Question
Why lakes freeze first at the surface?
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Answer
- In cold climate, temperature of water in ponds and lakes starts falling.
- On getting colder, water contracts. As a result, density of water increases and it goes down. To replace it, warmer water from below rises up. This process continues till temperature of water at the bottom of pond becomes 4 °C.
- Water, due to its anomalous behaviour possesses maximum density at 4 °C.
- If the temperature lowers further, ice is formed at the surface of pond with water below it.
- Ice being poor conductor of heat blocks the further heat exchange between atmosphere and water in the pond and maintains water below surface in liquid state.
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