During the Pliocene, the SVZ south of 38°S consisted of a broad volcanic arc. The area with volcanic activity 1 to 2 million years ago between 39°S-42°S was up to 300 km wide (if back-arc volcanism is included). A reduction in the convergence rate of the Nazca and the South American Plate from 9 cm per year to 7.9 cm per year 2-3 million years ago contributed to a narrowing of the southern SVZ that occurred possibly 1.6 million years ago. The southern part of the SVZ retained vigorous activity only in the west, especially around the Liquiñe-Ofqui Fault Zone, while eastern volcanoes such as Tronador and Cerro Pantoja became extinct.