake is in ~ 4° C, once the thickness of water is at its maximum. With further cooling (and without mechanical mixing) a stable, lighter class of water develops at the surface. As this class cools to its freeze point, ice begins to kind on the surface ar of the lake."

In deep lakes, water press may also play a role. The gravitational load of every the water higher up in the lake presses under on the water deep in the lake. The pressure enables the water close to the bottom the the lake to acquire cold there is no expanding and also rising. Due to the fact that of the pressure, the water at the bottom that deep lakes can become cold there is no freezing to ice.

Topics: density, freezing, frozen, ice, lake, lake ice, water, weather


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