Class 7 Geography Chapter 3 Question Answers - Our Changing Earth

Q1. What do you understand about endogenic and exogenic forces?
Ans: The forces that act in the interior of the earth are called endogenic forces, while the forces that work on the surface of the earth are called exogenic forces. Endogenic forces sometimes produce sudden movements and at the other times produce slow move-ments. Sudden movements like earthquakes and volcanoes cause mass destruction over the surface of the earth.

Q2. How are sea caves and sea arches formed?
Ans: The erosion and deposition of the sea waves gives rise to coastal landforms. From the striking of sea waves to the rocks, hollow like caves are formed in the rocks which are called sea caves. When these cavities become bigger and bigger only the roof of the caves remains, thus forming sea arches.

Q3. How do the rivers erode the landscape?
Ans: The running water in the river erodes the landscape. Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer.

Q4. How can the impact of earthquake be minimized?
Ans: Although earthquake cannot be predicted but impact can be minimized. Selecting safe spot, staying away from fire places, chimneys etc., and be preparation are the measures which may be helpful as safeguards.

Q5. What is focus and epicentre?
Ans: The place in the crust where the movement starts is called the ‘focus’ and the place on the surface above the focus is called the ‘epicentre’. Greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.

Q6. What is called sand dunes loess?
Ans: In the desert areas, when the wind stops blowing, the sand falls and gets deposited in low hill like structures. These are called sand dunes. When the grains of sand are very fine and light, the wind can carry it over long distances, when such sand is deposited in large areas, it is called loess.

Q7. Write a short note on Waterfall.
Ans: The running water in the river erodes the landscape. When the river tumbles at steep angle over very hard rocks or down a steep valley side it forms a waterfall.
There are thousands of small waterfalls in the world. The highest waterfall is Angel Falls of Venezuela in South America. The other waterfalls are Niagara falls located on the border between Canada and USA in North America and Victoria Falls on the borders of Zambia and Zimbabwe in Africa.

Q8. What do you understand about seismograph? Describe in brief.
Ans: An earthquake is measured with a machine called a seismograph. The magnitude of the earthquake is measured on the Richter scale. An earthquake of 2.0 or less can be felt only a little. When earthquake is measured over 5.0 on Richter scale, it can cause damage from falling things. A 6.0 or higher magnitude is considered very strong and 7.0 is classified as a major earthquake.