NCERT Textbook - Structure and Physiology | Geography (Prelims) by Valor Academy - UPSC PDF Download

 Page 1


PHYSIOGRAPHY
This unit deals with
• Structure and Relief; physiographic divisions
• Drainage systems: concept of water sheds — the Himalayan
and the Peninsular
UNIT
II
2024-25
Page 2


PHYSIOGRAPHY
This unit deals with
• Structure and Relief; physiographic divisions
• Drainage systems: concept of water sheds — the Himalayan
and the Peninsular
UNIT
II
2024-25
D
o you know that our earth also has  a
history.  The earth and its landforms
that we see today have evolved over a
very long time. Current estimation shows that
the earth is approximately 4600 million years
old. Over these long years, it has undergone
many changes brought about primarily by the
endogenic and exogenic forces. These forces have
played a significant role in giving shape to various
surface and subsurface features of the earth.  Y ou
have already studied  about the Plate Tectonics
and the movement of the Earth’s plates in the
book Fundamentals of Physical Geography
(NCERT, 2006).  Do you know that the Indian
plate was to the south of the equator millions of
years ago? Do you also know that it was much
larger in size and the Australian plate was a part
of it?  Over millions of years, this plate broke into
many parts and the Australian plate moved
towards the southeastern direction and the
Indian plate to the north. Can you map
different phases in the movement of the
Indian plate?  This northward movement
of the Indian plate is still continuing and it
has significant consequences on the
physical environment of the Indian
subcontinent.  Can you name some important
consequences of the northward movement
of the Indian plate?
It is primarily through the interplay of
these endogenic and exogenic forces and
lateral movements of the plates that the
present geological structure and geomorphologic
processes active in the Indian subcontinent came
into existence.  Based on the variations in its
geological structure and formations, India can  be
divided into three geological divisions. These
geological regions broadly follow the physical
features:
(i) The Penisular Block
(ii) The Himalayas and other Peninuslar
Mountains
(iii) Indo-Ganga-Brahmaputra Plain.
THE PENINSULAR BLOCK
The northern boundary of the Peninsular
Block may be taken as an irregular line
running from Kachchh along the western
flank of the Aravali Range near Delhi and
then roughly parallel to the Yamuna and
the Ganga as far as the Rajmahal Hills
and the Ganga delta. Apart from these,
the Karbi Anglong and the Meghalaya
Plateau in the northeast and Rajasthan
in the west are also extensions of this
block. The northeastern parts are
separated by the Malda fault in West
Bengal from the Chotanagpur plateau.  In
Rajasthan, the desert and other desert–
like features overlay  this block.
The Peninsula is formed essentially by
a great complex of very ancient gneisses
and granites, which constitutes a major
part of it. Since the Cambrian period, the
Peninsula has been standing like a rigid
block with the exception of some of its
western coast  which is submerged
beneath the sea and some other parts
changed due to tectonic activity without
affecting the original basement. As a part of
the Indo-Australian Plate, it has been subjected
to various vertical movements and block
faulting.  The rift valleys of the Narmada, the
Tapi and the Mahanadi and the Satpura block
STRUCTURE AND PHYSIOGRAPHY
CHAPTER
2024-25
Page 3


PHYSIOGRAPHY
This unit deals with
• Structure and Relief; physiographic divisions
• Drainage systems: concept of water sheds — the Himalayan
and the Peninsular
UNIT
II
2024-25
D
o you know that our earth also has  a
history.  The earth and its landforms
that we see today have evolved over a
very long time. Current estimation shows that
the earth is approximately 4600 million years
old. Over these long years, it has undergone
many changes brought about primarily by the
endogenic and exogenic forces. These forces have
played a significant role in giving shape to various
surface and subsurface features of the earth.  Y ou
have already studied  about the Plate Tectonics
and the movement of the Earth’s plates in the
book Fundamentals of Physical Geography
(NCERT, 2006).  Do you know that the Indian
plate was to the south of the equator millions of
years ago? Do you also know that it was much
larger in size and the Australian plate was a part
of it?  Over millions of years, this plate broke into
many parts and the Australian plate moved
towards the southeastern direction and the
Indian plate to the north. Can you map
different phases in the movement of the
Indian plate?  This northward movement
of the Indian plate is still continuing and it
has significant consequences on the
physical environment of the Indian
subcontinent.  Can you name some important
consequences of the northward movement
of the Indian plate?
