Wednesday, April 6, 2022

New Study Models Old Faithful

Finn, C.A., Bedrosian, P.A., Holbrook, W.S. et al. Geophysical imaging of the Yellowstone hydrothermal plumbing system. Nature 603, 643–647 (2022).

from VA Tech and USGS the imaging equipment

Many of us have childhood memories in the days before life was digital of road trips across America to visit Yellowstone National Park and see the eruptions of Old Faithful, the bubbling mud cauldrons of Artists Paint Pots, the crystal-clear water and iridescent colors of Grand Prismatic Spring, and the stacked travertine terraces of Mammoth Hot Springs. These wonders of the natural world 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 National Park. 

Now, in a newly published study Scientists from the U.S. Geological Survey, Virginia Technical University, and Aarhus University in Denmark used a combined electrical and magnetic mapping technique deployed using a helicopter to see beneath the surface and reveal some of the secrets of the park hidden almost a mile beneath the ground. 

The survey technique took advantage of the fact that water is a much better electrical conductor than rock. They used a sensitive electromagnet to measure variations in electrical conductivity and magnetic properties between wet and dry rock. The electromagnet was an 80-foot-wide hoop dangling beneath a low-flying helicopter that crisscrossed the park for weeks, mapping the water below ground. The USGS described it as being like a medical CAT scan building an image using data from a set of surface detectors. The really hard part was building the model to translate the data gathered into a tangible three dimensional image.  

It took years of work to produce the images that show the park’s geology profoundly shapes its hot springs. Hot hydrothermal fluids ascend nearly vertically, from depths of more than 1 kilometer to arrive at the park’s major hydrothermal fields. Along the way, they mix with shallower groundwater flowing within and beneath the park’s volcanic lava flows, which also are visible in the images. Faults and fractures are the pathways of the hydrothermal waters, while lava flow boundaries control the shallow groundwater aquifers. As fluids travels up to the surface, local constrictions in the pathways help induce boiling, degassing or conductive cooling that produce the varying and wonderous thermal features at Yellowstone National Park. 

Knowing how it works does not reduce the wonder of its existence.  

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