The mega-collision is between two of the gigantic slabs called plates that make up Earth’s outer layer. The Earth’s plates slowly move, carrying continents along with them. As they move, the plates either grind past each other, pull apart, or collide head-on like a train wreck.
Just such a head-on collision has pushed the Himalayas sky-high. The mountain range got its start about 40 million years ago, as India began slowly crunching into Asia. That collision is still going on, so the Himalayas keep getting taller. To find out how fast, geologists put a Global Positioning System (GPS) instrument near the summit of Mount Everest. They determined that each year, the mountain gains another 0.1576 inches.