Snow is formed of tiny crystals of frozen water that fall from the sky. Snow flakes have an infinite variety of shapes. They are usually hexagonal and may be flat, needle shaped or star shaped. No two snowflakes are exactly alike. Freshly fallen snow reflects about 95% of the sun’s heat back into the space. Do you know how snow fall takes place?
Due to sun’s heat there is a continuous evaporation of water from the seas, rivers, lakes, ponds etc. Since water vapour is lighter than air, it goes up in the atmosphere and turns into cloud. We know that the temperature decreases as we go higher in the atmosphere. Since the capacity of air to hold water vapour decreases with the fall in its temperature at a certain height a large quantity of water vapour gets accumulated in the air. The air having excess of water vapours is said to be supersaturated. Under this condition the water vapours condense on the dust and smoke particles present in the air. On further cooling, they get converted into snow particles. These particles combine with each other to form crystals of snow. When the air cannot bear their weight, they fall down as snow flakes and go on accumulating on the mountains.
Now the question arises: why does it snow on the mountains only? Why does it not fall in the plains too? In fact the possibility of snowfall at any place depends upon two factors – the altitude of the place above the sea-level and its distance from the equator. The higher the altitude of the place, the greater is the probability of snowfall there. Similarly the larger its distance from the equator, more are the chances of snowfall there. Even though the amount of snow formed in the atmosphere is very large, only a very small fraction of it falls down on the mountains in the form of snow. The remaining portion comes down as rains because while passing through hotter regions, it melts and turns into water. However, the temperature being low at the mountains, the snow does not melt into water there. It goes on piling up as snow and under the increasing weight of its accumulation layer after layer, it becomes harder and harder.
Snowfall is very useful for us. When snow melts in summer, the melted water flows to rivers and is used for irrigation purposes. Fresh snow is very light and a good insulator, protecting the underlying plants from severe cold. Snow is a bad conductor of heat because of the air trapped between its particles. As such it acts as a blanket for the earth. In colder regions, people make houses of snow as it provides excellent protection against cold weather. In hilly areas, the roofs of the houses are made in a slanting shape, so that snow does not accumulate there. It saves the inhabitants from the adverse-effects of snow and also prevents the roofs from collapsing.