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Question

Give reasons.

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

(ii) Flood plains are very fertile.

(iii) Sea caves are turned into stacks.

(iv) Buildings collapse due to earthquakes.


Solution

(i) In deserts, one can see rocks in the shape of a mushroom—with a narrower base and a wider top. These are known as mushroom rocks. Such rocks are formed when the winds erode the lower section of a rock more than the upper part.

(ii) Flood plains are formed as a result of the depositional activity of rivers. Rivers carry along with them eroded material like fine soil and sediments. When it overflows its banks, it deposits the eroded material and causes flood plains to be formed. The deposited material makes the land fertile.

(iii) Stacks are formed as a result of the erosional activity of the sea waves. When sea waves continuously strike rocks, cracks develop in them. As these cracks become larger and wider, hollow caves get formed on the rocks. These are called sea caves. As the waves keep striking the rocks, the cavities become bigger and bigger, with only the roof remaining at the end. Such structures are known as sea arches. Further erosion breaks the roof, and only walls remain. These wall-like features are known as stacks. Thus, sea caves are ultimately converted into stacks.

(iv) Earthquakes are the sudden vibrations caused within the Earth’s surface as a result of the movement of the Lithospheric plates. Such vibrations, when they are of a high intensity, cause damage to the things on the Earth’s surface. Various human-made (e.g., buildings) and natural (e.g., trees) constructions can break down and collapse under the effect of the vibrations because they are situated on the Earth’s surface.


Social Science
Our Environment
Standard VII

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