Ever been mesmerized by the swirling colors of Grand Prismatic Spring and wondered what fuels that otherworldly boil? It turns out that beneath the wild expanse of Yellowstone National Park lies one of the most closely watched volcanic systems on Earth.

A recent study discovered the exact location of the Yellowstone supervolcano's magma cap -- and hints at when it may erupt.

Yellowstone Caldera, the volcanic complex underneath Yellowstone National Park, is held at bay from eruption by a cap 3.8 meters underground.