Deep beneath Yellowstone National Park, one of the world's most dynamic volcanic systems, lies an enormous, previously unknown reservoir of hot, partly molten rock big enough to fill up the Grand Canyon 11 times, scientists say.

Researchers on Thursday said they used a technique called seismic tomography to produce for the first time a complete picture of the volcanic "plumbing system" at Yellowstone, from the Earth's mantle up to the surface.

Yellowstone, which straddles the borders of Wyoming, Idaho and Montana, and boasts a remarkable array of geothermal features, including geysers, mudpots, steam vents and hot springs, sits atop a supervolcano that has had three calamitous past eruptions.