What is it called when natural processes of change cause a mountain to be broken apart?

The natural process of change that can break apart mountains is called weathering. More specifically a form of mechanical weathering called frost action. At or close to the summit of mountains the temperature is quite low and this can cause water from rain or melting snow to freeze in cracks and crevasses in the rock. Repeated freezing and thawing can cause rocks to break apart because water increasing in volume by 9% when it freezes. This exerts pressure on the rocks causing them to break apart overtime.