The Andes Mountain Range spans the entire length of South America, along the western coast. This close-up shows that coast, which represents the western terrestrial edge of the South American Plate. The leading edge of the Nazca Plate is subducting below the South American Plate at a plate boundary known as a subduction zone. During this subduction some Nazca crust is scraped off along base of the Andes, adding height to the entire range.

The East Pacific Rise [the ridge to the left] is part of the global network of mid-ocean ridges that girdle the planet. As the sea-floor spreads on either side of this ridge, the Nazca Plate moves easterly while the Pacific Plate moves westerly. The Galapagos Islands, off the northwestern coast of South America, are the result of a "Hot Spot" that exists over a mid-ocean ridge.
     
Thanks to Bruce Heezen and Marie Tharpe.

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