A mountain that has been denuded is called a residual mountain. Denudation is the process by which the surface of the earth is lowered through the removal of rocks and soil by agents such as wind, water, and ice. Residual mountains are formed when resistant rocks or hard rocks are left behind after the denudation process has taken place. These mountains often have a flat top and steep sides, and are also referred to as inselbergs. They can be found in various parts of the world, including Africa, Australia, and South America.