Soil Formation – Geomorphic Processes

Soil forms continuously, but slowly, from the gradual breakdown of rocks through weathering. Soil can be formed in a number of different ways including chemical or physical means which often take place simultaneously. Weathering can be a physical, chemical or biological process:

• Physical weathering: breakdown of rocks from the result of a mechanical action. Temperature changes, abrasion (when rocks collide with each other) or frost can all cause rocks to break down.
• Chemical weathering: breakdown of rocks through a change in their chemical makeup. This can happen when the minerals within rocks react with water, air or other chemicals.
• Biological weathering: the breakdown of rocks by living things. Burrowing animals help water and air get into rock, and plant roots can grow into cracks in the rock, making it split.

The accumulation of material through the action of water, wind and gravity also contributes to soil formation. These processes can be very slow, taking many tens of thousands of years. Five main interacting factors affect the formation of soil:

• parent material—minerals forming the basis of soil
• living organisms—influencing soil formation
• climate—affecting the rate of weathering and organic decomposition
• topography—grade of slope affecting drainage, erosion and deposition
• time—influencing soil properties.

Interactions between these factors produce an infinite variety of soils across the earth’s surface.