Scientists have discovered a large reservoir of hot rock beneath the shallow, already-documented magma chamber of the Yellowstone national park 'supervolcano' in America.
The magma chamber is 4.5 times larger than the chamber above it, with enough magma to fill the Grand Canyon.
Researchers used a technique called seismic tomography to get a complete picture of the volcanic "plumbing system" at Yellowstone.
According to the Guardian, University of Utah seismologist Jamie Farrell said: "The existence of the second magma chamber does not make it any more or less likely that a large volcanic eruption at Yellowstone will occur. These findings do not change the current volcanic hazard at Yellowstone."
There is a 700,000 to one chance the volcano will erupt each year.
Farrell added: "These new findings do provide us, and other researchers, the information needed to gain a better understanding of how magma moves from the mantle to the surface."
The Washington Post reports that the volcanic system has been in place for around 17 million years.
The last eruption was around 640,000 years ago.
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