NCERT Solution for Class 7 Geography Chapter 3 - Our Changing Earth
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All our solutions for Chapter 3 - Our Changing Earth are prepared considering the latest CBSE syllabus, and they are amended from time to time. Our free NCERT Textbook Solutions for CBSE Class 7 Geography will strengthen your fundamentals in this chapter and can help you to score more marks in the examination. Refer to our Textbook Solutions any time, while doing your homework or while preparing for the exam.
NCERT Solution for Class 7 Geography Chapter 3 - Our Changing Earth Page/Excercise 17
Answer the following questions.
(i) Why do the plates move?
(ii) What are exogenic and endogenic forces?
(iii) What is erosion?
(iv) How are flood plains formed?
(v) What are sand dunes?
(vi) How are beaches formed?
(vii) What are ox bow lakes?
(i) The Lithospheric plates have a tendency to move, albeit very slowly and over a very long period of time, due to the movement of the molten magma inside Earth.
(ii) Different forces cause different types of Earth’s movements. The forces that are operational on the Earth's surface are called exogenic forces. On the other hand, the ones that work in the interior of Earth are called endogenic forces.
(ii) Erosion is the deterioration, disintegration and wearing away of Earth’s landscape by different factors like water, wind and ice, etc.
(iv) While coursing through a landscape that is plain, rivers sometimes overflow their banks. This results in the flooding of the nearby lands. As this happens, the water deposits layers of fine soil and sediments on the banks of the river. This results in the formation of a flat, fertile flood plain in the concerned areas.
(v) In desert landscapes, the wind transports sand particles from one place to another. When the wind stops blowing, the sand falls and gets deposited in low hill-like structures. These structures are known as sand dunes.
(vi) The erosional and depositional activities of the sea waves form different varieties of coastal landforms. Beaches are one such variety of coastal landforms. A beach is formed when sea waves deposit sediments on the sea shore.
(vii) Ox Bow lakes are crescent shaped lakes that are caused due to the trajectory of meandering rivers. The sides of the meanders created by the rivers are further eroded and deposited onto by the water. This causes the ends of the loop to come closer and closer. Eventually, the meander loop cuts off from the river course and forms a crescent shaped ox-bow lake.
Tick the correct answer.
(i) Which is not an erosional feature of the sea waves?
(c) Sea cave
(ii) The depositional feature of a glacier is:
(a) Flood plain
(iii) Which is caused by sudden movements of the Earth?
(c) Flood Plain
(iv) Mushroom rocks are found in:
(b) River valleys
(v) Ox bow lakes are found in:
(b) River valleys
(i) – (b) Beach
(ii) – (c) Moraine
(iii) – (a) Volcano
(iv) – (a) Deserts
(v) – (b) River valleys
NCERT Solution for Class 7 Geography Chapter 3 - Our Changing Earth Page/Excercise 18
Match the following:
(i) Glacier (a) Sea shore
(ii) Meanders (b) River of ice
(iii) Beach (c) Rivers
(iv) Sand dunes (d) Vibrations of Earth
(v) Waterfall (e) Hard bed rock
(vi) Earthquake (f) Deserts
(i) – (b) River of ice
(ii) – (c) Rivers
(iii) – (a) Sea shore
(iv) – (f) Deserts
(v) – (e) Hard bed rock
(vi) – (d) Vibrations of Earth
(i) Some rocks have a shape of a mushroom.
(ii) Flood plains are very fertile.
(iii) Sea caves are turned into stacks.
(iv) Buildings collapse due to earthquakes.
(i) In deserts, mushroom rocks are often found. These rocks have a narrow cylindrical base and a wide top. This happens when the wind erodes the lower part of the rock more than the upper part.
(ii) Flood plains are formed when rivers overflow and deposit eroded material like sediments and fine soil onto the banks. Such material is conducive for cultivation. Hence, flood plains are very fertile.
(iii) Sea caves are formed when sea waves erode the cracks and make them hollow. As the waves keep striking the rocks, the cavities keep becoming bigger and bigger and ultimately form sea arches. Further erosion by the waves breaks the roof, leaving only the walls. Such structures are known as stacks. Thus, through continuous erosion, sea caves are turned into stacks.
(iv) Earthquakes are, in effect, vibrations caused within the Earth surface. These vibrations are caused by the movement of the Lithospheric plates. Hence, earthquakes, especially when they are of high intensity, cause major damage to the structures above Earth’s surface. Hence, buildings are often damaged and tend to collapse due to earthquakes.
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