Peninsular Plateau and Coastal Plains: Relief and Rivers

After the Himalayas and the Northern Plains, the third and oldest of India's physical divisions is the Peninsular Plateau, and along its rim run the Coastal Plains. The plateau is a tableland of ancient crystalline, igneous and metamorphic rock, a surviving piece of the Gondwana landmass, while the coastal plains are young, level strips built by rivers and the sea. Between them they hold India's black cotton soil, most of its metallic minerals, its backwaters and its great deltas, which is why the topic appears in every general studies paper.

Extent and broad divisions of the plateau

The Peninsular Plateau is roughly triangular, with its base along the southern edge of the Northern Plains and its apex at Kanyakumari. It is divided by the Narmada valley into two blocks. North of the Narmada lie the Central Highlands, bounded by the Aravallis on the north-west and the Vindhyan range on the south; they include the Malwa plateau, Bundelkhand, Baghelkhand and, further east, the Chotanagpur plateau drained by the Damodar. The rivers of this block, the Chambal, Sind, Betwa and Ken, flow north-east into the Yamuna, which shows that the land tilts that way.

South of the Narmada lies the Deccan Plateau, edged by the Satpura, Mahadev, Kaimur and Maikal ranges in the north, by the Western Ghats on one side and the Eastern Ghats on the other. The Deccan slopes gently to the east, so the Mahanadi, Godavari, Krishna and Kaveri run east to the Bay of Bengal, while the Narmada and the Tapi are exceptions that flow west through rift valleys. A north-eastern extension of the same plateau, cut off by the Malda gap, forms the Meghalaya or Shillong plateau with its Garo, Khasi and Jaintia hills.

The Western and Eastern Ghats compared

The two ranges meet in the Nilgiri hills, whose highest point is Doddabetta at about 2,637 metres. South of the Nilgiris the Palakkad Gap, the widest break in the Western Ghats, carries the road and rail link between Kochi and Coimbatore. Further north the Thal Ghat and the Bhor Ghat open the way from Mumbai to Nashik and Pune. Beyond the gap rise the Anaimalai, Palani and Cardamom hills, and Anaimudi in the Anaimalai hills is the highest peak of peninsular India. The Western Ghats were inscribed as a UNESCO World Heritage Site in 2012 for their biodiversity.

Rocks, soils and minerals of the plateau

Large parts of Maharashtra, Madhya Pradesh, Gujarat and Karnataka are covered by the Deccan Trap, sheets of basalt poured out by fissure eruptions at the close of the Cretaceous period. Weathered basalt gives the black soil, also called regur, which holds moisture well and suits cotton. Elsewhere the old shield rocks carry India's metallic wealth: iron ore, manganese, bauxite, mica, copper and coal. The Chotanagpur plateau, with its coal and iron and the Damodar valley industries, is often called the Ruhr of India.

The Western Coastal Plain

The western coastal plain is a narrow strip, usually between fifty and a hundred kilometres wide, running from the Rann of Kachchh to Kanyakumari. It is a submergent coast, which is why it has good natural harbours such as Mumbai, Marmagao, Mangaluru and Kochi, and why its rivers end in estuaries rather than deltas; the Narmada and the Tapi are the clearest examples. From north to south it is divided into the Kachchh and Kathiawar coast of Gujarat, the Konkan coast of Maharashtra and Goa, the Kanara coast of Karnataka and the Malabar coast of Kerala. The Malabar section is known for its kayals, the shallow lagoons and backwaters of which Vembanad and Ashtamudi are the largest, used for fishing, inland navigation and the boat races of Kerala.

The Eastern Coastal Plain

The eastern coastal plain is wider, in places more than a hundred kilometres across, and stretches from the Ganga delta to Kanyakumari. It is an emergent coast, level and sandy, with few natural harbours, so its ports such as Chennai and Visakhapatnam have largely been built. Because the peninsular rivers reach the sea here with a gentle gradient and a heavy load, the coast carries the deltas of the Mahanadi, Godavari, Krishna and Kaveri. The northern section in Odisha is the Utkal coast, the middle section in Andhra Pradesh the Northern Circars, and the southern section in Tamil Nadu the Coromandel coast. Chilika in Odisha is the largest brackish-water lagoon in India; Pulicat lies on the Andhra Pradesh and Tamil Nadu border and shelters the Sriharikota launch site, and Kolleru lies between the Godavari and Krishna deltas. Nine states of India have a sea coast, and Gujarat has the longest coastline of them all.