Physiographic Divisions:

On the basis of prominent relief features, the peninsular plateau can be divided into three broad groups:

• The Central Highlands
• The Deccan Plateau
• The Northeastern Plateau.

Let’s take up these divisions one by one:

1. The Central Highlands

• The northern segment of the peninsular plateau is known as the Central Highlands.
• Location:
  1. North of Narmada river.
  2. They are bounded to the west by the Aravallis.
  3. Satpura ranges (formed by a series of scarped plateaus) lie in the South.
• General Elevation: 700-1,000 m above the mean sea level and it slopes towards the north and northeastern directions.
• These highlands consist of the:
  • Marwar upland – to the east of Aravallis in Rajasthan
    • A rolling plain carved by Banas river. [Rolling Plain: ‘Rolling plains’ are not completely flat; there are slight rises and fall in the land form. Ex: Prairies of USA]
    • Average elevation is 250-500 m above sea level.
  • Madhya Bharat Pathar – to the east of Marwar upland.
  • Malwa plateau – It lies in Madhya Pradesh between Aravali and Vindhyas. It is composed of extensive lava flow and is covered with black soils.
  • Bundelkhand plateau – It lies along the borders of UP and MP. Because of intensive erosion, semi-arid climate and undulating area, it is unfit for cultivation.
  • Baghelkhand plateau – It lies to the east of the Maikal range.
  • Chhotanagpur plateau – the north–east part of Peninsular plateau.
    • It Includes Jharkhand, parts of Chhattisgarh and West Bengal.
    • This plateau consists of series of step like sub-plateaus (locally called patlands – high-level plateau). It is thus famous as the Patland plateau and known as Ruhr of India.
    • Rajmahal Hills are the northeastern projection of Chhota Nagpur Plateau.
    • It is a mineral rich plateau.

• The extension of the Peninsular plateau can be seen as far as Jaisalmer in the West, where it has been covered by the longitudinal sand ridges and crescent-shaped sand dunes called barchans.
• This region has undergone metamorphic processes in its geological history, which can be corroborated by the presence of metamorphic rocks such as marble, slate, gneiss, etc.
• Most of the tributaries of the river Yamuna have their origin in the Vindhyan and Kaimur ranges. Banas is the only significant tributary of the river Chambal that originates from the Aravalli in the west.

2. The Deccan Plateau

• The Deccan Plateau lies to the south of the Narmada River and is shaped as an inverted triangle.
• It is bordered by:
  • The Western Ghats in the west,
  • The Eastern Ghats in the east,
  • The Satpura, Maikal range and Mahadeo hills in the north.
• It is volcanic in origin, made up of horizontal layers of solidified lava forming trap structure with step-like appearance. The sedimentary layers are also found in between the layers of solidified lava, making it inter–trapping in structure.
• Most of the rivers flow from west to east.
• The plateau is suitable for the cultivation of cotton; home to rich mineral resources and a source to generate hydroelectric power.
• The Deccan plateau can be subdivided as follows:
  • The Maharashtra Plateau – it has typical deccan trap topography underlain by basaltic rock, the regur.
  • The Karnataka Plateau (also known as Mysore plateau) – divided into western hilly country region of ‘Malnad’ and plain ‘Maidan’
  • Telangana Plateau

3. The Northeastern Plateau:

• The Meghalaya (or Shillong) plateau is separated from peninsular rock base by the Garo-Rajmahal gap.
• Shillong (1,961 m) is the highest point of the plateau.
• The region has the Garo, Khasi, Jaintia and Mikir (Rengma) hills.
• An extension of the Meghalaya plateau is also seen in the Karbi Anglong hills of Assam.
• The Meghalaya plateau is also rich in mineral resources like coal, iron ore, sillimanite, limestone and uranium.
• This area receives maximum rainfall from the south-west monsoon. As a result, the Meghalaya plateau has a highly eroded surface. Cherrapunji displays a bare rocky surface devoid of any permanent vegetation cover.

Hill ranges of the peninsula:

Most of the hills in the peninsular region are of the relict type (residual hills). They are the remnants of the hills and horsts formed many million years ago (horst: uplifted block; graben: subsided block).

The plateaus of the Peninsular region are separated from one another by these hill ranges and various river valleys.

