When most people think of volcanoes, they picture towering mountains like Vesuvius or Mount Fuji. 

But here’s the twist: nearly three-quarters of Earth’s volcanic activity happens under the ocean and it's massive. 

Submarine volcanoes erupt an estimated 3.4 cubic kilometers (0.8 cubic miles) of lava every year. To picture that: it’s about 3 Great Pyramids of Giza worth of rock poured into the ocean annually.

On land, by comparison, all the world’s volcanoes usually erupt less than 1 cubic kilometer (0.24 cubic miles) per year — less than a single Pyramid’s worth.

Along the mid-ocean ridges, molten rock is constantly bursting through the seafloor, creating new crust and reshaping the planet while hidden from view.

The largest single volcano on Earth, Tamu Massif, lies deep beneath the Pacific. It is bigger than the entire state of New Mexico, yet it remained undiscovered until 2013.

While we marvel at dramatic eruptions on land, the true heart of volcanic activity rumbles quietly below the waves.