For a glacier to grows it takes snowfall at their origin, the snow will get heavier, and the snow beneath it will become dense and become ice.
A good answer would be "caste". A caste system is the social hierarchy in India in which people are first assigned one of the four main castes (scholars, warriors, farmers, servers) and then additionally often also to smaller castes (farmers of rice, of bananas). The social mobility is very low.
