Portals into the guts of the world they burned bottomless cauldrons fueled by an ancient wrath bubbling and boiling thousands of miles beneath the surface and just waiting to burst through volcanoes are scattered across the planet about 1,500 active volcanoes can be found across the planet though countless others are on the ocean bottom most volcanoes whether ashore or underwater are located where tectonic plates meet actually the Ring of fireside a path that traces the boundaries between several tectonic plates round the Pacific Ocean contains about 75% of the planets volcanoes there are several types of volcanoes primarily classified by shape and size major types include stratovolcanoes which frequently appear as tall steep mountains shield volcanoes which are flatter and dome shaped calderas which are large depressions in the ground and mid-ocean ridges which are underwater chains of volcanic mountains regardless of their shape or size