EROSIONAL AND DEPOSITIONAL EVOLUTION OF KASEI VALLES, MARS: IMPLICATIONS FOR TIMESCALES OF FORMATION
We use a combination of topographic datasets (MOLA and HRSC) in ArcGIS to constrain channel cross-sectional area, depth, and regional/local slopes (cross-referenced with images from HRSC, CTX, and HiRISE).Elevation measurements are constrained by inferred water elevations from identified terraces and used to calculate discharge and bedrock erosion rates following the model of Sklar and Dietrich .
Previous research derived catastrophic fluid discharge rates of 105-109 m3/s [1,5-6] assuming a bulk sediment concentration of ~40% by volume . Our calculated fluid discharge is on the order of 106 m3/s, similar to previous work. The peak, instaneous erosion rates are 8-41 mm/yr for water depths between 25-100 m, under turblent flow conditions (Re≥104), and assuming an average grain size of 0.1 m . Using channel depths of 500-800 m and assuming the continuous bedrock erosion under constant flow, the minimum timescale of formation is 104-105 yrs, several orders of magnitude larger than previous estimates [5-6]. These erosion rates corresond to sediment fluxes of 105-106 kg/s. The time-integrated, erosive sediment volume is 1013-1014 m3, indicating a sediment concentration orders of magnitude lower than previous estimates. Our results imply long-lived flows that suggest a reevaluation of sediment and water budgets.
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