James St. Clair, a UW doctoral student, is lead author of
the paper, titled “Geophysical Imaging Reveals Topographic Stress Control of
Bedrock Weathering.” Steve Holbrook, a
professor of geology and geophysics; Cliff Riebe, an associate professor of
geology and geophysics; and Brad Carr, a research scientist in geology and
geophysics, are co-authors of the paper.
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| James St. Clair |
Geophysical imaging of the subsurface was conducted by UW’s
Center for Environmental Hydrology and Geophysics (WyCEHG). Scientists at MIT and the University of
Hawaii contributed numerical models of the stress distribution in the
subsurface.
Geophysical imaging uses different tools to create a
detailed picture of the composition, shape, and density of subsurface rock strata. Scientists can use a variety of technologies
to take measurements, and then combine those measurements into maps of the
mountain surface and interior. The team
performed seismic refraction and electrical resistivity surveys to look at the
depth to bedrock at three mountain
sites. These three sites were chosen
because they showed variant, or different, regimes of
mountain topography and tectonic stress.
Researchers used geophysical surveys to estimate the volume
of open pore space in the subsurface.
This is an indication of how much water the subsurface can hold. Computer models showing the state of stress
at those sites showed striking correlation with open pore space
measurements. This means that scientists
may be able to use measurements of the stress in the earth’s crust to see where
water can be stored. Stress in the earth’s crust creates fractures in the
earth’s subsurface, and those fractures create space to hold water.
“We found a
remarkable agreement between the predictions of those stress models and the
images of the porosity in the subsurface with geophysics at a large scale, at
the landscape scale,” Holbrook says.
“It’s the first time anyone’s really looked at this at the landscape scale.”
St. Clair is excited to be publishing research in Science, a prestigious scientific
journal. He feels lucky to work with
such a talented, experienced group of scientists. He believes that these results may be
extremely useful to hydrologists, geomorphologists, and geophysicists.
Steve Holbrook adds that there is still a lot of work to be
done to test this model in different environments. However, he says, “Now we have a theoretical
framework to guide that work, as well as unique geophysical data to suggest
that the hypothesis has merit.”
Written by Jess White
Written by Jess White
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