CBSE Class 7 - Our Environment - CH3 - Our Changing Earth (NCERT Solution)

Our Changing Earth

Gobi Desert - Sand Dunes

NCERT Chapter Solutions

Q1. Answer the following questions.

(i) Why do the plates move?

Answer: The movement of molten magma inside the earth causes plates move.


(ii) What are exogenic and endogenic forces?

Answer: The forces which act in the interior of the earth are known as endogenic forces and the forces which works on the surface of the earth are known as exogenic forces.


(iii) What is erosion?

Answer: Erosion is a process of scrapping, scratching and grinding of surface rocks. Erosion also causes removal or transportation of weathered soil from one place to another.


(iv) How are flood plains formed?

Answer: Fine eroded soil and other materials called sediments get deposited at river banks and flood plains are formed.


(v) What are sand dunes?

Answer: Small hills of sand are called sand dunes. These  sand dunes keep on moving from place to place due to fast blowing winds.


(vi) How are beaches formed?

Answer: Sediments deposited along the shores by sea waves form the beaches.


(vii) What are ox bow lakes?

Answer: Continuous erosion and deposition along the sides of the meanders causes ends of meanders loop come closer and closer. Over a long period of time, the meander loop cuts off from the river and form a cut off lake or ox bow lake.


Q2. Tick the correct answer.
(i) Which is not an erosional feature of sea waves?

(a) Cliff
(b) Beach
(c) Sea cave

Answer: (b) Beach


(ii) The depositional feature of a glacier is:

(a) Flood plain
(b) Beach
(c) Moraine

Answer: (c) Moraine


(iii) Which is caused by the sudden movements of the earth?

(a) Volcano
(b) Folding
(c) Flood plain

Answer:  (b) Folding


(iv) Mushroom rocks are found in:

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

Answer: (a) Deserts

(v) Ox bow lakes are found in:

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

Answer: (b) River valleys

Q3. 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

Answer:
(i) Glacier - (b) River of Ice
(ii) Meanders - (c) Rivers
(iii) Beach  - (a) Sea shore
(iv) Sand dunes - (f) Deserts
(iv) Waterfall - Hard Bedrock
(v) Earthquakes - (d) Vibrations of earth.


Q4. Give reasons.

(i) Some rocks have a shape of a mushroom.

Answer: Winds erode at different rate i.e. erodes more the lower section of the rock than the upper part, It forms mushroom rock.

(ii) Flood plains are very fertile.

Answer: The sediments brought by rivers deposited at river bank are rich in minerals and are highly fertile.

(iii) Sea caves are turned into stacks.

Answer: Erosion causes sea caves turn into stacks.

(iv) Buildings collapse due to earthquakes.

Answer: Buildings can't withstand the high vibrations caused due to earth quake and fell down.

Q6. For fun.
Solve the crossword puzzle with the help of given clues.
Across
2. Loop like bend of river
4. Solid form of water
7. Moving mass of ice
9. Sudden descent of water in bed of river
11. Natural cavity on weak rocks formed by action of waves
12. Embankment on river that keeps river in its channel
13. Large body of sea water
14. Dry area where sand dunes are found
15. Small hill of sand piled by action of wind
16. Flat plain formed by river deposits during time of flood


Down
1. Rise and fall of water caused by friction of wind on water surface
3. Flow of water in channel
5. Steep perpendicular face of rock along sea coast
6. Debris of boulder and coarse material carried by glacier
8. Crescent shaped lake formed by river meander
10. Fine sand deposited by action of wind
13. Isolated mass of rising steep rock near coastline
14. Alluvial tracts of land at mouth of river formed by river deposits

Answer: