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Question
Give reasons for the following:
Earth as a whole does not expand.
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Solution 1
About six important Convection Current Cells with over-riding six large plates have been identified below the Lithosphere. The Mid-Oceanic ridges from edges of the plates. For example, the Mid-Atlantic ridge is such a ridge. The molten matter from below adds new crust along such’ ridges. Taking the earth as a whole it has resulted in the spreading of the ocean floor at the rate of 1 cm to about 10 cm every year. It is called the constructive plate movement. At the same time, the crust at the other edges of the plates in oceanic trenches gets destroyed. It is called the destructive plate movement Consequently a balance exists and the Earth as a whole does not expand.
Solution 2
Inspite of various changes occurring within the earth it does not expand as it is affected by the centripital force of gravity working towards the centre of the earth
RELATED QUESTIONS
How are volcanoes formed?
What is‘magma’?
What do you understand by ‘Crater of the Volcano’?
Distinguish between the following pair of terms associated with vulcanicity:
Cinder Cone and Composite Cone
Match the items given in Column A with the correct ones in Column B.
| Column A | Column B |
| 1. A Rift valley lake | (a) Deccan Trap region of India |
| 2. A horst | (b) Fujiyama |
| 3. A basic lava sheet | (c) Tanganyika |
| 4. Composite cones | (d) Black forest plateau |
| 5. An active volcano | (e) Corndon Hill |
| 6. A Batholith | (f) The Alps |
| 7. A Phaccolith | (g) Upland of Britain is France |
| 8. A young Fold mountain | (h) Stromboli |
Name one useful feature of vulcanicity other than soil fertility.
How the theory of plate tectonics has explained the formation of mountains like Himalaya or Alps and of the volcanic islands.
Assertion (A): The Pacific Ocean includes two thirds of the world’s volcanoes.
Reason (R): The boundary along the Eastern and Western coast areas of the Pacific Ocean is known as the Pacific Ring of Fire.
The upper part of the earth’s crust ______.
Choose the odd one
Vesuvius, Stromboli, St.Helena, Etna.
