How Are Mountains Formed?

The most common and visible way mountains are formed is through the convergence of Earth’s tectonic plates. When two lithospheric plates collide, the immense pressure causes the crust to crumple and fold, creating mountain ranges. This process, called orogeny, results in the formation of long, linear mountain belts. The creation of the majestic Himalayas is one example of this process; it was formed as the Indian plate collided with the Eurasian plate, compressing and pushing up the continental crust of both plates to create some of the highest peaks on the planet (see also plate tectonics).

Volcanic activity is another significant contributor to mountain formation. As tectonic plates move, they can create openings in Earth’s crust, allowing magma to rise and solidify, forming volcanic mountains. Volcanism is particularly evident in such regions as the Pacific Ring of Fire, where the subduction of oceanic plates beneath continental plates leads to frequent volcanic eruptions and the creation of volcanic mountain chains (see also oceanic crust). The Andes in South America are a a prime example in which the subduction of the Nazca Plate beneath the South American Plate has given rise to a series of volcanic peaks (see also subduction zone).

Mountains can also form through block faulting (or normal faulting) and erosion. In block faulting, large blocks of crust are uplifted or tilted on either side of a crack, or rift, created by plate tectonics. Block faulting can create ranges with steep, rugged terrain, such as the Sierra Nevada Mountains in the United States. Additionally, uplift can occur when Earth’s crust is stretched and thinned, leading to the formation of rift valleys and their associated mountain ranges. The East African Rift System is a classic example of this kind of mountain building, where the pulling apart of the crust has resulted in the formation of highlands and volcanic mountains. In contrast, erosion rarely forms mountain chains, but in certain areas, including those that once were plateaus or broad uplifted regions, the wearing away of rock by wind, water, and glaciers has left what are known as residual mountains; one example is Mount Katahdin in Maine.