It is primarily through the interplay of
these endogenic and exogenic forces and
lateral movements of the plates that the
present geological structure and geomorphologic
processes active in the Indian subcontinent came
into existence.  Based on the variations in its
geological structure and formations, India can  be
divided into three geological divisions. These
geological regions broadly follow the physical
features:
(i) The Penisular Block
(ii) The Himalayas and other Peninuslar
Mountains
(iii) Indo-Ganga-Brahmaputra Plain.
THE PENINSULAR BLOCK
The northern boundary of the Peninsular
Block may be taken as an irregular line
running from Kachchh along the western
flank of the Aravali Range near Delhi and
then roughly parallel to the Yamuna and
the Ganga as far as the Rajmahal Hills
and the Ganga delta. Apart from these,
the Karbi Anglong and the Meghalaya
Plateau in the northeast and Rajasthan
in the west are also extensions of this
block. The northeastern parts are
separated by the Malda fault in West
Bengal from the Chotanagpur plateau.  In
Rajasthan, the desert and other desert–
like features overlay  this block.
The Peninsula is formed essentially by
a great complex of very ancient gneisses
and granites, which constitutes a major
part of it. Since the Cambrian period, the
Peninsula has been standing like a rigid
block with the exception of some of its
western coast  which is submerged
beneath the sea and some other parts
changed due to tectonic activity without
affecting the original basement. As a part of
the Indo-Australian Plate, it has been subjected
to various vertical movements and block
faulting.  The rift valleys of the Narmada, the
Tapi and the Mahanadi and the Satpura block
STRUCTURE AND PHYSIOGRAPHY
CHAPTER
2024-25
9 STRUCTURE AND PHYSIOGRAPHY
mountains are some examples of it.  The
Peninsula mostly consists of relict and residual
mountains like the Aravali hills, the Nallamala
hills, the Javadi hills, the Veliconda hills, the
Palkonda range and the Mahendragiri hills, etc.
The river valleys here are shallow with low
gradients.
You are aware of the method of
calculating the gradient as a part of your
study of the book Practical Work in
Geography– Part I  (NCERT, 2006).  Can
you calculate the gradient of the
Himalayan and the Peninsular rivers and
draw the comparisons?
Most of the east flowing rivers form
deltas before entering  into the Bay of
Bengal.  The deltas formed by the
Mahanadi, the Krishna, the Kaveri and the
Godavari  are important examples.
THE HIMALAYAS AND OTHER
PENINSULAR MOUNTAINS
The Himalayas along with other Peninsular
mountains are young, weak and flexible in their
geological structure unlike the rigid and stable
Peninsular Block. Consequently, they are still
subjected to the interplay of exogenic and
endogenic forces, resulting in the development
of faults, folds and thrust plains. These
mountains are tectonic in origin, dissected by
fast-flowing rivers which are in their youthful
stage. Various landforms like gorges, V-shaped
valleys, rapids, waterfalls, etc. are indicative of
this stage.
INDO-GANGA-BRAHMAPUTRA PLAIN
The third geological division of India
comprises the plains formed by the river
Indus, the Ganga and the Brahmaputra.
Originally, it was a geo-synclinal
depression which attained its maximum
development during the third phase of
the Himalayan mountain formation
approximately about 64 million years ago.
Since then, it has been gradually filled
by the sediments brought by the
Himalayan and Peninsular rivers.
Average depth of alluvial deposits in
these plains ranges from 1,000-2,000 m.
It is evident from the above discussion
that there are significant variations
among the different regions of India in
terms of their geological structure, which
has far-reaching impact upon other
related aspects.  Variations in the
physiography and relief are important
among these. The relief and physiography
of India has been greatly influenced by
the geological and geomorphological
processes active in the Indian
subcontinent.
PHYSIOGRAPHY
‘Physiography’ of an area is the outcome
of structure, process and the stage of
development. The land of India is
characterised by great diversity in its
physical features. The north has a vast
expanse of rugged topography consisting
of a series of mountain ranges with varied
peaks, beautiful valleys and deep gorges.
The south consists of stable table land
with highly dissected plateaus, denuded
rocks and developed series of scarps. In
between these two lies the vast north Indian
plain.
