Introduction
How Soil formed: soil formation as regulated by the effects of place, environment and history. Biochemical processes act to both create and destroy order with soil.
These alteration lead to the development of layers, formed soil horizon, distinguished by differences in colour, structure, texture and chemistry. These features occur in patterns of soil type distribution forming in response to differences in soil forming factors.
The soil develops through a series of changes. The starting point is weathering of freshly accumulated parent material. new soil increase in depth by a combination of weathering and deposition.
Soil formation is formed by the physical, chemical, and biological changes that take place continuously in the soil layer. Formation of soil can be divided into three stages:
- Stage -1 : Soil formation begins with the breaking down of rocks at the surface. The process of breaking down of rocks is known as weathering. Weathering may be by mechanical or chemical means.
- Stage – 2: Due to weathering and organic layer develops. Bacteria and other micro organic materials form the humus.
- Stage -3: Humus helps loose to soil grains to stay together and also make the soil more fertile.
While soils are usually formed by weathering of rocks it may also be formed deposition of material by agents of gradation. Alluvial soils in river valleys and deltas are formed by this process.
All over the world, there are different varieties of soil. Parent rock , climate, topography, vegetation cover are some of the important factors which are responsible for developing different types of soil are found depending upon different factors.
Types of Soil
The major types of soils found in India are: 1. Alluvial soils 2. Black soils 3. Red soils 4. laterite soils 5. Mountain soils 6. Desert soils.
1. Alluvial soils :
There are found over large parts of the country. Most of soils are derived from the sediments deposited by rivers.These are very fertile soils.
2. Black soils :
Black soils cover about 16% of the total geographical area of the country. The Black soils have been formed due to the weathering of the lava spread over large areas during volcanic activity in the Deccan plateau.Cotton is the most important crop which is grown in the Black soils.
3. Red soils :
These cover about 10% of the total geographical area of the country . Most of the red soils have been formed due to weathering of metamorphic rocks.
4. Laterite soils :
The laterite soils have been formed as a result of intense leaching . The soils are suitable for growing plantation crops like tea, coffee, rubber etc.
5. Mountain soils:
Mountain soils are not mature soils. They are found in the mountainous areas of India like Himalayas.
6. Desert soils:
Deserts soils are dry soils and are found in the Thar Desert.
Parent materials of Soil
The mineral material from which a soil forms is called parent material. Rock whether its origin is igneous, sedimentary and metamorphic is the source of soil mineral material and origin of all plant nutrients with exceptions of nitrogen, hydrogen and carbon. As the parent material is chemically and physically weathered, transported, deposited and precipitated, it is formed into soil.
1. Climate
The climate variables influencing soil formation are effective precipitation and temperature both of which affect the rates of chemical, physical and biological processes. Climate is dominant factor in soil formation and soils shows the distinctive characteristics of the climate zones in which they forms with a feedback to climate through transfer of carbon stopped in soil horizons back to the atmosphere.
2. Organism
Each soil has a unique combination of microbial, plants, animals and human influences acting upon it. Micro organism are particularly influential in the mineral transformations critical to the soil forming process.
3. Erosion
“Erosion is the wearing away of rocks on the surface of the earth by agents like running water, moving ice, wind and waves.”
Weathering and erosion take place almost everywhere and at all the time. Sometimes one process is more prominent than the other. The rate of weathering and erosion depends on the following factors:
1. Temperature and rainfall
2. Vegetation cover
3. Change in land use
4. Slope of the land
5. Type of soil
weathering and erosion are continuous processes and are responsible for changing the land surface features like mountains, hills, plateaus and plains.
The processes of weathering and erosion are called denudation.Agents of denudation: running water, wind, glaciers and waves are the major agents of denudation.
Different Landforms
1. Land forms made by wind
work of wind is more prominent in desert areas where soil particles are loose due to lack of moisture and vegetation. A deflation hollow and sand dunes are the most important land forms made by the wind.
1) Removal of sand through deflation leads to the formation of large depressions in the desert such depressions are called deflation hollows.
2) A Sand dune is the most important feature formed by the depositional work of wind. A dune is a hill or a mound of sand deposited by the wind.
Deposition of transported particles takes place when an obstacle lies in the path of the wind or due to a decrease in the velocity of the wind.
2.Land forms made by glaciers
Glaciers modify the landscape in a number of ways.They erode the surface, transport and deposit materials of all sizes ranging from boulders and sand to fine silt.
A glacier is a huge mass of ice that moves slowly down a mountain valley. It is made up of compact and re-crystallized snow. They occur in the areas having a permanent cover of snow and ice.
Erosional work of glaciers:
In a glacier the movement of ice is unequal.The top of the ice much faster than its bottom and the ice in the center also moves faster than the ice along the sides of the glacier. The cracks that appear on the glacier because of the splitting up of ice as a result of its unequal movement are known as ‘crevasses’.Mountain glaciers cannot dig a new valley but deepen, straighten as well as widen the pre- existing valley by eliminating irregularities during its passage. Such a through has steep sides and wider floor. Because of its typical shape, it is called a u- shaped valley.
Cirque: A cirque is an armchair shaped depression with a steep back wall. Circular or oval in shape these depressions occur near the summit regions of the mountains.It is formed due to the down slope movement of the glacier and the intensive shattering of the upland slopes. Process of plucking operates on the back wall thus making it steep and the movement of ice abrades the floor to make it smooth. Thus the depression is deepened into a steep horse-shoe shape.
Depositional work of a glacier: moraines are the result of depositional work of the glaciers. A mound of unsorted Rock material left behind by a glacier is called a moraines. Moraines appear as Long ridges or hills on an otherwise flat landscape.
3. Land forms made by sea waves
The sea is an active agent of gradation in coastal areas. Waves constantly act on the coast and change its shape. Even the hardest rock is under cut and broken into fragments by the impact of the sea waves.
Erosional work: The erosional action of sea waves leads to formation of cliffs, caves, inlets and sea arches.
1.Cliff: A cliff has a steep slope facing the sea. In the beginning the sea waves cut a groove in the rock at sea level.This groove keeps on widening with the passage of time.
2.Sea arch: If the rock formation along a coast differs in resistance, softer Rocks and eroded first and harder rocks stand about forming distinctive coastal pictures as arches.
3. Sea stack: Continued erosion of the headland may cause the arch to fall in,
leaving behind an isolated column known as a sea stack.
Depositional work of sea waves: Sea waves are also responsible for depositional features such as beaches, sandbars and lagoons.
1. Beach: A beach is formed due to the deposition of sand, gravel and pebbles on the shore between the low tide level and the coastline. Marina Beach in Chennai is one of the famous beaches in India.
2. Sandbars: Sometimes deposits of sand and gravel get built up on the sea floor parallel to the coastline not far from it. These narrow elongated deposits of sand are called sand bars.
3. Lagoon: If a sandbar grows in size and cuts off a portion of Sea from the main body of water, a saltwater lake is formed along the coast it is known as a lagoon.
Lagoons are connected to the open so through narrow outlet. On the Malabar coast India there are a number of lagoons. chilka lake in odisha and pulicat lake in tamilnadu are two famous lagoons on the sea coast.
Quick links
• What is weathering Its Process, types and factors
• What is Deforestation, its causes, effects and strategies to stop deforestation