NCERT Class 7 Geography Chapter 3: Our Changing Earth Completes Notes Part 1

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Our Changing Earth

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When start with class 7 chapter-3 Our Changing Earth, now this class totally focuses on the evolution of land forms. When we talk about evolution of land forms there are two basic ways under which we classify movement of earth. They can be either Endogenic forces or Exogenic forces. Now genic means “origin” or genies means origin. So when I talk about origin. It can be either Endogenic or Exogenic. Exogenic means those which are affected by outer phenomena or outside phenomena. Endogenic which is affected by inner phenomena or inner changes.

So origin which is base from within itself or inside the earth system would be known as endogenic forces. However factors are that affected the origin of land from outside would be Exogenic forces. So when I say Exogenic forces I can say wind, water, rain so all this are external forces which are affecting formation of landform this structure of mountain, rivers, the basic land scape of earth. However there are certain forces which are internal. They are for example volcano coming out or you have kind of earthquake movement that could be seen all those are internal forces which are endogenic in nature. So whenever we talk about earth movements we classify forces either Endogenic or Exogenic. Exogenic as I said could be either erosional or depositional. Depositional means whatever sediments have weathered away or have eroded away are finally getting settled down and that is known as depositional. So it can be by action of river, wind, sea-waves or glaciers.

Now when we talk about Endogenic forces this could be all of the sudden or this could be slow and gradual over the force of the time. When I say slow and gradual it can be formation of mountain ranges, formation of Himalayas for example of could be a classical example Diastrophic forces which is a kind of very slow process which has taken plays over centuries and centuries, however have sudden forces which are sudden. So eruption of earthquake is all of sudden, you have landslide that is accruing in mountain areas it is a kind of sudden change in the land scape. Volcanic activity region is all of the sudden so all these are kind of sudden phenomena. Now what we will be focus in today class, we have covered all this in great detail in individual classes. What we will be covering today as kind of summary of all this under one single head, so will start with the first one that is volcano.

Volcano

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Volcano

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You can refer those.

Image of Volcano

Image of Volcano

Now the first one is volcano. Now volcano erupts when the inner material gets to hot and unable to keep its self within the mountain region as a result it erupts. When it erupts it is flow of magma and this magma flows out throw and opening which is known as vent. The material what comes out known as lava. The upper most section where you kind of a leg formation once the material has erupted as known as crater and finally one’s you have the volcanic activities that freezes of or is vanish you have formation of lake that text place this formation are known as crater lake. When this crater gets bigger it’s known as coldena. The inner section of the mountain where you have the origin of volcanic activities as known as magma chamber and this is the basic material that flows and into the volcano now next is earthquake.

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