Based on these macro variations, India
can be divided into the following
physiographic divisions:
(1) The Northern and North-eastern
Mountains
(2) The Northern Plain
Figure 2.1 : A Gorge
2024-25
Page 4


PHYSIOGRAPHY
This unit deals with
• Structure and Relief; physiographic divisions
• Drainage systems: concept of water sheds — the Himalayan
and the Peninsular
UNIT
II
2024-25
D
o you know that our earth also has  a
history.  The earth and its landforms
that we see today have evolved over a
very long time. Current estimation shows that
the earth is approximately 4600 million years
old. Over these long years, it has undergone
many changes brought about primarily by the
endogenic and exogenic forces. These forces have
played a significant role in giving shape to various
surface and subsurface features of the earth.  Y ou
have already studied  about the Plate Tectonics
and the movement of the Earth’s plates in the
book Fundamentals of Physical Geography
(NCERT, 2006).  Do you know that the Indian
plate was to the south of the equator millions of
years ago? Do you also know that it was much
larger in size and the Australian plate was a part
of it?  Over millions of years, this plate broke into
many parts and the Australian plate moved
towards the southeastern direction and the
Indian plate to the north. Can you map
different phases in the movement of the
Indian plate?  This northward movement
of the Indian plate is still continuing and it
has significant consequences on the
physical environment of the Indian
subcontinent.  Can you name some important
consequences of the northward movement
of the Indian plate?
It is primarily through the interplay of
these endogenic and exogenic forces and
lateral movements of the plates that the
present geological structure and geomorphologic
processes active in the Indian subcontinent came
into existence.  Based on the variations in its
geological structure and formations, India can  be
divided into three geological divisions. These
geological regions broadly follow the physical
features:
(i) The Penisular Block
(ii) The Himalayas and other Peninuslar
Mountains
(iii) Indo-Ganga-Brahmaputra Plain.
THE PENINSULAR BLOCK
The northern boundary of the Peninsular
Block may be taken as an irregular line
running from Kachchh along the western
flank of the Aravali Range near Delhi and
then roughly parallel to the Yamuna and
the Ganga as far as the Rajmahal Hills
and the Ganga delta. Apart from these,
the Karbi Anglong and the Meghalaya
Plateau in the northeast and Rajasthan
in the west are also extensions of this
block. The northeastern parts are
separated by the Malda fault in West
Bengal from the Chotanagpur plateau.  In
Rajasthan, the desert and other desert–
like features overlay  this block.
The Peninsula is formed essentially by
a great complex of very ancient gneisses
and granites, which constitutes a major
part of it. Since the Cambrian period, the
Peninsula has been standing like a rigid
block with the exception of some of its
western coast  which is submerged
beneath the sea and some other parts
changed due to tectonic activity without
affecting the original basement. As a part of
the Indo-Australian Plate, it has been subjected
to various vertical movements and block
faulting.  The rift valleys of the Narmada, the
Tapi and the Mahanadi and the Satpura block
STRUCTURE AND PHYSIOGRAPHY
CHAPTER
2024-25
9 STRUCTURE AND PHYSIOGRAPHY
mountains are some examples of it.  The
Peninsula mostly consists of relict and residual
mountains like the Aravali hills, the Nallamala
hills, the Javadi hills, the Veliconda hills, the
Palkonda range and the Mahendragiri hills, etc.
The river valleys here are shallow with low
gradients.
You are aware of the method of
calculating the gradient as a part of your
study of the book Practical Work in
Geography– Part I  (NCERT, 2006).  Can
you calculate the gradient of the
Himalayan and the Peninsular rivers and
draw the comparisons?
Most of the east flowing rivers form
deltas before entering  into the Bay of
Bengal.  The deltas formed by the
Mahanadi, the Krishna, the Kaveri and the
Godavari  are important examples.
THE HIMALAYAS AND OTHER
PENINSULAR MOUNTAINS
The Himalayas along with other Peninsular
mountains are young, weak and flexible in their
geological structure unlike the rigid and stable
Peninsular Block. Consequently, they are still
subjected to the interplay of exogenic and
endogenic forces, resulting in the development
of faults, folds and thrust plains. These
mountains are tectonic in origin, dissected by
fast-flowing rivers which are in their youthful
stage. Various landforms like gorges, V-shaped
valleys, rapids, waterfalls, etc. are indicative of
this stage.
INDO-GANGA-BRAHMAPUTRA PLAIN
The third geological division of India
comprises the plains formed by the river
Indus, the Ganga and the Brahmaputra.
Originally, it was a geo-synclinal
depression which attained its maximum
development during the third phase of
the Himalayan mountain formation
approximately about 64 million years ago.
Since then, it has been gradually filled
by the sediments brought by the
Himalayan and Peninsular rivers.
Average depth of alluvial deposits in
these plains ranges from 1,000-2,000 m.
It is evident from the above discussion
that there are significant variations
among the different regions of India in
terms of their geological structure, which
has far-reaching impact upon other
related aspects.  Variations in the
physiography and relief are important
among these. The relief and physiography
of India has been greatly influenced by
the geological and geomorphological
processes active in the Indian
subcontinent.
