Old Faithful, Grand Prismatic Spring, Mammoth Hot Springs, Mud Volcano and Morning Glory Pool are just a few of the over 10,000 active hydrothermal features formed by the interaction of ground water with the heat remaining from the ancient volcano that formed Yellowstone. While these mesmerizing features are enjoyed by millions of visitors every year, the underground plumbing system has been mostly hidden. Until now.
Scientists from the U.S. Geological Survey, Virginia Technical University, and Aarhus University in Denmark used a combined electrical and magnetic mapping technique deployed on a helicopter to reveal this system across the entire park and to depths of 1-2 miles. The detail provided by this approach reveals the paths of fluids through each part of the system.
“This is the first time we’ve been able to create images of the subsurface plumbing system that feeds so many of the amazing features of Yellowstone,” said Carol Finn, USGS research geophysicist and first author. “It’s also one of the largest and highest-resolution airborne geophysical surveys over a hydrothermal area in the world.”
The survey technique took advantage of the fact that water is a much better electrical conductor than rock, by using a sensitive electromagnet to measure variations in electrical conductivity and magnetic properties between wet and dry rock. The instrument was deployed on an 80-foot-wide hoop dangling beneath a low-flying helicopter as it crisscrossed the park for weeks, mapping out water at depth. This was comparable to a medical CAT scan using data from a set of surface detectors. Flying the survey was only part of the challenge and translating all the data into something tangible took years of painstaking work.
“We generated more than 100,000 models spanning the entire park – but it’s the overarching view from poring over them all that gives us insight into what controls the nature and distribution of the Park’s thermal features,” said Paul Bedrosian, a co-author who led the modeling effort. “It boils down to three factors – where the underlying magma resides, the location of fractures and faults, and the elevation of the surface relative to groundwater.”
The models show most thermal features are located above buried faults and fractures that act as fluid conduits. Shallow horizontal pathways contribute colder groundwater into the system, which mixes with hot fluids from the conduits. As fluids ascend toward the surface, local constrictions help induce boiling, degassing or conductive cooling that produce the diversity of thermal features at Yellowstone National Park.
The study’s models and original data have allowed other scientists to expand upon the findings with new studies across a range of disciplines. This includes microbiologists looking at microbiological diversity in groundwater, geologists mapping lava flows and estimating eruptive volumes, hydrologists modeling flow paths and groundwater, and economic geologists who study the formation of gold deposits.
“Observations and results from this study can be used by scientists from around the world to better understand how Yellowstone’s hydrothermal systems work and their influences on biology, ecology, geology and hazards,” said Mike Poland, Scientist-in-Charge at the USGS Yellowstone Volcano Observatory. “Without the new geophysical data, we had no way of knowing these pathways existed.”
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