EROSIONAL AND DEPOSITIONAL EVOLUTION OF KASEI VALLES, MARS: IMPLICATIONS FOR TIMESCALES OF FORMATION

Kasei Valles is the largest channel system on Mars at ~3000 km long, ~500 km wide, and ~3 km deep. It is widely believed to have been carved by catastrophic floods of water originating from Echus Chasma during Mars’ early history [1-3]. The Kasei channels likely formed through a complex interplay of volcanic, tectonic and surface processes, including formation mechanisms ranging from lava flows to glacial scouring [1]. Here, we reexamine the channels and focus our analysis on evidence for fluid flow for the creation of islands and bars located east of Sharanov Crater (28°N, 55°W). Using these erosional and depositional features, we estimate ranges for formation timescales, discharge rates and sediment fluxes.

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 [4].

Previous research derived catastrophic fluid discharge rates of 10⁵-10⁹ m³/s [1,5-6] assuming a bulk sediment concentration of ~40% by volume [7]. 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 [6]. 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.

[1] Carr (1979) JGR, 84, 2995-3007.

[2] Baker (1982) The Channels of Mars.

[3] Harrison and Grimm (2008) JGR, 113, E02002.

[4] Sklar and Dietrich (2004) WRR, 40, W06301.

[5] Andrews-Hanna and Phillips (2007) JGR, 112, E08001.

[6] Kleinhans (2005) JGR, 110, E12003.

[7] Komar (1980) Icarus, 42, 317-329.