While plate tectonics are driven by the internal heat of the earth, the processes of erosion are dynamic processes that shape the surface of the earth. Driven by the energy of the sun, and responding to the earth’s gravitational force, they reduce higher elevations. Although slow-acting in the eyes of man, they are nevertheless fast-acting by geological standards. If present rates of erosion were to continue unchanged, continents would be reduced to sea level in less than 50 million years (one percent of geologic time). 

Erosion, defined as the downhill motion of materials under the influence of gravity, usually involves some fluid or medium to move the materials. By far the most active of these media is water, both in its liquid and solid states. 

Erosional processes are classified as follows: 

I. Erosion without a medium: - 

• mass wasting

A. water 

• surface water - 
• ground water - 
• glaciers - 
• coastal -
B. wind -
• aeolian