Question

What are the effects of anomalous water expansion?

Answer 1

During winter in cold countries, the temperature falls below $0^{o}C$. Water in lakes, seas or rivers will be frozen. Let us see how this happens.
The water at the surface, in contact with the cold atmosphere, loses heat and its temperature decreases. It becomes denser, sinks and is replaced by less dense water from the bottom. This process repeats itself so that the overall temperature of the water decreases.
Had water been like any other liquid, the whole depth of the water would have been frozen and aquatic life would have been destroyed completely.
Thanks to the anomalous expansion of water, when the temperature reaches $4^{o}C$, the water remains at the surface of the lake,sea or river. This is because as temperature decreases from $4^{o}C$ to $0^{o}C$, water expands. The water is still less dense and thus remains at the surface. Only a small layer of water at the surface thus becomes frozen. Ice itself is less dense than water.