About 50 million years ago, this fast moving plate had completely closed the Tethys Ocean. The existence of the Tethys has been proved by sedimentary rocks settled on the ocean floor, and the volcanoes that fringed its edges. Since these sediments were light, they crumpled into mountain ranges rather than sank to the floor. The Indian plate is still driving horizontally below the Tibetan Plateau, which forces the plateau to move upwards.