1. The Aravalli Mountain Range:

• It is a relic of one of the oldest fold mountains of the world.
• Its general elevation is only 400-600 m, with few hills well above 1,000 m.
• At present, it is seen as a discontinuous ridge from Delhi to Ajmer and rising up to 1722m (Gurushikhar peak in Mount Abu) and thence southward.
• It is known as ‘Jarga’ near Udaipur and ‘Delhi Ridge’ near Delhi.
• Dilwara Jain Temple, the famous Jain temple is situated on Mt. Abu.

2. Vindhyan Ranges:

• They rise as an escarpment running parallel to the Narmada-Son valley.
• General elevation: 300 to 650 m.
• Most of them are made up of sedimentary rocks of ancient ages.
• They act as a watershed between Gangetic and peninsular river systems.

3. Satpura ranges:

• Satpura range is a series of seven mountains (‘Sat’ = seven and ‘pura’ = mountains).
• The seven mountain ranges or folds of Satpura’s are:
  • Maikal Hills
  • Mahadeo Hills near Pachmarhi
  • Kalibhit
  • Asirgarh
  • Bijagarh
  • Barwani
  • Arwani which extends to Rajpipla Hills in Eastern Gujarat.
• Satpura ranges run parallel between Narmada and Tapi, parallel to Maharashtra-MP border.
• Dhupgarh (1,350 m) near Pachmarhi on Mahadev Hills is the highest peak of the Satpura Range.
• Amarkantak (1,127 m) is another important peak. Amarkantak is the highest peak of the Maikal Hills from where two prominent rivers – the Narmada and the Son originate.
• Note that three rivers originate from the three sides of Maikal hills (as shown in the following map) but, from Amarkantak, only two rivers (the Narmada and the Son) originate (and not Mahanadi).

4. Western and Eastern Ghats:

• The Western Ghats:
  • These are a faulted part of the Deccan plateau running parallel from the Tapi valley to a little north of Kanyakumari (1600km). Their western slope is like an escarpment while eastern slope merges gently with the plateau.
  • Their average elevation is about 1,500 m with the height increasing from north to south.
• The Eastern Ghats are in the form of residual mountains which are not regular but broken at intervals.
• The Eastern and the Western Ghats meet each other at the Nilgiri hills.
• A brief comparison between them:

Note: The Western Ghats are continuous and can be crossed through passes only. There are four main passes which have developed in the Western Ghats. These are:

• Thal Ghat – It links Nasik to Mumbai.
• Bhor Ghat – It links Mumbai to Pune.
• Pal Ghat – This pass is located between the Nilgiris and the Annamalai mountains. It is in Kerala and connects Kochi and Chennai.
• Senkota Pass – This pass located between the Nagercoil and the Cardamom hills links Thiruvananthapuram and Madurai.

For the geographical location of these passes, see the following map:

Significance of the Peninsular Region:

• Rich in mineral resources: The peninsular region of India is rich in both metallic and non-metallic minerals. About 98% of the Gondwana coal deposits of India are found in the peninsular region.
• Agriculture: Black soil found in a substantial part of the peninsula is conducive for the cultivation of cotton, maize , citrus fruits etc. Some areas are also suitable for the cultivation of tea, coffee, groundnut etc.
• Forest Products: Apart from teal, sal wood and other forest products, the forests of Western and Eastern Ghats are rich in medicinal plants and are home to many wild animals.
• Hydel Power: many rivers, which have waterfalls. They help in the generation of hydroelectric power.
• Tourism: There are numerous hill stations and hill resorts like Ooty, Mahabaleshwar, Khandala, etc.

Now that we are done with this part, let’s try to attempt some questions from the past UPSC examinations:

Prelims:

1995

Question: Which one of the following mountain ranges is spread over only one state in India?

A) Aravalli

B) Satpura

C) Ajanta

D) Sahyadri

Ans. C

1997

Question: Consider the map given below:

The places marked A,B, C, and D in the map are respectively

A) Rift valley region, Chattisgarh plain, Rain shadow region, and Chotanagpur Plateau

B) Chattisgarh plain , Chotanagpur Plateau, Rift valley region, Rain shadow region

C) Rift valley region, Chattisgarh plain, Chotanagpur Plateau and Rain shadow region

D) Chattisgarh plain , Rain shadow region, Chotanagpur Plateau, Rift valley region,

Ans. C

2005

Question: Which one of the following statements is not correct?

A) The Western Ghats are relatively higher in their northern regions.

B) The Anaimudi is the highest peak in the Western Ghats

C) Tapi river lies to the south of Satpura

D) The Narmada and the Tapi river valleys are said to be old rift valleys.

