Most of Earth's Volcanoes Are Hidden on the Ocean Floor

The volcanoes most people picture stand on land. But the greatest number of the Earth's volcanoes are hidden from view, on the ocean floor.

The remotely operated vehicle Jason gets a close look at magma explosions and lava flows on West Mata volcano. Credit: NOAA.

Why volcanoes form where they do

Volcanic eruptions happen only in certain places, not at random, because the Earth's crust is broken into rigid slabs called tectonic plates. The plates "float" on a hotter, softer layer inside the Earth, and as they move they spread apart, collide or slide past one another.

Where they are

• Plate boundaries. Sixty percent of all active volcanoes are at the boundaries between tectonic plates.
• The Ring of Fire. Most volcanoes lie along a belt called the "Ring of Fire" that encircles the Pacific Ocean.
• Hot spots. Some, like those that formed the Hawaiian Islands, rise in the interior of plates, at places called hot spots.

Land versus sea

Most of the active volcanoes we see on land occur where plates collide. The greatest number, though, are on the ocean floor, along the spreading ridges where plates pull apart.

Sources

Based on "Do volcanoes occur in the ocean?" from NOAA's National Ocean Service, a work of the United States government in the public domain.