Indian Physical Geography: Structure, Himalaya, plains and desert

India’s location, geology and physiographic

divisions India lies wholly in the northern and eastern hemispheres, between about 8°4′ N and 37°6′ N and 68°7′ E and 97°25′ E. It covers about 3.28 million sq km, 2.4% of the world’s land, and holds about a sixth of its people. The Tropic of Cancer (23°30′ N) cuts it almost in half and passes through eight states: Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura and Mizoram. Indian Standard Time is set on 82°30′ E, which passes near Mirzapur.

The east–west spread of about 30° of longitude means a two-hour gap in sunrise between Arunachal and Gujarat. Prelims 2015 asked which one of the following pairs of States of India indicates the easternmost and westernmost State: Arunachal Pradesh and Gujarat (option d).

Geologists see three Indias. The Peninsula is a block of the ancient Gondwana land, among the oldest and most stable rock on Earth. The Himalaya and the north-east hills are young fold mountains, pushed up as the Indian plate drove into Asia. Between them, the Indo-Gangetic plain is a trough filled with river silt. From these come six physiographic divisions: the Himalaya, the northern plains, the peninsular plateau, the Indian desert, the coastal plains and the islands.

Mains 2022 asked: Discuss the natural resource potentials of ‘Deccan Trap’. Mains 2022 Its basalt weathers into black cotton soil, which holds moisture and suits cotton, soybean and sugarcane. Its rock is a strong building stone. Laterite caps on the plateau hold bauxite (Kolhapur, Amarkantak). Its rivers drop over steps to give hydropower (Koyna). Cave-cut heritage (Ajanta, Ellora, Elephanta) brings tourism. The limits: groundwater is held only in cracks, so wells run dry, and the black soil cracks and erodes when bare.

The Himalaya

The Himalaya run in an arc about 2,400 km long from the Indus in the west to the Brahmaputra in the east. They are widest in Kashmir (about 400 km) and narrowest in Arunachal (about 160 km). They block cold Central Asian winds, catch the monsoon, feed perennial rivers with snow and glaciers, and hold forests, minerals, hydropower and pilgrim sites.

Prelims 2022 paired peaks with ranges: Namcha Barwa Garhwal Himalaya 2. Nanda Devi Kumaon Himalaya 3. Nokrek Sikkim Himalaya. Only Nanda Devi–Kumaon is right (option b). Namcha Barwa marks the eastern end of the Himalaya, where the Tsangpo bends round it; Nokrek is the highest peak of the Garo Hills in Meghalaya, and a biosphere reserve.

Height decides vegetation. Prelims 2014 asked: If you travel through the Himalayas, you are likely to see which of the following plants naturally growing there? Oak and rhododendron, yes; sandalwood, no, because it grows in the dry deciduous forests of Karnataka and Tamil Nadu (option a). Going up: tropical sal forests in the foothills, then oak and chestnut, then deodar, pine, spruce and fir, then birch and rhododendron, then alpine meadows (bugyals in Uttarakhand, margs in Kashmir).

Prelims 2017 said: In India, the Himalayas are spread over five States only. That is wrong: they cover the UTs of Ladakh and Jammu and Kashmir and the states of Himachal Pradesh, Uttarakhand, Sikkim, West Bengal (Darjeeling) and Arunachal Pradesh, with the Purvachal hills in the north-east. The same question said that Pulicat Lake is spread over two States only, which is right (Andhra Pradesh and Tamil Nadu), and that the Western Ghats cover five states, which is wrong (six). So the answer was 3 only (option b).

Mains 2020 asked: How will the melting of Himalayan glaciers have a far-reaching impact on the water resources of India? Mains 2020 In the short run, more melt means floods and glacial lake outburst floods (Kedarnath 2013, South Lhonak in Sikkim 2023). In the long run, less ice means less summer flow in the Indus, Ganga and Brahmaputra, just when crops and cities need it most. That hurts irrigation, hydropower, drinking water, groundwater recharge in the plains, and river-sharing with neighbours.

The northern plains and the Indian desert

The northern plains, about 7 lakh sq km, were built by the Indus, Ganga and Brahmaputra and their tributaries, dropping silt into the trough in front of the Himalaya. They are flat (the land falls only about 200 m from Delhi to the Bay of Bengal), fertile and well watered. They are among the most densely populated farmlands on Earth.

Rainfall and crops change from west to east. Prelims 2011 said: The lower Gangetic plain is characterised by humid climate with high temperature throughout the year. The best pair of crops there is paddy and jute (option c). Westward, the Punjab–Haryana plain is drier and grows wheat with canal and tube-well irrigation.

Mains 2025 asked: Discuss the distribution and density of population in the Ganga River Basin with special reference to land, soil and water resources. Mains 2025 Density is very high (Bihar has over

1,100 persons per sq km by the 2011 Census) because of deep khadar soils, flat land, perennial rivers and groundwater, and an old history of settled farming. It thins out at the edges: in the Shiwalik and Terai belt, in the Chambal ravines and on the drier south-western margins. Pressure shows in tiny landholdings, falling water tables, floods in north Bihar and migration out.

The Indian desert (Thar) lies west of the Aravallis, with under 15 cm of rain in the far west. It was under the sea in the Mesozoic era. It has sand dunes (barchans), few rivers (the Luni is the main one, ending in the Rann of Kutch) and salt lakes.

Prelims 2021 asked: With reference to India, Didwana, Kuchaman, Sargol and Khatu are the names of Prelims 2021 saline lakes (option d), in Rajasthan’s inland drainage, like the much bigger Sambhar, India’s largest inland salt lake.