Our Changing Earth - Geography NCERT Notes for UPSC

The lithosphere is broken into a number of plates known as the Lithospheric plates. These plates move around slowly due to the movement of the molten magma in a circular manner inside the Earth. The movement of these plates causes changes on the surface of the Earth. The Earth movements are the result of various forces acting on the plates. Navigate further to understand our changing earth and add more knowledge to your UPSC CSE preparation.  

Various forces inside the Earth

• The forces which act in the interior of the Earth are called Endogenic forces.
• The forces that work on the surface of the Earth are called Exogenic forces.

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

Earthquakes: The vibrations on the surface of Earth due to the movement of Lithospheric plates are called as earthquakes. 

• The place in the crust where the movement starts is called the focus.
•  The place on the surface above the focus is called the epicentre. 
• The greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.

Major landforms and their evolution

Different landforms on the surface of the Earth are created by two processes: weathering and erosion.

• Weathering is the breaking up of the rocks on the Earth’s surface. 
• Erosion is the wearing away of the landscape by different agents like water, wind, and ice. 

Landforms formed by Rivers

• Meanders: As the river enters the plain, it twists and turns to form large bends known as meanders.

• Ox-bow Lake: Meander loop cuts off from the river and forms a cut-off lake, called as ox-bow lake.
• Floodplains: Sometimes the river overflows its banks which lead to the flooding of the neighbouring areas. As it floods, it deposits layers of fine soil and other material called sediments along its banks. This leads to the formation of a flat fertile floodplain.
• Levees: These are raised banks.
• Distributaries: 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. These distributaries help in extending the delta.

Coastal landforms

The erosion and deposition of the sea waves gives rise to coastal landforms.

• Sea caves: Hollow-like caves formed on the rocks are known as Sea caves.
• Sea arches: As the cavities become bigger and bigger, only the roof of the caves remains, thus forming sea arches. 
• Stacks: Further, erosion breaks the roof and only walls are left. These wall-like features are called stacks.
• Sea cliffs: The steep rocky coast rising almost vertically above seawater is called a sea cliff. 

Landforms formed by Ice

• Glaciers are “rivers of ice” which too erode the landscape by bulldozing soil and stones to expose the solid rock below.
• Glaciers carve out deep hollows there. As the ice melts they get filled up with water and become beautiful lakes.
• The material carried by the glacier such as rocks big and small, sand and silt gets deposited. These deposits form glacial moraines.

Landforms formed by Winds

An active agent of erosion and deposition in the deserts is wind. 

• In deserts, various rocks in the shape of a mushroom, commonly called mushroom rocks are found.
• Sand dunes: These are formed by the deposition of sand by the wind in low hills – like structures.
• When such sand is deposited in large areas, it is called loess. 
• Large deposits of loess are found in China. 

Important Terms and Facts

• Lithospheric plates: The Earth’s crust consists of several large and some small, rigid, irregularly shaped plates (slabs) which carry continents and the ocean floor.
• There are three types of earthquake waves: 
  • P waves or longitudinal waves,
  • S waves or transverse waves,
  • L waves or surface waves.

• An earthquake is measured with a machine called a Seismograph.
• The magnitude of the earthquake is measured on the Richter scale.
• 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.

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Plate tectonics is the theory that explains the movement and interaction of Earth's lithospheric plates. It plays a crucial role in the formation of mountains through processes like subduction, collision, and uplift. Additionally, plate tectonics is also responsible for seismic activity, leading to earthquakes along plate boundaries.