Almost All of Earth's Volcanoes Are Under the Ocean

When people picture a volcano, they picture a mountain on land. Most volcanoes are nowhere near land. NASA states that almost all of Earth’s volcanoes are hidden under the oceans. There is plenty of room for them. Earth’s global ocean covers about 71 percent of the planet’s surface, has an average depth of about 2.3 miles, or 3.6 kilometers, and contains 97 percent of Earth’s water. NASA gives a striking example of what the water hides. Hawaii’s Mauna Kea volcano is taller from base to summit than Mount Everest, but most of it is underwater. Mountains are hidden there as well. Earth’s longest mountain range is also underwater, NASA notes, at the bottom of the Arctic and Atlantic oceans. Beneath the sea the crust is thinner too, only about 3 miles thick.