During the summer, sunlight warms the surface water. A boundary called the thermocline forms several feet below the surface. The thermocline separates the warm surface water from the colder, deeper water. Since cold water is denser than warm water, it stays below the lighter, warm water. The two layers can mix if there is a severe storm or as the seasons change.
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Why is a lake or pond warm on the surface and cold beneath?
Last Updated: February 15, 2008
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