Weathering
Weathering is the process of change, especially decomposition, of rockss and other sediments due to chemical changes or mechanical processes such as the expansion of freezing water or the growth of roots into rock cracks. Weathering is often confused with erosion which is the movement of rock or weathering products by water, wind, ice, or gravity. Weathering is only the chemical or mechanical breakdown, not the movement.The breakdown products, after chemical weathering of rock and sediment minerals and the leaching out (loss) of the more soluble parts, when combined with decaying organic material, is called soil.
The first-stage formation of caves, when limestone joints are enlarged due to the solution of the calcium carbonate, by the inorganic and humic acids in the water, is a kind of weathering. The sub-surface breakdown of rock on hillsides is also a common mode of weathering. Where rock is especially resistant to subsoil weathering, rock outcrops occur, but more often the rock decomposition is taking place unseen due to chemical forces.