Class 7 Geography

Changing Earth

NCERT Solution

Give Reasons

Question 1: Some rocks have a shape of a mushroom.

Answer: Because the winds erode the lower section of the rock more than the upper part.

Question 2: Flood plains are very fertile.

Answer: Because they are formed on the flooding of rivers, by the deposit of fine soil layers and other material called sediments along the banks of the river.

Question 3: Sea caves are turned into stacks.

Answer: Increase in the cavities of the sea caves and the erosion of the roof of the sea arches.

Question 4: Buildings collapse due to earthquakes.

Answer: Because of generation of waves that propagate through the soil and create movement at the building's foundation.

Multiple Choice Questions:

Question 1: Which is not an erosional feature of sea waves?

  1. Cliff
  2. Beach
  3. Sea cave

Answer: (b) Beach

Question 2: The depositional feature of a glacier is:

  1. Flood plain
  2. Beach
  3. Moraine

Answer: (c) Moraine

Question 3: Which is caused by the sudden movements of the earth?

  1. Volcano
  2. Folding
  3. Flood plain

Answer: (a) Volcano

Question 4: Mushroom rocks are found in:

  1. Deserts
  2. River valleys
  3. Glaciers

Answer: (a) Deserts

Question 5: Ox bow lakes are found in:

  1. Glaciers
  2. River valleys
  3. Glaciers

Answer: (b) River valleys

Answer the following questions:

Question 1: Why do the plates move?

Answer: The tectonic plates move because of the movement of molten magma inside the earth.

Question 2: What are exogenic and endogenic forces?

Answer: The forces that act in the interior of the earth are called endogenic forces. The exogenic forces are the forces that work on the exterior (surface) of the earth.

Question 3: What is erosion?

Answer: The wearing away of landscape by different agents like wind, water and ice.

Question 4: How are flood plains formed?

Answer: When the river overflows its banks, the neighbouring areas get flooded. When the river floods, it deposits layers of fine soil and other material called sediments along the banks of the river. This leads to the formation of a floodplain.

Question 5: What are sand dunes?

Answer: They are low hill–like structures when the blowing wind (which lifts and transports sand from one place to another), stops blowing. The sand falls and gets deposited in low hill–like structures called sand dunes.

Question 6: How are beaches formed?

Answer: The sea waves deposit sediments along the shores. This leads to the formation of beaches.

Question 7: What are ox bow lakes?

Answer: Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer. When this happens, over a course of time, the meander loop cuts off from the river and forms a cutoff lake. Such a lake is also called an ox-bow lake.

Match the following:

Column IColumn II
(a) Glacier(1) Sea shore
(b) Meanders(2) Desert
(c) Beach(3) River of ice
(d) Sand dunes(4) River
(e) Waterfall(5) Vibrations of earth
(f) Earthquake(6) Hard bedrock

Answer: (a) 3, (b) 4, (c) 1, (d) 2, (e) 6, (f) 5