Our Changing Earth

Q1. Answer the following questions.

(i) Why do the plates move?

Ans:

Plates move due to the movement in the molten magma found in the interior of the earth.

(ii) What are exogenic and endogenic forces?

Ans:

1. Exogenic Forces - Exogenic forces are those forces which act & cause changes on the surface of the earth. Examples: Weathering, gradation, erosion, deposition.
2. 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?

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Erosion is the wearing away of the landscape by different agents like running water, glacier, wind, ground water and sea waves.

(iv) How are flood plains formed?

Ans :

Flood plains are formed in the following manner:

1. During rains rivers overflow their banks which leads to the flooding of the nearby areas.
2. As it floods, the river deposits layers of fine soil & other material called sediments along its banks.
3. This leads to the formation of a flat fertile flood plain.

(v) What are sand dunes?

Ans:

Sand dunes are heaps of sand deposited at a place by the wind’s action in the desert areas.

(vi) How are the beaches formed?

Ans:

1. Sea waves erode the coasts and carry the eroded material in the form of  sediments.

2. Sea waves deposit these sediments along the shore forming beaches.

(vii) What are the ox-bow lakes?

Ans:

1. When the meander loop is cuts off from the main river to form a cut-off lake.
2. As its shape is like an ox-bow, it is called a ox-bow lake.

Q2. Tick the correct answer.

(i) Which is not an erosional feature of sea waves?

Ans: (a) Cliff

(ii) The depositional feature of a glacier is

Ans: (c) Moraine

(iii) Which is caused by the sudden movements of the Earth 

Ans: (a) Volcano

(iv) Mushroom rocks are found In

Ans: (a) Deserts 

(v) Ox bow lakes are found In

Ans: (b) River valleys

Q3. Match the following.

Ans:

Q4. Give Reasons.

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

Ans:

Some rocks have the shape of a mushroom, because:

1. Wind is the active agent of erosion & deposition in the deserts.
2. The wind erodes the lower section of the rocks more that the upper section.
3. Thus, these rocks have narrower base and wider top forming the shape of the mushroom.

(ii) Flood plains are very fertile.

Ans:

Flood plains are very fertile because:

1. During rains rivers overflow their banks which leads to the flooding of the nearby areas.
2. As it floods, the river deposits layers of fine soil & other material called sediments along its banks.
3. This deposited silt makes the flood plains fertile.

(iii) Sea caves are turned into stacks.

Ans:

Sea caves are turned into stacks because:

1. The sea waves cause erosion & deposition to form coastal landforms.
2. Sea waves continuously strike the rocks making them hollow to form sea caves. 
3. Due to further erosion, the roof breaks and only the walls of the caves remain.
4. These wall-like structures are stacks.

(iv) Buddings collapse due to earthquakes.

Ans:

Buildings collapse due to earthquakes because:

1. Most buildings are not built earthquake-proof.
2. When the earthquakes strike, the buildings are not capable of resisting the vibrations of the earthquakes.
3. They tear apart due to shallow foundation, sub-standard interior material, and lack of adequate steel.
4. They collapse and fall down.

Q5. Identify the picture and state the name & type of the picture.

Ans:

Photograph	Name of Feature	Type
	Waterfall	Erosional
	Meander	Both erosional & depositional
	Flood Plain	Depositional

Q6 Solve the crossword puzzle with the help of given clues

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