Origin of the stepped topography of the Martian poles

Abstract

The circumpolar stepped topography observed within the Martian polar regions can have originated from one of a limited number of processes, including (i) erosion of resistant layers, (ii) erosion rates inversely proportional to slope gradient, (iii) basal sapping, and (iv) bistable rates of erosion and deposition. The last mechanism appears most likely to operate on the polar escarpments, driven by ablation of volatiles on the dark scarps and deposition on the icy flats. Decreasing albedo and a corresponding increase in radiation input caused by dust accumulations on the ablating layered deposits on steeper slopes provides a metastable erosion rate model sufficient to produce a stepped topography. Wind erosion is presuured later to remove the loose excess residual dust which accumulated during ablation of the scarps. The ablation of the scarps contemporaneously with ice accumulation on the flats implies the layered deposits exposed on the scarps have formed beneath overlying flats, and the observed unconformities within these deposits can due to the exposure of deposits laid down under more than one flat with different gradients. The linearity and mutual parallelism of the scarps is a result of scarp retreat on a regional slope or with a prefered direction of scarf retreat. The spiral arrangement of the scarps is probably due to more rapid retreat of scarps facing slightly west of the equatorward meridian, that is, in the direction of greatest solar and atmospheric warming. The model suggest, but does not prove, that the layered deposits are mostly water ice, with small amounts of codeposited silicate dust and volcanic ash.