Lapotre, Mathieu G. A. and Lamb, Michael P. and Williams, Rebecca M. E. (2016) Canyon formation constraints on the discharge of catastrophic outburst floods of Earth and Mars. Journal of Geophysical Research. Planets, 121 (7). pp. 1232-1263. ISSN 2169-9097. http://resolver.caltech.edu/CaltechAUTHORS:20160915-085917972
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Catastrophic outburst floods carved amphitheater-headed canyons on Earth and Mars, and the steep headwalls of these canyons suggest that some formed by upstream headwall propagation through waterfall erosion processes. Because topography evolves in concert with water flow during canyon erosion, we suggest that bedrock canyon morphology preserves hydraulic information about canyon-forming floods. In particular, we propose that for a canyon to form with a roughly uniform width by upstream headwall retreat, erosion must occur around the canyon head, but not along the sidewalls, such that canyon width is related to flood discharge. We develop a new theory for bedrock canyon formation by megafloods based on flow convergence of large outburst floods toward a horseshoe-shaped waterfall. The model is developed for waterfall erosion by rock toppling, a candidate erosion mechanism in well fractured rock, like columnar basalt. We apply the model to 14 terrestrial (Channeled Scablands, Washington; Snake River Plain, Idaho; and Ásbyrgi canyon, Iceland) and nine Martian (near Ares Vallis and Echus Chasma) bedrock canyons and show that predicted flood discharges are nearly 3 orders of magnitude less than previously estimated, and predicted flood durations are longer than previously estimated, from less than a day to a few months. Results also show a positive correlation between flood discharge per unit width and canyon width, which supports our hypothesis that canyon width is set in part by flood discharge. Despite lower discharges than previously estimated, the flood volumes remain large enough for individual outburst floods to have perturbed the global hydrology of Mars.
|Additional Information:||© 2016 American Geophysical Union. Received 22 APR 2016; Accepted 10 JUN 2016; Accepted article online 13 JUN 2016; Published online 9 JUL 2016; Corrected 17 AUG 2016. The authors are grateful to Liliya Posiolova of Malin Space Science Systems for assistance with CTX DEM generation and the students of Ge121a at Caltech for sharing grain size data collected within the Drumheller channel, Washington, in the fall of 2013. We also thank Paul Carling and an anonymous reviewer for their constructive comments which improved this manuscript. Support was provided by the NASA Earth and Space Science Fellowship 12-PLANET12F-0071, NSF grants EAR-1147381 and 1529110, and NASA grant NNX13AM83G. Derived data are available in appendices and tables.|
|Errata:||In the originally published version of this article, there was an error in Figure 3 and a typo in the related captions. The figure has been replaced and the typo has been changed from “dimensionless 1-D stress” to “normalized upstream stress.” These modifications do not change the conclusions of this article. This version may be considered the authoritative version of record.|
|Subject Keywords:||bedrock canyons; megafloods; paleohydraulics; waterfall; toppling; Mars|
|Official Citation:||Lapotre, M. G. A., M. P. Lamb, and R. M. E. Williams (2016), Canyon formation constraints on the discharge of catastrophic outburst floods of Earth and Mars, J. Geophys. Res. Planets, 121, 1232–1263, doi:10.1002/2016JE005061.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||29 Sep 2016 23:47|
|Last Modified:||02 Feb 2017 18:23|
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