Repeated aqueous flooding from the Cerberus Fossae: Evidence for very recently extant, deep groundwater on Mars

The geomorphology and topography of the Cerberus Plains region of Mars show three spatially and temporally distinct, young, aqueous flood channel systems. Flood geomorphology in each of these channels, as seen in Mars Orbiter Camera images, consists of streamlined forms, longitudinal lineations, and a single occurrence of transverse dunes, features similar to those in the flood-carved terrain of the Channeled Scabland in the northwestern United States. As additional geomorphic evidence of flooding, small cones (interpreted as phreatic) are found preferentially in the channels or at their distal ends. Glaciers, lava flows, and CO2-charged density flows are each inconsistent with these geomorphic features. Mars Orbiter Laser Altimeter data show two of the three channel systems (Athabasca Valles and an unnamed northern channel system) emanating from the Cerberus Fossae; we suggest that the third channel system (Marte Vallis) also originated at the fissures. The discharges for two of the three systems (Athabasca Valles and Marte Vallis) have been estimated from surface topography to have been on the order of 10(6) m(3)/s. Crater counts indicate that the channels are not only young (extreme Late Amazonian), but also were carved asynchronously. Geomorphic evidence suggests that two of the channels (Athabasca and Marte Valles) experienced more than one flood. Emanation from volcanotectonic fissures instead of chaotic terrain distinguishes these Cerberus Plains channels from the larger, older circum-Chryse channels. Groundwater must have collected in a liquid state prior to flood onset to flow at the estimated discharge rates. Lack of large-scale subsidence near the channels' origination points along the Cerberus Fossae indicates that this groundwater was at least several kilometers deep. (C) 2002 Elsevier Science (USA).