The presence of many volcanoes on the Pacific Ocean side of South America is primarily associated with the subduction of one tectonic plate beneath another. The tectonic setting in this region involves the convergence of the Nazca Plate and the South American Plate.

Specifically, the Nazca Plate, an oceanic plate, is subducting beneath the South American Plate, a continental plate. As the Nazca Plate descends into the Earth's mantle, it melts, forming magma. This magma, being less dense than the surrounding rock, rises through the overlying South American Plate, leading to volcanic activity along the subduction zone.