Scientists at Virginia Tech and U.S. Geological Survey used an 80-foot diameter electromagnet to survey the subsurface of the Yellowstone National Park and learn more about the water system, a press release said.
The Yellowstone National Park is a geologic feature that barely needs an introduction. Millions of visitors travel to this site every year to see bubbling mud cauldrons, crystal clear waters, and the brilliant colors of the Grand Prismatic Spring. The towering eruptions of water at the Old Faithful are also a huge attraction but also add intrigue to the visit when one wonders where does the water come from?
Probing the subsurface
"Our knowledge of Yellowstone has long had a subsurface gap,” Steven Holbrook, Professor of Geosciences at Virginia Tech explained. “It’s like a ‘mystery sandwich’ — we know a lot about the surface features from direct observation and a fair amount about the magmatic and tectonic system several kilometers down from geophysical work, but we don’t really know what’s in the middle."
To find out, the team used a unique instrument called SkyTEM which is a large loop of wire towed below a helicopter. The loop's diameter was 80 feet and by sending electricity through it, the researchers created electromagnetic pulses that were sent towards the subsurface and received responses from electrically conductive bodies therein.
Since a helicopter can travel at speeds of 40-50 mph, the researchers were able to quickly survey large swaths of the 3,500-mile national park. The data they gathered consists of more than 2,500 miles of helicopter lines that not only look beneath the hydrothermal features in the park but also how these features are connected over great distances.
The 'Plumbing' at Yellowstone
Data captured by the team of scientists shows that the hot springs at the park are a result of the site's geology. Faults and fractures in the subsurface contribute to how the hydrothermal waters rise from more than half a mile from under the ground in near-vertical ascents.
Beneath the park's volcanic flows are shallower groundwater aquifers that are controlled by the lava boundaries but mix with hot water rising from the depths as it shoots towards the sky.
The new research also sheds light on different chemistries and temperatures that have been seen at different sites within the Park. While these were earlier thought to be a result of unknown deep processes, subsurface data from the site has shown that the differences are just a result of variations in the mixing of shallow groundwater. Interestingly, the data shows that hydrothermal systems in the Park that are up to six miles apart are also linked to each other.
The data has also sparked interest from other scientific disciplines such as biologists and hydrologists that have previously studied the site extensively. Findings from the data have been published in the journal Nature.
Abstract: The nature of Yellowstone National Park’s plumbing system linking deep thermal fluids to its legendary thermal features is virtually unknown. The prevailing concepts of Yellowstone hydrology and chemistry are that fluids reside in reservoirs with unknown geometries, flow laterally from distal sources and emerge at the edges of lava flows1,2,3,4. Here we present a high-resolution synoptic view of pathways of the Yellowstone hydrothermal system derived from electrical resistivity and magnetic susceptibility models of airborne geophysical data5,6. Groundwater and thermal fluids containing appreciable total dissolved solids significantly reduce resistivities of porous volcanic rocks and are differentiated by their resistivity signatures7. Clay sequences mapped in thermal areas8,9 and boreholes10 typically form at depths of less than 1,000 metres over fault-controlled thermal fluid and/or gas conduits11,12,13,14. We show that most thermal features are located above high-flux conduits along buried faults capped with clay that has low resistivity and low susceptibility. Shallow subhorizontal pathways feed groundwater into basins that mixes with thermal fluids from vertical conduits. These mixed fluids emerge at the surface, controlled by surficial permeability, and flow outwards along deeper brecciated layers. These outflows, continuing between the geyser basins, mix with local groundwater and thermal fluids to produce the observed geochemical signatures. Our high-fidelity images inform geochemical and groundwater models for hydrothermal systems worldwide.