Several earth processes contribute to the formation of mountains. Some, such as Mount Saint Helens in Washington state and Mount Vesuvius in Italy, are the result of volcanic processes. Others are formed by erosion or cracks in the earth through which heated rock seeps, such as the Sierra Nevada.
However, the primary force that creates large mountains is earth movement, as one plate of the Earth's crust either collides with another or is forced under it in a process called subduction. The pressure pushes materials up along the fault lines, resulting in hills and mountains.
When two parts of the Earth's crust move against each other, one may subduct, or slide beneath the other, creating an uplift on one side and a gap through which molten rock can push. At this subduction collision margin, the emerging rock solidifies, resulting in mountains of varying heights.
The Cascades of the northwestern United States, part of the Pacific's tectonically active Ring of Fire, resulted from this process. The Appalachian Mountains, running from Newfoundland to the southern United States, also were created from subduction, as plates moved in the Paleozoic area more than 300 million years ago.
Mountains also form when one plate collides with another, creating a massive uplift along the collision line. The Himalayas, formed when India, originally a large island, moved northward and slammed into Asia about 40 million years ago, stretch along the border between India and Tibet.
Home to Mount Everest, the Himalayas continue to rise at more than a centimeter per year. As India continues to press into Asia, stresses building in this area account for major earthquakes and continued volcanic activity in Asia and Indonesia.
On the southern end of the Ring of Fire, the Andes Mountains, created by the subduction of the Antarctic and Nazca plates beneath the South American plate, stretch more than 7,000 miles along the South American coast. Like other mountain ranges created from subduction processes, the Andes range includes several volcanoes. Since the Ring of Fire is a seismically active zone, the area experiences numerous earthquakes along these shifting plate lines.