NCERT Solutions class 7 Geography Chapter 3. Our Changing Earth NCERT Exercise

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1. 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?

Answer:

(i) The plates move due to endogenic forces acting in the interior of the earth.

(ii) The forces that act in the interior of the earth are called endogenic forces. The forces that act on the earth's surface are called exogenic forces.

(iii) Erosion is the wearing away of the landscape by different agents like water, wind and ice.

(iv) When rivers outflow their banks, they cause floods in the neighbouring areas. The flood water takes away fine soil and other material and deposited them along the banks. The deposition leads to the formation of flood plains.

(v) Winds lifts and carry sand from one place to another. When they stop blowing, sand falls and gets deposited in low hill-like structure called sand dunes. 

(vii) When a river enters the plain, it forms a large bend which is cut-off from the main stream in due cource of time. The cut-off stream takes the form of a lake called ox-bow.  
2. Tick the correct answer.
(i) Which is not an erosional feature of sea waves?
(a) Cliff (b) Beach (c) Sea cave
(ii) The depositional feature of a glacier is:
(a) Flood plain (b) Beach (c) Moraine
(i) Why do the plates move?
(iii) Which is caused by the sudden movements of the earth?
(a) Volcano (b) Folding (c) Flood plain
(iv) Mushroom rocks are found in:
(a) Deserts (b) River valleys (c) Glaciers

(i) Glacier (a) Sea shore
(ii) Meanders (b) Mushroom rock

(v) Ox bow lakes are found in:

(a) Glaciers (b) River valleys (c) Deserts

Answer:

(i)-(a) (ii)-(c) (iii)-(a) (iv)-(a) (v)-(b)

Q3. Match the following.

(i) Glacier(a) sea-shore                                                            (ii) Meander (b) River of ice

(iii) Beach (c) Rivers
(v) Waterfall (e) Vibrations of earth
(iv) Sand dunes (d) Rivers
(vi) Earthquake (f) Sea cliff
(g) Hard bed rock
(h) Deserts

Answer:

Q4.Give reasons.
(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.

Answer:

(i) Because winds erode the lower section of the rock more than the upper part. Therefore, such rocks have narrower base and wider top.

(ii) Flood plains are formed when the river overflow its banks. It deposits layers of fine soil and other material called sediments which are very fertile.

(iii) After the formation of sea caves when cavities become bigger only the roof of cave remain, sea arches are formed. Further, erosion breaks the roof and only walls are left. These wall like features are called stacks.

(iv) In a earth quake the vibrations travel outwards from the epicentre as waves. The surface starts vibrating which lead to shaking of structures built on the earth's surface and thus building collapase. 
Q5. Activity.
Observe the photographs given below. These are various features made by a
river. Identify them and also tell whether they are erosional or depositional or
landforms formed by both.

Answer: