Seismologists from the University of Utah have discovered a massive pool of hot, partly molten rock hidden deep beneath Yellowstone’s supervolcano – a reservoir that is more than four times larger than the shallower, more well-known magma chamber there.
The researchers, who reported their discovery Thursday in the journal Science, captured images of the rock 12 to 28 miles beneath the volcano, and said that there was enough magma in the new reservoir to fill the entire 1,000-cubic-mile Grand Canyon eleven times over.
They also were able to image the continuous underground volcanic structure for the first time, said first author Hsin-Hua Huang, a postdoctoral researcher in geology and geophysics. Those images include the previously-seen upper crustal magma chamber, as well as the never-before-imaged lower crustal reservoir that connects it to the hotspot plume.
Yellowstone volcano “a gold mine of data”
“For a seismologist, Yellowstone is a gold mine of data,” study co-author Jamie Farrell, a postdoctoral researcher and a member of Utah’s Seismology and Active Tectonics Research Group, told redOrbit via email. “Since Yellowstone is such dynamic system, it seems we are always learning something new and seeing new and interesting things. It’s always fresh and exciting and this project was no different.”
Thanks to the new research, Farrell explained that the researchers “now have a complete picture of the Yellowstone plumbing system from deep in the mantle to the upper-crust,” and that they can “use this data to model how heat and magmatic fluids are transferred from deep in the Earth to the shallow crust. Results of this type of modeling could give us real insights into what type of things we should look for if magma is moving into shallower depths.”
“We still have a lot to learn about the volcano but I think we are really getting a good picture of this volcano,” the Utah seismologist added, “and I believe that these types of findings will help us better understand not only Yellowstone, but other volcanic systems as well… We are not quite there yet but this is a big step in the right direction.”
No increased risk of an eruption
Contrary to popular belief, the magma chamber and reservoir are not filled with molten rock, the study authors explained in a statement. Rather, the majority of the rock there is hot, largely solid, and spongelike with just a few pockets of molten rock. According to the study, the upper magma chamber contains an average of about nine percent molten rock (previous estimates had placed it as between five and 15 percent) while the lower one is approximately two percent melt.
Huang, Farrell and their colleagues pointed out that the volcano’s plumbing system is no larger and no closer to erupting than previously believed. However, thanks to advanced technology, the seismologists said that they were able to create a complete and detailed image of the system that carries molten rock upward from the top of Yellowstone’s plume (located 40 miles underground) to the magma reservoir and the magma chamber located above it.
Neither the magma chamber nor the reservoir are growing larger, Farrell said, but the team was able to see them better than ever before using new imaging techniques. Likewise, Utah professor and study co-author Robert B. Smith noted that the “actual hazard is the same, but now we have a much better understanding of the complete crustal magma system.”
Exploring the anatomy of a supervolcano
Prior to this new researcher, experts believed that the Yellowstone volcano features partially molten rock moving upwards from the hotspot plume through either a series of horizontal and vertical cracks (also known as sills and dikes), or as blobs. They still believe that these cracks move hot rock from the plume head to the reservoir, then to the shallow magma chamber.
At the bottom of the Yellowstone system is a plume that originates from depths of at least 440 miles in Earth’s mantle, and perhaps as much as 1,800 miles deep within the planet’s core. The plume conduit is roughly 50 miles wide as it comes up through the mantle, then spreads out. A previous study said that the plume head was 300 miles wide, but the new study suggests that it could be smaller than that. The Utah team’s data cannot say for certain.
Hot, partially molten rock rises in dikes from the top of the plume to the bottom of the newfound reservoir, which measures 30 miles northwest to southeast and 44 miles southwest to northeast. The 2,500-cubic mile upper magma chamber rests below the volcano’s 40-by-25-mile caldera, or giant crater. Farrell said that it is said to be shaped like a giant frying pan located about three to nine miles beneath the surface, with its so-called handle rising towards the northeast.
The shallow magma chamber was once believed to be 1,000 cubic miles, but Farrell and Smith showed earlier this year that it is actually 2.5-times larger than that, a finding which is supported by the new study. Also, the magma reservoir discovery – which was made using seismic imaging methods similar to medical CT scans – explains why Yellowstone’s soil and geothermal features emit more CO2 than can be explained by gases from the magma chamber, the authors said.
Check out our video on the topic: Seismologists discover deeper Yellowstone magma