Soil Formation

                                                                Soil Formation

Soil may be categorized as residual and transported. Residual soils are formed from the weathering of rocks and practically remain at the location of origin with little or no movement of individual soil particles. Transported soil are those that have formed at one location but are transported and deposited at another location.

1. Residual Soils.

Weathering ( Due to climate effects) and leaching of water-soluble materials in the rock are the geological process in the formation of these soils. The rate of rock decomposition is greater than the rate of erosion or transportation of weathering materials and results in the accumulation of residual soils. As the leaching action decreases with depth, there is progressively lesser degree of rock weathering from the surface downwards, resulting in reduced the soil formation, until one finally encounters unaltered rock. residual soils generally comprise a wide range of particles sizes, shapes and composition.

2. Transported Soils.

Weathered materials have been moved from their original location to new location by one or more of the transportation agencies, viz., water, glacier, wind and gravity and transported soils. such deposits are further classified depending on the mode of transportation causing the deposit.

(a) Water transported Soils : Swift-running water is capable of moving a considerable volume of soil. Soil may be transported in the form of suspended particles or by rolling and  sliding along the bottom of the stream. The size of the particle that can be suspension is related to the square of the velocity of the flowing water. Particles transported by water range in size from boulders to clay.

(B) Wind-transported Soils : Like water , wind can erode, transport and  deposit fine-grained soils. Soils carried by wind are subsequently deposited ass aeolian deposits. Dunes are formed due to the accumulation of such wind-deposited sands. Dunes are a rather common occurrence in the desert area of Africa, Asia and USA. Sands from dunes may be  used to a limited extent for construction purposes.

(C) Gravity Deposit : Gravity can be transported materials only for a short distance. As the movement is limited, there is no appreciable change in the material moved. Gravity deposits are termed talus. They includes the materials at the base of cliff and  landslide  deposits. The talus materials at the cliff is formed