NCERT Solutions for Class 7 Social Studies (Geography) Chapter 3 – Our Changing Earth
Our Changing Earth Summary
This chapter from the NCERT Geography book gives detailed information about:
1. The changing Environment on Earth and its Effects
2. Case Study on Earthquake
3. Major Land Forms
a. Work of River
b. Work of Sea Waves
c. Work of Ice
d. Work of Wind
Q 1. Answer the following questions.
(i) Why do the plates move?
Answer: The movement of molten magma inside the earth results in the movement of plates.
(ii) What are exogenic and endogenic forces?
Answer: The movement of the Earth is divided on the basis of the forces, which cause them. So, the forces that act, in the interior of the earth are called Endogenic forces and the forces that work on the surface of the earth are called Exogenic forces.
(iii) What is erosion?
Answer: Erosion is defined as the wearing away of the landscape by different agents like water, wind and ice. The process of erosion and deposition creates different land-forms on the surface of the earth.
(iv) How are flood plains formed?
Answer: When a river overflows its banks, it results in the flooding of the area surrounding it. When it floods, it deposits a layer of fine soil and other material called sediments. Thus, forming a fertile layer of soil called flood plains.
(v) What are sand dunes?
Answer: 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 the low hill-like structures. These are called sand dunes. They are mostly found in desert areas.
(vi) How are beaches formed?
Answer: The sea waves deposit sediments along the seashores. This results in the formation of beaches.
(vii) What are the ox-bow lakes?
Answer: When the river enters the plains, it twists and turns forming large bends known as meanders. In due course of time, the meander loops start to cut off the river and form cut off lakes, known as the ox-bow lakes.
Q 2. Tick the correct answer.
(i) Which is not an erosional feature of sea waves?
(a) Cliff
(b) Beach
(c) Sea cave
Answer: b
(ii) The depositional feature of a glacier is:
(a) Flood plain
(b) Beach
(c) Moraine
Answer: c
(iii) Which is caused by the sudden movements of the earth?
(a) Volcano
(b) Folding
(c) Flood plain
Answer: a
(iv) Mushroom rocks are found in:
(a) Deserts
(b) River valleys
(c) Glaciers
Answer: a
(v) Ox bow lakes are found in:
(a) Glaciers
(b) River valleys
(c) Deserts
Answer: b
Q 3. Match the following.
Answer
(i) Glacier (c) River of ice
(ii) Meanders (d) Rivers
(iii) Beach (a) Sea shore
(iv) Sand dunes (h) Deserts
(v) Waterfall (g) Hard bedrock
(vi) Earthquake (e) Vibrations of earth
4. Give reasons.
(i) Some rocks have the shape of a mushroom.
Answer: Some rocks have a shape of a mushroom because, in deserts, wind erodes the lower section of the rock more than the upper section which makes the base of the rock narrow and the upper part wide, giving it the shape of a mushroom.
(ii) Flood plains are very fertile.
Answer: Flood plains are very fertile because at times when river water overflows, it results in the flooding of the neighbouring areas. This deposits a layer of fine soil and other sediments at
the banks of the river, which leads to fertile flood plains.
(iii) Sea caves are turned into stacks.
Answer: When the cavities in the sea caves become bigger and bigger, only the roof of the caves are leftover, which forms sea arches. Further, due to erosion, the roof vanishes and only the walls stay intact, turning the sea caves into stacks.
(iv) Buildings collapse due to earthquakes.
Answer: When the lithospheric plates move, the surface of the earth vibrates and then these vibrations travel outwards from the epicentre in the form of waves, which leads to sudden movement and results in the collapse of buildings.
Very Short Answer Type Questions
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.
2. How do the lithospheric plates move?
Answer: They move around very slowly, just a few millimeters each year.
3. What is a volcano?
Answer: A volcano is a vent or opening in the earth’s crust through which molten material erupts suddenly.
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’.
5. Name the three types of earthquake waves.
Answer:P waves or longitudinal waves
S waves or transverse waves
L wave or surface waves.
6. What is a seismograph?
Answer: A seismograph is a machine which measures an earthquake
7. Name the scale on which the magnitude of the earthquake is measured.
Answer: Richter scale.
8. Which earthquake is classified as a major earthquake?
Answer: An earthquake of 7.0 magnitude is classified as a major earthquake.
9. Where is Victoria Falls located?
Answer: Victoria Falls is located on the borders of Zambia and Zimbabwe in Africa.
10. What is delta?
Answer: The collection of sediments from all the mouths forms a delta. It is a triangular-shaped landmass.
11. Name some coastal landforms.
Answer: Sea caves, sea arches, stacks, and sea cliffs.
12. How are glacial moraines formed?
Answer: The material carried by the glacier such as rocks big and small, sand and silt gets deposited. These deposits form glacial moraines.
13. Name the two processes which wear away the landscape.
Answer: Weathering and erosion.
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.
15. Name a few rivers of the world that form a delta?
Answer: Nile, Zaire, Ganga-Brahmaputra, Hwangotto, Murray-Darling, Amazon, etc.
16. Mention the work of ice.
Answer: Glaciers are rivers of ice that 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.
17. What is an earthquake? What are some common earthquake prediction methods?
Answer: When the lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all around 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.
18.. Give an account of earthquake preparedness.
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 fireplaces, areas around chimneys, windows that shelter including mirrors and picture frames. Moreover, we should spread awareness amongst our friends and family members.
Our Environment is the NCERT Geography book for students in Class 7. For NCERT Solutions for Class 7 Social Science, visit the linked article.
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