External forces - responsible for changes - class-VIII

Answer: A- 3; B- 4; C- 1; D- 2

Land use: Land is used for different purposes such as agriculture, forestry, mining, building houses, roads and setting up of industries. This is known as land use.

Humus: Humus is defined as black organic matter formed in soil due to the decay of dead plant and animal matter.

Rock dams: These are the artificial embankments created by constructing mould of soil, clay, sand and rock. Main function is to prevent floods and soil erosion

Arable land: It is the land suitable for agriculture.

• Row of trees planted in the coastal areas to check the wind movement is called Shelter Belts.
  

The most appropriate method to verify soil erosion on steep slopes is terrace cultivation.Terrace farming is a method of farming whereby “steps” known as terraces are built onto the slopes of hills and mountains. When it rains, instead of rain carrying away the soil nutrients and plants down the slope, they flow to the next terrace. Every step has an outlet which channels water to the next step.

Over irrigation is main cause of land degradation in Punjab due to waterlogging leading to increase in salinity and alkalinity in the soil. Punjab, Haryana, Uttar Pradesh are the states facing issue of land degradation.

Afforestation is the most effective method for soil conservation on hill slopes because tree roots bind the soil together, preventing erosion caused by water runoff.

Terracing, contour cultivation, and afforestation are all well-established and effective methods of soil conservation. Therefore, none of the options listed are 'not' effective.

 Ploughing in a wrong way i.e. up and down the slope. It forms channels for the quick flow of water leading to soil erosion. 

1:The denudation of the soil cover and
subsequent washing down is described as soil
erosion. Wind blows
loose soil off flat or sloping land known as wind
erosion. It is very high in the state of Rajasthan.
2:It causes soil loss, dryness and deterioration of soil structure, nutrient and productivity losses and air pollution. Suspended dust and dirt is inevitably deposited over everything.

Steps can be cut out on the slopes making terraces. Terrace cultivation restricts erosion. Western and central Himalayas have well developed terrace farming. 

Soil erosion causes by water, mining, air.

Human activities like deforestation, overgrazing, construction and mining etc. lead to soil erosion. 

A terrace in agriculture is a piece of sloped plane that has been cut into a series of successively receding flat surfaces or platforms, which resemble steps, for the purposes of more effective farming. This method is called terracing. It is very useful in soil conservation in hilly or mountain areas.

Soil conservation is a method of protecting soil from getting eroded either by wind or by water.

• Few soil conservation methods include:
  
• Graduated terrace steps which are commonly used to farm on hilly or mountainous terrain. Terraced fields decrease both erosion and surface runoff.
  
• Wind breaks: Row of trees or a fence, wall, or screen that provides shelter or protection of soil from the wind.
  
• Conservation tillage is a method of preparing soil from getting eroded. This technique involves leaving the previous year crop residues until the next crop is planted.

Red soil develops on crystalline igneous rocks
in areas of low rainfall in the eastern and
southern parts of the Deccan plateau. Yellow
and red soils are also found in parts of Odisha,
Chhattisgarh, southern parts of the middle
Ganga plain and along the piedmont zone of
the Western Ghats. These soils develop a
reddish colour due to diffusion of iron in
crystalline and metamorphic rocks. It looks
yellow when it occurs in a hydrated form.

Reforestation is the natural or intentional restocking of existing forests and woodlands that have been depleted, usually through deforestation. Reforestation activities promote the gradual depletion of CO2 from the atmosphere through absorption during photosynthesis.

Ploughing along the contour lines can decelerate the flow of water down the slopes. This is called contour ploughing. Contours act like bunds. Terraces are levelled into step-like small fields with even slope.

Dustbowl catastrophe is nothing but the dust storm that greatly damaged the ecology of US and Canadian prairies. The main reason for this storm was the wind erosion. Hence to prevent such catastrophes people should be taught well to prevent soil erosion. 

In the states of Punjab, Haryana, western Uttar Pradesh, over irrigation is responsible for land degradation due to waterlogging leading to increase in salinity and alkalinity in the soil. 

The running water cuts through the clayey soils and makes deep channels known as gullies. The land becomes unfit for cultivation and is known as bad land. In the Chambal basin, such lands are called ravines. Chambal is in the state of Madhya Pradesh.

Natural vegetation reflects the combined effects of relief and climate. The formation and development of soil is very much influenced by the growth of vegetation. The decayed leaf material adds much needed humus to soil thereby increasing its fertility.

Afforestation and proper management of grazing can help to some extent. 

The running water cuts through the
clayey soils and makes deep channels as
gullies. The land becomes unfit for cultivation
and is known as bad land. In the Chambal
basin such lands are called ravines.

