Evolution of Cascadia Landscapes: Drainage Reorganization Inferred from Topographic Transformations and Dendrochronological Dating of Landslide-Dammed Lakes
| dc.contributor.advisor | Roering, Joshua | |
| dc.contributor.author | Struble, William | |
| dc.date.accessioned | 2021-04-27T20:45:05Z | |
| dc.date.available | 2021-04-27T20:45:05Z | |
| dc.date.issued | 2021-04-27 | |
| dc.description.abstract | Landscapes evolve through the contributions of uplift and erosion over myriad spatiotemporal scales. Over long timescales (>103 yr), tectonics and climate set landscape and drainage basin form. Over societally relevant timescales essential for quantifying hazards, earthquake-triggered landslides directly link active tectonics and surface processes. In this dissertation, I clarify the timing of bedrock landsliding as well as the scale of landforms responsible for setting the geometry and position of drainage divides throughout the Cascadia forearc.Despite the presence of >20,000 mapped bedrock landslides in the Oregon Coast Range (OCR), no single slope failure has been definitively linked with the last major Cascadia Subduction Zone (CSZ) earthquake, which occurred in January 1700 AD. I utilize dendrochronology of 'ghosts forests' at landslide-dammed lakes, which provides seasonal accuracy, to establishing the timing of dam emplacement. In Chapter II, I determine that the landslides that formed Klickitat and Wasson Lakes, Oregon, occurred in the winters of 1751/52 and 1819/20, respectively. I additionally demonstrate that, while 14C dating of landslides has corroborative power, landslide ages are ambiguous and sometimes thousands of years too old when using 14C alone. I build on this dendrochronological technique in Chapter III to establish the timing of 20 landslides in the OCR. None of these landslides date to 1700 AD. Notably, however, at least 4 landslide dams temporally cluster to the winter of 1889/90 AD, coincident with regionally significant flooding likely triggered by a series of atmospheric rivers. I further establish that landslide dams are preferentially preserved at small to intermediate catchment areas and valley widths, where large wood accumulated upstream of landslide deposits armors the dams. Finally, in Chapter IV, I consider how long-wavelength landforms set drainage basin extent and stability. I utilize continuous wavelet transforms to observe that at wavelengths >~30 km, the Willamette Valley extends along the entire CSZ, a landform I term the Cascadia Forearc Lowland (CFL). Further, by smoothing topography to progressively longer wavelengths, I establish that synthetic drainage networks consolidate into margin-parallel rivers at wavelengths >30 km, coincident with the CFL and in agreement with field observations of stream capture. This dissertation includes previously published and unpublished co-authored material. | en_US |
| dc.identifier.uri | https://hdl.handle.net/1794/26189 | |
| dc.language.iso | en_US | |
| dc.publisher | University of Oregon | |
| dc.rights | All Rights Reserved. | |
| dc.subject | Dendrochronology | en_US |
| dc.subject | Drainage Reorganization | en_US |
| dc.subject | Landslides | en_US |
| dc.subject | Subduction Zones | en_US |
| dc.subject | Tectonics | en_US |
| dc.subject | Wavelets | en_US |
| dc.title | Evolution of Cascadia Landscapes: Drainage Reorganization Inferred from Topographic Transformations and Dendrochronological Dating of Landslide-Dammed Lakes | |
| dc.type | Electronic Thesis or Dissertation | |
| thesis.degree.discipline | Department of Geological Sciences | |
| thesis.degree.grantor | University of Oregon | |
| thesis.degree.level | doctoral | |
| thesis.degree.name | Ph.D. |
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