Physiography of India: Physical Divisions and PYQs

Physiography is the study of the land itself: how the surface of India is built, how each block of it was formed, and what that means for its rivers, soils and settlements. India is divided into six physical divisions, and almost every geography paper begins here, because the divisions are the frame on which rivers, climate, soils and crops are later hung. This note takes the six divisions in order, with the ranges, peaks, passes and terms examiners ask for.

The Himalayan mountains

The Himalayas are young fold mountains, raised where the Indian plate collided with the Eurasian plate, and they are still rising. They run about 2,400 kilometres in an arc from the Indus gorge in the west to the Brahmaputra gorge in the east. From north to south they fall into three parallel ranges. The Himadri or Greater Himalaya is the innermost and loftiest, carrying the highest peaks and the great glaciers such as the Gangotri and the Siachen. The Himachal or Lesser Himalaya lies south of it and contains the Pir Panjal, the Dhauladhar and the Mahabharat ranges, the vale of Kashmir, the Kangra and Kullu valleys and the hill stations of Shimla, Mussoorie and Nainital. The Shiwaliks, the outermost and lowest range, are built of gravel and unconsolidated sediment brought down by the rivers; the flat-floored valleys between the Shiwaliks and the Lesser Himalaya are called duns, of which Dehra Dun is the best known.

Along their length the Himalayas are divided by rivers into the Punjab Himalaya between the Indus and the Satluj, the Kumaon Himalaya between the Satluj and the Kali, the Nepal Himalaya between the Kali and the Teesta, and the Assam Himalaya between the Teesta and the Dihang. Beyond the eastern bend the ranges turn south as the Purvanchal, which includes the Patkai Bum, the Naga hills, the Manipur hills and the Mizo or Lushai hills. North of the Greater Himalaya lie the Trans-Himalayan ranges, the Karakoram, the Ladakh and the Zaskar, which are structurally part of the Tibetan block.

The Northern Plains

The Northern Plains were built by the alluvium of three river systems, the Indus, the Ganga and the Brahmaputra, filling a great foredeep in front of the rising mountains. They are among the most fertile and densely settled tracts on earth. Four belts run across them. The Bhabar is the narrow pebble-strewn strip at the foot of the Shiwaliks, where the streams sink underground. The Terai is the marshy, once-forested belt south of it, where the same streams reappear. The Bhangar is the older alluvium, lying above the flood level and often bearing lime nodules called kankar. The Khadar is the newer alluvium of the active floodplains, renewed every year and the most fertile of the four. The Brahmaputra plain in Assam holds Majuli, the largest river island in the country.

The Peninsular Plateau

The peninsular block is the oldest part of India, a fragment of the ancient landmass of Gondwana made of crystalline igneous and metamorphic rocks. It is broadly divided into the Central Highlands, north of the Narmada, which include the Malwa plateau, the Bundelkhand upland and the Chotanagpur plateau with its coalfields, and the Deccan Plateau to the south. The Deccan is bordered by the Western Ghats or Sahyadri, a continuous wall broken only by passes such as the Thal Ghat, the Bhor Ghat and the Palghat Gap, and by the discontinuous Eastern Ghats, cut through by the rivers running to the Bay of Bengal. The northern Deccan is covered by the Deccan Trap, sheets of basalt poured out by fissure eruptions, which weather into the black regur soil. The Aravalli range in the north-west is the oldest fold mountain system in India, worn down to low residual hills, and the Vindhya and Satpura ranges enclose the rift valleys in which the Narmada and the Tapi flow westward.

The Indian Desert

West and north-west of the Aravalli lies the Thar or Great Indian Desert, a sandy waste of crescent-shaped barchan dunes and longitudinal dunes, receiving less than 150 millimetres of rain a year. Its streams are seasonal and the Luni is the only river of any size; many watercourses end in inland saline depressions instead of reaching the sea.

The Coastal Plains and the Islands

The western coastal plain, between the Western Ghats and the Arabian Sea, is narrow and is a submerged coast, which gives it good natural harbours and the backwater lagoons of Kerala such as the Vembanad. It is named in sections as the Kachchh and Kathiawar coast, the Konkan, the Kannad plain and the Malabar coast. The eastern coastal plain is broad and level, an emergent coast with sandbars and lagoons such as Chilika and Pulicat but few good harbours; it carries the deltas of the Mahanadi, the Godavari, the Krishna and the Kaveri, and is called the Northern Circars in the north and the Coromandel coast in the south. India has two island groups. The Andaman and Nicobar Islands in the Bay of Bengal are of volcanic and tectonic origin, are separated from one another by the Ten Degree Channel, and include Barren Island, the only active volcano in the country, and Indira Point in Great Nicobar, the southernmost point of Indian territory. Lakshadweep, in the Arabian Sea, is a group of coral atolls and reefs built on a submarine ridge.

Peaks and passes worth memorising

Why the divisions matter

The six divisions explain most of the rest of the syllabus. The Himalayas block the cold Central Asian winds and force the monsoon to shed its rain on India. The plains give the country its wheat and rice belt and its densest population. The plateau supplies almost all its metallic minerals and its black cotton soil. The desert, the coasts and the islands fix the limits of settlement, the ports and the maritime boundary. Learn the divisions first and the rest of Indian geography falls into place.