The subcontinent's subsequent collision with the Eurasian Plate and subduction under it gave rise to the Himalayas, the planet's highest mountains, which abut India in the north and the north-east. The Kanchenjunga is the highest mountain bordering India and Nepal. The Nanda Devi is the second highest peak and the highest mountain located entirely within India. 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 lies the Thar Desert, which is cut off by the Aravalli Range.
The original Indian plate survives as peninsular India, the oldest and geologically most 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 the south the remaining peninsular landmass, the Deccan Plateau, is flanked on the west and east 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 kilometres (4,700 mi) long; of this distance, 5,423 kilometres (3,400 mi) belong to peninsular India and 2,094 kilometres (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.
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; the latter's 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.