Soil Science

Eluviation / Illuviation

Definition

Water percolating through a soil profile can carry matter (e.g., clay, soil organic matter) in suspension. The removal of soil material from a soil horizon by this means is called eluviation (from Greek meaning "washing out"), and its deposition in a lower horizon is known as illuviation ("washing into").

Watch the animation to see how eluviation removes clay particles from the pores in a matrix of sand grains.

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A and B horizons

Eluviation and illuviation of clay will tend to produce a sandy surface horizon and a clayey subsurface horizon, and this concept is built into the way soil horizons are named.

 

For example: An A horizon is a ____ horizon?

 
All horizons are considered to be ELUVIAL horizons. In contrast, an underlying B horizon is considered to have accumulated soil material from above and so is an illuvial horizon.

Other mechanisms

Other ways that clay may be lost from the A horizon include

  • Destruction (weathering) of clay minerals
  • Lateral movement of clay over an impermeable B horizon.
  • Selective loss by erosion of clay brought to the surface by bioturbation (see Soil Mixing)

 

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