Class 7 Geography Social Science Chapter 3 Our Changing Earth

Class 7 Geography Social Science Chapter 3 Our Changing Earth

Very Short Answer Type Questions

Question  1   What do you know about the lithospheric plates?
Answer: The earth’s crust consists of several large and some small, rigid, irregularly— shaped plates, Le., slabs which cany continents and the ocean floor.
Question  2. How do the lithospheric plates move?
Answer:  They move around very slowly, just a few millimeters each year.
Question  3. What is a volcano?
Answer:  A volcano is a vent or opening in the earth’s crust through which molten material erupts suddenly.
Question  4.  Define focus’ and ‘epicentre’. [Imp.]
Answer: 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’.
Question  5.  Name the three types of earthquake waves.
  1. P waves or longitudinal waves
  2. S waves or transverse waves
  3. L wave or surface waves.
Question  6.  What is a seismograph? [V. Imp.]
Answer:  A seismograph is a machine which measures an earthquake.
Question  7.  Name the scale on which the magnitude of the earthquake is measured.
Answer: Richter scale.
Question  8. Which earthquake is classified as a major earthquake?
Answer: An earthquake of 7.0 magnitude is classified as a major earthquake.
Question  9. Where is Victoria Falls located? [Imp.]
Answer: Victoria Falls is located on the borders of Zambia and Zimbabwe in Africa.
Question  10. What is a delta?
Answer: The collection of sediments from all the mouths forms a delta. It is triangular shaped landmass.
Question  11. Name some coastal landforms.
Answer:  Sea caves, sea arches, stacks and sea cliff.
Question  12. How are glacial moraines formed?                              [V. Imp.]
Answer:  The material carried by the glacier such as rocks big and small, sand and silt gets deposited. These deposits form glacial moraines.
Question  13. Name the two processes which wear away the landscape.
Answer: Weathering and erosion.
Question  14. What does the process of erosion and deposition create?
Answer: The process of erosion and deposition create different landforms on the surface of the earth.
Question  15. Name a few rivers of the world that form a delta?
Answer: Nile, Zaire, Ganga-Brahmaputra, Hwangotto, Murray-Darling, Amazon, etc.

Short Answer Type Questions

Question  1. Mention the work of ice.
Answer:  Glaciers are rivers of ice which erode the landscape by destroying soil and stones to expose the solid rock below. Glaciers carve out deep hollows. As the ice melts they get filled up with water and become beautiful lakes in the mountains. The material carried by the glacier such as rocks big and small, sand and silt gets deposited. These deposits form glacial moraines.
Question  2. What is earthquake? What are some common earthquake prediction methods?[V. Imp.]
Answer:  When the lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all round the earth. These vibrations are called earthquakes. Some common earthquake prediction methods include studying animal behaviour, fish in the ponds get agitated, snakes come to the surface.
Question   3.  Give an account of earthquake preparedness.            [V. Imp.]
Answer:  Earthquake is a natural calamity which we cannot stop. But we can minimise its impact if we are prepared before-hand.
During an earthquake, we should shift to some safe spot. We should hide under a kitchen counter, table or desk against an inside comer or wall. We should stay away from fire places, areas around chimneys, windows that shelter including mirrors and picture frames. Moreover, we should spread awareness amongst our friends and family members.

Long Answer Type Questions

Question  1.  Explain the work of a river.                [V. Imp.]
Answer:  The running water in the river erodes the landscape. When the river tumbles at steep angle over very hard rocks or down a deep valley side it forms a waterfall. While entering the plain the river twists and turns and forms large bends which are known as meanders. 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, which is also called ox-bow lake. Sometimes, the river overflows its banks causing flood in the neighboring areas. As it floods, it deposits layers of fine soil and other material called sediments along its banks. As a result—fertile floodplain is formed. The raised banks are called levees.
As the river approaches the sea, the speed of the flowing water decreases and the river begins to break up into several streams known as distributaries. Then a time comes when the river becomes very slow and it begins to deposit its load. Each distributary forms its own mouth. The collection of sediments from all the mouths forms a delta, which is a triangular landmass.
Question  2. Give an account of the work of wind. [V. Imp.]
Answer:  Wind is an active agent of erosion and deposition in the deserts. In deserts we often notice rocks in the shape of a mushroom, known as mushroom rocks. Winds erode the lower section of the rock more than the upper part. Therefore, such rocks have narrower base and wider top. When the wind blows, it lifts and transports sand from one place to another. When the wind stops blowing the sand falls and gets deposited in low hill-like structures. These are called sand dunes. When the grains are very fine and light, the wind can carry it over long distances. When such sand is deposited in large area, it is called loess.

Courtesy : CBSE