GEOGRAPHY (VII)-LESSON -3 OUR CHANGING EARTH LESSON NOTES

GEOGRAPHY (VII)-LESSON -3

OUR CHANGING EARTH

LESSON NOTES

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v LITHOSPHERE PLATES

Ø The lithosphere is broken down into a number of plates known as the Lithosphere plates. These plates move slowly due to some forces which causes changes on the surface of the earth. These are two forces- 

§  The forces which act in the interior of the earth are known as endogenic forces. These causes sudden movement as Earthquake and volcanic eruptions.

§  The forces which work on the surface of the earth are called as exogenic forces.These causes slow movement as weathering, erosion, deposition and gradation.

v VALCANO

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

v EARTHQUAKES

Ø The vibrations caused by the movement of the lithospheric plates are called earthquakes.

Ø The place in the crust where the movement starts is known as the focus.

Ø The epicentre of the earthquake is the place on the surface above the focus. Maximum damage occurs near the epicentre.

Ø The vibrations travel from focus to epicenter through waves. There are three types of earthquake waves-

§  P waves or longitudinal waves

§  S waves or transverse waves

§  L waves or surface waves

Ø An Earthquake measured by an instrument that is known as seismograph. It is measured on Richter scale.

Ø Some common earthquake prediction methods include studying animal behaviour, fish in the ponds get agitated, snakes come to the surface.

Ø Earthquake preparedness

§  During an earthquake, one can take shelter under a kitchen counter, table or desk, against an inside corner or wall.

§  One should be away from fireplaces, areas around chimneys, windows, etc.

§  Spread awareness amongst your friends and family members.

v MAJOR LANDFORMS

Ø The landforms continuously changing by these process-

Ø Weathering -The breaking up of the rocks on the earth’s surface is called as weathering.

Ø Erosion -The wearing away of the landscape by different agents like water, wind, etc. is called as Erosion.

Ø Deposition-The eroded material carried away by water, wind and deposited eventually is known as deposition.

v WORK OF A RIVER

Ø The running water erodes the landscape and the eroded material (sediments) also deposited. This erosion and deposition creates many landforms on the surfaces as-

§  When the river tumbles at a steep angle over very hard rocks or down a steep valley side it forms a waterfall.

§  Large bends formed by twisting and turning of the river while entering the plain are called meanders.

§  A cut-off lake formed due to cut off of a meander loop is known as an ox bow lake.

§  The fertile areas formed by the deposition of fine soil and other material (sediments) during floods are known as flood plains.

§  The raised banks of the rivers are known as Levees.

§  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.

§  The triangular deposits at the mouth of a river is known as delta, It is very fertile.

v WORK OF SEA WAVES

Ø The erosion and deposition of the sea waves give rise to coastal landforms. These landforms are known by different names as-

§  Due to erosion work of sea waves Hallow like caves are formed on the rocks at the coast which are known as sea caves.

§  When these cavities become very big, only the roof of the caves remains, forming sea arches.

§  When the roof of sea arches breaks due to erosion and only walls are left. These wall-like features are known as stacks.

§  The steep rocky coast rising almost vertically above seawater is called sea cliff.

§  The sea waves deposit sediments along the shores forming beaches.

v WORK OF GLACIER

Ø Rivers of ice is known as glacier. Many landforms also created by the erosion and deposition process of glacier.

Ø The landscape is eroded by bulldozing soil and stones and deep hollows are created, which changed into beautiful lakes.

Ø The eroded material carried by the glacier such as rocks, sand and silt gets deposited and forms glacial moraines.

v WORK OF WIND

Ø The wind is an active agent of erosion and deposition in the deserts. Due to the deposition and erosion many landforms are created in desert areas.

Ø When winds erode the lower section of the rock more than the upper part.so such rocks have narrower base and wider top, that are known as mushroom rocks.

Ø The wind 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.

Ø When very fine and light and gets deposited in large areas, it called loess. Large deposits of loess are found in China.

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