PHYSIOGRAPHY
‘Physiography’ of an area is the outcome
of structure, process and the stage of
development. The land of India is
characterised by great diversity in its
physical features. The north has a vast
expanse of rugged topography consisting
of a series of mountain ranges with varied
peaks, beautiful valleys and deep gorges.
The south consists of stable table land
with highly dissected plateaus, denuded
rocks and developed series of scarps. In
between these two lies the vast north Indian
plain.
Based on these macro variations, India
can be divided into the following
physiographic divisions:
(1) The Northern and North-eastern
Mountains
(2) The Northern Plain
Figure 2.1 : A Gorge
2024-25
10 INDIA : PHYSICAL ENVIRONMENT
Figure 2.2 : India : Physical
2024-25
Page 5


PHYSIOGRAPHY
This unit deals with
• Structure and Relief; physiographic divisions
• Drainage systems: concept of water sheds — the Himalayan
and the Peninsular
UNIT
II
2024-25
D
o you know that our earth also has  a
history.  The earth and its landforms
that we see today have evolved over a
very long time. Current estimation shows that
the earth is approximately 4600 million years
old. Over these long years, it has undergone
many changes brought about primarily by the
endogenic and exogenic forces. These forces have
played a significant role in giving shape to various
surface and subsurface features of the earth.  Y ou
have already studied  about the Plate Tectonics
and the movement of the Earth’s plates in the
book Fundamentals of Physical Geography
(NCERT, 2006).  Do you know that the Indian
plate was to the south of the equator millions of
years ago? Do you also know that it was much
larger in size and the Australian plate was a part
of it?  Over millions of years, this plate broke into
many parts and the Australian plate moved
towards the southeastern direction and the
Indian plate to the north. Can you map
different phases in the movement of the
Indian plate?  This northward movement
of the Indian plate is still continuing and it
has significant consequences on the
physical environment of the Indian
subcontinent.  Can you name some important
consequences of the northward movement
of the Indian plate?
It is primarily through the interplay of
these endogenic and exogenic forces and
lateral movements of the plates that the
present geological structure and geomorphologic
processes active in the Indian subcontinent came
into existence.  Based on the variations in its
geological structure and formations, India can  be
divided into three geological divisions. These
geological regions broadly follow the physical
features:
(i) The Penisular Block
(ii) The Himalayas and other Peninuslar
Mountains
(iii) Indo-Ganga-Brahmaputra Plain.
THE PENINSULAR BLOCK
The northern boundary of the Peninsular
Block may be taken as an irregular line
running from Kachchh along the western
flank of the Aravali Range near Delhi and
then roughly parallel to the Yamuna and
the Ganga as far as the Rajmahal Hills
and the Ganga delta. Apart from these,
the Karbi Anglong and the Meghalaya
Plateau in the northeast and Rajasthan
in the west are also extensions of this
block. The northeastern parts are
separated by the Malda fault in West
Bengal from the Chotanagpur plateau.  In
Rajasthan, the desert and other desert–
like features overlay  this block.
The Peninsula is formed essentially by
a great complex of very ancient gneisses
and granites, which constitutes a major
part of it. Since the Cambrian period, the
Peninsula has been standing like a rigid
block with the exception of some of its
western coast  which is submerged
beneath the sea and some other parts
changed due to tectonic activity without
affecting the original basement. As a part of
the Indo-Australian Plate, it has been subjected
to various vertical movements and block
faulting.  The rift valleys of the Narmada, the
Tapi and the Mahanadi and the Satpura block
STRUCTURE AND PHYSIOGRAPHY
CHAPTER
2024-25
9 STRUCTURE AND PHYSIOGRAPHY
mountains are some examples of it.  The
Peninsula mostly consists of relict and residual
mountains like the Aravali hills, the Nallamala
hills, the Javadi hills, the Veliconda hills, the
Palkonda range and the Mahendragiri hills, etc.
The river valleys here are shallow with low
gradients.
You are aware of the method of
calculating the gradient as a part of your
study of the book Practical Work in
Geography– Part I  (NCERT, 2006).  Can
you calculate the gradient of the
Himalayan and the Peninsular rivers and
draw the comparisons?
Most of the east flowing rivers form
deltas before entering  into the Bay of
Bengal.  The deltas formed by the
Mahanadi, the Krishna, the Kaveri and the
Godavari  are important examples.
THE HIMALAYAS AND OTHER
PENINSULAR MOUNTAINS
The Himalayas along with other Peninsular
mountains are young, weak and flexible in their
geological structure unlike the rigid and stable
Peninsular Block. Consequently, they are still
subjected to the interplay of exogenic and
endogenic forces, resulting in the development
of faults, folds and thrust plains. These
mountains are tectonic in origin, dissected by
fast-flowing rivers which are in their youthful
stage. Various landforms like gorges, V-shaped
valleys, rapids, waterfalls, etc. are indicative of
this stage.