Black soils are black in colour and are also
known as regur soils. Black soil is ideal for
growing cotton and is also known as black
cotton soil. It is believed that climatic condition
along with the parent rock material are the
important factors for the formation of black soil.
This type of soil is typical of the Deccan trap
(Basalt) region spread over northwest Deccan
plateau and is made up of lava flows. They
cover the plateaus of Maharashtra, Saurashtra.

In recent years, multi-purpose projects and
large dams have come under great scrutiny
and opposition for a variety of reasons.
Regulating and damming of rivers affect their
natural flow causing poor sediment flow and
excessive sedimentation at the bottom of the
reservoir, resulting in rockier stream beds and
poorer habitats for the rivers’ aquatic life. Dams
also fragment rivers making it difficult for
aquatic fauna to migrate, especially for
spawning. The reservoirs that are created on
the floodplains also submerge the existing
vegetation and soil leading to its decomposition
over a period of time.

In Punjab and Haryana, intensive agriculture and the use of canal systems have led to significant over-irrigation, which causes waterlogging and soil salinity, damaging the soil.

Ploughing along contours on a slope prevents soil being washed away by rainwater or by surface run off. Contours act like bunds. Terraces are levelled into step like small fields with even slope.

 Ploughing in a wrong way i.e. up and down the slope form channels for the quick flow of water leading to soil erosion. 

Wind erosion refers to the movement and deposition of soil particles by wind. It occurs when soil devoid of vegetation is exposed to high velocity of wind. Rajasthan is the region facing the highest levels of soil erosion due to the dry winds present in the region.

• Soil conservation is a method of protecting soil from getting eroded either by wind or by water.
  
• Soil erosion is also caused due to defective methods of farming. Ploughing in a wrong way i.e. up and down the slope form channels for the quick flow of water leading to soil erosion. 
  
• The rest of the methods help in soil conservation.
  

Arid soils develop due to high temperature and evaporation.

On hilly slopes, terraces act as bunds and prevent the soil from being washed away by running water. 

• Soil erosion is the loss of top fertile layer of soil either by wind or by water.
  
• India is facing this problem in many parts. The area affected by soil erosion is 5, 00,000 square kilometres. It adversely affects productivity and economy of the country.
  
• There are many techniques to prevent soil erosion. But important step is to increase planting of trees or afforestation.
  

• Arid soils range from red to brown in colour. 
  
• They are generally sandy in texture and saline in nature. In some areas the salt content is very high and common salt is obtained by evaporating the water. 
  
• Due to the dry climate, high temperature, evaporation is faster and the soil lacks humus and moisture. 
  
• After proper irrigation these soils become cultivable as has been in the case of western Rajasthan.
  

Strip cropping is a method or farming in which more than one variety of crops are grown in different strips.

One of the important crop that is usually grown along with other crops is gram. This is because it has good soil holding capacity and prevents soil erosion.

Soil formation is a complex process involving weathering of rocks, deposition of materials, and denudation processes. All these contribute to the creation of soil layers.

Moraines is any glacially formed accumulation of unconsolidated glacial debris that occus in both currently and formerly glaciated regions on the earth. These are formed of the debris of glaciers. They are not formed due to river erosions.

Alluvial soil is considered the most fertile and useful soil for agriculture in India due to its high nutrient content and ability to support a wide range of crops.

Deforestation removes the protective cover of vegetation, leaving the soil exposed to wind and water, which is the primary driver of soil erosion.

Deforestation is a cause of soil erosion, not a result of it. The other options (siltation, reduced water percolation, and loss of fertility) are direct consequences of the erosion process.

Running water, wind, and the sea (waves) are natural agents that physically transport soil. Industries are a human activity, not a natural agent of erosion.

In the Kambam valley of Tamil Nadu, the specific climatic and geographical conditions make wind erosion a common and significant issue.

The glaciers carry sediments with them. These sediments are called moraines. Depending on the location of the deposits, moraines can be divided into four type.

The depositional work of glacier produces landforms like:-

• Drumlins
• Eskers

The eroded materials gets carried away by agents like running water, glaciers, wind, sea waves and groundwater. These all work on erosion, transportation and deposition of eroded materials.

The erosional work of glaciers produces landforms like:-

• Cirques
• Horns
• Hanging valleys
• Sheepbacks

Running water flows naturally in a direction according to gravity along the slope and makes its own way. This is called a flow of water. When many such flows of water come together, a river is formed.

The glaciers carry sediments with them. These sediments are called
moraines. Depending on the location of the deposits, moraines can be
divided into four type.

The riverbed and the river banks get eroded because of the fast flow of water, sand particles, pebbles etc, and the various tributaries joining the main river. All these lead to the formation of gorges, V-shaped valleys and waterfalls.

Following are the factor responsible for erosional transportational and depositional work of a river:-

• Slope of land
• The type of rock
• Volume of water flowing in the river
• The length of flow
• Volume of sediments in the river

Depending on the location of the deposits, moraines can be
divided into four type which are as follow:-

• Ground Moraines
• Lateral Moraines
• Medial Moraines
• Terminal Moranies

 The Jakobshavn Glacier in Greenland is one of the fastest moving
glaciers in the world. It moves at the rate of 46m per day.

