Volcanoes form when magma leaks through the earth's crust and onto the surface. The word "volcano" comes from Vulcan, the Roman god of fire believed to live within volcanoes. There are over 1500 active volcanoes worldwide, with most located along tectonic plate boundaries in the "Ring of Fire" in the Pacific Ocean. The three main types of volcanoes are composite, cinder, and shield volcanoes, which erupt in different ways.