The origin of the soil is nothing but the mechanical disintegration and chemical decomposition of rocks. Generally when big rocks gets exposed to atmosphere, with time they get disintegrated and decomposes forming natural soil. Basically on the formation of the soil, it can be grouped into 2 categories namely : Residual Soil and Transported Soil.
What is Residual Soil
At the time of weathering of rocks (breaking down of rocks due to weathering effects and atmosphere), if the product generated remains in the same position of their origination is called as residual soil.
Residual soil tends to lie over rock bed.
Most of the time Igneous rocks such as basalt/ granite and Sedimentary rocks such as shale, sandstone/ limestone are prior materials or products of residual soils.
Black cotton soil and lateritic soils also falls into the example of residual soils.
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What is Transported Soil
Here in case of transported soil the originated soil due to weathering of rocks moves or travells from its place of origin and gets redeposited at another place. The soil can be transported due to wind, water, ice or any other atmospheric agent.
Basically the transportation method decides the characteristics of transported soil. The characteristics which might get effected due to method of transportation are :
- Particle Size
- Surface Texture
- Shape
- Degree of Sorting
The transported soil is further classified based on their transportation and deposition method.
Alluvial Deposits
The natural soil which is generally been deposited due to suspension (highly diffused mixing of water and soil) in running water are called as Alluvial Deposits.
Marine Deposits
The soil which is normally been deposited due to suspension in sea water are called as marine deposits.
Lacustrine Deposits
The soil which is deposited because of the suspension in fresh still water is called as lacustrine deposits. Generally lake water is best example to find such deposits.
Aeoline Deposits
Many times the soil particles gets carried away due to heavy wind effect. The soil particles which travells due to blowing of wind from their originated place to other place is called as aeoline deposits.
Glacial Deposits
Ice also plays important role in terms of moving soil soil particles from one place to other. The soil deposits transported due to melting of ice are called as glacial deposits.
Colluvial Deposits
Gravity plays important role in the transportation of these soil deposits. The loose unconsolidated sediments gets deposited below or at the base of hill slope. These deposits are called as colluvial deposits
This occurs mainly because of rainwash, continuous creep towards downside etc.
Transportation Effects on Soil Sediments
Effects on Water Transported Soil :
- Size : It is observed that the sediments transported through water tends to reduce their size and abrasion in suspended load is seen.
- Shape : Sand and gravels tends to gain round surface.
- Surface Texture : Generally the sand becomes smooth in nature and attains shiny and polished look.
- Sorting : Considerable sorting takes place.
Effects on Air Transported Soil :
- Size : Considerable reduction in the size of the sediments take place.
- Shape : Sediments generally gain more degree of rounding than water transported sediments.
- Surface Texture : This impact creates frosted surfaces.
- Sorting : Progressive and more considerable sorting takes place.
Effects on Ice Transported Soil :
- Size : The sediments get considered grinding and this impact often changes its size.
- Shape : Angular particles are created due to this type of transportation.
- Surface Texture : The sediments attain striated surface texture.
- Sorting : In this case very less amount of sorting takes place.
Effects on Soil Transported due to Gravity :
- Size : It has considerable impact.
- Shape : Non- spherical and angular particles are created.
- Surface Texture : Similar as of ice transported soil, it also generates striated surface texture.
- Sorting : Generally no sorting takes place.
Besides these examples there are many more examples of soils which are formed by the different methods of transportation and deposition.
Transported soils and residual soils are formed by different agencies of nature. Some of these are listed below :
1. Humus :
Humus is dark drown organic type of soil. It generally consist of decomposed vegetative matter.
2. Gumbo :
These soil is sticky in nature. Moreover it dark colored clay which is more plastic.
3. Muck :
These soil mainly originates due to imperfect drainage conditions. It is mostly found in swamps and is mainly deposited due to flooding of river.
This soil consist mixture of inorganic soil, fine particles and decomposed black organic matters.
4. Bentonite :
Bentonite is nothing but the chemically adhered volcanic ash formed due to weathering.
5. Fill :
When a transporting agent for a transported soil itself is a human then it is called as a fill. When the human transports and dumps a soil deposit is called as fill and this entire process is called as filling.
In this case mainly for large quantities, machines are used for dumping the soil such as bulldozers, trucks, scrappers.
6. Hard Pan :
When the soil cannot be drilled with the normal or ordinary drilling/ boring tools it is called as hard pan. These cohesive soils generally has a extremely hard surface.
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