The Himalayas and the Roof of the World

The Himalayas are the direct product of continental collision. India, once part of the Gondwanan supercontinent, broke away roughly 120 million years ago and drifted north across the ancient Tethys Ocean at speeds of up to about 15 centimeters per year, among the fastest plate motions ever reconstructed from the geologic record. When the Indian and Eurasian continental plates finally met, the oceanic crust between them was consumed and the two continental masses, each too buoyant to subduct, crumpled and thickened instead, throwing up the Himalayan chain and the Tibetan Plateau behind it. Paul Molnar and Paul Tapponnier's influential 1975 paper in Science, "Cenozoic Tectonics of Asia: Effects of a Continental Collision," modeled this deformation as a rigid-block extrusion process, showing how the collision's effects propagated thousands of kilometers into Asia's interior, producing the Tien Shan and reactivating faults as far as Lake Baikal. India continues to converge with Asia today at roughly 4 to 5 centimeters per year, and the range continues to rise, punctuated by devastating releases of accumulated strain such as the magnitude-7.8 Gorkha earthquake that struck Nepal in April 2015.