A massive chamber holding enough magma to fill the Grand Canyon more than 11 times over is hiding beneath the steaming volcanic system of Yellowstone National Park in Wyoming.

We knew of a smaller magma chamber closer to surface, holding some 10,000 cubic kilometres of magma and feeding heat upwards. The newly discovered reservoir sits under it and has a volume of 46,000 cubic kilometres. Together, the two form the largest known magma reservoir in the world.