EXTERNAL FORCES

As we have seen in the pervious chapter, the earth's crust is undergoing geological changes caused by the internal processes (earth movements, earthquakes, volca­noes, etc.), which create new relief features, such as mountains, plateaus and plains. Meanwhile, there are ex­ternal processes that are working vigorously to wear away the surface. The interaction of the internal and external processes gives rise to the great diversity of present-day landforms.

The external forces that produce physical features-Le., those forces which operate on earth's surface-cause them by (i) denudation or (ii) deposition. The forces of denuda­tion are weathering and erosion. The forces of deposition are water, ice, wind and living organisms.