Humidity is important in both physical disintegration and chemical de­composition of rocks. As we know, in the polar regions as well as the mountain regions (mostly above snow-line) the intermittent freezing of water present in the porespaces and fissures of rocks split the rock apart and thus cause their disintegration.

Water is an active chemical agent due to the fact that it always dissociates partly into ions of hydrogen (H+) and the hvdroxy lions (OH-). Many of the reactions are controlled by the hydrogen ion con­centration.

It affects the solubility of substances and accordingly affects the chemical decomposition of rocks, thereby eliminating all the unstable minerals present in the rocks.