NCERT-GEOGRAPHY-CLASS-07-CHAPTER-03

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Lithosphere

The lithosphere is the combination of the Earth

Crust, and
the solid upper portion of the mantle.

It simply means the combined joint portion of the crust and the solid upper belt of the mantle known as the lithosphere.

Lithospheric plates

The vertical breakaway portion of the lithosphere is known as the lithospheric plates.
We have 7 major and around 15 minor plates.

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Magma & Volcano

Molten or semi-molten material, which, in its mixture, has molten rocks, ash, gases, and water vapour, is known as magma.
It is formed in the mantle portion of the Earth and is a product of heat and pressure fluctuation.
The route through which Magma comes to the Earth's surface is known as a "vent".
When the molten magma erupts from the Earth's surface through a vent known as a "volcano".

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Tectonic Movement

The lithospheric plates are not static, but are always in a continuous movement, which is known as a tectonic movement.

The tectonic movement in the interior of the lithosphere is caused by the movement of magma inside the Earth, in a circular path, known as "convective currents".

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Endogenetic forces

The meaning of the word "Genic" means something new being/ about to be created.
When this "genic force" comes from inside, it is known as endogenic force, which is processed through two mechanisms-

"Diastrophic", which is the slow rate of movement, and
The second is "Epeirogrnic" involving the faster outcome through volcanic eruption and earthquake.

Exogenetic forces

The forces that act on the surface/ Crust of the Earth or come outside of Earth are known as exogenic forces.
The forces are "denuadation" in nature.
The agents of exogenic forces are-

River,
Wind,
sea waves,
Groundwater, and
glaciers.

Earthquakes

Due to the tectonic movement/release of energy from inside the Earth, a set of vibrations on the surface of the Earth is generated all around.
These vibrations are known as an earthquake.

Focus

A point inside the crust of Earth from where the earthquake waves started.

Epicenter

The point above the Earth's surface which vertical/ at 180 degrees to the focus is known as the epicentre.
Earthquake vibrations travel outward from the epicentre, known as earthquake waves.

Types of earthquake waves

We have 02 kinds and four types of earthquake waves that are-

longitudinal P waves,
S wave is a transverse wave, categorised as a "body wave".
"L" -&- "R" waves are categorised as "surface waves".
In earthquake waves, Love waves (L-waves) and Rayleigh waves (R-waves) are the most important earthquake waves from the human-experience point of view, because they travel along the Earth’s surface and are mainly responsible for the strong shaking and damage that we feel during an earthquake.
Body waves, such as P-waves and S-waves, travel through the Earth’s interior and are comparatively less effective in producing destructive surface shaking.

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Seismograph

An instrument through which an earthquake is measured.

Weathering

Post weathering Scenarion of Rocks

The natural process through which the wearing and tearing down (sedimentation) of the Earth's surface began.
Through this process, rocks break into sediments.

Erosion

Taking away that weathering material (sediments) through the different natural agents-

River,
Wind,
sea waves,
Groundwater, and
Glaciers are known for their erosion.

Waterfall

Waterfall: a stream of water tumbling down from a hard Rock surface or down to a steep valley side, known as a waterfall.
Creation of the waterfall is an interplay between hard rock -&- soft rocks.
Hard rocks at the top and less susceptible to erosion against soft rocks at lower strata are more susceptible to erosion.
"Jog Falls" was created by the Sharavati River dropping 253 m (830 ft).
It is the third-highest waterfall in India, after the "Nohkalikai Falls", with a drop of 335 m (1,099 ft) in Meghalaya. It is fed by the rain and is located on the edge of the "Cherrapunji Plateau."
The second-highest fall is "Dudhsagar Falls" with a drop of 310 m (1,020 ft) in the Indian state of Goa.

Meanders

Meanders are large twists and turns formed by a river when it enters a plain area, which is generally considered the second stage of the river.
In this stage, the river’s slope becomes gentle, but its lateral erosion becomes more active compared to the first stage.
As a result, the river erodes the outer bank and deposits sediments on the inner bank. This continuous process of erosion and deposition causes the river channel to bend gradually, forming large curves known as "meanders".
In more detail, with a pictorial study of the image.

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Oxbow lake

In a gradual process,
At the banks of the meander, the erosion and deposition process in the simultaneous process gets starting,
which causes the loops of the meander to cut off from the river.

This cut-off loop, filled with water, as a product, transform in to a separates water bodies formed along the bank of the river, known as an oxbow lake.
In Bihar, over the river "Buri Gandak", we have India's largest oxbow lake.