Ans. A

Question: Which one of the following is the correct sequence of the given hills starting from the north and going towards the south?

A) Nallamalai Hills – Nilgiri Hills – Javadi Hills – Anaimalai Hills

B) Anaimalai Hills – Javadi Hills – Nilgiri Hills – Nallamalai Hills

C) Nallamalai Hills – Javadi Hills – Nilgiri Hills – Anaimalai Hills

D) Anaimalai Hills – Nilgiri Hills – Javadi Hills – Nallamalai Hills

Ans. C

2007

Question: In which state is the Guru Shikhar peak located?

1. Rajasthan
2. Gujarat
3. Madhya Pradesh
4. Maharashtra

Ans. A

1. Punjab Plains:

• The Punjab plains form the western part of the northern plain.
• In the east, the Delhi-Aravalli ridge separates it from the Ganga plains.
• This is formed by the Indus and its tributaries; like Jhelum, Chenab, Ravi, Beas and Sutlej. A major portion of these plains is in Pakistan.
• It is divided into many Doabs (do-“two” + ab- “water or river” = “a region or land lying between and reaching to the meeting of the two rivers”).
  

  

   

• Important features:
  • Khadar rich flood plains known as ‘Betlands’ or ‘Bets’.
  • The rivers in Punjab-Haryana plains have broad flood plains of Khadar flanked by bluffs, locally known as Dhayas.
  • The northern part of this plane adjoining the Shivalik hills has been heavily eroded by numerous streams, which are called Chhos.
  • The southwestern parts, especially the Hisar district is sandy and characterized by shifting sand-dunes.

2. Ganga Plains:

• The Ganga plains lie between the Yamuna catchment in the west to the Bangladesh border in the East.
• The lower Ganga plain has been formed by the downwarping of a part of the Peninsular India between Rajmahal hills and the Meghalaya plateau and subsequent sedimentation by the Ganga and Brahmaputra rivers.
• The main topographical variations in these plains include Bhabar, Tarai, Bhangar, Khadar, levees, abandoned courses etc.
• Almost all the rivers keep on shifting their courses making this area prone to frequent floods. The Kosi river is very notorious in this respect. It has long been called the ‘Sorrow of Bihar’.
• The northern states, Haryana, Delhi, UP, Bihar, part of Jharkhand and West Bengal in the east lie in the Ganga plains.
• The Ganga-Brahmaputra delta: the largest delta in the world. A Large part of the coastal delta is covered tidal forests called Sunderbans. Sunderbans, the largest mangrove swamp in the world gets its name from the Sundari tree which grows well in marshland. It is home to the Royal Tiger and crocodiles.

3. Brahmaputra Plains:

• This plain forms the eastern part of the northern plain and lies in Assam.
• Its western boundary is formed by the Indo-Bangladesh border as well as the boundary of the lower Ganga Plain. Its eastern boundary is formed by Purvanchal hills.
• The region is surrounded by high mountains on all sides, except on the west.
• The whole length of the plain is traversed by the Brahmaputra.

• The Brahmaputra plains are known for their riverine islands (due to the low gradient of the region) and sand bars.
• The innumerable tributaries of the Brahmaputra river coming from the north form a number of alluvial fans. Consequently, the tributaries branch out in many channels giving birth to river meandering leading to the formation of bill and ox-bow lakes.
• There are large marshy tracts in this area. The alluvial fans formed by the coarse alluvial debris have led to the formation of terai or semi-terai conditions.

Significance of this region:

• The plains constitute less than one-third of the total area of the country but support over 40 percent of the total population of the country.
• Fertile alluvial soils, flat surface, slow moving perennial rivers and favourable climate facilitate an intense agricultural activity.
• The extensive use of irrigation has made Punjab, Haryana and western part of Uttar Pradesh the granary of India (Prairies are called the granaries of the world).
• Cultural tourism: Several sacred places and centres of pilgrimage are situated in these plains e.g. Haridwar, Amritsar, Varanasi, Allahabad, Bodh Gaya etc.
• The sedimentary rocks of plains have petroleum and natural gas deposits.
• The rivers here have very gentle gradients which make them navigable over long distances.

Now that we are done with this part, let’s try to attempt some questions from the past UPSC examinations:

Prelims:

2000

Question: Assertion (A): The frequency of floods in North Indian plains has increased during the last couple of decades.

Reason(R): There has been reduction in the depth of river valleys due to deposition of silt.

