Topic outline

    • Our Changing Earth

      Q20. What are the processes that create different landforms on the surface of the earth?

      Ans. The process of erosion and deposition create different landforms on the surface of the earth.


      Q21. Define the term focus and epicenter.

      Ans. The place in the crust where the movement starts is called the focus. The place on the surface above the focus is called the epicentre.


      Q22. Why are the flood plains very fertile?

      Ans. The flood plains are very fertile because these plains are formed by the fine soil and sediments brought by the flood water.


      Q23. What is a delta?

      Ans. A delta is a feature formed when rivers drop off sediments in low-lying areas, usually as they enter the ocean, sea or an estuary. It is sometimes shaped like a triangle.

      Q24. How does waterfall form?

      Ans. The running water in the river erodes the landscape. When the river tumbles at steep angle over very hard rocks or down a steep valley side it forms a waterfall.


      Q25. What are some other methods used to predict an earthquake?

      Ans. Some common earthquake prediction methods adopted locally by people include studying animal behaviour; fish in the ponds get agitated, snakes come to the surface.


      Q26. What are earthquakes?

      Ans. When the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all-round the earth. These vibrations are called earthquakes.


      Q27. What are sand dunes?

      Ans. When the wind blows, it lifts and transports sand from one place to another. When it stops blowing the sand falls and gets deposited in low hill – like structures. These are called sand dunes.


      Q28. What are the three types of earthquake waves?

      Ans. There are three types of earthquake waves:

      1. P waves or longitudinal waves

      2. S waves or transverse waves

      3. L waves or surface waves

      Q29. Name some waterfalls.

      Ans. The highest waterfall is Angel Falls of Venezuela in South America. The other waterfalls are Niagara Falls located on the border between Canada and USA in North America and Victoria Falls on the borders of Zambia and Zimbabwe in Africa.


      Q30. What are exogenic and endogenic forces?

      Ans. Exogenic forces - The forces that work on the surface of the earth are called as Exogenic forces.

      Endogenic forces - The forces which act in the interior of the earth are called as Endogenic forces.


      Q31. How are flood plains formed?

      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 material called sediments along its banks. This leads to the formation of a flat fertile flood plain.


      Q32. What are ox bow lakes?

      Ans. Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer. In due course of time the meander loop cuts off from the river and forms a cut-off lake, also called an ox-bow lake.

      Q33. Why some rocks have a shape of a mushroom?

      Ans. Winds erode the lower section of the rock more than the upper part. Therefore, such rocks have narrower base and wider top which resembles a mushroom. These rocks in the shape of a mushroom, commonly called mushroom rocks.


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