Overview
With a surface area of over 3 million square kilometers, the Indian territory is fairly geographically and geologically cohesive. It can be divided as follows: the Himalayan region and its foothills to the north and east; the Indo-Gangetic plain, which forms a wide strip at the foot of the Himalayan range; the Thar desert zone to the north-west, wedged between the Indus plain (Pakistan) and the Aravalli range (eastern Rajasthan) ; the Deccan plateau in the center, framed by the Satpura (northern Maharashtra), Western Ghats and Eastern Ghats ranges; the coastal strip running from Mumbai to Calcutta, bordered by the Arabian Sea and the Bay of Bengal, and the Western and Eastern Ghats. The Lakshadweep Islands (off the coast of Kerala and in the continuity of the Maldives) and the Andaman and Nicobar Islands in the Bay of Bengal, off the coast of Burma, are added to the continental plate.
The Himalayas
80 million years ago, India was an island 6,400 kilometers off the coast of Asia. The northward-moving Indian Plate collided with the Eurasian Plate around 62 million years ago. This dating was obtained in 2020 using a multidisciplinary approach combining stratigraphic, sedimentological and geochronological studies. The Indian plate continues to advance by around 5 centimetres per year, sinking beneath the Eurasian plate and triggering regular high-magnitude earthquakes. The sea that separated India from Asia disappeared with the collision. But there are signs of it. The summit of Mount Everest, in Nepal, is made of marine limestone.
The Himalayas form a 2,400-kilometer-long impenetrable natural barrier in the shape of an arc. It separates the Indian subcontinent from East Asia. The range begins in the Karakoram, a region bordering Pakistan, India and China. It ends in Assam, in northeast India, where the Brahmaputra River flows. Some geologists link the Himalayan range to its western and eastern foothills, in Baluchistan and Burma. Beyond this expert debate, the Himalayas correspond to a geological formation of three parallel chains forming a mountainous block 250 to 400 kilometers wide. The sub-Himalayan range, also known as the "Shivalik Hills", is the lowest of these. It rises above the Indian Indo-Gangetic plateau. Its average elevation is 1,200 metres. The second range, known as the "Lower Himalayas", rises between 2,000 and 5,000 metres. It is mainly located in India, and forms the main relief of the states and territories of Jammu and Kashmir, Ladakh, Himachal Pradesh, Uttarakhand, northern West Bengal, Sikkim and Arunachal Pradesh. The third range, or "High Himalaya", is the oldest geologically speaking, and the highest. It is home to 10 of the 14 peaks over 8,000 metres high. Of these, only one is in India: Kanchenjunga (8,586 m), straddling southern Nepal and Sikkim.
The geological formation of these three ranges differs from one another, and corresponds to events of different periods. The oldest chain is the "High Himalayas", essentially composed of fossilized marine sediments. The Tethys Sea disappeared when it met the Eurasian Plate. The Lower Himalayan range is made up mainly of crystalline rocks, but also of sedimentary series. The sub-Himalayan range has a geology formed in the Tertiary era. Despite the Himalayas' proximity to the tropics, areas above 5,000 metres are snow-covered all year round. The meaning of the word Himalaya comes from the Sanskrit, meaning "abode of snow". The Himalayas are home to numerous glaciers, which flow into the lower valleys to form rivers.
River plains
The Ganges and Brahmaputra rivers, among the longest in the world, flow directly from Himalayan glaciers. The Ganges rises at the foot of the Gangotri glacier in Uttarakhand. The Brahmaputra crosses Tibet from west to east, before reaching Assam, forming the world's deepest valley. It continues its course through Bangladesh. The two rivers meet north of the Bay of Bengal, where they flow into the world's largest delta, the Sundarbans. Together with the Indus valley in Pakistan, these three rivers irrigate the Indo-Gangetic plateau, which follows the contours of the Himalayan chain. The low elevation of the land, 350 meters above sea level, creates the illusion of geographical uniformity. In reality, the Indo-Gangetic plain comprises a number of different zones. At the foot of the Shivalik hills is a thin strip of rock and pebbles unsuitable for agriculture. Just below, the Tarai zone forms a belt of tall grass and sal forests, with clay soil. On the Brahmaputra side, the approach to the valley, known as the Douars, consists of alluvial floodplains. The Ganges plateau is criss-crossed by numerous tributaries that form silty tongues of land. This area is considered the granary of India. It stretches from Punjab to Haryana, then forms a wide band around the Ganges valley and the Brahmaputra river. The Indo-Gangetic plateau is the world's largest alluvial zone. Flat, fed by underground springs and sparsely forested, it is the world's largest agricultural area.
