Published online today in JGR-Planets:

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Mangold, N.; Costard, F.; Forget, F.
Debris flows over sand dunes on Mars: Evidence for liquid water
J. Geophys. Res. Vol. 108 No. E4
10.1029/2002JE001958
18 April 2003

Abstract

This study focuses on the formation and physical properties of the gullies observed over large Martian dunes, especially those of the Russell crater (54°S, 347°W). Geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid. The occurrence of levees implies that these flows are debris flows with a yield strength characteristics of Bingham plastic materials. We apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities. We obtain average velocities in the range of 1 to 7 m s-1 and apparent viscosities of 2.8 to 46,000 Pa s, with an average at 740 Pa s, compared with the 0.001 Pa s of pure water. These viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40% of H2O. These properties are typical of water-holding debris flows but not of pure water surface runoff or CO2 driven flows. The debris flows over dunes are oriented on south-facing slopes like other recent gullies. Meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes.

Received 15 July 2002; revised 15 November 2002; accepted 4 February 2003; published 18 April 2003.

Keywords: water on Mars, debris flow, ground ice, dune, climate, mass wasting.

Index Terms: 6225 Planetology: Solar System Objects: Mars; 6207 Planetology: Solar System Objects: Comparative planetology; 1824 Hydrology: Geomorphology (1625); 1823 Hydrology: Frozen ground; 5470 Planetology: Solid Surface Planets: Surface materials and properties.

Citation: Mangold, N., F. Costard, and F. Forget, Debris flows over sand dunes on Mars: Evidence for liquid water, J. Geophys. Res., 108 (E4), 5027, doi:10.1029/2002JE001958, 2003.