Abstract:
A suite of sinuous ridges with branching and braided morphologies forms an anastomosing network in southern Argyre Planitia, Mars. Several modes of origin have been proposed for the Argyre ridges. Imagery from the High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) aboard Mars Reconnaissance Orbiter (MRO) and Mars Orbiter Laser Altimeter (MOLA) topographic data sets from Mars Global Surveyor (MGS) are used to constrain processes involved in formation of the Argyre ridges. We find the characteristics of the ridges and associated layered deposits consistent with glaciofluvial-lacustrine processes and conclude that the ridges are most likely eskers. In particular, variations in ridge height appear to be related to the surrounding surface slope; ridge height increases with descending slopes and decreases with ascending slopes. This characteristic is observed in terrestrial eskers and is related to subice flow processes. The nature of some eroding beds in the ridges suggests induration. If the Argyre ridges are indeed eskers, the southern Argyre basin was once covered by the margin of a large, thick, stagnating or retreating ice deposit that extended for hundreds of kilometers or more. During ridge formation, water flowed on top, within, or beneath the ice deposit; the continuity and preservation of the ridges suggests that flow was primarily at the base of the ice. The dimensions (up to hundreds of meters tall and several kilometers wide), aspect ratio, and extent (hundreds of kilometers) of the ridges, as well as preliminary calculations of discharge, suggest that a significant amount of water was available.
