| Abstrakt: |
Variations in uplift, erosion, climate, and bedrock are commonly invoked as key controls on drainage basin morphology, yet the scale of landforms that define changes in regional drainage networks has not been addressed, limiting our ability to predict their planform evolution. Here we use two‐dimensional (2D) continuous wavelet transforms of topography in Cascadia to highlight dominant topographic features at different scales. Surprisingly, our wavelet analysis shows that for wavelengths >30 km, the Cascadia Forearc Lowland (CFL) spans the entire margin. Separately, we compare observed catchment boundaries with synthetic boundaries generated on topography filtered with 2D Gaussian functions. We observe reorganization of synthetic drainage networks from an arc‐to‐coast drainage system into arc‐spanning, margin‐parallel river systems, akin to the modern Willamette River and coincident with the CFL. In concert with field observations of stream capture and Willamette Valley expansion, we propose that the Cascadia forearc is actively transitioning to a predominately margin‐parallel river system. Plain Language Summary: River networks form as a result of the cumulative effects of bedrock uplift and erosional processes. Spatial variations in uplift, climate, and bedrock erodibility are typically considered to be the primary controls on the extent of drainage basins, yet the scale of landforms associated with drainage reorganization have not been systematically addressed. Here, we apply several filtering and topographic transformation techniques (two‐dimensional continuous wavelet transforms and Gaussian filters) to extract landforms of variable scale and compare them to synthetic drainage networks in the Cascadia forearc. We observe that drainage networks mapped on filtered topography highlight growth of the Cascadia Forearc Lowland at scales >30 km. Integration of these "synthetic" drainage networks into a margin‐parallel river system, similar to the modern Willamette Valley, supports field observations of stream capture and river network reorganization. We propose that these methods are useful for predicting future drainage configurations and isolating the relevant tectonic processes responsible for changing river networks. Key Points: Continuous wavelet transforms reveal the dominant landforms defined by different wavelengthsSynthetic drainages reveal that Cascadia is transitioning to a margin‐parallel river system, supported by field observations of captureThe Jaccard Similarity Index quantifies the scale‐dependency of drainage network boundaries as topographic wavelength increases [ABSTRACT FROM AUTHOR] |
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