Lithosphere plates

Chapter 3

Our Changing Earth

The earth’s crust consists of several large and some small, rigid, irregularly shaped plates which carry continents and the ocean floor.These plates are known as Lithospheric plates. These plates move around very slowly, just a few millimetres each year. This is because of the movement of the molten magma inside the earth.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.

Endogenic forces- The forces which act in the interior of the Earth.

Exogenic forces- The forces that work on the surface of the Earth.

Endogenic forces

Literal meaning of dope means inside genic means origin.Endogenic forces sometimes produce sudden movements and at the other time produce slow movements.Sudden movements like earthquakes and volcanoes caused mass destruction over the surface of the earth.


Volcano is a vent in the Earth's crust, through which molten material erupts suddenly. It is well known that the earth’s interior is very hot and as the depth increases from the surface, the temperature too increases and heat rises, ultimately, the heated rock (magma) begins rising slowly towards the surface. They escaping gases provide the driving force for volcanic eruptions, and these volcanic gases are known as steam. Then, this gas-filled magma rises and collect in large pools called magma chambers. As the magma becomes lighter in weight, it rises through channels. When it reaches the surface, it discharges out of vents or openings at the top of the channels. Thus, when the magma(molten rock) discharges out of the vents is known as lava.

A calderais a volcanic feature formed by the collapse of a volcano into itself, making it a large, special form of a volcanic crater.

Earthquakes and Epicentre

When the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all round the earth. These vibrations are called 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. Greatest damage is, usually closest to the epicenter and the strength of the earthquakedecreases away from the centre.

There are 3 types of earthquake waves.

P waves or longitudinal waves.

S waves or transverse waves.

L waves or surface waves.

Although earthquake cannot be predicted. However, the impact can certainly be minimised if we have prepared beforehand.Some common earthquake prediction methods adopted locally by people include studying animal behaviour,fish in the pond get agitated,snakes come out of the surface.


An earthquake is measured with a machine called a seismograph. The magnitude of the earthquake is measured on the Richter scale. An earthquake of 2.0, or less can be felt only a little.An earthquake over 5.0 can cause damage from things falling.A 6.0 or higher magnitude is considered very strong and 7.0 is classified as a major earthquake.

Earthquake preparedness

Where do we take shelter during an earthquake.

Safe spot- Under a kitchen counter, table or desk against an inside corner or wall.

Stay Away from.- Fire places, areas around chimneys, windows that shatter including mirrors and picture frames.

Be prepared- Spread awareness amongst your friends and family members and face any disaster confidently.

Exogenic forces

Literal meaning of exo means outside genic means origin.



Major landforms

Major Landforms

Landscape is being continuously worn away by 2 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 iceThe eroded material is carried away or transported by water, wind, etc, and eventually deposited.This process of erosion and deposition create different landforms on the surface of the earth.

Work of a river

The running water in the river erodes the landscape.When the river tumbles at steep angle over very hard rocks or down a steep valley side it forms a waterfall.As the river enters the plain it with twists and turns forming large bends known as meanders. Due to continuous erosion and deposition along the sides of the meander, oxbowlake is created overtime. When the river overflows its banks, it leads to the flooding of the neighbouring areas.Asit floods, it deposits layer of fine soil and other materials called sediments along its banks.This led to the formation of a flat fertile floodplain. The raised banks are called levees. As the river approaches the sea the speed of the flowing water decreases and the river begins to break up.The breaking of river into a number of streams is called distributaries.The river becomes so slow that it begins to deposit its load.East distributary forms its own mouth. The collection of sediments from all the mouth forms a delta.

There are thousands of small waterfalls in the world. 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 fallson the borders of zambia and zimbabwe in africa.

Work of sea waves

The erosion and deposition of the sea waves give rise to coastal landforms.Seawaves continuously strike at the rocks.Cracks develops and with they become larger and wider.Thus hollow like caves are formed on the rocks, which are called sea caves. Overtime, these cavities become bigger and bigger only the roof of the caves remainwhich resultsinformation of sea arches.Further, erosion breaks the roof and only walls are left. These walls life features are called stacks.The steep rocky coast rising almost vertically above sea water is called Seacliff. The seawaves deposit sediments along the shores forming beaches.

Work of Ice

A Glacier is a large mass of ice continuously moving over land surface, which too erode the landscape by bulldozing soil and stones to expose the solid rock below. Glaciers carve out deep hollows.As the ice melts, they get filled up with water and become beautiful lakes in the mountains. The material carried by the glacier, such as rocksbig and small, sand and siltget deposited. These deposits form glacial moraines.

Work of wind

Mushroom rocks
sand dunes

An active agent of erosion and deposition in the desert is wind.In deserts, rocks are present in the shape of a mushroom, commonly called mushroom rocks.Winds erodethe lower section of the rock more than the upper part.Therefore, such rocks havenarrower base and wider top.When the wind blows, it lifts and transport sand from one place to another.When it stops blowingthe sand falls and get deposited in low hill like structure which are called sand dunes. 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. Large deposits of loess is found in China.

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