The physical properties of ice

Ice has a singular property, which is apparently banal, but which has important repercussions on the life of the entire planet. While most substances decrease in volume when changing from the liquid state to the solid state, the property of water is that it is less dense in the solid state than in the liquid state: in fact, maximum density of water is reached at a temperature of 4°C.
This implies that ice is lighter than an equivalent quantity of liquid water, therefore ice floats on water : this can be seen when sipping a drink in a glass full of ice cubes. However, in nature, the same phenomenon can be seen in the icebergs and in the formation of sea and lake ice.
If ice did not have this property, ice formed on the surface of a sheet of water (a lake or a sea) would sink, accumulating on the bottom. This would finally form thick deposits of ice on the bottom of seas and lakes, which would soon be transformed into large masses of ice, and the summer heat would only produce a minor layer of liquid water near the surface. The consequences of this property on the life of our planet are therefore very easy to imagine.
As a result of this property, when water freezes its volume increases. This is easy to test, when we put a bottle of water in the freezer, the pressure of the ice can break the bottle – if the bottle is full, the ice does not have space to expand and the container cannot deform, as in the case of a glass bottle. In nature, this process is very important : the pressure of water freezing inside small cracks in a rock can be so great that the rock breaks into small fragments. This process, called cryoclastic weathering (from Greek cryo, kryos : cold and clast, klastos: broken), (freeze-thaw weathering or frost shattering) is responsible for mechanical weathering of rocks in the high mountains, and produces large stretches of sharp debris, which are a characteristic feature in mountain landscapes above the limit of arboreous vegetation (that mountain climbers and excursionists call “screes” – those who are familiar with the mountains know how tiring it is to walk on this large gravel!).

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