Rain, wind, frost and ice are the tools that nature uses to make even the largest mountains gradually crumble down. This process is known as erosion and takes millions of years to complete its work. Some of the erosion results from the chemical decay of rocks caused by various substances in the atmosphere, and can be seen, for example, in the flaking of basalt. When this happens the rain breaks up the rock even more and washes it away.

The atmosphere also has a physical effect on rocks. Changes in the air temperature is one such effect. Rocks expand in heat, as any solid does, and contract or shrink in cold. This constant expansion and concentration eventually helps to crumble the rock.

Another physical force is the continual freezing and thawing of ice. This is a powerful factor because the water often freezes after running deep into the rock through a crack. The ice then acts from within the rock to break it up.