Investigations into the Cerberus outflow channels, Mars

Abstract

Mars Orbiter Camera (MOC) images and Mars Orbiter Laser Altimeter (MOLA) data on the Mars Global Surveyor (MGS) spacecraft show evidence for three catastrophic outflow channels around the Cerberus Plains region, Mars. The morphologies seen in MOC images located within channels seen in gridded MOLA topography are similar to those found in catastrophic flood terrains on Earth, such as the Channeled Scabland. Thus, they indicate the channels' formation by catastrophic flood flow. The morphologies and topography also counterindicate the channels' formation by lava, glaciers or CO₂-charged density flows. Crater counting on lineated terrain, interpreted as diluvially eroded, gives model ages for the channels of extreme Upper Amazonian, ranging from 2-8 Ma for the youngest to 35-140 Ma for the oldest. The distinct age ranges, as well as the geographic/geologic relationships, indicate that the last flood flows down each of the channels were not contemporaneous. Two, and possibly all three, of the channels originate at the Cerberus Fossae volcano-tectonic fissures, although lack of erosion around the channels' origin at the fissures suggests the fissures have been recently reactivated. Neither magmatic melting of ground ice nor gravity-driven groundwater flow can produce a volumetric discharge at a rate commensurate with that estimated from the surface topography. Geomorphic evidence suggests floodwater ponded temporarily in Athabasca Vallis. Two paleoflood height indicators, which are separated by thirty-five kilometers along channel, have very similar heights. This may be explained by temporary ponding of floodwater behind a large crater in the channel, and consequent deposition of sediment in this slower flow. An additional factor contributing to the similar heights of the paleoflood indicators may be post-eruption subsidence near the origin of the channel, although this possibility, without the hypothesized ponding, cannot explain the preferential location of the streamlined forms up slope of the crater.