Using vibrations to see into Yellowstone's magma reservoir
Utah geophysicists locate the top of the potentially explosive underground formation that drives Yellowstone's hydrothermal features
University of Utah
image:
Portable seismometer deployed at Yellowstone.
view moreCredit: Jamie Farrell, University of Utah
Beneath Yellowstone lies a magma reservoir, pulsing with molten and superheated rock and exsolved gases. Scientists have long known about the chamber’s existence, but have yet to precisely locate its uppermost boundary and characterize the contents of the chamber closest to the surface—information crucial for understanding the potential perils this volcanic feature poses.
That changed this week with new research by seismologists from the University of Utah and the University of New Mexico (UNM) who used hundreds of portable seismometers and a mechanical vibration source to render 2D seismic reflection images of the ground beneath Yellowstone’s caldera.
Using artificial seismic waves, the team determined that the top of the chamber is 3.8 kilometers, or about 12,500 feet, below Earth’s surface, and it is sharply delineated from the rock strata above, according to findings published in the journal Nature. The researchers also determined the portion of the uppermost magma chamber that is comprised of volatile gases and liquids.
“The depth of 3.8 kilometers is important,” said coauthor Jamie Farrell, a U research associate professor of geology and geophysics and chief seismologist for the Yellowstone Volcano Observatory, operated by the U.S. Geological Survey. “We know what pressures are going to be and how bubbles are going to come out of the magma. One thing that makes these eruptions so devastating is that if gases are trapped, they become very explosive as they decompress.”
The good news is that these findings indicate the long-dormant Yellowstone Volcano is in no immediate danger of eruption.
This is because much of the volatile gas released from the magma escapes through Yellowstone’s surface geothermal features, such as Mud Volcano, without accumulating to dangerous levels, according to coauthor Fan-Chi Lin, professor in Utah’s Department of Geology & Geophysics.
“When the magma rises from the deeper crust, volatile materials such as CO2 and H2O exsolve from the melt. Due to their buoyancy, they tend to accumulate at the top of the magma chamber,” he said. “But if there’s a channel, they can escape to the surface.”
A high-silica type of igneous rock called rhyolite makes up Yellowstone’s magma chamber, which spans an area 55 miles by 30 miles, dropping to a depth of 10 miles below the surface. Beneath it is an even larger reservoir made of low-silica basalt and containing far less molten rock, according to a University of Utah study published in 2015 in Science.
The volcano blew catastrophically 630,000 years ago and many wonder if it’s getting ready for another eruption. Such fears are unwarranted, and the new findings are further evidence of that, according to Farrell.
For decades, scientists have studied Yellowstone’s intriguing magmatic system that drives the geysers, mudpots and thousands of other hydrothermal features that draw millions of visitors to Yellowstone National Park each year.
The U’s Seismograph Stations oversee a network of fixed seismometers at Yellowstone to monitor its frequent earthquakes. Seismic waves from these natural events have long helped scientists characterize the magma chamber, similar to the way CT scans image tissue inside the human body, but the representations are blurry. To achieve greater resolution in the new study, Farrell and Lin’s team deployed an array of 650 portable geophones along Yellowstone National Park’s roads at 100- to 150-meter intervals. Instead of waiting for earthquakes to happen, they brought in a Vibroseis truck, typically used in oil and gas exploration to image subsurface formations and deposits.
“In a sense, we're causing our own earthquakes, and we record all that data on the seismometers,” Farrell said. “And since we put so many out, we can get a higher resolution image of the subsurface.”
The team vibrated the ground at 110 locations, delivering 20 treatments lasting 40 seconds each.
Seismic waves propagate in two forms, known as S-waves and P-waves, which travel at different speeds and behave differently when they strike molten rock. Leveraging the properties of these waves, the researchers were able to locate the top of the chamber and determined that 86% of the upper portion is solid rock, with pore spaces comprising the remaining 14%. These pore spaces are about half filled with molten material and half with volatile gases and liquid, the researchers discovered.
This research is providing crucial clues about the structure of the magma body, according to USGS’s Mike Poland, the scientist in charge at the Yellowstone Volcano Observatory.
“That helps us understand more about the heat engine that's powering Yellowstone and about how melt is distributed. That can have ramifications for how we perceive the volcanic hazard,” he said. “Yellowstone in many ways is a laboratory volcano, and what we learn at Yellowstone can be used to better understand volcanoes in other parts of the world that are a lot more active, but are harder to study. Examples might be Campi Flegrei in Italy or Santorini in Greece, which is mostly submarine.”
He likened recent breakthroughs in seismic imaging to advances in digital cameras that have enabled vast leaps in photographic resolution. Prior studies, which relied on natural seismic events, led by Farrell, Lin, and other seismologists, pictured the magma chamber as an “amorphous blob” beneath Yellowstone. Now it’s coming into sharper focus with the help of artificially generated seismic waves.
“Over the years, different techniques have used the older data, and then there have been new data collection efforts like the one that in geoscientists from Utah and New Mexico that have allowed for increased resolution,” Poland said. “Similar techniques are being used in other places where you put out huge numbers of seismometers and then you record both the background earthquakes and you make your own seismic energy, which allows you to target specific things. These developments are allowing us to see into volcanoes in just really unprecedented ways.”
The study, titled “A sharp volatile-rich cap to the Yellowstone magmatic system,” was published April 16 In the journal Nature. The research was supported by grants from the National Science Foundation and the Brinson Foundation. Lead authors include Chenglong Dan and Wenkai Song of the University of New Mexico and Brandon Schmandt of Rice University.
Read more about University of Utah’s geophysical research on the Yellowstone magma chamber and hydrothermal features.
U scientists plumb the depths of the world’s tallest geyser
A pool at Yellowstone is a thumping thermometer
Scientists see a deeper Yellowstone magma
A Vibroseis rig at work in Yellowstone National Park. To avoid disturbing park visitors, researchers used this equipment, which propagates artificial seismic waves through the ground, at night.
Credit
Jamie Farrell, University of Utah.
Journal
Nature
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
A sharp volatile-rich cap to the Yellowstone magmatic system
Article Publication Date
16-Apr-2025
Inside Yellowstone’s fiery heart: Rice University researchers map volatile-rich cap, offering clues to future volcanic activity
Rice University
image:
Brandon Schmandt and Chenglong Duan (Photo credit: Linda Fries/Rice University).
view moreCredit: Linda Fries/Rice University
Beneath the steaming geysers and bubbling mud pots of Yellowstone National Park lies one of the world’s most closely watched volcanic systems. Now a team of geoscientists has uncovered new evidence that sheds light on how this mighty system may behave in the future — and what might keep it from erupting. The findings were recently published in Nature.
A team of researchers from Rice University, University of New Mexico, University of Utah and the University of Texas at Dallas have discovered a sharp, volatile-rich cap just 3.8 kilometers beneath Yellowstone’s surface. This cap, made of magma, acts like a lid, helping to trap pressure and heat below it. Using innovative controlled-source seismic imaging and advanced computer models, their findings suggest that the Yellowstone magma reservoir is actively releasing gas while remaining in a stable state.
The research, led by Rice’s Chenglong Duan and Brandon Schmandt along with collaborators, provides new insight into how magma, volatiles and fluids move within Earth’s crust. The project was supported by the National Science Foundation.
“For decades, we’ve known there’s magma beneath Yellowstone, but the exact depth and structure of its upper boundary has been a big question,” said Schmandt, professor of Earth, environmental and planetary sciences. “What we’ve found is that this reservoir hasn’t shut down — it’s been sitting there for a couple million years, but it’s still dynamic.”
Previous studies suggested the top of Yellowstone’s magma system could lie anywhere from 3 to 8 kilometers deep — an uncertainty that left geologists debating how the magma system today compares with conditions before prior eruptions.