Floodplains

When the river stream is overflowing,
The water breaks the bank of the river (Natural Levees) and enters the nearby area in the form of a flood.
As floodwater tends to stay in the flooded area, it deposits its sediments, which is a layer of fine soil, over there.
It leads to the formation of a plain area known as a floodplain.

Implication of Decantation in the Formation of Flood Plains 🤔-

As we know, decantation is a process in which muddy water is left undisturbed for some time so that the heavier sediments settle down at the bottom.
A similar process takes place during floods. When a river overflows its banks, floodwater spreads into the nearby low-lying areas with high velocity. After spreading over the land, the velocity of water gradually decreases, and the water remains stagnant for some time. During this period, a process similar to decantation begins.
The heavier and finer alluvial sediments carried by the river start settling down on the land surface.
When the floodwater finally retreats back into the river channel, it leaves behind a thick layer of fertile sediments.
Over repeated floods, these deposited sediments create broad, flat, and fertile plains along the river valley. These depositional landforms are known as "flood plains".

Levees

In the deposition process,
Due to the depositional activities, the banks of the river rose because of sediments, silt, and other material
are pushed aside by the flowing river called levees.

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Distributaries

Due to the lower gradient of a slope or almost negligible slope gradient,
In addition to heavy sediment loads,
The main river stream breaks into the various streams known as distributaries.

Delta

Delta formation generally takes place in the third or old stage of a river, where the slope gradient becomes almost negligible or nearly zero near the river mouth.
Due to this extremely gentle slope, the river loses most of its velocity and transporting capacity.
Throughout its long course from the mountains to the plains, the river carries a huge amount of sediments such as sand, silt, clay, and other alluvial materials. When the river finally reaches the sea or ocean, the very low gradient makes it difficult for the river to carry this heavy sediment load further.
As a result, deposition begins near the river mouth. Continuous sediment accumulation blocks the main channel of the river, causing the river to divide into several smaller channels known as "distributaries".
Between these distributaries, large-scale alluvial deposition takes place over time. Gradually, a triangular or fan-shaped depositional landform emerges at the mouth of the river. Since this landform resembles the Greek letter “Δ” (Delta), it is known as a delta landform.

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Waves

Wind, a movement of air under the influence of atmospheric pressure from "P+" to "P-".
When there is friction between the wind & water body, surface water leads to continuous disturbance, which causes waves in the water body.

Sea caves

Sea waves, along the sea coast, give rise to the coastal landforms through the process of erosion and deposition.
This process, when the sea wave continuously hits a rock, led to the formation of a hollow cave, known as a sea cave.

Sea arches

With the continuous hitting of the sea caves by sea /ocean waves, with the passage of time, the opening is now done by another hand / through caves.
As a result, now the only roof, with the support of stacks, remains known as sea arches.

Stacks

When the roof of the sea arches also diminishes, and only the walls are there, known as a sea stack, another marine landform example.
Found over the west coast of India.

Sea Cliff

On the coast, due to the continuous erosion by sea waves, a vertical eroded wall of stone(s) rises/emerge against the propagation direction of waves known as a sea Cliff.

Beaches

As sea waves,
through the process of backwash deposit sediments along the shore
A new kind of landform forms, known as a beach.

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River of Ice

The glaciers are known as the river of ice.
We have studied these earlier chapters also.

Glacier moraines

In glacier movement -

When the big and small-sized rocks,
sand, and
Silt is carried away with the ice and gets deposited
Then these deposits are known as glacier moraines.

Mushroom rocks

In the desert area, when we see a mountain of sand in the shape of a mushroom known as a mushroom rock.
As a special feature of desert areas, the shape of these mushroom rocks is the work of wind through the process of erosion.
In desert areas, wind erodes the lower section or the lower part of the Rock more than the upper section;

Either the density of sand particles is higher, or
In lower strata, we have soft rock subjected to higher erosion than the upper strata's hard rock, where the erosion rate is slower.

As a result, the rocks take the shape of a mushroom.

Sand dunes

A low hill-like structure in the desert area
It is the outcome product of deposit channel activities of the wind known as sand dunes.

Loess

In the wind deposition process, the deposition of clay, because being lighter in weight, over a large area is known as loess.

Loess plateau, the largest landform in the world,
Multan Belt of Pakistan
The Land of Shri Ganga Nagar district of Rajasthan is a classic example of it.

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