Eroding Cascadia— Sediment and solute transport and landscape denudation in western Oregon and northwestern California

Geological Society of America Bulletin
By: , and 

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Abstract

Riverine measurements of sediment and solute transport give empirical basin-scale estimates of bed-load, suspended-sediment, and silicate-solute fluxes for 100,000 km2 of northwestern California and western Oregon. This spatially explicit sediment budget shows the multifaceted control of geology and physiography on the rates and processes of fluvial denudation. Bed-load transport is greatest for steep basins, particularly in areas underlain by the accreted Klamath terrane. Bed-load flux commonly decreases downstream as clasts convert to suspended load by breakage and attrition, particularly for softer rock types. Suspended load correlates strongly with lithology, basin slope, precipitation, and wildfire disturbance. It is highest in steep regions of soft rocks, and our estimates suggest that much of the suspended load is derived from bed-load comminution. Dissolution, measured by basin-scale silicate-solute yield, constitutes a third of regional landscape denudation. Solute yield correlates with precipitation and is proportionally greatest in low-gradient and wet basins and for high parts of the Cascade Range, where undissected Quaternary volcanic rocks soak in 2−3 m of annual precipitation. Combined, these estimates provide basin-scale erosion rates ranging from ∼50 t ∙ km−2 ∙ yr−1 (approximately equivalent to 0.02 mm ∙ yr−1) for low-gradient basins such as the Willamette River to ∼500 t ∙ km−2 ∙ yr−1 (∼0.2 mm ∙ yr−1) for steep coastal drainages. The denudation rates determined here from modern measurements are less than those estimated by longer-term geologic assessments, suggesting episodic disturbances such as fire, flood, seismic shaking, and climate change significantly add to long-term landscape denudation.

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Publication type Article
Publication Subtype Journal Article
Title Eroding Cascadia— Sediment and solute transport and landscape denudation in western Oregon and northwestern California
Series title Geological Society of America Bulletin
DOI 10.1130/B35710.1
Volume 133
Issue 9-10
Year Published 2021
Language English
Publisher Geological Society of America
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center, Oregon Water Science Center
Description 24 p.
First page 1851
Last page 1874
Country United States
State California, Oregon, Washington
Other Geospatial Cascade range
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