On this page, you will find NCERT Class 7 Geography Chapter 3 Notes Pdf free download. CBSE Class 7 Social Science Notes Geography Chapter 3 SST Our Changing Earth will seemingly help them to revise the important concepts in less time.
Our Changing Earth Class 7 Notes Social Science Geography Chapter 3
CBSE Class 7 Geography Chapter 3 Notes Understanding The Lesson
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. movement of these plates causes changes on the surface of the earth.
4. 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.
5. 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.
6. A volcano is a vent (opening) in the earth’s crust through which molten material erupts suddenly.
7. 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.
8. Greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.
9. Although earthquake cannot be predicted but impact can be minimized. Recognizing safe spot, staying away from fire places, chimneys, windows etc., are the measures which may be helpful as safeguards.
10. The landscape is being continuously worn away by two processes—weathering and erosion.
11. 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.
12. 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.
13. 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.
14. Glaciers are rivers of ice which erode the landscape by bulldozing soil and stones to expose the solid rocks below.
15. The material carried by the glaciers, such as rocks, sand and silt gets deposited. These deposits form glacial moraines.
16. An active agent of erosion and deposition in the deserts is wfind. It makes rocks in shape of a mushroom called mushroom rocks.
17. When the wind stops blowing, the sand falls and gets deposited in low hill like structures. These are called sand dunes.
18. 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.
Notes of Geography Class 7 Chapter 3 Important Terms
Focus: A place of movement inside the earth.
Epicentre: A place on surface above the focus.
Meander: In the plains, large bends of rivers.
Distributary: When river streams form new stream.
Erosion: Corrosion of earth due to water, wind and ice etc.
Waterfall: When the river tumbles at steep angle over very hard rocks or down a steep valley side it forms a waterfall.