How do plate motions create mountains?
Plate tectonic processes create some of the world's most beautiful places. The North Cascades Mountains in Washington State are a continental volcanic arc. The mountains currently host some glaciers and there are many features left by the more abundant ice age glaciers. Changes in altitude make the range a habitable place for many living organisms.
Converging Plates
Converging plates create the world's largest mountain ranges. Each combination of plate types — continent-continent, continent-ocean, and ocean-ocean — creates mountains.
Converging Continental Plates
Two converging continental plates smash upwards to create gigantic mountain ranges (Figure below). Stresses from this uplift cause folds, reverse faults, and thrust faults, which allow the crust to rise upwards. As was stated previously there is currently no mountain range of this type in the western U.S., but we can find one where India is pushing into Eurasia.
[Figure 1]
(a) The world’s highest mountain range, the Himalayas, is growing from the collision between the Indian and the Eurasian plates. (b) The crumpling of the Indian and Eurasian plates of continental crust creates the Himalayas.
Subducting Oceanic Plates
Subduction of oceanic lithosphere at convergent plate boundaries also builds mountain ranges. This happens on continental crust, as in the Andes Mountains (Figure below), or on oceanic crust, as with the Aleutian Islands, which we visited earlier. The Cascades Mountains of the western U.S. are also created this way.
[Figure 2]
The Andes Mountains are a chain of continental arc volcanoes that build up as the Nazca Plate subducts beneath the South American Plate.
Diverging Plates
Amazingly, even divergence can create mountain ranges. When tensional stresses pull crust apart, it breaks into blocks that slide up and drop down along normal faults. The result is alternating mountains and valleys, known as a basin-and-range (Figure below). In basin-and-range, some blocks are uplifted to form ranges, known as horsts, and some are down-dropped to form basins, known as grabens.
[Figure 3]
(a) Horsts and grabens. (b) Mountains in Nevada are of classic basin-and-range form.
Summary
Converging or diverging plates cause mountains to grow.
Subduction of oceanic crust beneath a continental or oceanic plate creates a volcanic arc.
Tensional forces bring about block faulting, which creates a basin-and-range topography.
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