PUBLICATIONS Journal of Geophysical Research: Planets RESEARCH ARTICLE Canyon formation constraints on the discharge of catastrophic 10.1002/2016JE005061 outburst floods of Earth and Mars Key Points: Mathieu G. A. Lapotre1, Michael P. Lamb1, and Rebecca M. E. Williams2 • A new model for canyon formation through waterfall retreat combines 1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA, 2Planetary flood hydraulics and erosional mechanics Science Institute, Tucson, Arizona, USA • The model is used as a paleohydraulic tool to estimate the discharge of megafloods on Earth and Mars Abstract Catastrophic outburst floods carved amphitheater-headed canyons on Earth and Mars, and the • Compared with previous estimates, steep headwalls of these canyons suggest that some formed by upstream headwall propagation through predicted discharges are lower, fl durations higher, and water waterfall erosion processes. Because topography evolves in concert with water ow during canyon erosion, volumes are similar 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 fl fl Correspondence to: related to ood discharge. We develop a new theory for bedrock canyon formation by mega oods based M. G. A. Lapotre, on flow convergence of large outburst floods toward a horseshoe-shaped waterfall. The model is developed
[email protected] 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; Citation: and Ásbyrgi canyon, Iceland) and nine Martian (near Ares Vallis and Echus Chasma) bedrock canyons and Lapotre, M.