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Progressive incision of the Channeled Scablands by outburst floods

Larsen, Isaac J. and Lamb, Michael P. (2016) Progressive incision of the Channeled Scablands by outburst floods. Nature, 538 (7624). pp. 229-232. ISSN 0028-0836.

[img] Image (JPEG) (Extended Data Figure 1: Computational mesh resolution) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 2: Hillshade maps of the study reach for each bed elevation) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 3: Bed shear stress as a function of discharge for sites on the Moses Coulee knickzone) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 4: Flood depth versus time for a typical simulation) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 5: Cumulative bed stress probability density functions) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 6: Boulder size data) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 7: Locations of the areas used to calculate mean bed shear stress) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 8: Example model output showing the upper and lower shear stress thresholds for block sliding) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 9: Schematic illustrating the method for defining the discharge range predicted by the threshold shear stress model) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 10: Predicted channel cross-sectional areas and widths) - Supplemental Material
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The surfaces of Earth and Mars contain large bedrock canyons that were carved by catastrophic outburst floods. Reconstructing the magnitude of these canyon-forming floods is essential for understanding the ways in which floods modify planetary surfaces, the hydrology of early Mars and abrupt changes in climate. Flood discharges are often estimated by assuming that the floods filled the canyons to their brims with water; however, an alternative hypothesis is that canyon morphology adjusts during incision such that bed shear stresses exceed the threshold for erosion by a small amount. Here we show that accounting for erosion thresholds during canyon incision results in near-constant discharges that are five- to ten-fold smaller than full-to-the-brim estimates for Moses Coulee, a canyon in the Channeled Scablands, which was carved during the Pleistocene by the catastrophic Missoula floods in eastern Washington, USA. The predicted discharges are consistent with flow-depth indicators from gravel bars within the canyon. In contrast, under the assumption that floods filled canyons to their brims, a large and monotonic increase in flood discharge is predicted as the canyon was progressively incised, which is at odds with the discharges expected for floods originating from glacial lake outbursts. These findings suggest that flood-carved landscapes in fractured rock might evolve to a threshold state for bedrock erosion, thus implying much lower flood discharges than previously thought.

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Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2016 Macmillan Publishers Limited, part of Springer Nature. Received 22 April 2016; Accepted 31 August 2016; Published online 12 October 2016. This research was supported by a Caltech Texaco Prize Postdoctoral Fellowship, collaborative NSF (1529528, 1529110) funding to I.J.L. and M.P.L., and a NASA (NNX13AM83G) award to M.P.L. We thank E. Simon, M. Lapotre and S. Roberts for assistance and advice with the hydraulic modelling, and participants in the Caltech field methods course for field assistance. Author Contributions: I.J.L. and M.P.L. designed the study and wrote the manuscript. I.J.L. conducted the hydraulic simulations. Code availability: The hydrodynamic code ANUGA is open-source and available for download at The PYTHON scripts used to implement ANUGA are available from the authors by request. Data availability: Digital elevation data are available from the University of Washington Geomorphological Research Group website ( All simulation results and data are available from the authors by request. The authors declare no competing financial interests. Reviewer Information: Nature thanks J. Venditti and the other anonymous reviewer(s) for their contribution to the peer review of this work.
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Caltech Texaco Prize Postdoctoral FellowshipUNSPECIFIED
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Official Citation:Progressive incision of the Channeled Scablands by outburst floods Isaac J. Larsen and Michael P. Lamb Nature 538, 229–232 (13 October 2016) doi:10.1038/nature19817
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71140
Deposited By: Tony Diaz
Deposited On:17 Oct 2016 16:55
Last Modified:17 Oct 2016 16:55

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