The volcanoes you can name - Vesuvius, Etna, Fuji, Kilauea - are all on land, where humans can see them. But they’re a small fraction of the volcanoes actually on Earth. The vast majority lie underwater, hidden by the ocean. Geologists estimate there are well over a million underwater volcanoes around the planet, with thousands active at any given time.
Most form along the underwater ridges where the tectonic plates pull apart, gently leaking lava onto the seafloor. Others build up in chains, sometimes growing so tall their tops break the surface and become islands. Hawaii, Iceland, and the Galápagos are all the visible peaks of much taller volcanoes whose bases sit on the seabed thousands of meters below.
In fact, measured from its base on the seafloor to its summit, Mauna Kea in Hawaii is over 10,000 meters tall - making it actually taller than Mount Everest. Most of it is just underwater, where we never see it.
