NCERT Class 7 Geography Chapter 3 - Our Changing Earth

Chapter 3 - Our Changing Earth

Question 1: What is earthquake? Give an account of earthquake preparedness.
Answer: The movement of lithospheric plates, causing the vibration on the surface of the Earth, these vibrations are called earthquake.
Earthquake preparedness
• One must stay indoors until the shaking stops.
• One must stay away from bookshelf and heavy things.
• The shelter must be under table or a bed.

Question 2: How is glacier moraines formed?
Answer: Glacier carves out deep hallows. As the ice melts they get filled with water and become beautiful lakes in the mountains. The material carried by the glacier such as rock-big and small, sand and silt gets deposited. These deposits form glacier moraine.

Question 3: What is delta?
Answer: Delta is a triangular land form that a river forms near its mouth (where it meets the ocean or sea). Since, river deposits most of its sediments near the mouth, these deposited sediments force the river to split in several distributaries and this region is called delta.

Question 4: Define the following terms
a) Focus
b) Epicentre
Answer:
a) This is a place where the earthquake occurs. It is the origin of the seismic energy.
b) The place above the focus is called Epicentre. Vibrations travel outwards from it as waves.

Question 5: What is volcano?
Answer: A volcano is a vent (opening) in the earth's crust through which molten magma erupts suddenly.

Question 6: What are exogenic and endogenic forces?
Answer:
• Endogenic forces: The forces which act in the interior of the earth are called endogenic forces. Example: Volcano and Earthquake.
• Exogenic forces: The forces which act on the surface of the earth are called exogenic forces. Example: Wind, Sea waves etc.

Question 7: Give reasons
a) Some rocks have a shape of mushroom.
b) Flood plains are very fertile
c) Sea waves are turned into stacks.
Answer:
a) Some rocks are in a shape of mushroom because in the desert the active agent is wind. Due to wind, the lower section of wind is eroded more than the upper section.
b) Because they are formed on the flooding of rivers, by the deposit of fine soil layers and other material called sediments along with the bank of river.
c) Increase in cavity of the sea caves and the erosion of the roof of the sea arches.