A map showing the distribution of volcanic structures on the Earth's surface

This map shows the location of active, inactive, and extinct volcanoes throughout the world. Each individual volcano is shown as a single, red triangle. In many places in the world, there are so many volcanoes in a small area that they appear on this map as a cluster instead of individual triangles. These areas include the Andes Mountains in South America, Iceland in the North Atlantic Ocean, the Philippine Islands, and the East African Rift Zone. Although some volcanoes are extinct or have not erupted in recent times, these areas still may exhibit tectonic activity as the magma below (or the crustal plates) shift in geologic time. Generally, there is a strong relationship between where the volcanoes are, and where tectonic activity occurs on Earth; at subduction zones, divergent boundaries, transform boundaries, and "hot spots." From this map, it is easy to see the famous "Ring of Fire" that encompasses most of the Pacific Ocean, where the boundaries of this ocean comprise subduction zones in the east, north, and west, a transform boundary in California, and a deep trench formation south of the Islands of Japan.

Credit: Dylan Prentiss, Department of Geography, University of California, Santa Barbara

For more info: http://www.geog.ucsb.edu/~dylan/mtpe/geosphere/wh/vol/volcanoes.html