Scientists at Yellowstone National Park have uncovered a large, underground magma cap that is likely crucial to containing one of Earth's largest volcanic systems. Hidden 2.4 miles (3.8km) beneath Yellowstone's northeast caldera, the cap acts as a lid for the intense heat and pressure below it, which could otherwise cause large-scale eruptions.

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