Glaciers move at different velocities daily ranging from 1 cm to 1 m. The Jakobshavn Glacier in Greenland is one of the fastest moving glaciers in the world. It moves at the rate of 46m per day.

The movement of air is called wind. Wind is a gaseous agent of erosion. The erosional, transportational and depositional work of wind is more prominent in deserts and semi-arid region.

Wind carries small sand particles, small pebbles, etc. along with it. These particles cause erosion along rocks coming in the way due to friction. This leads to formation of mushroom rocks, deflation hollows, yardangs, etc.

Afforestation is the process of planting trees on a large scale, which helps to stabilize the soil and prevent erosion.

Chernozems are known as the richest soils (3), Black soil is rich in calcium carbonate (1), Laterite contains aluminium compounds (2), Terra Rosa is formed in limestone (4), and Alluvial soil is a mixture of clay, sand, and silt (5).

Ploughing along the contour lines can
decelerate the flow of water down the slopes.
This is called contour ploughing. This is the best method to reduce the soil erosion in the hilly areas.

Khadar, Bangar, and Bhabar are all types of alluvial soils classified by their age and location in river plains. Regur (Black soil) is formed from volcanic rock, making its formation process distinct.

• Ploughing along the contour lines can decelerate the flow of water down the slopes. This is called contour ploughing. 
• Steps can be cut out on the slopes making terraces. Terrace cultivation restricts erosion. 
• Large fields can be divided into strips. Strips of grass are left to grow between the crops. This breaks up the force of the wind. This method is known as strip cropping. Strip cropping method reduce the soil erosion
  

Contour ploughing, terracing, and crop rotation are all effective soil conservation techniques. Shifting cultivation is generally considered harmful to soil as it involves clearing and burning land.

In India, ravine erosion and gullies cause the most severe and widespread damage to land, followed by issues like alkalinity, salinity, and water-logging.

A glacier erodes through a process called ‘plucking’ in which it lifts pieces of rock and transports them. These pieces of rock and the moving ice together act like a sandpaper on the surface of the rock over which they flow. In the Himalayan region, the glacier is the major weathering agent.

Gully erosion occurs when water flows in narrow channels during heavy rain, cutting deep trenches into the soil. This process is responsible for the formation of the extensive Chambal Ravines.

Black soils are rich in soil nutrients, such as calcium
carbonate, magnesium, potash and lime. These
soils are generally poor in phosphoric contents.

Mulching is the process of covering the topsoil with plant material such as leaves, grass, twigs, crop residues, straw etc. it helps in soil conservation.

As noted previously, over-irrigation in Punjab and Haryana has led to waterlogging and soil salinity, which are the primary causes of soil degradation in those regions.

Coastal erosion is a significant issue in many Indian states, but Kerala is widely cited in geographical studies for its severe and persistent coastal erosion problems due to its specific coastline characteristics and high population density along the shore. While other states also face erosion, Kerala's situation is often highlighted as particularly critical.

 The running water cuts through the clayey soils and makes deep channels known as gullies. The land becomes unfit for cultivation and is known as bad land. In the Chambal basin such lands are called ravines. 

Deserts soils are usually light coloured with minimal humus content due to which the plant productivity is low. Also the water retaining capacity is very less. However they are rich in minerals-calcium carbonate (caliche), gypsum, and/or salts.

Caves, arches, stacks, and stumps are erosional features that are commonly found on a headland. Cracks are widened in the headland through the erosional processes of hydraulic action and abrasion. As the waves continue to grind away at the crack, it begins to open up to form a cave.

• Soil erosion is the loss of top fertile layer of soil either by wind or by water.
  
• Sheet Erosion: Uniform removal of the top soil just like a sheet. It is resulted because of water flow.
  

Gypsum can form anywhere where the right combination of mineral elements occurs and evaporation happens. It occurs as clumps of crystals or in thick beds. Gypsum beds were formed in shallow sea basins. These geologic areas are called evaporation basins because as the climate changed from tropic to arid the water evaporated concentrating the minerals it held. Gypsum formations can also occur in tidal flats along coastlines, in lagoons, deltas, hot springs, volcanic areas, desert water tables and even on plant roots.

Gradation is the process of leveling the land surface by erosion and deposition, not just the deposition itself. The other statements are correct geographical definitions: cliffs are formed by wave erosion, beaches by wave deposition, and river erosion is most intense in the upper course.

Weathering is the breakdown of rocks, soils, and minerals through contact with the Earth's atmosphere, water, and biological organisms. It occurs in situ, meaning it does not involve the transport or carrying away of the material, which distinguishes it from erosion.