That changed after Schmandt conducted a high-resolution seismic survey in the northeastern part of the caldera. A 53,000-pound vibroseis truck — typically used for oil and gas exploration — essentially generated tiny earthquakes to send seismic waves into the ground. These waves reflected off subsurface layers and were recorded at the surface, revealing a sharp boundary at about 3.8 km depth.
“The motivation behind my research is to advance structural seismic imaging beyond the limits of conventional travel-time methods,” said Duan, a postdoctoral research associate. “Using a wave-equation imaging technique I developed during my Ph.D. for irregular seismic data, we made one of the first super clear images of the top of the magma reservoir beneath Yellowstone caldera.”
“Seeing such a strong reflector at that depth was a surprise,” Schmandt said. “It tells us that something physically distinct is happening there — likely a buildup of partially molten rock interspersed with gas bubbles.”
To better understand what causes this signal, Duan and Schmandt modeled various rock, melt and volatile combinations. The best match they determined is a mixture of silicate melt and supercritical water bubbles within a porous rock matrix resulting in a volatile-rich cap with about 14% porosity, half of which is occupied by fluid bubbles.
As magma rises and decompresses in volcanic systems, gases like water and carbon dioxide exsolve from the melt, forming bubbles. In some cases, these bubbles can accumulate, increasing buoyancy and potentially driving explosive eruptions.
But present conditions at Yellowstone appear to tell a different story.
“Although we detected a volatile-rich layer, its bubble and melt contents are below the levels typically associated with imminent eruption,” Schmandt said. “Instead, it looks like the system is efficiently venting gas through cracks and channels between mineral crystals, which makes sense to me given Yellowstone’s abundant hydrothermal features emitting magmatic gases.”
Schmandt likened the system to “steady breathing” with bubbles rising and releasing through the porous rock — a natural pressure-release valve that lowers eruption risk.
Getting these results was anything but easy. The research team not only completed the field survey in the midst of the COVID-19 pandemic, but they also had to coordinate the project within a busy and carefully protected national park. This meant they could only operate the heavy vibroseis truck at night and only from designated roadside turnouts. More than 600 seismometers were temporarily deployed to record the vibroseis truck signals, then recovered a few weeks later. Collaboration with University of Utah professor Jamie Farrell, a Yellowstone geophysics expert and seismic network operator, was essential to making this unusual survey possible, Schmandt said.
Processing the data proved just as difficult. Yellowstone’s complex geology — known for scattering seismic waves — produced noisy data that were initially hard to interpret. But with persistence and many discussions with Schmandt, Duan said he kept going, refining his approach again and again until the numbers finally told a clear story.
“The challenge was that the raw data made it almost impossible to visualize any reflection signals,” Duan said. “We used the STA/LTA function to enhance coherent seismic reflections, and this was the first time we had innovatively applied STA/LTA data within the wave-equation imaging algorithm.”
Duan said that just like traversing the rocky landscape of Yellowstone, tenacity is key for navigating its mysteries underground.
“When you see noisy, challenging data, don’t give up,” Duan said. “After we realized the standard processing was not going to work, that’s when we got creative and adapted our approach.”
By identifying this sharp, volatile-rich cap beneath Yellowstone, Schmandt’s team has established a new benchmark for monitoring the volcano’s activity. Future research could attempt to detect any shifts in melt content or gas accumulation that may serve as early warning signs of unrest.
Beyond Yellowstone, the study offers broader insights into onshore subsurface imaging with potential applications not only for volcano monitoring but also for carbon storage, energy exploration and hazard assessment.
“Being able to image what’s happening underground is important for everything from geothermal energy to storing carbon dioxide,” Schmandt said. “This work shows that with creativity and perseverance, we can see through complicated data and reveal what’s happening beneath our feet.”
Journal
Nature
Article Title
A sharp volatile-rich cap to the Yellowstone magmatic system
Article Publication Date
16-Apr-2025