Ans. A (Both A and B are true and R is the correct explanation of A)

Question: Assertion (A): Ganga plain is the most densely populated part of India.

Reason(R): Ganga is the most harnessed river of India.

Ans. C (A is true but R is false)

Mains:

Question: Write a short note on Tarai region. (2008/2marks)

These divisions have been demarcated by river valleys:

1. Punjab Himalayas:
   • A large portion of Punjab Himalayas is in Jammu and Kashmir and Himachal Pradesh. Hence they are also called the Kashmir and Himachal Himalaya.
   • Major ranges: Karakoram, Ladakh, Pir Panjal, Zaskar and Dhaola Dhar.
   • The general elevation falls westwards.
   • The Kashmir Himalayas are also famous for Karewa formations.
     • ‘Karewas’ in Kashmiri language refer to the lake deposits, found in the flat-topped terraces of the Kashmir valley and on the flanks of the Pir Panjal range.
     • These deposits consist of clays, silts and sands, these deposits also show evidence of glaciation.
     • The occurrence of tilted beds of Karewas at the altitudes of 1500-1800m on the flanks of the Pir Panjal strongly suggests that the Himalayas were in process of uplift as late as Pliocene and Pleistocene (1.8mya to 10kyears ago)
     • Karewas are famous for the cultivation of Zafran, a local variety of saffron.
2. Kumaon Himalayas
3. Nepal Himalayas:
   • Tallest section of Himalayas
4. Sikkim Himalayas:
   • Teesta river originates near Kanchenjunga
   • Jelep la pass- tri-junction of India- China-Bhutan
5. Assam Himalayas:
   • Himalayas are narrower in this region and Lesser Himalayas lie close to Great Himalayas.
   • Peaks: Namcha Barwa, Kula Kangri
   • Bengal ‘Duars’
   • Diphu pass- tri-junction of India- China-Myanmar
   • The Assam Himalayas show a marked dominance of fluvial erosion due to heavy rainfall.

Glaciers and Snowline:

• Snowline: The lower limit of perpetual snow is called the ‘snowline’. The snowline in the Himalayas has different heights in different parts, depending on latitude, altitude, amount of precipitation, moisture, slope and local topography.

1. The snowline in the Western Himalaya is at a lower altitude than in the Eastern Himalaya. E.g. while the glaciers of the Kanchenjunga in the Sikkim portion hardly move below 4000m, and those of Kumaon and Lahul to 3600m, the glaciers of the Kashmir Himalayas may descend to 2500m above the sea level.

• It is because of the increase in latitude from 28°N in Kanchenjunga to 36°N in the Karakoram (Lower latitude —> warmer temperatures —> higher snowline).
• Also, the Eastern Himalayas rise abruptly from the planes without the intervention of High ranges.
• Though the total precipitation is much less in the western Himalayas, it all takes place in the form of snow.

2. In the Great Himalayan ranges, the snowline is at a lower elevation on the southern slopes than on the northern slopes. This is because the southern slopes are steeper and receive more precipitation as compared to the northern slopes.

• Glaciers: The main glaciers are found in the Great Himalayas and the Trans-Himalayan ranges (Karakoram, Ladakh and Zaskar). The Lesser Himalayas have small glaciers, though traces of large glaciers are found in the Pir Panjal and Dhauladhar ranges. Some of the important glaciers are:

Key differences between the Eastern and Western Himalayas:

Important Passes in India:

A pass is a narrow gap in a mountain range which provides a passageway through the barrier.

• Pir Panjal Pass – It provides the shortest and the easiest metal road between Jammu and the Kashmir Valley. But this route had to be closed down as a result of partition of the subcontinent.
• Banihal Pass – It is in Jammu and Kashmir. The road from Jammu to Srinagar transversed Banihal Pass until 1956 when Jawahar Tunnel was constructed under the pass. The road now passes through the tunnel and the Banihal Pass is no longer used for road transport.
• Zoji La (Pass) – It is in the Zaskar range of Jammu and Kashmir. The land route from Srinagar to Leh goes through this pass.
• Shipki La (Pass) – It is in Himachal Pradesh. The road from Shimla to Tibet goes through this pass. The Satluj river flows through this pass.
• Bara Lacha Pass – It is also in Himachal Pradesh. It links Mandi and Leh by road.
• Rohtang Pass – It is also in Himachal Pradesh. It cuts through the Pir Panjal range. It links Manali and Leh by road.
• Niti Pass – It is in Uttarakhand. The road to the Kailash and the Manasarovar passes through it.
• Nathu La (Pass) – It is in Sikkim. It gives way to Tibet from Darjeeling and Chumbi valley. The Chumbi river flows through this pass.
• Jalep La (Pass) – At the tri-junction of India- China-Bhutan. The Teesta river has created this pass.

