Large asymmetric polar scarps on Planum Australe, Mars: Characterization and evolution

Numerous scarps with similar characteristics have been observed in the polar layered deposits of Planum Australe, Mars. They are referred to as LAPSs (for Large Asymmetric Polar Scarps) because of their typical cross-section featuring a trough between a straight slope on one side with outcrops of layered deposits and a convex slope on the other side without any outcrops. These LAPSs are restricted to the outlying region of Ultimi Lobe. Topographic data, optical images, and subsurface radar observations have been analyzed and compared to produce a complete morphologic and stratigraphic description of these scarps. In all, 167 LAPS-like features have been identified. All have similar dimensions and characteristics and appear to be deep depressions in the ice. The polar deposits have an average thickness of 1 km in this region and the LAPS depressions commonly reach half of that thickness. Subsurface data indicate that the depressions could reach bedrock at certain locations. Many surface features of the polar deposits of Mars are considered to be consequences of depositional and/or erosion processes. We propose a mechanical failure of the ice for the LAPSs origin, given the striking similarities in shape and size they show with rollover anticlines above listric faults commonly observed as a crustal extension mode on Earth. This tectonic scenario would imply a substantial outward sliding of the polar deposits in the region of Ultimi Lobe and a low basal shear stress. No information is available to determine whether such a system could be active at present. Confirmation of the mechanical failure hypothesis of these LAPSs on Mars is of major importance as it could be a macro-expression of fundamental differences between ice-sheet behavior under martian and terrestrial conditions. (C) 2010 Elsevier Inc. All rights reserved.