Geological research suggests that the South American plate is moving west away from the Mid-Atlantic Ridge: "Parts of the plate boundaries consisting of alternations of relatively short transform fault and spreading ridge segments are represented by a boundary following the general trend."[2] As a result, the eastward-moving and more dense Nazca plate is subducting under the western edge of the South American plate, along the continent's Pacific coast, at a rate of 77 mm (3.0 in) per year.[3] The collision of these two plates is responsible for lifting the massive Andes Mountains and for creating the numerous volcanoes (including both stratovolcanoes and shield volcanoes) that are strewn throughout the Andes.[4][5]
Gómez Tapias, Jorge; Montes Ramírez, Nohora E.; Almanza Meléndez, María F.; Alcárcel Gutiérrez, Fernando A.; Madrid Montoya, César A.; Diederix, Hans (2015). Geological Map of Colombia. Servicio Geológico Colombiano. pp. 1–212. Retrieved 2019-10-29.