Chapter 3 – Our Changing Earth
Answer the following questions.
(i) Why do the plates move?
(ii) What are exogenic and endogenic 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 move because of the movement of the molten magma inside the earth.
(ii) Exogenic forces. The forces that work on the surface of the earth are called as exogenic forces.
Endogenic forces. The forces that act in the interior of the earth are called as endogenic forces.
(iii) Erosion is the wearing away of the landscape by different agents like water, wind and ice.
(iv) During floods, layers of fine soil and other material called sediments are deposited on the river bank. This leads to the formation of a flat fertile floodplains.
(v) Sand dunes are low hill-like structures formed by the deposition of sand in the deserts.
(vi) Beaches are formed when the sea waves deposit sediments along the shores of the sea.
(vii) When the meander loop is cut off from the main river, it forms a cut-off lake. As its shape is like an ox bow, it is also known as ox-bow lake.
Tick the correct answer.
(i) Which is not an erosional feature of sea waves?
(a) Cliff (b) Beach (c) Sea cave
(ii) The depositional feature of a glacier is:
(a) Flood plain (b) Beach (c) Moraine
(iii) Which is caused by the sudden movements 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
(v) River Valleys
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
(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 deserts, winds usually erode the lower section of the rock more than the upper part. Therefore, such rocks have narrower base and wider top, which take the shape of a mushroom.
(ii) Flood plains are formed by the deposition of fine soil and other material called sediments on the river banks. As the soil and sediments are brought by flood water, they are very fertile.
(iii) Sea waves strike at the rocks. As a result cracks develop which become bigger over time and hollow like caves are formed on the rocks. They are called sea caves. These cavities become bigger and bigger and a time comes when only the roof of the caves remain to form sea arches. Further erosion breaks the roof and only walls are left. These wall like features are called stacks. In this way, sea caves are turned into stacks.
(iv) Most of the buildings are not safe enough to resist the vibrations of the earthquakes. They are not made earthquake-proof. They collapse tearing apart due to shallow foundation and lack of adequate steel in the interior design.
Observe the photographs given below. These are various features made by a river. Identify them and also tell whether they are erosional or depositional or landforms formed by both.