Topographic map of India.
India, the major portion of the Indian subcontinent, sits atop the Indian tectonic plate, a minor plate within the Indo-Australian Plate.
India's defining geological processes commenced seventy-five million years ago, when the Indian subcontinent, then part of the southern supercontinent Gondwana, began a northeastwards drift—lasting fifty million years—across the then unformed Indian Ocean. The subcontinent's subsequent collision with the Eurasian Plate and subduction under it, gave rise to the Himalayas, the planet's highest mountains, which now abut India in the north and the north-east. In the former seabed immediately south of the emerging Himalayas, plate movement created a vast trough, which, having gradually been filled with river-borne sediment, now forms the Indo-Gangetic Plain. To the west of this plain, and cut off from it by the Aravalli Range, lies the Thar Desert.
The original Indian plate now survives as peninsular India, the oldest and most geologically stable part of India, and extends as far north as the Satpura and Vindhya ranges in central India. These parallel ranges run from the Arabian Sea coast in Gujarat in the west to the coal-rich Chota Nagpur Plateau in Jharkhand in the east. To their south, the remaining peninsular landmass, the Deccan Plateau, is flanked on the left and right by the coastal ranges, Western Ghats and Eastern Ghats respectively; the plateau contains the oldest rock formations in India, some over one billion years old. Constituted in such fashion, India lies to the north of the equator between 6°44' and 35°30' north latitude and 68°7' and 97°25' east longitude.
India's coast is 7,517 kilometers (4,700 mi) long; of this distance, 5,423 kilometers (3,400 mi) belong to peninsular India, and 2,094 kilometers (1,300 mi) to the Andaman, Nicobar, and Lakshadweep Islands. According to the Indian naval hydrographic charts, the mainland coast consists of the following: 43% sandy beaches, 11% rocky coast including cliffs, and 46% mudflats or marshy coast.
The Himalayas form the mountainous landscape of Northern India. Seen here is Ladakh in Jammu & Kashmir.
Major Himalayan-origin rivers that substantially flow through India include the Ganges (Ganga) and the Brahmaputra, both of which drain into the Bay of Bengal. Important tributaries of the Ganges include the Yamuna and the Kosi, whose extremely low gradient causes disastrous floods every year. Major peninsular rivers whose steeper gradients prevent their waters from flooding include the Godavari, the Mahanadi, the Kaveri, and the Krishna, which also drain into the Bay of Bengal; and the Narmada and the Tapti, which drain into the Arabian Sea. Among notable coastal features of India are the marshy Rann of Kutch in western India, and the alluvial Sundarbans delta, which India shares with Bangladesh. India has two archipelagos: the Lakshadweep, coral atolls off India's south-western coast; and the Andaman and Nicobar Islands, a volcanic chain in the Andaman Sea.
India's climate is strongly influenced by the Himalayas and the Thar Desert, both of which drive the monsoons. The Himalayas prevent cold Central Asian Katabatic wind from blowing in, keeping the bulk of the Indian subcontinent warmer than most locations at similar latitudes. The Thar Desert plays a crucial role in attracting the moisture-laden southwest summer monsoon winds that, between June and October, provide the majority of India's rainfall. Four major climatic groupings predominate in India: tropical wet, tropical dry, subtropical humid, and montane.