Catastrophic Flooding in Osuga Valles, Mars: Implications For Its Paleoflood Hydrology and Formation

Abstract

Satellite imagery of Mars has shown large flood-like features known as outflow channels across its surface. Previous studies have used a variety of techniques involving complex 1D equations and 2D models for outflow channels in Chryse and Elysium Planitia to estimate the magnitudes and depths of floods. In this study, we use both 1D and 2D flow equations and the 2D computer hydraulic model HEC-RAS version 6.6 to estimate stage-discharge relationships within Osuga Valles. Additionally, we use 1D groundwater and fracture flow equations, and the 2D thermal model HYDROTHERM to simulate pressure and temperature changes within the subsurface. The site of interest is Osuga Valles, an outflow channel that contains unique features suggesting pressure-dominated floods from groundwater that cover approximately 168 km of fluvially eroded channels. The varying depths along the channel suggest the floods are catastrophic, excavating between 250 to over 1,000 meters in depth. All channels appear to terminate into a relatively small collapsed basin, without indication of any surface flows beyond this terminus. High-resolution Digital Terrain Models (DTM) from HRSC, CTX and HiRISE are used to capture cross-sectional profiles and relative elevations of Paleo Stage Indicators (PSI’s) to provide supporting evidence for flood depths. From the HEC-RAS results, we find that the roughness of the channel bed in Osuga Valles does not greatly influence the depth for each flow rate, and the last flood that most likely filled the channel based on PSI is approximately 5 x 10^7 m3/s. However, our subsurface analysis counters this and suggests the last flood was several orders of magnitude smaller than simulated with HEC-RAS and short-lived. Permeabilities of the fractures within the aquifer for producing such large-scale flooding range from 1.4 x 10^-6 to 2.5 x 10^-6 m2, which converts to over ~1,400,000 darcies.