Physiography: Deserts, Coastal Plains and Islands

The Great Indian Desert

The Great Indian Desert, also known as the Thar Desert, is a large arid region in the northwestern part of the Indian subcontinent that covers an area of 200,000 km2 and forms a natural boundary between India and Pakistan. It is the world's 17th largest desert.

Size and Location

The Great Indian desert lies to the northwest of Aravali hills

  • About 85% of the Thar Desert is located within India, with the remaining 15% in Pakistan. 
  • It forms approximately 5% (~4.56%) of the total geographic area of India. 
  • More than 60% of the desert lies in the state of Rajasthan, and it extends into Sindh, Gujarat, Punjab, and Haryana. 
  • The desert comprises:
    • a very dry part, the Marusthali region in the west, and 
    • a semi-desert region in the east with fewer sand dunes and slightly more precipitation.

It extends between: 

  • Aravalli Hills in the north-east
  • Great Rann of Kutch along the coast and
  • Alluvial plains of the Indus River in the west and north-west

Physiography

It is a land of undulating topography dotted with longitudinal dunes and barchans. This region receives low rainfall below 150 mm per year; hence, it has arid climate with low vegetation cover. It is because of these characteristic features that this is also known as Marusthali.

It is believed that during the Mesozoic era, this region was under the sea. This can be corroborated by the evidence available at:

  • Wood fossils park at Aakal. The approximate age of the woodfossils is estimated to be 180 million years.
  • Marine deposits around Brahmsar, near Jaisalmer.

Though the underlying rock structure of the desert is an extension of the Peninsular plateau, yet, due to extreme arid conditions, its surface features have been carved by physical weathering and wind actions. Some of the well pronounced desert land features present here are mushroom rocks, shifting dunes and oasis (mostly in its southern part).

On the basis of orientation, the desert can be divided into two parts:
  1. northern part sloping towards Sindh and
  2. southern part sloping towards Rann of Kachchh.

Most of the rivers in this region are ephemeral. The Luni river flowing in the southern part of the desert is of some significance. Low precipitation and high evaporation makes it a water deficit region. There are some streams which disappear after flowing for some distance and present a typical case of inland drainage by joining a lake or playa.

Lakes and playas have brackish water which is the main source of obtaining salt.

  • Salt water lakes within the Thar Desert include the Sambhar, Kuchaman, Didwana, Pachpadra and Phalodi in Rajasthan and Kharaghoda in Gujarat. 
  • These lakes receive and collect rain water during monsoon and evaporate during the fat season. 
The salt is derived by weathering of rocks in the region.

The Coastal Plains

India has a long coastline. On the basis of location and active geomorphological processes, it can be broadly divided into two:

  1. western coastal plains
  2. eastern coastal plains

Western Coastal Plains

The Western Coastal Plains is a strip of coastal plain 50 kilometres in width between the west coast of India and the Western Ghats hills, which starts near the south of the Tapti River.
  • These plains are narrow in middle and broader towards north and south.
  • These are submerged coastal plains. It is believed that the city of Dwaraka which was once a part of the Indian mainland situated along the west coast is submerged under water.
  • Because of submergence, it is a narrow belt and provides natural conditions for development of ports and harbours. Kandla, Mazagaon, JLN port Navha Sheva, Marmagao, Mangalore, Cochin, etc. are some of the important natural ports located along the west coast.
  • Extending from the Gujarat coast in the north to the Kerala coast in the south, the western coast may be divided into following divisions:
    • Gujarat: Kachchh andKathiawar coast
    • Maharashtra and Goa: Konkan coast
    • Karnataka: Kanara or the "Karavalicoast coast (as per NCERT, it is also called as Goan coast)
    • Kerala: Malabar coast
  • The rivers flowing through this coastal plain do not form any delta.
  • The Malabar coast has got certain distinguishing features in the form of ‘Kayals’ (backwaters), which are used for fishing, inland navigation and also due to its special attraction for tourists. Every year the famous Nehru Trophy Vallamkali (boat race) is held in Punnamada Kayal in Kerala.

Eastern Coastal Plains

The Eastern Coastal Plains is a wide stretch of landmass of India, lying between the Eastern Ghats and the Bay of Bengal. It stretches from Tamil Nadu in the south to West Bengal in the north.

