Spatial patterns of bedrock weathering at the hillslope scale inferred via drilling and multi-scale geophysical methods

dc.contributor.advisorRempe, Daniella M.
dc.contributor.committeeMemberPaine, Jeffrey G.
dc.contributor.committeeMemberTisato, Nicola
dc.creatorLee, Shawn S.
dc.creator.orcid0000-0002-6782-8916
dc.date.accessioned2018-10-12T17:17:29Z
dc.date.available2018-10-12T17:17:29Z
dc.date.created2018-08
dc.date.issued2018-08-17
dc.date.submittedAugust 2018
dc.date.updated2018-10-12T17:17:30Z
dc.description.abstractThe critical zone (CZ) comprises the near-surface region of the Earth where biological, physical and chemical weathering processes form porous soil and weathered bedrock from initially fresh bedrock. The structure of the CZ plays an integral role in near-surface processes including water cycling, however this subsurface structure is unmapped relative to surface topography, outside of isolated boreholes, road cuts, and landslides. Here, we characterize this structure and its variability within the Coastal Belt of the Franciscan in the Northern California Coast Ranges to test the hypothesis that there exists a relationship between weathering profile structure and topography. We compare spatially detailed data from boreholes from the Eel River Critical Zone Observatory (ERCZO) with surface seismic refraction and electrical resistivity surveys to develop the most probable seismic velocities associated with interfaces between (1) saprolite and weathered bedrock and (2) weathered and fresh bedrock. P-wave velocities calculated via regression ranged from 350-610 m/s for saprolite and soil, 610-1910 m/s for weathered bedrock, and > 1910 m/s for fresh bedrock. Extending these results to three hillslopes lacking borehole data reveals a common weathering profile structure, whereby weathering depth increases upslope across hillslopes and weathering thickness is roughly parallel to the ground surface along ridgelines. The maximum thickness of weathering, at the topographic divide, appears to scale with hillslope length. Significant seismic anisotropy, reflecting dominant bedding or fracture orientation, is evident in a subset of transects. Electrical resistivity tomograms reveal a consistent, shallow 2-8 m resistive layer associated with the weathered bedrock vadose zone underlain, in many cases, by a conductive zone which we propose reflects a seasonal groundwater system within weathered bedrock. Our seismic and electrical imaging therefore reveals a consistent structure across different hillslopes. In this tectonically active environment, we find that weathering profiles penetrate deeply beneath hillslopes in a broadly systematic pattern. This suggests consistency in weathering process across the landscape that operates at the hillslope scale where channels remain fresh and ridgetops show deep weathering.
dc.description.departmentEarth and Planetary Sciences
dc.format.mimetypeapplication/pdf
dc.identifierdoi:10.15781/T2RX93Z69
dc.identifier.urihttp://hdl.handle.net/2152/68881
dc.language.isoen
dc.subjectSeismic
dc.subjectRefraction
dc.subjectResistivity
dc.subjectTomography
dc.subjectRegression
dc.subjectBorehole
dc.subjectMoisture
dc.subjectHillslope
dc.subjectTopography
dc.titleSpatial patterns of bedrock weathering at the hillslope scale inferred via drilling and multi-scale geophysical methods
dc.typeThesis
dc.type.materialtext
thesis.degree.departmentGeological Sciences
thesis.degree.disciplineGeological sciences
thesis.degree.grantorThe University of Texas at Austin
thesis.degree.levelMasters
thesis.degree.nameMaster of Science in Geological Sciences

Access full-text files

Original bundle

Now showing 1 - 1 of 1
Loading...
Thumbnail Image
Name:
LEE-THESIS-2018.pdf
Size:
7.73 MB
Format:
Adobe Portable Document Format

License bundle

Now showing 1 - 2 of 2
No Thumbnail Available
Name:
PROQUEST_LICENSE.txt
Size:
4.45 KB
Format:
Plain Text
Description:
No Thumbnail Available
Name:
LICENSE.txt
Size:
1.84 KB
Format:
Plain Text
Description: