NCERT Solutions Class 7th Geography Social Science Chapter – 3 Our Changing Earth Notes What is our changing earth? What is erosion?What are sand dunes ? Why is our Earth changing? What are the 3 changes of Earth? What changes Earth for kids? How we are changing the planet? Why is Earth important? How can kids save Earth? What are the 5 lines on Save Earth?What are 10 ways to save Earth? Why save the earth? How can we save the earth life? How can we save the world? What is the earth essay? What is Earth 10 lines? What is called a Earth? Why is it called Earth? Who first named Earth? Who gave Earth its name? What are 5 facts about Earth?
NCERT Solutions Class 7th Geography Social Science Chapter – 3 Our Changing Earth
Chapter – 3
Our Changing Earth
Notes
Lithospheric Plates
The lithosphere is broken into a number of plates known as the Lithospheric plates. These plates move around very slowly because of the movement of the molten magma inside the earth. The molten magma inside the earth moves in a circular manner. The movement of these plates causes changes on the surface of the earth. • The earth movements are divided on the basis of the forces, which cause them. These forces are called Endogenic forces and Exogenic forces.
Endogenic forces
The forces, which act in the interior of the earth are called Endogenic forces. Endogenic forces sometimes produce sudden movements and at other times produce slow movements.
Sudden movements like earthquakes and volcanoes cause mass destruction over the surface of the earth.
Exogenic forces
The forces that work on the surface of the earth are called Exogenic forces.
Volcano
A volcano is a vent in the earth’s crust, through which, molten material erupts suddenly.
Earthquake
When the Lithospheric plates move, the surface of the earth vibrates and it travels all around the earth. These vibrations are called earthquakes.
Focus
The place in the crust where the movement starts is called the focus.
Epicentre
The place on the surface above the focus is called the epicentre. Vibrations travel outwards from the epicentre as waves. The greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.
Some common earthquake prediction methods adopted locally by people include studying animal behaviour; fish in the ponds get agitated, snakes come to the surface.
Major Land forms
The landscape is being continuously worn away by two processes – weathering and erosion. • Weathering: Weathering is the breaking up of the rocks on the earth’s surface.
Erosion
Erosion is the wearing away of the landscape by different agents like water, wind and ice. The eroded material is carried away or transported by water, wind, etc. and eventually deposited. This process of erosion and deposition creates different landforms on the surface of the earth.
Work of a River
Waterfall– When the river tumbles at steep angle over very hard rocks or down a steep valley side, it forms a waterfall.
Meanders
As the river enters the plain it twists and turns forming large bends known as meanders.
Cut – off Lake
Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer. In due course of time the meander loop cuts off from the river and forms a cut-off lake, also called an ox-bow lake.
Floodplain
As it floods, the river deposits layers of fine soil and other material called sediments along its banks. This leads to the formation of a flat fertile floodplain. The raised banks are called levees.
Distributaries
When 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.
Delta
The river becomes so slow that it begins to deposit its load. Each distributary forms its own mouth. The collection of sediments from all the mouths forms a delta.
Work of Sea Waves
Sea caves – The erosion and deposition of the sea waves give rise to coastal landforms and they continuously strike at the rocks developing cracks. The cracks become larger and wider over time. Due to which, hollow like caves are formed on the rocks. They are called sea caves.
Sea Arches
When these cavities become bigger and bigger only the roof of the caves remain, it forms sea arches.
Stacks
Erosion breaks the roof and only walls are left and these wall-like features are called stacks.
Sea cliff
The steep rocky coast rising almost vertically above seawater is called sea cliff.
Work of Ice
Glaciers– Glaciers are “rivers of ice,” which 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 in the mountains.
Glacial Moraines
The material carried by the glacier such as rocks big and small, sand and silt gets deposited and forms glacial moraines.
Work of wind
Wind – In the desert, an active agent of erosion and deposition is wind.
Mushroom Rocks
In deserts, rocks can be shaped like a mushroom, commonly called mushroom rocks.
Sand Dunes
When the wind blows, it lifts and transports sand from one place to another. When it stops blowing the sand falls and gets deposited in low hill like structures. These are called sand dunes.
Loess
When the grains of sand are very fine and light, the wind can carry it over very long distances. • When such sand is deposited in large areas, it is called loess.
What is the ‘Lithosphere’?
The lithosphere is the solid, outer part of the Earth. The lithosphere includes the brittle upper portion of the mantle and the crust, the outermost layers of Earth’s structure.
What are ‘Glaciers’?
A glacier is a large, perennial accumulation of crystalline ice, snow, rock, sediment and often liquid water that originates on land.
What are ‘Sea Caves’?
A cave formed in a cliff by wave action of an ocean or lake is called as a Sea cave.
Question. 1 Name a few rivers of the world that form a delta?
Nile, Zaire, Ganga-Brahmaputra, Hwangotto, Murray-Darling, Amazon, etc.
Question. 2 Name some coastal landforms.
Sea caves, sea arches, stacks, and sea cliffs.
Question. 3 What is delta?
The collection of sediments from all the mouths forms a delta. It is a triangular-shaped landmass.
Question.4 Where is Victoria Falls located?
Victoria Falls is located on the borders of Zambia and Zimbabwe in Africa.
Question. 5 Name the scale on which the magnitude of the earthquake is measured.
Richter scale.
Question. 6 Which earthquake is classified as a major earthquake?
An earthquake of 7.0 magnitude is classified as a major earthquake.
Question. 7 How do the lithospheric plates move?
They move around very slowly, just a few millimeters each year.
Question. 8 What is a seismograph?
A seismograph is a machine which measures an earthquake.
Question. 9 What is a volcano?
A volcano is a vent or opening in the earth’s crust through which molten material erupts suddenly.
Question. 10 Name the three types of earthquake waves.
• P waves or longitudinal waves • S waves or transverse waves • L wave or surface waves.
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