Q. Discuss the structure and evolution of the Peninsular India? [40 BPSC/1995]

Q. Discuss the structure and evolution of the Peninsular India? [40 BPSC/1995]

Ans:

Peninsular India is the oldest part of Indian landmass. It is roughly inverted triangular in shape with its base coinciding with the southern edge of the great plain of North India. Apex of it is at Kanniyakumari. It is bounded on the west by the Arabian Sea, on the east by the Bay of Bengal. Even though it is a stable block of land, it has underwent some major changes during it’s evolution.

The structure of the Peninsular India:

• Roughly inverted triangle in shape.
• It comprises the diverse topological and climatic patterns and is an aggregation of several smaller plateaus, hill ranges interspersed with river basins and valleys.
• The structure of Peninsular India can be divided into:
  • The Great Indian Plateau:
    • The Great Indian Plateau lies to the South of the Great Northern Plains.
    • This is the largest physiographic division of our country. It covers an area of about 16 lakh square km, i.e., about half of the total area of the country.
    • It is an old rocky plateau region.
    • The topography consists of a series of plateaus and hill ranges interspersed with river valleys.
    • Aravalli hills mark the north-western boundary of the plateau region. Its northern and north-eastern boundary is marked by the northern edge of the Bundelkhand Plateau,Kaimur and Rajmahal Hills.
    • The Western Ghats (Sahyadry) and the Eastern Ghats mark the western and eastern boundaries respectively of this Great Plateau.
    • Most of the area of the plateau has a height of more than 400 metres above sea level. The highest point of plateau region is the Anaimudi peak (2965 m).
    • The general slope of this plateau is towards east. It is indicated by the flow of the peninsular rivers flow west to east.
      • Narmada-Tapti are the exceptions which flow from east to west in a rift.
    • River Narmada divides the peninsular block of India into two parts.
      • The Central Highlands:
        • The region lying to the north of the Narmada is called the Central Highlands. i.e. It extends between river Narmada and Great Northern Plains.
        • The Aravallis form the west-northwestern edge of the Central Highlands. These hills extend from Gujarat, through Rajasthan to Delhi in the northeasterly direction for a distance of about 700 km.
          • The highest peak of the Aravalli hills is Gurushikhar (1722 m) near Mt. Abu.
        • Malwa plateau forms the dominant part of the Central Highlands.
          • It lies to the southeast of Aravallis and to the north of Vindhyachal Range. River Chambal, Betwa and Ken drain the Malwa Plateau before they join Yamuna.
        • The part of the Central Highlands which extends to the east of Malwa Plateau is known as Bundelkhand and is further followed by Baghelkhand and the well known Chhotanagpur Plateau.
        • Vindhyachal Range forms the southern edge of Malwa Plateau. The slope of Vindhayachal Range towards Narmada valley is absolutely steep and forms escarpments.
        • The valley of Narmada is situated between the Satpuras and the Vindhyas. River Narmada flows from east to west in this valley and falls into the Arabian Sea.
      • The Penninsular plateau (aka Deccan Plateau):
        • the region lying to the south of Narmada is called the penninsular plateau.
        • This physiographic division is the largest region of the Great Indian Plateau.
        • The shape of this plateau is triangular.
          • One of the sides of this triangle is marked by the line joining Kanya Kumari with Rajmahal Hills and this line passes through the Eastern Ghats.
            • The ranges of Eastern Ghats is known as poorvadri also.
            • The Eastern Ghats are not continuous like the Sahyadris. Mahanadi, Godavari, Krishna, Pennar and Kaveri rivers have dissected this range at many places.
          • The second arm is marked by the Satpura Range, Mahadeo Hills, Maikal Range and the Rajmahal Hills.
          • The third arm is marked by the Sahyadris (Western Ghats).
            • The Sahyadri Range forms the sharp edge of the Penninsular Plateau.
            • The height of the Sahyadris increases from north to south. Anaimudi peak (2695 m) situated in Kerala is the highest peak of southern India.
        • The area of this Penninsular Plateau is about 7 lakh square km and the height ranges from 500 to 1000 metres above sea level.
        • The Deccan Traps: The Deccan plateau is partially covered by the Deccan Traps. It is made up of lava flows or igneous rocks. It is spread over the whole of Maharashtra and parts of Gujarat and Madhya Pradesh, thereby making it one of the largest volcanic provinces in the world.
  • The Coastal plains:
    • The Great Plateau of India is surrounded by plains on all sides. In the north lies the Great Northern Plain and in south, along the east and west lie the Coastal Plains.
    • East Coastal Plain:
      • extends along the coast of the Bay of Bengal from Ganga Delta in the north to Kanyakumari in the south.
      • This plain is broader than the western coastal Plains.
      • This plain includes the deltas of the rivers Mahanadi, Godavari, Krishna and Kaveri.
      • Chilka, Pulicat and Koluru lakes are the famous lagoons of this plain.
    • West Coastal Plain:
      • extends along the Arabian Sea from the Rann of Kutchch in the north to Kanyakumari in the south.
      • Except for the Gujarat plain, the western coastal plains are narrower than the eastern coastal plain.
        • From southern Gujarat upto Mumbai this plain is comparatively broader, but it narrows southwards of Mumbai.
        • Occasionally rocky domes and hills are visible in the plains of Gujarat, the Rann of Kutchch and the plains of Kathiawar. The plains of Gujarat are made up of black soil.
      • The coastal strip extending for about 500 km between Daman in the north and Goa in the south is called Konkan.
        • This region is highly dissected and the coast line is indented or irregular with several natural harbours.
        • A number of small and seasonal rivers flow through this region.
      • The coast from Goa to Mangalore is called the Karnataka coast.
      • The coast from Mangalore upto Kanyakumari is called the Malabar coast.
      • Here the coastal plain is wider. There are a number of long and narrow lagoons (e.g. Vembanad).