  • These are broader as compared to the western coastal plain.
  • The eastern coast is an emergent coast. Because of its emergent nature, it has less number of ports and harbours. The continental shelf extends up to 500 km into the sea, which makes it difficult for development of good ports and harbours.
  • There are well developed deltas here, formed by the rivers flowing eastward in to the Bay of Bengal. These include the deltas of Mahanadi, Godavari, Krishna and Kaveri.
  • There are seven major port located on the east coast of India i.e. Tuticorin (Tamil Nadu), Chennai (Tamil Nadu), Ennore (Tamil Nadu), Visakhapatnam (Andhra Pradesh), Paradip (Odisha), Haldia & Kolkata (West Bengal), and Port Blair (Andaman & Nicobar Island).
  • Eastern coast is locally known by various names
    • Utkal Plains (northern part): between Cossye and Rushikulya Rivers
    • Northern Circars (central part): between Rushikulya and Krishna Rivers
    • Coromandel Coast (Southern part): south of river Krishna till the Southern tip of Mainland India at Cape Comorin.
  • Cape Comorin is a place where it merges with the Western coastal plains.
    Beaches on Eastern Coastal Plains
    • Baruva, Andhra Pradesh
    • Bheemili, Andhra Pradesh
    • RK Beach, Visakhapatnam
    • Rushikonda, Visakhapatnam
    • Yarada, Visakhapatnam
    • Manginapudi Beach, Andhra Pradesh
    • Serenity Beach, Pondicherry
    • Marina Beach, Chennai


    • Bakkhali Beach, West Bengal
    • Digha Beach, West Bengal
    • Mandarmoni Beach, West Bengal
    • Tajpur Beach, West Bengal
    • Shankarpur Beach, West Bengal
    • Pir Jahania, Odisha
    • Chandaneswar, Odisha
    • Chandipur, Odisha
    • Konarak, Odisha
    • Puri, Odisha
    • Gopalpur, Odisha

The Islands

Terminology

  • Island or isle: It isany piece of sub-continental land that is surrounded by water.
  • Islets: These are very small islands such as emergent land features on atolls. 
  • Riverine island: An island located in a river. Sedimentary islands in the Ganges delta are called chars.
  • Lake island: It is an island in a lake. 
  • Archipelago: A grouping of geographically or geologically related islands is referred to as an archipelago.

There are two major island groups in India - Bay of Bengal group and Arabian Sea group.

Bay of Bengal island group

  • This group consists of about 572 islands/islets. This group is situated roughly between 6°N-14°N and 92°E -94°E.
  • The entire group of island is divided into two broad categories – the Andaman in the north and the Nicobar in the south. They are separated by a water-body which is called the  Ten degree channel
  • There are two important archipelagos in this group. Great Andaman is the main archipelago or island group of the Andaman Islands, whereas Ritchie's Archipelago consists of smaller islands. 
    Ritchie's Archipelago

    Ritchie's ArchipelagoRitchie's Archipelago is a cluster of smaller islands which lie 20 km east of Great Andaman, the main island group of the Andaman Islands.

    The archipelago is named after an 18th-century British marine surveyor, John Ritchie, who spent nearly two decades in the employ of the Council of Bengal charting and documenting the Andaman's and surrounding regions.

    The individual islands are largely named after British generals and civil officials serving in India at the time of the Indian Rebellion of 1857.

  • The two principal groups of islets include the Ritchie’s archipelago and the Labrynth island.
  • It is believed that these islands are an elevated portion of submarine mountains.
  • Some smaller islands are volcanic in origin. Barren island, the only active volcano in India is also situated in the Nicobar islands.
  • The coastal line has some coral deposits, and beautiful beaches.
  • These islands receive convectional rainfall and have an equatorial type of vegetation.

Arabian Sea Island Group

There are several islands in the Arabian Sea, with the most important ones from India being Lakshadweep Islands. The Lakshadweep Islands (formerly known as the Laccadive, Minicoy, and Aminidivi Islands) is a group of islands in the Laccadive Sea region of Arabian Sea located at a distance of 280 km-480 km off the Kerala coast.

The archipelago is a Union Territory and is governed by the Union Government of India. The islands form the smallest Union Territory of India

  • The islands of the Arabian sea include Lakshadweep and Minicoy. These are scattered between 8°N-12°N and 71°E -74°E longitude.
  • The entire island group is built of coral deposits.
  • There are approximately 36 islands of which 11 are inhabited.
  • Minicoy is largest island
  • The entire group of islands is broadly divided by the Ten degree channel, north of which is the Amini Island and to the south of the Canannore Island. 
  • The Islands of this archipelago have storm beaches consisting of unconsolidated pebbles, shingles, cobbles and boulders on the eastern seaboard.