NCERT Class 7 Geography Chapter 3 - Our Changing Earth Notes

Chapter 3 - Our Changing Earth Notes

1. The lithosphere is broken into a number of plates known as the Lithospheric plates.

2. Movement of the molten magma inside the earth occurs thereby the Lithospheric plates are moved very slowly just a few millimetres each year.

3. 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.

4. Endogenic forces sometimes produce sudden movements and at the other times produce slow movements. Sudden movements like earthquakes and volcanoes cause mass destruction over the surface of the earth.

5. A volcano is a vent (opening) in the earth’s crust through which molten material erupts suddenly.

6. Vibration in the surface of earth is called earthquakes. 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.

7. Greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.

8. The landscape is being continuously worn away by two processes - weathering & erosion.

9. 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.

10. As the river approaches the sea, the speed of the flowing water decreases and the river begins to break up into a number of streams called distributaries. Each distributary forms its own mouth. The collection of sediments from all the mouths forms a delta.

11. 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.

12. Glaciers are rivers of ice which erode the landscape by bulldozing soil and stones to expose the solid rocks below.

13. The material carried by the glaciers, such as rocks, sand and silt gets deposited. These deposits form glacial moraines.

14. An active agent of erosion and deposition in the deserts is wind. It makes rocks in shape of a mushroom called mushroom rocks.

15. When the wind stops blowing, the sand falls and gets deposited in low hill like structures. These are called sand dunes.

16. 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.

17. The Earth’s crust consists of several large and some small, rigid, irregular-shaped plates (slabs) which carry continents and the ocean floor are called Lithospheric Plates.

18. There are 3 types of Earthquake waves:
a) P waves or longitudinal waves
b) S waves or transverse waves
c) L waves or surface waves

19. An Earthquake is measured with a machine called 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. An Earthquake over 5.0 can cause damage from things falling. A 6.0 or higher magnitude is considered very strong and 7.0 is classified as a major Earthquake.

20. The highest waterfall is Angel Falls of Venezuela in South America. Niagara Falls is located between USA and Canada in North America and Victoria Falls on the borders of Zambia and Zimbabwe in Africa.

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