NCERT Class 7 Geography Chapter 3: Our Changing Earth Completes Notes Part 3

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Our Changing Earth

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Weathering & Erosion

  • Weathering: Breaking up of the rocks on the earth’s surface.

  • Erosion: Wearing away of the landscape by different agents like water, wind and ice.

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    Weathering & Erosion - 3 Types and 6 Agents

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Now when I say you have a big rock, this is a rock now this rock breaks up into small rocks and this process is known as weathering.

Now this particles would be transferred to far-off places by the action of wind water sea waves or glaciers the four agents that we have talked about and once they are transferred or moved from one place to the next place this process is known as Erosion. Erosion is process of the movement of fragmented particles of rock from one place to another place.

Water (River) Action

  • Waterfall – Angel Falls (Venezuela – Highest)

    • Niagara Falls (b/w Canada & USA)

    • Victoria Falls (b/w Zambia & Zimbabwe in Africa)

  • Meander – Twists and turns

  • Floodplains – fertile flat areas

  • Leeves – Raised banks

  • Oxbow Lake

  • Delta

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    Tenacious Rivers - 5 Major Fluvial Erosional Landforms

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    7 Major Fluvial Depositional Landforms - Carving the Face of the Earth

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Now first external force is the river action so underwater will be talking about two one is River action and one is Sea waves action. So River action, what happens is water as we know the river behaves like a human being it’s in this stage of Youth, Maturity and Old age. So when it’s in the stage of Youth it is very active and as it moves towards its old age it becomes very slow in mind. so when it’s youthful stage you would see features like waterfall so what would happen is there is ordinate arrangement of Hard rock, soft rock and you would have differential erosion that means soft rock would be eroded more as compare to hard rock so there would be depressions that would be seen in soft rock and then you would have formations like this and that would lead to formation of water falls. Worldwide highest water falls Angel Falls in Venezuela now there are some water falls which form the marketing like between two nations for example Niagara Falls is a demarcation between Canada and United states. You have Victoria Falls demarcation between Zambia & Zimbabwe in Africa then you have during the youthful stage since there is lot of movement of water you would have a kind of wavy movement and this wavy movement is what is known as meander it has lots of turns and twist along the side of meanders you would have flute plains that would be seen and there would be raised embarkment that would be seen on both the sides which are known as leeves.

Now some time what happen this meandering river which can be seen here cuts off from its main course and this section establishes itself as a separate lake and is its of size shape of a oxbow and hence it is known as oxbow lake and finally on the old stage the river meets the ocean body and it becomes very slow and sluggish so as a result it carries a lot of sediment which it has collected through the path from youthful stage Maturity stage and that sediment slowly and gradually deposits when it reaches the final stage and therefore towards the final stage you have formation of what is known as delta.

Now India is unique to itself because in India you can see the major rivers that drain towards east have formation of deltas so you have Krishna, Godavari, Mahanadi, Kaveri which have Delta formation however the rivers which rain towards west that is into the Arabian sea they drain directly in the form of a series and they do not form of deltas. Now the next important concept is see action.

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