NCERT Solutions for Class 7 Geography Chapter 3 Our Changing Earth contains answers to the exercise questions given in the “Our Environment”. All the answers provided here are accurate and simple that will help you understand the concepts easily and continue your studies without a doubt. These solutions will also help you to score higher marks with the help of well-illustrated answers.
Class 7 Geography Chapter 3 Our Changing Earth Questions and Answers
Question 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 as Endogenic forces and the forces that work on the surface of the earth are called as Exogenic forces.
(iii) What is erosion?
Answer: Erosion is the weathering or wearing away of the landscape by different agents like wind, water and ice.
(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: In deserts, when wind blows, it lifts and transports sand from one place to another. When it stops blowing, the sand particles fall and get deposited in low hill-like structures called sand dunes.
(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: As the river enters the plain it twists and turns forming large bends 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. Eventually, the meander loop cuts off from the river and forms a cut-off lake, known as the ox-bow lakes.
Question 2: Tick the correct answer.
(i) Which is not an erosional feature of sea waves?
(a) Cliff
(b) Beach
(c) Sea cave
Answer: (a) Cliff
(ii) The depositional feature of a glacier is:
(a) Flood plain
(b) Beach
(c) Moraine
Answer: (c) Moraine
(iii) Which is caused by the sudden movements of the earth?
(a) Volcano
(b) Folding
(c) Flood plain
Answer: (a) Volcano
(iv) Mushroom rocks are found in:
(a) Deserts
(b) River valleys
(c) Glaciers
Answer: (a) Deserts
(v) Ox bow lakes are found in:
(a) Glaciers
(b) River valleys
(c) Deserts
Answer: (b) River valleys
Question 3: Match the following.
| (i) Glacier | (a) Sea shore |
| (ii) Meanders | (b) Mushroom rock |
| (iii) Beach | (c) River of ice |
| (iv) Sand dunes | (d) Rivers |
| (v) Waterfall | (e) Vibrations of earth |
| (vi) Earthquake | (f) Sea cliff |
| (g) Hard bedrock | |
| (h) Deserts |
Answer:
| (i) Glacier | (c) River of ice |
| (ii) Meanders | (g) Hard bedrock |
| (iii) Beach | (a) Sea shore |
| (iv) Sand dunes | (h) Deserts |
| (v) Waterfall | (d) Rivers |
| (vi) Earthquake | (e) Vibrations of earth |
Question 4: Give reasons.
(i) Some rocks have the shape of a mushroom.
Answer: Some rocks have a shape of a mushroom because, in desserts, wind erodes the lower section of rock more than the upper section. Due to this, the lower part of the rock becomes narrow and the upper part becomes wide, giving it the shape of a mushroom.
(ii) Flood plains are very fertile.
Answer: 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) 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: During an earthquake, vibrations are produced within the earth’s surface as a result of the movement of the Lithospheric plates. When these vibrations travel outwards from the epicentre as waves, this leads to a sudden movement of the Earth’s surface which results in the collapse of buildings.