Geomorphic Processes Notes in English Class 11 Geography Chapter-5 Book-Fundamental of Physical Geography

 

 Introduction 

• The differences in the internal forces operating within the Earth that form the Earth's crust are responsible for the differences in the Earth's outer surface. 

•  The Earth's surface is continuously affected by external forces induced by energy from the Sun.

• The surface of the earth is continuously affected by the external forces generated within the Earth's sphere and the internal forces generated inside the Earth.

• External forces are called exogenic and internal forces are called endogenic forces.

• The result of the actions of exogenous forces is the wearing down of raised landforms and filling up of basins/low areas.

• Endogenetic forces continually uplift or build up parts of the surface and thus exogenetic processes fail to even out the variations in relief.

Floor Balance 

• The reduction of the difference between the relief features on the surface through erosion is called Gradation.

• Humans are dependent on the land for their survival and use it extensively.

• Most of the land surface has been shaped over a very long period of time and its potential is declining at a very rapid rate due to its use, misuse and abuse by humans.

• Necessary steps can be taken to reduce the harmful effects caused by human use and to preserve it for the future.

Geomorphic processes 

1. Endogenic forces

2. Exogenic forces

1. Endogenous forces

i. Lamina deformation process 

• Epeirogenic forces 

• Sharp ridge/mountain 

ii. Contingency process 

• Earthquake 

• Volcano 

i. Lamina deformation process 

• Plate deformation refers to the process in which bending, folding, faulting or fractures are created in the Earth's crust and unevenness is generated on the surface.

• This process works very slowly inside the earth and its effect is visible after a very long time.

Epeirogenic forces 

• Epeirogenic forces 

• bulge upward 

• sinking down 

• These forces act vertically and cause the continents to warp and move downwards i.e. a large continental mass is pushed up and down.

mountain girl 

• Tensile force

• Breakage 

• fault 

• Compressive force

• Wrapping 

• folds 

ii. Contingency process 

• Movements generated by sudden endogenous forces are included in it. 

• The events arising from this are sudden and suddenly they bring about destructive changes above and below the surface of the earth. 

• Earthquakes and volcanoes are the main sudden movements.

Volcanism

• The ejection of molten rock or other materials from below, in the form of lava and gases, from a crack or hole in the Earth's uppermost surface is called volcanism.

• The process includes both the lava coming up and solidifying there.

2. External forces

1. Weathering 

2. Mass circulation 

3. Erosion and deposition

1. Weathering

• Weathering is the process in which rocks are broken down and disintegrated by external agents

• Such as: wind, rain, temperature, micro-organisms, animals, etc.

Types of Weathering 

I. Chemical 

II. Physical 

III. Biological 

I. Chemical weathering

• Chemical weathering can be understood through the following examples

• If a lump of salt is kept in a moist place, it melts and gets destroyed. Similarly, if iron is kept in an open place, it gets rusted and slowly gets destroyed and gets mixed with the soil.

• Melting of salt and destruction of iron are chemical processes and the same process happens with rocks which is called chemical weathering.

Types of Chemical Weathering

1. Solution

• Many types of minerals present in rocks, such as nitrate, sulphate and potassium, dissolve in water and thus in areas with high rainfall and humid climate, rocks containing such minerals get weathered.

2. Carbonation

• Carbon dioxide dissolved in rainwater produces organic acid. This acid dissolves limestone-containing rocks, causing their weathering.

3. Hydration

• Some rocks, such as calcium sulphate, absorb water, expand and become weak, and then break down.

4. Oxidation

• Rusting of iron is a good example of oxidation. This process occurs when rocks come in contact with oxygen gas and this process takes place due to the mixing of atmosphere and oxygenated water.

II. Physical weathering

• Physical weathering causes rocks to break down into smaller pieces

• For which :- factors like gravitational force, changes in temperature, alternation of dry and humid conditions are responsible.

II I.  Biological weathering

• Weathering and physical changes caused by the growth or movement of organisms transfer minerals and human activities also help in biological weathering.

• New surfaces are created by burrowing by creatures like earthworms, termites, rats etc.

• The roots of plants exert a powerful impact on surface materials and break them apart mechanically.

Importance of Weathering

• Rocks break down into smaller pieces and help in soil formation.

• Weathering helps in concentration of valuable minerals like iron, manganese, copper etc. in the rocks because other substances get leached out due to weathering

• They move and the minerals accumulate at one place.

Large circulation

• It includes all those movements in which large debris of rocks move along the slope due to the direct effect of gravity.

• Gravity is helpful in large circulation.

• This means that not only air, water and snow carry debris from one place to another, but debris also carries air, water and snow with itself.

1. Landslides

• The movement of material down a slope at a rapid speed.

• Depends on rock structure, erosion, and slope geometry.

2. Omission

• The sliding and backward movement of rock or debris units down a slope.

• Rotational slippage.

3. Debris slide

• Rapid rolling or sliding of debris.

• without rotation, especially on steep slopes.

4. Rockfall

• The sliding of rock blocks along a bed joint or fault.

• Very destructive on steep slopes.

5. Shell collapse

• The free fall of rock fragments from a steep slope or cliff.

• Occurs from shallow layers, separate from rock avalanches.

6. Erosion

• Cutting, scraping of rocks and carrying the debris from one place to another by flowing water, groundwater, glaciers, wind, waves and currents is called erosion.

7. Deposition

• Deposition is the result of erosion. When the slope decreases, the deposition of the eroded material begins.

Soil

• Soil is a dynamic medium in which chemical, physical, and biological activities continually take place.

• It is the result of weathering and degradation, which contribute to soil formation.

• Soil is evolving and changeable.

Soil formation processes

1. Pedogenesis:

• The process of soil formation, which mainly depends on weathering.

2. Weathered Material:

• The base of the soil, which is formed by the weathering of rocks.

• Humus accumulates in the weathered mantle through biological activity, which increases the fertility of the soil.

Factors of Soil Formation

1. Basic substance

• The basic element of soil formation is rock or deposit.

• Local rock: Rock weathered in place, also called residual soil.

• Transported deposits: Deposits brought from an outside source, such as soil brought by a river.

• Different soils can be formed on the same rocks and the same soil can be formed on different rocks.

• When soil is new, it has a close connection with the rock.

2. Topography

• The slope and shape of the site affect the depth and development of the soil.

• The soil is thin on steep slopes.

• In flat areas the soil becomes deep and thick.

• There is good percolation of water which favours soil development.

• There is good aggregation of organic matter, which can cause the soil to become darker in colour.

3. Climate

• The chemical and biological processes of soil are different in hot and cold climates.

• Cold climate: There is abundance of humus as bacterial growth is slow.

• Hot climate: Organic matter gets oxidised quickly, reducing the amount of humus.

4. Biological activities

• Plants and animals: Add organic matter, moisture, and nitrogen to the soil.

• Humus: Formed from dead remains of plants, which increases the fertility of the soil.

• Bacteria: perform nitrogen fixation, which is essential for plants.

• Soil pests: such as ants, termites, and earthworms affect the properties of the soil by repeatedly moving it up and down.

5. Time

• Soil matures as the soil formation processes continue over a long period of time.

• Soils composed of recently deposited alluvial or glacial till are considered young and have less developed horizons.