Ncert 7th social geography solution chapter 3 our changing earth.

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1.Fill in the blanks.

a. Earthquake and volcanoes cause mass destruction over the surface of the earth.
b. The place on the surface above the focus is called the epicentre.
c. Weathering is the breaking up of the rocks on the earth's surface.
d.ox bow lakes are found in river valley


2. Answer the following.

a. why do the plates move?
The plates move because of the movement of the molten magma inside the earth and this movement can causes changes on the surface of the earth.

b. What are exogenic and endogenic forces?
* The forces which act in the interior of the earth are called as Endogenic forces e.g. earthquake,volcano,landslides and building mountains.
* The forces that work on the surface of the earth are called as Exogenic forces e.g. erosion and deposition by river,wind,sea-waves,glaciers.

c. What is erosion?
Erosion is the wearing away of the landscape by different agent like water,wind and ice.

d. How are flood plains are formed?
As it floods,it deposits layer of fine soil and other materials called sediments along its banks. This leads to the formation of a flood plain.

e. What are sand dunes?
The wind blows,it lifts and transport sand from one place to another. When it stops blowing the sand falls and get deposited in low hill- like structures. These are called sand dunes.

f. What are ox bow lakes?
The meander loop cuts from the river and forms a cut- off lakes is known as ox bow lakes.

3. Give reasons 
a. Some rocks have a shape of a mushroom.
Ans: In deserts one can see the rocks in the shape of a mushroom, commonly called mushroom rocks.wind erode the lower section of the rock more than the upper part.Therfore,such rocks have narrower base and wider top.

b. Flood plains are very fertile.
Ans: At times,the river overflows its banks,this leads to the flooding of the neighbouring areas. As it floods,it deposits layers of fine soil and other materials called sediments along its banks. This leads to the formation of a flat fertile flood plain.

c. Sea caves are turned into stacks.
Ans: As the cavities of the sea caves become bigger and bigger only the roof of the caves remains thus forming sea arches. Erosion breaks the roof and only walls are left. These wall like features are called stacks.

d. Buildings collapse due to earthquakes.
Ans: Building collapse because of the movement in tectonic plates under the surface of the earth which send out vibrations in all the direction causing an effect to anything built on the crust.





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