India collides with Asia

About 50 million years ago, the Indian plate, a huge slab of Earth's crust carrying the landmass of India, began to collide with Asia. The impact has never stopped. India is still pushing north at about 5 centimeters a year, about as fast as a fingernail grows, and the crumpling of crust where the two meet created the Himalayas, the highest mountain range on Earth, and the Tibetan Plateau, a vast raised region about 4,500 meters above sea level on average. The collision also produced the world's highest peak, Mount Everest, at 8,849 meters.

The story starts with the break-up of the southern supercontinent Gondwana, around 130 million years ago, when India separated from Africa and Antarctica and began drifting north across the Tethys Ocean. It moved quickly for a plate, at times at 15 to 20 centimeters a year. The exact start of the collision is debated, with estimates ranging from about 60 to 40 million years ago, because the contact was a gradual process and happened at different times along the margin. Once the ocean floor between had been consumed, two continents met face to face.

Continental crust is too light to sink deep into the mantle, so instead of one plate diving under the other, the crust crumpled, folded and stacked up, and the Indian plate slid under Tibet, doubling the thickness of the crust there to about 70 kilometers. Rocks that were once seabed were pushed up to the heights. Erosion and the collapse of rocks continue, and rivers such as the Indus, Ganges, Brahmaputra, Yangtze and Mekong cut through the range and carry huge amounts of sediment to the sea. The mountains and plateau also affect the weather, as they block moist air and help drive the monsoon, though how much they shaped it over time is still studied.