HR: 0830h
AN: P11B-1036    [PDF]
TI: Theoretical Modeling of Outflow Channels and Chaos Regions on Mars
AU: * Hanna, J C
EM: jhanna@levee.wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University, One Brookings Drive, St. Louis, MO 63130 United States
AU: Phillips, R J
EM: phillips@wustite.wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University, One Brookings Drive, St. Louis, MO 63130 United States
AB: The Martian outflow channels are the largest fluvial features in the Solar System, and yet there are still many unanswered questions regarding the nature of the floods and their origins. Previous studies have focused mainly on interpretations of the observed fluvial geomorphology and topography of the channels, as well as simplified open-channel flow calculations. However, such interpretations are often ambiguous and do not allow for detailed reconstruction of the number, timing, duration, or magnitude of the floods. We here take a different approach and attempt to model theoretically the outflow channel floods emanating from chaos regions above pressurized aquifers. Modeling was done using a finite difference code to represent the flow within the aquifer. The aquifer properties were modeled using the megaregolith aquifer model of {\it Hanna and Phillips} [2003]. We find that a series of floods from a particular chaos region is likely to ensue from a single aquifer pressurization event, due to the slow diffusion of the pressure wave within the aquifer. The peak discharges and volumes predicted are consistent with the size and catastrophic nature of the channels. However, the results suggest that some commonly held assumptions in the interpretation of the channel geomorphology are incorrect. It is unlikely that the outflow channels achieved bankfull flow in their present configuration, and calculations based on this assumption significantly overestimate the peak discharge. For a flood from Iani Chaos at the head of Ares Valles, our predicted peak discharge is on the order of 10$^{7}$ m$^{3}$s$^{-1}$, several orders of magnitude lower than that based on the assumption of bankfull flow. The predicted volume of a single flood is approximately 3000 km$^{3}$, with the total volume being dependent upon the actual number of flood episodes. While the hydrologic models of the martian crust are poorly constrained, our model results give us valuable insight into the nature of the floods. Ultimately, through a combination of geomorphic studies and theoretical modeling, it may be possible to gain greater insight into the floods themselves, as well as the driving forces behind them and the implications for the volatile and climate history of Mars.
DE: 1821 Floods
DE: 1829 Groundwater hydrology
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting