Our Changing Earth
Class 7 CBSE Guide NCERT Solutions for Geography (Our Environment)
NCERT answers of Chapter 3 exercise questions
Question.1: Answer the following questions:
(i) Why do the plates move?
(ii) What are Exogenic and Exogenic forces?
(iii) What is erosion?
(iv) How are flood plains formed?
(v) What are Sand Dunes?
(vi) How are Beaches formed?
(vii) What are Ox-Bow Lakes?
(i) The plates are floating on magma which is molten. The plates move due to the movement of this molten magma inside the earth.
(ii) The forces which originate in the interior of the earth and bring about changes both in the interior and on the surface of the earth are called as Endogenic Forces. Example: volcanoes, earthquakes.
Forces which originate in the atmosphere and also on the surface of the earth and cause changes on the surface of the earth are called as Exogenic Forces. Example: weathering, erosion.
(iii) Erosion is the wearing away of the landscape by due to the actions of different agents like water, wind glacier, groundwater, sea waves etc.
(iv) Due to heavy rains sometimes rivers overflow their banks causing flood in these areas. The deposition of a layer of fine and other materials over plains in the form of sediments during flood leads to the formation of Flood Plains.
(v) Heaps of sand deposited at a place by the wind action in desert areas are termed as Sand Dunes.
(vi) Beach is the plain formed by the deposition of debris brought by the sea waves along the sea shore.
(vii) Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer which sometimes cut off from the river and forms a cut-off lake. Because of its ox bow like shape such lakes are called 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 Wave
(ii) The depositional feature of glacier is-
(a) Flood Plain (b) Beach(c) Moraine
(iii) Which is caused by the sudden movement of the earth?
(a) Volcano (b) Folding (c) Flood Plain
(iv) Mushroom Rocks are found in -
(a) Deserts (b) River Valleys (c) Glaciers
(v) Ox-Bow Lakes are found in -
(a) Glaciers (b) River Valleys (c) Deserts
Answer: (i) b(ii) c(iii) a (iv) a (v) b.
Question.3: Match the following:
|(i) Glacier||(a) Sea Shore|
|(ii) Sea Shore||(b) River of Ice|
|(iii) Beach||(c) Rivers|
|(iv) Sand Dunes||(d) Vibrations of Earth|
|(v) Waterfall||(e) Hard Bed Rock|
|(vi) Earthquake||(f) Deserts|
Answer: (i)-b. (ii)-c. (iii)-a. (iv)-f. (v)-e. (vi)-d.
Question.4: 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.
(i) In desert, wind is the most active agent for erosion. When rocks come on the way of running dust storms, the suspended particles mostly sand erode the lower section of the rock more than the upper part. In the long course of time due to such erosion some rocks have a shape of a mushroom having narrower base and wider top.
(ii) Flood plains are very fertile because new silt and other fertile materials brought by flood water are deposited in the form of sediments in these areas which make them most suitable for cultivation.
(iii) The sea waves strike the coasts and erode the soft rocks while the hard rocks remain comparatively less eroded. In this way the sea caves are formed. With the continuous erosion, sea caves become bigger and bigger so, at a certain point the roofs of the caves come down while the walls of remain standing just like pillars. These pillar-like structures are called as Stacks.
(iv) During earthquakes, high velocity powerful waves propagate through the surface of the earth which create sudden movements. Buildings not able to withstand the jerk collapse.
NCERT solutions of In Text Question
Question: Find out the percentage of Carbon Dioxide and Ozone in the atmosphere.
Answer: Carbon dioxide = 0.03%, Ozone = 0.000006%
Our Changing Earth - further study