It’s already had three cataclysmic eruptions over the last 2 million years, covering much of North America in ash and creating the massive crater 40 kilometers long (25 miles long) and 60 kilometers wide (37 miles wide) that we now call Yellowstone National Park. But for the first time, scientists have imaged in 3D the whole magmatic network that makes up one of the world’s most dynamic volcanic systems, and they discovered enough magma to fill the Grand Canyon not just once or twice, but eleven times over.
This new research, carried out by a group of seismologists from the University of Utah and published in the journal Science, has allowed scientists to solve a long-running mystery of how the already well-known shallower reservoir—which holds around 10,000 cubic kilometers (2,400 cubic miles) of magma just below the surface—connects with the magma plume that feeds it from 70 km (43 miles) down.
“For the first time, we have imaged the continuous volcanic plumbing system under Yellowstone,” explained lead author Hsin-Hua Huang, a postdoctoral researcher in geology and geophysics. “That includes the upper crustal magma chamber we have seen previously plus a lower crustal magma reservoir that has never been imaged before and that connects the upper chamber to the Yellowstone hotspot plume below.”
Previous research revealed that the top of the unknown “blob-shaped” magma reservoir is deeper than the shallower reservoir. This, coupled with the puzzle that the smaller cache alone could not account for the observed large daily flux of 45 kilotons of CO2, led the scientist to suspect that there might be something more lurking in Yellowstone's depths.
By using the seismic activity data from thousands of earthquakes that shake the park each year, the researchers were able to build up a 3D picture of what was going on deep below the surface, and reveal for the first time the presence of the larger pocket containing an estimated 46,000 cubic kilometers (11,000 cubic miles) of molten rock. Combined with the smaller chamber, they now form the largest known magma reservoir in the world.
Counter to most people's belief, the magma chamber is not full of liquid molten rock. Instead, the rock is hot, mostly solid and sponge-like, with pockets of molten rock within it. This means that while the total volume of magma might fill the Grand Canyon eleven times, the molten rock only accounts for around 10% of this.
However, before you rush out to stock up on bottled water and gasoline, the scientists are keen to stress that the danger it poses is no greater than before; it simply means that we have a better understanding of the processes that have gone into shaping the volcano in the first place. “The magma chamber and reservoir are not getting any bigger than they have been," explains co-author Jamie Farrell, "it’s just that we can see them better now using new techniques."