Low-Gradient Debris Slopes and Implications for Water-Driven Sediment Transport Processes on Mars

Details Low-Gradient Debris Slopes and Implications for Water-Driven Sediment Transport Processes on Mars Low-Gradient Debris Slopes and Implications for Water-Driven Sediment Transport Processes on Mars

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p12a0365p&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #P12A-0365

Mathematics

Logic

1823 Frozen Ground, 1824 Geomorphology (1625), 5415 Erosion And Weathering, 5470 Surface Materials And Properties, 6225 Mars

Scientific paper

Topographic profiles of kilometer-scale debris slopes on Mars have weak upward concavity and mean slopes of ~20°, well below the angle of repose. The debris slope gradients do not appear to vary systematically with aspect, latitude, presence or absence of the recently discovered gullies, or geologic context. Terrestrial debris slopes formed by dry rockfall are steeper than 20° and have straight profiles, but other sediment transport processes can produce concave slopes with comparably low gradients. Successive mass flows and gravitational creep are both known to produce concave debris slopes. Overlapping, lobate deposits, which are commonly observed on terrestrial slopes shaped by mass flows, are not visible on ungullied Martian slopes at the resolution of Mars Orbiter Camera (MOC) images (>=1.4 m/pixel). The disturbance process most likely to cause gravitational creep on Mars is repeated freezing and sublimation of near-surface ground ice. Features resembling tensional cracks on some slopes suggest downslope movement of partially frozen debris, and surveys of both Viking [1] and MOC [2] images have identified a variety of landforms associated with cyclic freezing and thawing of ground ice on Earth. Furthermore, Mars Odyssey results [3] suggest that water ice is abundant at high Martian latitudes and that the volume fraction of ice may exceed the porosity of the regolith, a condition amenable to ice-driven creep. Numerical simulations of debris slope development demonstrate that gravitational creep can reproduce the morphology of Martian slopes. Estimates of bedrock erosion rates on Mars and a model fit to a mean Martian debris slope profile suggest a time scale of debris slope development between 20 Myr and 2 Gyr. This range is consistent with estimated rates of ice-driven creep. The near absence of impact craters on the surveyed slopes implies recent resurfacing by emplacement of new material or reworking of existing material. Thus, the low-gradient debris slopes on Mars seem to be evidence of an extended period of Amazonian geomorphic activity involving water that has only recently been punctuated by the formation of gullies. {[1]} Squyres, S.W., M.H. Carr, Science 231, 249-252 (1986).\{[2]} Seibert, N.M., J.S. Kargel, Geophys. Res. Lett. 28, 899-902 (2001).\{[3]} Boynton, W.V., W. C. Feldman, S. W. Squyres et al., Science 297, 81-85 (2002).

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