Volcanism does not occur randomly on the Earth’s surface. About 95% of the active volcanoes are located at or near plate boundaries (Figs. A and B in Appendix). Most active volcanoes develop in fold belts that coincide with earthquake zones. A large number of recent and extinct volcanoes form alignments or are located in narrow bands, along tectonically active zones of the Earth, such as mid-ocean ridges, continental margins (e.g. the western coast of the Americas), and island arcs (e.g. the Aleutians, Lesser Antilles; Fig. A in Appendix). Other aligned edifices are closely associated with fault systems along rift valleys (e.g. East African Rift, West Antarctic Rift)West Antarctic Rift.