New study of Yellowstone National Park shines new light on once hidden
details of the famous American landmark

Date:
March 23, 2022
Source:
Virginia Tech
Summary:
Those who have visited the park may have asked themselves, 'Where
does all the hot water come from?' A study now provides stunning
subsurface images that begin to answer that question.



FULL STORY ==========================================================================
The geysers and fumaroles of Yellowstone National Park are among the most iconic and popular geological features on our planet. Each year, millions
of visitors travel to the park to marvel at the towering 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.


========================================================================== Those who have visited the park may have asked themselves, "Where does
all the hot water come from?" A study published this week in Nature, co-authored by Virginia Tech's W. Steven Holbrook and colleagues from
the U.S. Geological Survey and Aarhus University in Denmark, provides
stunning subsurface images that begin to answer that question.

The research team used geophysical data collected from a helicopter
to create images of Yellowstone's subsurface "plumbing" system. The
method detects features with unusual electrical and magnetic properties indicative of hydrothermal alteration.

"The combination of high electrical conductivity and low magnetization is
like a fingerprint of hydrothermal activity that shows up very clearly
in the data," said Holbrook, a professor of geophysics and head of the Department of Geosciences in Virginia Tech's College of Science. "The
method is essentially a hydrothermal pathway detector." Images from the
study show that the park's geology profoundly shapes its hot springs. Hot hydrothermal fluids ascend nearly vertically, from depths of more than
1 km (or .62 miles), 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 guide the ascent of hydrothermal waters,
while lava flow boundaries control the shallow groundwater aquifers.

The project fills in a longstanding knowledge gap about the underpinnings
of Yellowstone's charismatic hydrothermal features. Much is known about
the park's surface hydrothermal features, including the chemistry and temperature of mud pots and springs, the eruption interval of geysers, and
the unique thermophilic bacteria that live in and around those features.



========================================================================== Likewise, scientists have a growing body of knowledge about the deeper
heat sources and tectonic activity by tracking earthquakes that occur
there. But little is known about how the surface hydrothermal features
are connected to each other and to the deeper sources of heat and fluids.

"Our knowledge of Yellowstone has long had a subsurface gap," Holbook
said.

"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. This project has enabled
us to fill in those gaps for the first time." To collect the data,
the team used a unique instrument called "SkyTEM" that consists of a
large loop of wire towed beneath a helicopter. As the helicopter flies,
the loop sends downward repeated electromagnetic signals that provoke
a response from electrically conductive bodies in the subsurface.

That response is recorded and later analyzed to produce detailed
cross-sections along the flight lines. The technique is highly effective
in environments like Yellowstone: hydrothermal fluids alter the rocks
they pass through, turning rock into clay minerals -- for example,
the surface mud pots -- that have heightened electrical conductivity
but suppressed magnetization.

Because the helicopter is able to travel at speeds of 40 to 50 mph while
towing the SkyTEM instrument, scientists involved in the study were able
to cover large swaths of the sprawling, 3,500-square-mile national park, Holbrook said.



==========================================================================
"One of the unique aspects of this dataset is its extensive coverage of
this huge system," Holbrook added. "We were able not just to look deep
beneath the hydrothermal features, but also to see how adjacent features
might be connected in the subsurface across great distances. That's never
been possible before." One of the mysteries addressed by the new work
is whether different hydrothermal areas in the park show contrasting
deep fluid sources and pathways. The team found a remarkable similarity
in the deep structure beneath areas such as Norris Geyser Basin and
Lower Geyser Basin, suggesting that contrasts in the chemistry and
temperatures of those areas are not caused by deep processes. Instead,
variable degrees of mixing with shallow groundwater likely create the
wide variety of hot spring characteristics in the park.

Overall, the project generated more than 2,500 miles of helicopter lines,
an enormous amount of data, according to Holbrook. Upon the study's
publication last month, the research team released the data so that
others can undertake additional research.

"The data set is so big that we've only scratched the surface with this
first paper," Holbrook added. "I look forward to continuing to work on
this data and to seeing what others come up with, too. It's going to
be a data set that keeps on giving." Before coming to Virginia Tech in
2017, Holbrook was part of the Department of Geology and Geophysics at
the University of Wyoming in Laramie, Wyoming. He also co-directed the
Wyoming Center for Environmental Hydrology and Geophysics.

He said, "I've made several field trips to collect ground-based
geophysical data in Yellowstone. The airborne data covers a lot
more ground much more quickly than we could by hiking gear into the backcountry, though." Carol Finn of the U.S. Geological Survey and
lead author on the study said, "While the airborne data were still being collected, we saw the first images over Old Faithful and knew instantly
that our experiment had worked -- that we could, for the first time,
image the fluid pathways that had long been speculated." She added,
"Our work has sparked considerable interest across a range of disciplines, including biologists looking to link areas of groundwater and gas mixing
to regions of extreme microbiological diversity, geologists wanting to
estimate volumes of lava flows, and hydrologists interested in modeling
flow paths of groundwater and thermal fluid. With the paper as a guide
and the release of the data and models, we will enable research in these diverse scientific communities." One mystery that Holbrook is interested
in pursuing further is evidence for distant connections between isolated surface hydrothermal areas. The SkyTEM data show evidence for subsurface linkages between hydrothermal systems that are up to 6 miles apart.

"That might have implications for the co-evolution of thermophilic
bacteria and Archaea," Holbrook said. "The notion that airborne
geophysical data could illuminate something about the life of microscopic organisms living around hot springs is a fascinating idea."

========================================================================== Story Source: Materials provided by Virginia_Tech. Note: Content may be
edited for style and length.


========================================================================== Related Multimedia:
* SkyTEM_instrument_being_flown_over_Old_Faithful ========================================================================== Journal Reference:
1. Carol A. Finn, Paul A. Bedrosian, W. Steven Holbrook, Esben Auken,
Benjamin R. Bloss, Jade Crosbie. Geophysical imaging of the
Yellowstone hydrothermal plumbing system. Nature, 2022; 603 (7902):
643 DOI: 10.1038/ s41586-021-04379-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220323125112.htm

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