B) The North-Eastern Hills and Mountains

The Brahmaputra marks the eastern border of Himalayas. Beyond the Dihang gorge, the Himalayas bend sharply towards south and form the Eastern hills or Purvanchal.

• These hills run through the northeastern states of India.
• These hills differ in scale and relief but stem from the Himalayan orogeny.
• They are mostly composed of sandstones (i.e. Sedimentary rocks).
• These hills are covered with dense forests.
• Their elevation decreases from north to south. Although comparatively low, these hill ranges are rather forbidding because of the rough terrain, dense forests and swift streams.
• Purvanchal hills are convex to the west.
• These hills are composed of:
  • Patkai Bum – Border between Arunachal Pradesh and Myanmar
  • Naga Hills
  • Manipuri Hills – Border between Manipur and Myanmar
  • Mizo Hills.
• Patkai Bum and Naga Hills form the watershed between India and Myanmar.
• Extension of Purvanchal continues in Myanmar as Arakan Yoma –then Andaman and Nicobar Islands.

The importance of Himalayan Region:

• Climatic Influence – The altitude of the Himalayas, their sprawl and extension intercept the summer monsoon. They also prevent the cold Siberian air masses from entering into India. The climatic influence of the Himalayas will be dealt in detail in the next articles.
• Defence
• Source of perennial rivers
• Source of fertile soils
• Generation of hydroelectricity
• Forest wealth
• Orchards
• Minerals – The Himalayan region is rich in minerals e.g. gold, silver, copper, lead etc. are known to occur. Coal is found in Kashmir. But at present level of technological advancement, it is not possible to extract these minerals. Also, it is not economically viable.
• Tourism
• Pilgrimage

Now that we are done with this part, let’s try to attempt some questions from the past UPSC examinations:

Prelims:

2012:

Question: When you travel in Himalayas, you will see the following:

1. Deep gorges
2. U-turn river courses
3. Parallel mountain ranges
4. Steep gradients causing land sliding

Which of the above can be said to be evidences for Himalayas being young fold mountains?

1. 1 and 2 only
2. 1, 2 and 4 only
3. 3 and 4 only
4. 1, 2, 3 and 4

Ans. D

2003

Question: Nanda Devi peak forms part of:

A. Assam Himalayas

B. Kumaon Himalayas

C. Nepal Himalayas

D. Punjab Himalayas

Ans. B [Nandadevi – Uttarakhand]

1997

Question: Examine the map of Jammu and Kashmir given below

The mountain ranges marked 1, 2, 3 and 4 are respectively:

a) Ladakh, Zaskar, Karakoram and Pir Panjal

b) Karakoram, Ladakh, Zaskar and Pir Panjal

c) Karakoram, Zaskar, Pir Panjal and Ladakh

d) Ladakh, Pir Panjal, Karakoram and Zaskar

Ans. B

1995

Question: The alpine vegetation in western Himalayas is found only upto a height of 3000m while in Eastern Himalayas it is found upto a height of 4000m. The reason for this variation in same mountain range is that:

A. Eastern Himalayas are higher than western Himalayas

B. Eastern Himalayas are nearer to equator and sea than Western Himalayas

C. Eastern Himalayas get more rainfall than western Himalayas

D. Eastern Himalayan rocks are more fertile than western Himalayas

Ans. C

Question: The Indian subcontinent was originally a part of a huge mass called

A. Jurassic landmass

B. Aryavarta

C. Indiana

D. Gondwana continent

Ans. D

Question: Arakan Yoma, the extension of the Himalayas is located in

A. Baluchistan

B. Myanmar

C. Nepal

D. Kashmir

Ans. B

Mains:

• Write a short note on Karewas. (2marks 2005)
• Bring out the causes for more frequent occurrence of landslides in the Himalayas than in the Western Ghats. (10 marks 2013)

• The Himalayas, and
• The Northeastern hills (Purvanchal).

A) The Himalayas:

The name “Himalaya” means “the abode or house of snow” in Sanskrit (i.e. hima “snow”, and ālaya “abode or house”). The Himalayas are the highest and longest of all young fold mountains of the world. The Pamir, known as the roof of the world, connects the Himalayas with the high ranges of Central Asia.

