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ICSE-IX-Geography

10: Denudation

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    Section : I
    Short Answer Questions
  • Qstn #1
    What do you mean by denudation ?
    Ans : Denudation is the wearing away of landmass by various processes like weathering, erosion mass movement and transportation. It results in lowering the level of land, rounding exposed rock surfaces and levelling the peaks.
  • Qstn #2
    Name important factors which affect work of a river.
    Ans : Various factors affect erosion, transportation and deposition work of a river. Important factors include the following :
    1. Velocity of water
    2. Volume of water
    3. Load
  • Qstn #3
    What is the main function of a river in its upper course in land formation ?
    Ans : In the upper course the dominant activity of a river is erosion. Many land forms are shaped by this activity of the river. Along its course, it erodes bed and banks, and carries large boulders of rock with it. Under the impact of rush of water.
  • Qstn #4
    Name two important land forms of river erosion.
    Ans : The two landforms resulting from erosion in the upper course of a river are the following :

    1. V-shaped Valleys : It is formed from a stream eroding downward, through a process, called down cutting. These valleys are formed in the initial stages of rivers and have steep slopes.

    2. I-shaped Valley : In regions of hard rocks it develops almost vertically in an I shape. River valleys are normally formed in areas of sufficient rainfall and where rocks are not very hard or resistant.
  • Qstn #5
    How is a waterfall formed ?
    Ans : Waterfall : A waterfall is generally formed due to large differences in the rate of erosion. The smaller differences lead to formation of step-like features known as rapids. The water that falls down the edge of a hard resistant rock may have at the bottom a soft rock. It is this soft rock that gets eroded fast and creates a hollow basin called plunge pool. Some of the world’s highest and best known falls are Angel Falls (986 m) in Venezuela and Yosemite fall (778 m), California, USA.
  • Qstn #6
    State the main function of a river in its middle course.
    Ans : At this stage, the gradient is reduced, and the river flows more slowly. The middle course of the river begins when it leaves the mountains area and enters the plains. In the middle course the energy required to transport the materials is just enough to drag large particles. Fine particles remain suspended in water, large particles are just dragged along the bed of the river and smaller ones are rolled down in the centre. The river also gets widened as a result of great volume of water and the impact of the load.
  • Qstn #7
    How are meanders formed ?
    Ans : River meanders are bends of longitudinal courses. S-shaped meanders which are common to most rivers result when channel-forms a curved path. These are the result of both erosion and deposition work of rivers.
    Meanders generally form under conditions of a gentle slope and sufficient water in rivers. The river flow is diverted by an obstruction allowing the river to do lateral erosion work.
  • Qstn #8
    Name two landforms in the lower course of a river.
    Ans :
    1. Delta :
      The river divides itself into many distributaries. These distributaries are also subdivided into mini-distributaries. This is due to deposition of sediments over a large area near the mouth of rivers. Such sedimentation occurs on the sides of the stream, at the mouth, in the front part as well as in the bed of the river. The deposition over a large area results in a triangular-shaped formation called delta. It resembles the Greek letter A The Ganga-Brahmaputra delta is growing towards the sea. It is also one of the largest in the world.
    2. Oxbow lakes are also formed in the lower course of a river.
  • Qstn #9
    Where is wind erosion most predominant ?
    Ans : The wind erosion is most predominant in arid regions. Since there is little vegetation or moisture to bind the loose surface materials, the effects of wind erosion are more pronounced in the desert region.
  • Qstn #10
    What are known as Deflation Hollows ?
    Ans : Deflation Hollows : Deflation involves the lifting as well as the blowing away of loose materials from the ground. The sands and pebbles are carried in the air or driven along the ground. The finer dust and sands may be deposited even outside the desert margins. Deflation results in the lowering of the land surface to create depressions called deflation hollows.
  • Qstn #11
    Name one chief landform of wind deposition ?
    Ans : Hamada is the hard bedrock exposed after sweeping away of the dust and sand by the wind.
  • Qstn #12
    Name two chief types of sand dunes.
    Ans : The following two types of sand dunes are seen

    1. Barchan : These are moon-shaped dunes. They are live dunes which advance steadily before winds that blow from a particular direction. They are found in the deserts of the Sahara. These are initially formed by an accumulation of sand at an obstacle, such as a heap of rocks. These occurs transversely to the wind, so that their horns thin out and become lower in the direction of the wind.

    2. Longitudinal Dunes or Seifs : These are long and narrow sand-ridges which grow parallel to the direction of the prevailing wind. They are found in the interior parts of deserts. In the Libyan desert, they are known as Seifs (means ‘sword’ in Arabic). In the Thar Desert they are confined to the western margin, where the force of south-west monsoon influences their formation. An important feature of such a dune is that in its crest line there are rise and fall patterns. Seifs are found in the Sahara, Iran, Thar Desert (India) and West Australia. These sand dunes are stationary and they remain in a fixed position.
  • Qstn #13
    State three chief characteristics of barchans.
    Ans :
    1. Barchans are moon-shaped dunes. They are live dunes which advance steadily before winds that blow from a particular direction.
    2. They occurs transversely to the wind, so that their horns thin out and become lower in the direction of the wind.
    3. The windward side is convex and gently-sloping while the leeward side (being sheltered) is concave and steep.
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