Spatially Variable Increase in Rock Uplift in the Northern U.S. Cordillera Recorded in the Distribution of River Knickpoints and Incision Depths. Issue 5 (23rd May 2019)

• Record Type: Journal Article
• Authors: Mitchell, Nate A.; Yanites, Brian J.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 5(2019)
• Page Start: 1238
• Page End: 1260
• Publication Date: 2019-05-23
• Subjects: bedrock rivers -- knickpoints -- incision -- rock uplift -- Salmon River -- landscape evolution; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2018JF004880
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: Landscape evolution is driven by factors like tectonics and climate, and unraveling such factors can reveal the history recorded in landscape morphology. The northern U.S. Cordillera features many potential drivers, such as the Yellowstone plume, the extrusion of a large igneous province, and the drainage of large lakes. Among this complex geologic history, the drivers of transient incision in the Clearwater and Salmon watersheds of central Idaho are not well understood. To constrain the pattern of regional incision, we analyze the morphologies of 80 individual tributaries underlain by single lithologies. From north to south across our study area, knickpoint elevations increase from about 800 to 2, 200 m, and incision depths increase from about 300 to 1, 200 m. We use both numerical and analytical models to demonstrate that such a gradient could represent spatial variations in rock uplift. These findings suggest that transience is driven by a spatially variable increase in rock uplift that has disrupted a low‐relief paleolandscape, and the high steepness values of main drainages suggest that high rock‐uplift rates are still maintained to the present. Changes in rock uplift may be related to interactions between the Yellowstone plume and the lithosphere, although base level fall from the drainage of the Lake Idaho down the proto‐Snake River may be superimposed over these patterns in rock uplift. We show that careful, quantitative analyses of river profiles in geologically complex regions can differentiate between the influences of rock uplift and far‐field base level changes. Key Points: Knickpoint elevations and incision depths of individual tributaries in the Clearwater and Salmon watersheds increase from north to south Bedrock river morphologies indicate that a spatially variable increase in rock uplift caused the dissection of a low‐relief paleolandscape We support our findings with numerical model simulations and a review of previous analytical work on transient bedrock river behavior