OUR CHANGING EARTH-CLASS-7-SST(EXERCISE QUESTIONS)

CHAPTER-3  (OUR CHANGING EARTH)          

CLASS-VII

GEOGRAPHY                                  

EXERCISE QUESTIONS

*********************************************

Q1. Answer the following questions briefly:

i) Why do the plates move?
Answer: Plates move due to the movement in the molten magma found in the interior of the earth.

ii)  What are exogenic and endogenic forces?
Answer: 
Exogenic forces:
 Exogenic forces are those forces which act on the surface of the earth and cause changes on the surface of the earth.
 Examples: weathering, erosion, deposition.
 Endogenic forces:
 Endogenic forces are those forces which originate in the interior of the earth and cause changes on the surface of the earth.
 Examples:  volcanoes and earthquakes.

iii)  What is erosion?
Answer: 
The wearing away of the landscape by different agents like running water,  glacier,  wind,  ground water and sea waves.

iv)  How are flood planes formed?
Answer:
Plains are formed in the following manners:
1.  During rains rivers over flow their banks.
2.  This leads to the flooding of the nearby areas.
3.  After the flood has receded,  a layer of fine material and other material is deposit over the plain in the form of sediments.
4.  This leads to the formation of the floodplain.

v)  What are sand dunes?
Answer:-
Sand dunes:
Sand dunes are heaps of sand deposit at the place by the winds action in the desert areas.

vi) How are the beaches formed?
Answer:
Formation of beaches:
 1.Sea waves strike the coasts.
2.  They erode the coasts and carry the eroded material in the form of silt and other materials.
3.  When they withdraw they deposit the silt and other materials(sediments) along the shore,  forming wide beaches.

vii) What are the ox-bow lakes?
Answer:  Ox-bow lakes:
1.  When the meander loop is cut off from the main river,  it forms a cut off lake.
2. Its shape is like an ox-bow.
3.  Hence, the cut off lake is called ox-bow lake.

Q. 2. Tick the Correct answer:

(i) Which is not an erosional feature of sea waves?
a) Cliff
b) Beach
c) Sea cave

 ii) The deposional feature of a glacier is....
a)  Flood plains
b)  beach
c)  Moraine 

iii) Which is caused by the sudden moment of the earth?
Answer:
a)  Volcano
b)  folding 
c) flood plains

iv)  Mushroom rocks are found in ....
a)  Deserts 
b) river- valley
c)  glaciers 

v) Ox-bow lakes are found in......
a) glaciers 
b) river valleys
c)  desert 

Answer:
 (i) – (a), (ii) – (c), (iii)-(a) , (iv) -(a), (v)-(b)

Q.3. Match the following:
i)  glacier                  a) she shore
ii)  meanders.          b)  mushroom rock 
iii) beach.                 c)  rivers of ice 
iv) Sand dune           d) Rivers 
v) waterfall               e) Vibration of earth
vi)  Earthquake.        f) Sea Cliff
                                     g) Hard bed rocks
                                     h)  desserts 
Answer: 
(i)-c, (ii)-g, (iii)-a ,(iv)-h ,(v)-d ,(vi)-e

Q4. Give reasons:

i)  Some rocks have the shape of mushroom.
Answer.
i)  Some rocks have the shape of mushroom because of the following reasons:
.  When rocks fall in the course of running dust storms,  this suspended particles of sand strike the lower portion of the rocks and Erode them.
. The upper portions of the rocks remain unaffected/uneroded.
.  In course of time the rocks take up the shape of mushroom.

ii)  Flood plains are very fertile.
Flood plains are very fertile because of the following reasons:

.  They are made of the silt and other material brought by floods.
.  Due to spread of the new silt,  the flood plains are fertile areas.

iii)  Sea caves are turned into stacks. 
Sea caves are turned into stacks because of the following reasons: 

.  The sea waves strike the coast and erode its soft rocks. Hard rocks remain uneroded.  This action results in the formation of sea cave.
.  In course of the time the roofs of the cave also come down due to erosion and the arms/walls of the caves remain standing like pillars.
. These pillers-like formations are termed as stacks.

iv) Buildings collapse due to earthquakes.
Buildings collapse due to earthquakes because of the following reasons:

.  Most buildings are not built/made earthquake proof.
.  When the earthquakes strike,  the buildings are not capable of resisting the vibrations of the earthquakes.
.  They tear apart due to shallow foundation sub -standard interior material,  and lack of adequate Steel.
.  They collapse and fall down like pack of papers or cards.