You are watching: Why does a lake freeze from the top down instead of from the bottom up?
Warm water mostly gets more thick as it gets chillier, and also therefore sinks. This reality might lead you to think that ice must form on the bottom of a lake first. But a funny point happens to water as it gets even chillier. Colder than 4° Celsius (39° Fahrenheit), water starts broadening and becomes much less thick as it gets colder. As a result, close to freezing, chillier water floats to the height and the warmer water sinks to the bottom. The density of water as a role of temperature have the right to be seen in the plot on the best. Eventually, the cearliest water, which has floated to the height of the lake in winattempt problems, freezes to form a layer of ice. Right when the water freezes to ice, the ice becomes significantly much less thick than the water and also continues to float on the lake"s surface.
Ice is much less thick than water bereason of the method it develops a hexagonal crystalline framework. Each water molecule is composed of two hydrogen atoms bonded to the bottom of an oxygen atom. When ice develops, the hydrogen atoms of one water molecule create weak hydrogen bonds via the optimal of the oxygen atoms of 2 other water molecules. Lining up the water molecules in this pattern takes up more room than having them jumbled randomly together (as is the situation in liquid water). And bereason the very same mass of molecules takes up even more space once frozen, ice is much less dense than liquid water. For this exact same reason, water listed below 4° Celsius becomes significantly much less thick as it gets cooler. Close to freezing temperatures, the molecules in the liquid water begin to line up right into the space-filling hexagonal structure.
In the winter, temperatures in a lake obtain cshed sufficient to freezing that the chillier water is much less dense and also floats to the top. Public domajor image, source: Christopher S. Baird.
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The textbook River and also Lake Ice Engineering by George D. Ashton states, "As a lake cools from over 4° C, the surchallenge water loses warm, becomes even more dense and sinks. This process proceeds until all the water in the lake is at 4° C, as soon as the thickness of water is at its maximum. With even more cooling (and without mechanical mixing) a secure, lighter layer of water forms at the surchallenge. As this layer cools to its freezing allude, ice starts to develop on the surface of the lake."
In deep lakes, water pressure might also play a function. The gravitational weight of all the water greater up in the lake presses dvery own on the water deep in the lake. The press enables the water close to the bottom of the lake to acquire cold without broadening and also rising. Due to the fact that of the pressure, the water at the bottom of deep lakes deserve to end up being cold without freezing to ice.
Topics: density, freezing, frozen, ice, lake, lake ice, water, weather
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