The Thar Desert
Located in north-western India, the Thar Desert forms a natural border between Rajasthan and Pakistan. It is bounded by the Indo-Gangetic plain to the north, Sindh (Pakistan) to the west, Kachchh (Gujarat) to the south and the Aravalli range (Rajasthan) to the east. This vast 220,000 km² semi-desert area was formed in the Precambrian era (between 4 and 2.5 billion years ago). Sandy plains alternate with small rocky hills. The monsoon skirts the desert from the east, which receives little rainfall. The result is sparse vegetation, mainly bushes and shrubs.
The Deccan plateau
This vast plateau occupies central and much of southern India. It is bounded to the north by the Satpura range, which crosses Maharashtra from east to west, the Western Ghats to the west and the Western Ghats to the east. The soil consists mainly of sandstone, granite and basalt. The average altitude is 600 meters. Protected by the Ghats from wind and rain, the climate is semi-arid and scorchingly hot in summer, especially where the altitude is lower. Nevertheless, the region is crossed by long rivers that flow into the Bay of Bengal: the Godavari rises in Maharashtra, near Nashik, and flows into the Bay of Bengal after a journey of 1,500 km; the Krishna River rises in southern Madhya Pradesh; the Cauvery (or Kaveri) rises in western Karnataka and flows through the state, then into Tamil Nadu.
The Western Ghats
The western coast of the Indian peninsula is criss-crossed by the Western Ghats chain, which stretches 1,600 km from Gujarat in the north to Tamil Nadu in the south. Also known as the Sahyadri Mountains, they intercept the sea and are subject to heavy rainfall, particularly during the monsoon season. This particular climate, combined with a favorable topography, creates unique conditions for the development of biodiversity. There are almost 40 national parks and nature reserves in these mountains. The average altitude of the mountain range is 1,200 meters. Its highest peak is Anamundi (Kerala), at 2,695 meters, making it the highest mountain outside the Himalayas. Thanks to year-round mild temperatures and abundant rainfall, the southern Western Ghats (Ooty, Munnar, Periyar...) are ideal for growing tea and spices (pepper, cardamom, star anise, cinnamon...). Several major rivers have their sources on the eastern flank of the Western Ghats: Godavari, Krishna, Cauvery and Tungabhadra. As a result, the Western Ghats chain is also a major center of power generation. There are many reservoirs here.
The Eastern Ghats
The Eastern Ghats lie between the Deccan Plateau and the Bay of Bengal, forming a line parallel to the east coast of the Indian peninsula. This discontinuous mountain range has been eroded by the great rivers that flow from the Western Ghats into the Bay of Bengal. The average elevation of the range is 700 meters. Vegetation is less abundant and diverse than in the west, due to lower rainfall and intensive logging in the early 20th century, notably for railroad construction.
The coastal strip
A narrow coastal strip runs between the Ghats and the Arabian Sea (to the west) and the Bay of Bengal (to the east). In the west, the coast is subdivided into two main sections: the Konkan coast, stretching from Mumbai to south of Goa, and the Malabar coast, stretching from Karnataka to south of Kerala and the tip of Kanyakumari. To the east, the coastal plain known as the Coromandel Coast stretches from southern West Bengal to the mouth of the Cauvery. These plains, which are no more than 70 km wide, are ideal for farming, particularly rice, wheat and cotton.
Islands and archipelagos
India's coastline is only a few islands long: 7,500 km! Mumbai, which was originally built on 7 islands, has swallowed up this fragmented division through soil artificialisation and infilling. The small archipelago of Sriharikota, 70 km north of Chennai, forms a natural barrier protecting the coast here. The Sundarbans mangrove zone in West Bengal forms a labyrinth of islands and islets whose contours change with the water level. The Andaman and Nicobar archipelagos, made up of 572 islands, close the Indonesian island chain to the north. On the Arabian Sea side, the Lakshadweep archipelago faces Kerala, in line with the Maldives. Only a few of its 27 islands are open to tourists.
