# why does water at 4 degree celsius so special and why does the water below a frozen lake does not freeze??

Arun
25757 Points
5 years ago
Dear Venkatesh

In General, Order of Density is - Solid> Liquid> Gas.

But Nature is Incomplete until we discuss the Exceptions produced by it.

One of its most Amazing Exceptions is Water. Anomaly in it is that, Unlike the normal liquids, its Density does not keep on Increasing on decreasing the Temperature. However, the Density Increases till a certain Temperature ( 4 degree Celsius ) then starts decreasing till the normal Freezing point ( Zero degree Celsius ).

Only Due to this Anomaly, the Density of Ice (a Solid) at Zero Degree Celsius is less Dense than that of Water (Solid being less dense than Liquid). That is why when we keep a piece of Ice on the Surface of Water, the Ice floats.

Now let us assume a Pond with water inside it (Obviously! Its a Pond XD). When the Temperature of Surrounding starts decreasing the Temperature of water will also decrease in the following manner -

Firstly, The Surface Water is going to cool; As the water cools the density increases and the surface water drowns to the bottom and the bottom water rises up. This will continue till the whole water comes at 4 degree Celsius.

Now, further cooling will occur but as the Surface Water is going to get affected first, it will cool first. But now the Density won’t increase, instead the Density is going to decrease, which means that the Surface Water, instead of drowning (like before), would keep on floating on the top, disallowing the Bottom Water to come up and further cool. So, the surface water keeps on cooling till it gets converted to ice continuing to float on the Surface of Water keeping the inside of water at a Temperature of 4 degree Celsius.

This Anomaly allows the Aquatic Organism to survive in freezing cold, as the temperature below is warmer than above.

Regards