The evolution of the peninsular India:

• Largely the Peninsular India has been a stable landmass but it has gone through some major changes with time.
• The Great Plateau is the part of very ancient landmass, called Gondwana land. It was formed due to the breaking and drifting of Gondwana land.
  • From the earliest time it has been above the level of the sea. Therefore, it has been subjected to large scale denudation.
  • Its mountains are generally of relic type. They are composed of very hard rocks, which have withstood the ravages of denudation more effectively than the surrounding regions.
  • Because of their old age, all the rivers have almost attained their base level and have built up broad and shallow valleys. The dominant rock formations, especially those in the southern parts, are of metamorphic origin with frequent occurrences of granites.
  • Reasons for eastward tilt:
    • when India broke apart from Gondwana there was lowering of the eastern side of the shield.
    • the Deccan volcanic flow tilted to east due to the Western margin undergoing uplift.
      • The erosion has stripped material away from the Western margin. All that eroded sediment has been deposited  within basins in the Arabian sea. This removal of weight has led to the crust rebounding and tilting in an easterly direction.
    • The oceanic lithosphere in the Bay of Bengal is colder and denser and it is sinking and dragging down the peninsular region with it.
    • The Bengal sediment fan i.e. the pile of sediment eroded from the Himalayas throughout  the Cenozoic and deposited in the Bay of Bengal is weighing the crust down and exerting a dragging down effect on the Indian peninsular region.
• The faults or rifts between the Vindhyas and the Satpuras through which the Narmada and Tapi river flow were probably caused when the Himalayas began to emerge from the Tethys Sea of the olden times.
• The Deccan Traps was formed during the movement of Indian plates towards the Asian plates by the outpouring of lava. This started somewhere around 60 million years ago and continued for a long period of time.
  • The volcanic hotspot that produced the Deccan traps is considered to lie under the present day island of Reunion in the Indian Ocean.
• The Western Ghats are the mountainous faulted and eroded edge of the Deccan Plateau. It evolved due to a combination of factors:
  • Geologic evidence indicates that they were formed during the break-up of the supercontinent of Gondwana some 150 million years ago. I.e. the Crustal doming and rifting which preceded the drifting of the Indian subcontinent resulted in an initial escarpment along the western margin of India.
  • Recession of the Ghats to the east due to marine erosion. The erosion has stripped material away from the Western margin forming the coastal plain and the steep Western Ghat escarpment.
  • Development of westerly drainage.
  • Gradual post glacial rise in sea level resulting in drowned valleys, estuaries and lagoons.
• The eastern Ghat:
  • It is older than the Western Ghats and have a complex geologic history related to the assembly and breakup of the ancient supercontinent of Rodinia and the assembly of the Gondwana supercontinent.
  • The breakup of Gondwanaland produced Permian-Triassic rift basins along what is now the eastern margin of India.
  • The river delats has created many passes and broader coastal plain.
• The lakes (Chilka, Pulicat and Koluru lakes) lakes have been formed by enclosing small parts of the Bay of Bengal behind sand bars.