Let’s begin by understanding how the Himalayas came into being:

Origin and development:

According to the theory of Continental Drift, the world was made up of a single continent through most of the geologic time. That continent eventually separated and drifted apart; forming the seven continents we have today.

Source

• About 200 million years ago: Pangaea broke apart leading to the formation of two landmasses – “Laurasia in North” and “Gondwanaland in South”. Both the landmasses were separated by a shallow sea called “Tethys Sea”. The size of Tethys sea kept on decreasing due to movement of landmasses towards each other
• About 40 to 50 million years ago: The two large landmasses, India and Eurasia, driven by plate movement, collided. As a result, the sediments accumulated in Tethys Sea (brought by rivers) were compressed, squeezed and series of folds were formed, one behind the other, giving birth to folded mountains of the Himalayas.

Source

Recent studies show that India is still moving northwards at the rate of 5cm/year and crashing into the rest of Asia, thereby constantly increasing the height of Himalayas.

Evidence to prove that the Himalayas are still rising:

• Fossil formation found in Shivalik hills:

Similar fossils have also been found in the Tibet Plateau. This indicates that in the past, Tibetan plateau and Shivalik hills shared a common location, similar level and thus similar vegetation, life etc.; then Tibetan plateau got uplifted.

• Desiccation of lakes of Tibet:

In the Tibet plateau, we find deposits which are generally found in lakes. This indicates that lakes once existed in Tibet but because of upliftment the water got discharged and deposits remained.

• Frequent Earthquakes
• Youthful nature of rivers (High erosion, v-shaped valleys etc.)

The North-South Division of the Himalayas

The Himalayas consist of a series of parallel mountain ranges:

1. The Greater Himalayan range, which includes:
   • The Great Himalayas(Himadri), and
   • The Trans-Himalayan range
2. The Lesser Himalayas (or Himachal), and
3. The Outer Himalayas (or Shiwalik).

The Himalayan Ranges and Important Peaks

• Formation of these ranges: The Himadri and Himachal ranges of the Himalayas have been formed much before the formation of Siwalik range. The rivers rising in the Himadri and Himachal ranges brought gravel, sand and mud along with them, which was deposited in the rapidly shrinking Tethys Sea. In course of time, the earth movements caused folding of these relatively fresh deposits of sediments, giving rise to the least consolidated Shiwalik range.
• Characteristic Features:
  • Notice in the map shown above that the Himalayas form an arcuate curve which is convex to the south. This curved shape of the Himalayas is attributed to the maximum push offered at the two ends on the Indian peninsula during its northward drift. In the north-west, it was done by Aravalis and in the Northeast by the Assam ranges.
  • Syntaxis/ Syntaxial bends: The gently arching ranges of the Himalayan mountains on their Western and Eastern extremities are sharply bent southward in deep Knee-bend flexures that are called syntaxial bends. On both the ends, the great mountains appear to bend around a pivotal point. The western point is situated south of the Pamir where the Karakoram meets the Hindu Kush. A similar sharp, almost hairpin bend occurs on the eastern limit of Arunachal Pradesh where the strike of the mountain changes sharply from the Easterly to Southerly trend. Besides these two major bends, there are a number of minor syntaxial bends in other parts of Himalayas.
    

    

    Syntaxial Bends of Himalayas

  • The Himalayas are wider in the west than in the east. The width varies from 400 km in Kashmir to 150 km in Arunachal Pradesh.The main reason behind this difference is that the compressive force was more in the east than in the west. That is why high mountain peaks like Mount Everest and Kanchenjunga are present in the Eastern Himalayas.
  • The ranges are separated by deep valleys creating a highly dissected topography.
  • The southern slopes of the Himalayas facing India are steeper and those facing the Tibetan side are generally gentler.

Let’s take up these Himalayan mountain ranges one by one:

• Indus-Tsangpo Suture Zone: It represents a belt of tectonic compression caused by the underthrusting of the Indian shield/ plate against the Tibetan mass. It marks the boundary between Indian and Eurasian plates. The suture zone stretches from the North Western Himalayan syntaxis bordering the Nanga Parbat to the East as far as the Namche Barwa Mountain. Tha Karakoram range and the Ladakh plateau lie to the north of ITSZ and originally formed a part of the European plate.
• Main Central Thrust Zone: This separates the Higher Himalayas in the north from lesser Himalayas in the south. It has played an important role in the tectonic history of these mountains.
• Main Boundary Thrust: It is a reverse fault of great dimensions which extends all the way from Assam to Punjab and serves to separate the outer Himalayas from the lesser Himalayas.
• Himalayan Frontal Fault: It is a series of reverse faults that demarcates the boundary of the Shivalik from of the Himalayan province from the alluvial expanse of the Indo-Gangetic plains.

