Hydrological modeling of outflow channels and chaos regions on Mars

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The Martian outflow channels were carved by the eruption of catastrophic floods from groundwater aquifers. This study models the time evolution of a typical outflow channel flood originating within a chaos region. The flood initiates when superlithostatic pore pressures within a confined aquifer lead to the propagation of hydrofractures through the confining cryosphere to the surface. The peak discharges are modulated by diffusion of the flood pulse within the chaos region, resulting in a rapid rise in discharge immediately after flood initiation. Later flow is limited by diffusion through the aquifer and is sensitive to the variation of the hydraulic properties with changing pore pressure. After the termination of the flood by freezing within the chaos region much of the aquifer remains pressurized. Diffusion of the excess pressure from the undrained portions of the aquifer back toward the chaos region triggers a second flood, ultimately resulting in a periodic series of floods. For Iani Chaos at the source of Ares Valles, modeled peak discharges on the order of 106to 107m3s−1were obtained, with total volumes of individual floods ranging from 600 to 5000 km3and a minimum period between successive floods of ∼44 years. The cumulative flood volume depends upon the number of floods, which is a function of the volume of pressurized aquifer or the duration of recharge from distant sources. These results suggest that individual channels were likely carved by large numbers of floods and were unlikely to have experienced bankfull flow in their final state.