The Ring of Fire.

Most volcanoes are located on the continents edges, along island chains or beneath the sea forming long mountain ranges. More than half of the world's active volcanoes above sea level encircle the Pacific Ocean to form the circum-Pacific "Ring of Fire." The ring of fire makes up seventy five percent of the worlds dormant and active volcanoes. More than half of the world's active volcanoes above sea level are part of the ring. The Ring …

…the centers if the ocean floor, or areas of rifting on continental plates, and the final area is at hot spots where there are individual plumes of magma that rise to the surface. http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/description_plate_tectonics.html geography.about.com/cs/earthquakes/a/ringoffire.htm news.bbc.co.uk/1/hi/world/136248.stm www.pbs.org/wnet/savageearth/ hellscrust/html/sidebar3.html http://www.platetectonics.com/book/page_14.asp