Chapter 3: Our Changing Earth
Why does our earth change ?
Endogenic and Exogenic Forces
Volcano
Earthquake
Bhuj Earthquake: A Case Study
Major Landforms
Work of River
Formation of Ox-Bow
Formation of Flood Plains
Formation of Delta
Work of Sea Waves
Work of Ice
Work of Wind
Full chapter 3 in English
Questions and Answers
Test Yourself
The Lithospheric plates move around because of the movement of the molten magma inside the Earth.
Earth’s movements are divided on the basis of the forces which cause them. The ones that work on the Earth’s surface are called exogenic forces while the ones that work in the Earth’s interior are called endogenic forces. The erosional and depositional activities of wind and water are examples of exogenic forces. Earthquakes and volcanoes are examples of endogenic forces.
Erosion is the weathering or wearing away of the landscape by different agents like wind, water and ice.
During its course through a plain, a river sometimes overflows its banks. This leads to the flooding of the neighboring areas. As it floods, the river water deposits layers of fine soil and sediments on its banks. This leads to the formation of a flat, fertile flood plain.
In deserts, when wind blows, it lifts and transports sand from one place to another. When it stops blowing, the sand particles fall and get deposited in low hill-like structures called sand dunes.
The erosional and depositional activities of the sea waves give rise to different coastal landforms. A beach is one such coastal landform. It is formed when the sea waves deposit sediments along the sea shore.
An ox-bow lake is a crescent-shaped lake formed by a meandering river. During its journey through a plain, a river twists and turns to form meanders. Erosion and deposition occur constantly along the sides of a meander, thereby causing the ends of its loop to come closer and closer. In due course of time, the meander loop cuts off from the river and forms a cut-off, crescent-shaped ox-bow lake.
Give reasons:
Some rocks have the shape of a mushroom, because of the following reasons:
- When’ rocks fall in the course of running dust-storms, the suspended particles of sand strike the lower portion of the rocks and erode them.
- The upper portions of the rocks remain unaffected/uneroded.
- In course of time the rocks take up the shape of a mushroom.
Flood plains are very fertile because of the following reasons:
- They are made of the silt and other material brought by floods.
- Due to spread of the new silt, the flood plains are fertile areas.
Sea caves are turned into stacks because of the following reasons:
- The sea waves strike the coasts and erode the soft rocks. Hard rocks remain uneroded. This action results in the formation of sea caves.
- In course of time the roofs of the caves also come down due to erosion and the arms/walls of the caves remain standing like pillars. • These pillars-like formations are termed as stacks.
Buildings collapse due to earthquakes because of the following reasons:
- Most buildings are not built/made earthquake-proof.
- When the earthquakes strike, the buildings are not capable of resisting the
vibrations of the earthquakes. - They tear apart due to shallow foundation, sub-standard interior material, and lack of adequate steel.
- They collapse and fall down like a pack of papers/cards.
In deserts, when wind blows, it lifts and transports sand from one place to another. When it stops blowing, the sand particles fall and get deposited in low hill-like structures called sand dunes.
The erosional and depositional activities of the sea waves give rise to different coastal landforms. A beach is one such coastal landform. It is formed when the sea waves deposit sediments along the sea shore.
An ox-bow lake is a crescent-shaped lake formed by a meandering river. During its journey through a plain, a river twists and turns to form meanders. Erosion and deposition occur constantly along the sides of a meander, thereby causing the ends of its loop to come closer and closer. In due course of time, the meander loop cuts off from the river and forms a cut-off, crescent-shaped ox-bow lake.