There are more than 550 active volcanoes in the world, almost all of which are located at convergent tectonic plate boundaries. This includes all of the volcanoes in the Pacific Ring of Fire, such as Japan's Mount Fuji, as well as Mount Saint Helens, Popocafepetl in Mexico and Azul in the Andes Range.
All of these volcanoes occur when an oceanic plate slides beneath a continental plate and is turned into magma, which then rises back to the surface to form a volcano. The Cascade Mountains that run along the coast of Oregon and Washington were created by the collision between the oceanic Juan de Fuca plate and the North American continental plate. In South America, the Nazca plate is sliding underneath the continental plate, which created Azul, Cotopaxi and the other Andes volcanoes.
There are also many submarine volcanoes located throughout the Pacific Ring of Fire, as well as many islands created by volcanic activity. One of the most famous underwater volcanoes is Krakatau in Indonesia, which caused the deaths of nearly 40,000 people when it erupted in 1883. Many of the other Indonesian islands also feature both dormant and active volcanoes, as do many of the other Micronesian islands in the South Pacific.