INDO-GANGA-BRAHMAPUTRA PLAIN
The third geological division of India
comprises the plains formed by the river
Indus, the Ganga and the Brahmaputra.
Originally, it was a geo-synclinal
depression which attained its maximum
development during the third phase of
the Himalayan mountain formation
approximately about 64 million years ago.
Since then, it has been gradually filled
by the sediments brought by the
Himalayan and Peninsular rivers.
Average depth of alluvial deposits in
these plains ranges from 1,000-2,000 m.
It is evident from the above discussion
that there are significant variations
among the different regions of India in
terms of their geological structure, which
has far-reaching impact upon other
related aspects.  Variations in the
physiography and relief are important
among these. The relief and physiography
of India has been greatly influenced by
the geological and geomorphological
processes active in the Indian
subcontinent.
PHYSIOGRAPHY
‘Physiography’ of an area is the outcome
of structure, process and the stage of
development. The land of India is
characterised by great diversity in its
physical features. The north has a vast
expanse of rugged topography consisting
of a series of mountain ranges with varied
peaks, beautiful valleys and deep gorges.
The south consists of stable table land
with highly dissected plateaus, denuded
rocks and developed series of scarps. In
between these two lies the vast north Indian
plain.
Based on these macro variations, India
can be divided into the following
physiographic divisions:
(1) The Northern and North-eastern
Mountains
(2) The Northern Plain
Figure 2.1 : A Gorge
2024-25
10 INDIA : PHYSICAL ENVIRONMENT
Figure 2.2 : India : Physical
2024-25
11 STRUCTURE AND PHYSIOGRAPHY
(3) The Peninsular Plateau
(4) The Indian Desert
(5) The Coastal Plains
(6) The Islands.
The North and Northeastern Mountains
The North and Northeastern Mountains consist
of the Himalayas and the Northeastern hills.
The Himalayas consist of a series of parallel
mountain ranges. Some of the important
ranges are the Greater Himalayan range,
which includes the Great Himalayas and
the Shiwalik. The general orientation of these
ranges is from northwest to the southeast
direction in the northwestern part of India.
Himalayas in the Darjiling and Sikkim regions
lie in an eastwest direction, while in Arunachal
Pradesh they are from southwest to the
northwest direction. In Nagaland, Manipur and
Mizoram, they are in the northsouth direction.
The approximate length of the Great Himalayan
range, also known as the central axial range, is
2,500 km from east to west, and their width varies
between 160-400 km from north to south. It  is
also evident from the map that the Himalayas
stand almost like a strong and long wall between
the Indian subcontinent and the Central and East
Asian countries.
Himalayas are not only the physical barrier,
they are also a climatic, drainage and cultural
divide.  Can you identify the impact of Himalayas
on the geoenvironment of the countries of South
Asia?  Can you find some other examples of
similar geoenvironmental divide in the world?
The Northern Plains
The northern plains are formed by the
alluvial deposits brought by the rivers –
the Indus, the Ganga and the Brahmaputra.
These plains extend approximately 3,200 km
from the east to the west. The average width
of these plains varies between 150-300 km.
The maximum depth of alluvium deposits
varies between 1,000-2,000 m. From the
north to the south, these can be divided into
three major zones: the Bhabar, the Tarai and
the alluvial plains. The alluvial plains can be
further divided into the Khadar and the
Bhangar.
Bhabar is a narrow belt ranging between
8-10 km parallel to the Shiwalik foothills at
the break-up of the slope. As a result of this,
the streams and rivers coming from the
mountains deposit heavy materials of rocks
and boulders, and at times, disappear in this
zone. South of the Bhabar is the Tarai belt, with
an approximate width of 10-20 km where most
of the streams and rivers re-emerge without
having any properly demarcated channel,
thereby, creating  marshy and swampy
conditions known as the Tarai. This has a
luxurious growth of natural vegetation and
houses a varied wildlife.
The south of Tarai is a belt consisting of
old and new alluvial deposits known as the
Bhangar and Khadar respectively. These
plains have characteristic features of mature
stage of fluvial erosional and depositional
landforms such as sand bars, meanders, ox-
bow lakes and braided channels. The
Brahmaputra plains are known for their
riverine  islands and sand bars. Most of
these areas are subjected to periodic floods
Figure 2.3 : The Himalayas
Figure 2.4 : Northern Plain
2024-25