The Geological Timescale

When did the dinosaurs get extinct? When did the birds first appear on earth? What about the beginning of life itself?

To answer these questions, geologists use a special timeline called the Geological Time Scale. It is a record of Earth’s Geologic history based on radiometric dating and the record of ancient life preserved in layers of rocks.

The geological timescale is broken up into larger and smaller subdivisions which help us understand how the various historical events fit together. These time intervals are not equal in length like the hours in a day. Instead, the time intervals are variable in length because geologic time is divided using significant events in the history of the Earth. The various intervals are:

Let’s watch a video to understand this division better:

The geological timescale thus looks like:

The Geological Timescale

Note: Due to lack of sufficient information about the Precambrian Eon, there is no subdivision into eras etc. At the same time, it is important to note that the Precambrian time constitutes about 86.7% of Earth’s history.

The Indian Geological History:

Major events in the geological history of India:

• Peninsular India was a part of the old landmass since the formation of the Earth’s Crust
• The upheaval of Himalayas in the tertiary period.
• Aggradational formation of the Indo-Gangetic plain during the Pleistocene period. It continues till today through sedimentation in the floodplains of the rivers and the lower part of the Gangetic plain.

Based on this complex and varied geological history, the Geological Survey of India has classified rock systems of the country into 4 major divisions:

 

Let us study the basic features of each of these:

 

1. The Archaean rock system (Early Pre-Cambrian)

The Archaean group of rocks consists of two systems-(a) Achaean granites and gneisses, and (b) Dharwarian sedimentary:

• Archaean Gneisses and Schists (pre 2500 million years)
  • The Archean System contains the first formed rocks of the earth.
  • The rocks are primarily gneisses and granites, having no marks of fossils.
  • They often underlie the strata formed subsequently and the system is generally known as the basement complex or fundamental gneisses.
  • The Archaean rocks cover two-thirds of the peninsular India. They also occur in roots of the mountain peaks all along the Greater Himalayas, trans-Himalayan ranges of Zaskar, Ladakh and Karakoram.
• Dharwar System (2500-1800 million years ago)
  • The weathering of the Archaean rocks yielded the earliest sediments and formed the oldest sedimentary strata, the Dharwar system.
  • These are found today in metamorphic forms and do not contain fossils.
  • These rocks occur in scattered patches in parts of Karnataka, Tamil Nadu, central and eastern parts of Chotanagpur plateau, Meghalaya plateau, Aravalis, Himalayan region etc as shown on the map.

The Archaean rocks are economically the most important rocks because they possess valuable minerals like high-grade iron ore, manganese, copper, lead, gold, quartzite, slates, mica, etc.

1. The Purana Rock System (Late Pre-cambrian):

The Archaean gneiss and the Dharwar rocks underwent further erosion leading to the formation of the Purana Rock system.

The Purana rock system is further subdivided into (i) the Cuddapah and (ii) the Vindhyan

• The Cuddapah
  • These rocks are generally without fossils
  • These formations, named after the Cuddapah district in Andhra Pradesh are sedimentary metamorphic formations.
  • These are found in Andhra Pradesh, southern Chhattisgarh, Odisha and along the main axis of Aravallis.
  • The metallic content in ores of Cuddapah rocks is low and at places uneconomical for extraction.
• The Vindhyan
  • This system derives its name from the Vindhyan mountains
  • Consists of enormous sedimentary deposits. In some tracts, Vindhyan rocks are buried under the Deccan lava.
  • It stretches from Sasaram in Bihar to Chittorgarh in Rajasthan with the exception of the central tract of Bundelkhand gneiss.
  • The well-known diamond mines of Panna and Golconda lie in the Vindhayan region.
  • This rock system is well known for red sandstone, sandstone, durable stones, ornamental stones, raw materials for lime, glass, cement and chemical industries.

