Today scientists understand that volcanic eruptions are surface reminders of Earth's still hot interior. Volcanic eruptions do not occur just anywhere. Sixty percent of all active volcanoes are found at crustal plate boundaries such as the Pacific Plate, which has become known as the Ring of Fire because of the active volcanoes on its perimeter. These floating pieces of the crust are moving about very slowly on the hotter interior. Where the plates are moving apart or colliding with one another, volcanoes may form.
Many volcanoes form oceanic islands in the Pacific Ocean or Mediterranean Sea.
The Northern Hemisphere has approximately two thirds of the land-based volcanoes. Not all volcanoes erupt and not all eruptions are explosive. Volcanologists label volcanoes active , dormant , and extinct , depending on the likelihood of an eruption occurring. Volcanoes that will never erupt again are considered extinct. . About sixty volcanoes are actively erupting each year.