2. The Dravidian Rock system (Cambrian to middle carboniferous)

• These formations do not occur in the peninsular plateau as it was above the sea level at that time but are found in continuous sequence in the Himalayas.
• They contain abundant fossils in them
• Coal formation started in the Carboniferous age. Carboniferous in geology means coal-bearing. [Most of the coal found in India is not of the Carboniferous period; High-quality coal of Great Lakes Region-USA, U.K and Ruhr region is Carboniferous coal].

3. The Aryan Rock system (Upper Carboniferous to recent)

The Aryan Rock System

• The Gondwana System:
  • The peninsula during the Upper Carboniferous period experienced crustal movements, which led to the formation of basin-shaped depressions. These depressions had countless terrestrial plants and animals, which were buried to from coal deposits in India known as the Gondwana Rocks.
  • These rocks have also marks of climatic changes from arctic cold to tropical and desert conditions.
  • These Rocks are found mainly in the Damodar, the Mahanadi and the Godavari valleys of the peninsula.
  • Gondwana rocks contain nearly 98 percent of India’s coal reserves. Gondwana coal is much younger than the Carboniferous coal and hence its carbon content is low.
• Jurassic System:
  • The marine transgression in the latter part of the Jurassic gave rise to thick series of shallow water deposits in Rajasthan and in Kuchchh.
  • Coral limestone, sandstone, conglomerates and shales occur in Kuchchh.
  • Another transgression on the east coast of the Peninsula is found between Guntur and Rajahmundry.
• The Deccan Trap:
  • Towards the end of the Mesozoic era, intensive volcanic activity took place, which flooded with lava vast areas of Maharashtra and other parts of the Deccan known as the Deccan traps.
  • The volcanic rocks contain some thin fossiliferous sedimentary layers found between the lava flows. This indicates that the lava flows was not continuous. The volcanic activity led to two great events
    1. Breakup of the Gondwanaland masses
    2. Uplift of the Himalayas out of the Tethys Sea.
  • Present Deccan Trap covers about 5 lakh sq km mainly in parts of Kuchchh, Saurashtra, Maharashtra, the Malwa plateau and northern Karnataka.
  • The weathering of these rocks for a long time has given birth to black cotton soil known as ‘regur’.
• Tertiary System
  • Eocene to Pliocene about 60 to 7 million years ago.
  • The tertiary is the most significant period in India’s geological history because the Himalayas were born and India’s present form came into being in this period.
• The Pleistocene and recent formations (The quaternary period)
  • Quaternary is the name proposed for very recent deposits, which contains fossils of species with living representatives
  • These include Satluj-Ganga-Brahmaputra plains and Karewa formations of the Kashmir valley.

Geological Divisions of India:

Geologic divisions are marked by geologists as regions of similar rocks, structures and geologic history [Recall the brief geological history of India discussed above]. Geologically, India is divided into 3 major regions (also called the Triple Tectonic division):

1. The Peninsular Plateau region – It also includes the Shillong Plateau and the Kutchch Kathiawar region (Outliers)
2. The Extra-peninsular region – the mountainous region of Himalayas.

• The Himalayas 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.

3. The Indo-Gangetic Plain between the above two.

In addition to these, there are 2 minor divisions:

• The Coastal Plains (Eastern and western)
• The Islands (Lakshadweep and Andaman and Nicobar)

Physiographic divisions of India

Physiography deals with the study of surface features. This includes the landforms (mountains and valleys, their shape and steepness), the way rivers flow across the land, and the way in which the land erodes. Geographers recognize physiographic divisions based on the shape of the land.

There is a close relationship between India’s physiographic and geologic divisions as geology affects the way the land erodes.

The Indian landmass can be divided into the following broad physiographic units:

• The Northern and Northeastern Mountains
• The Northern plains
• The Thar Desert
• The Peninsular Plateau
• The Coastal Plains
• The Islands

 

In the next articles, we will study each of these divisions in detail. [For the next article on the Himalayan mountains, click here]

But before we proceed to the next article, let’s look at the following question from a past UPSC examination:

Prelims:

1997:

Question: Match List I with List II and select the correct answer using the codes given below the lists:

List I List II

A) Deccan Traps 1) Late cenozoic

B) Western Ghats 2) Pre-cambrian

C) Aravalli 3) Cretaceous Eocene

D) Narmada-Tapi alluvial deposits 4) Cambrian

5) Pleistocene

a) A-3 B-5 C-1 D-4

b) A-3 B-1 C-2 D-5

c) A-2 B-1 C-3 D-4

d) A-1 B-4 C-2 D-5

Ans. b