Posted by Dr. Ernst Hauber
Lobate debris aprons (LDA) are distinctive geomorphic landforms showing evidence for the creep and deformation of ice-rich debris in Martian mid-latitudes [e.g., Carr and Schaber, 1977; Squyres, 1978, 1979; Lucchitta, 1984].
They extend for up to 15 km from mesas or plateau scarps and show distinct flow lobes in plan view and convex-upward profiles in cross section with steep termini (see image). Where LDA are confined in narrow valleys, they are termed lineated valley fill and show a particular surface texture characterized by generally valley-parallel lineations. A third type of landform which is genetically connected to creep of ice and debris is termed concentric crater fill and is characterized by creep of material downwards along the inner slopes of impact craters. LDA were first described in detail by Carr and Schaber  and Squyres [1978; 1979], who ascribed them to downslope transport of erosional debris mixed with ice, analogous to terrestrial rock glaciers [e.g., Barsch, 1996]. Squyres  and Squyres and Carr  mapped the global distribution of LDA and found a strong concentration in two latitudinal bands with a width of 25°, centered at 40°N and 45°S. He concluded that this latitudinal dependence implies a climatic influence on their formation.
Besides these macro-scale landforms, a concentration of small-scale viscous flow features in the same latitudinal belts was later observed by Milliken et al.  on high-resolution Mars Orbiter Camera (MOC) data. Virtually no viscous flow features were reported equatorwards of ±30°. It has been shown first by Squyres  on the basis of photoclinometry and later by Mangold and Allemand  as well as Li et al.  on the basis of MOLA topographic profiles that the cross-section shape of LDA can be approximated by the flow law of polycrystalline ice [Glen, 1955] and the flow relation of ice [Vialov, 1958; Paterson, 1984]. Colaprete and Jakosky  modelled flow of ice under Martian conditions and found that (a) temperatures 20 to 40 K higher than present average mid-latitude temperatures (~210 K), (b) ice contents ≥80%, and (c) net accumulation rates of ≥1 cm year-1 are required to create LDA of the observed size.
Ice in LDA may have several origins. Water ice could form by direct condensation of ice from the atmosphere [Squyres, 1978] or by snow precipitation [Squyres, 1989]. It could also accumulate by water vapour diffusion down into the regolith and subsequent condensation [Mellon and Jakosky, 1995]. Finally, groundwater may seep into debris and create interstitial ice [Lucchitta, 1984; Squyres, 1989; Mangold and Allemand, 2001]. Recently, Head and colleagues (e.g., Head et al., 2006) investigated LDA’s and the related lineated valley fill in detail on the basis of new high-resolution data and linked their formation to climate changes due to Late Amazonian obliquity-driven climate change.
LDA are young landforms. The clastic particles in the LDA might come from rock falls that accumulated at the base of scarps [Squyres, 1978; Colaprete and Jakosky, 1998] or, alternatively, from landslides [Lucchitta, 1984; Mangold and Allemand, 2001]. Crater counts yielded low crater densities, and absolute ages of less than 100 Ma have been derived [e.g., Squyres, 1978; Mangold, 2003; Berman et al., 2003; Head et al., 2005; Li et al., 2005]. However, morphologic evidence for past (~ 1 Ga) LDA, the locations of which are preserved as depressions, indicate that LDA might have formed at lower latitudes than observed today, implying a different climate (Hauber et al., 2008).
Barsch, D., Rock Glaciers, Springer, Berlin, 331 pages, 1996.
Berman, D. C., W. K. Hartmann, and D. A. Crown, Debris Aprons, Channels, and Volcanoes in the Reull Vallis Region of Mars, Lunar Planet. Sci., XXXIV, abstract 1879, 2003. [Abstract]
Carr, M. H. and G. G. Schaber, Martian permafrost features, J. Geophys. Res., 82, 4039-4054, 1977. [Abstract]
Colaprete, A. and B. M. Jakosky, Ice flow and rock glaciers on Mars, J. Geophys. Res., 103, p. 5897, 1998. [Abstract]
Glen, J. W., The Creep of Polycrystalline Ice, Proc. Royal Soc. London, Series A, Math. Phys. Sci., 228(1175), 519-538, 1955.
Hauber, E., S. van Gasselt, M. Chapman, and G. Neukum, Geomorphic evidence for former lobate debris aprons at low latitudes on Mars: Indicators of the Martian paleoclimate, J. Geophys. Res., 2008, VOL. 113, E02007, doi:10.1029/2007JE002897. [Abstract]
Head, J. W., G. Neukum, R. Jaumann, H. Hiesinger, E. Hauber, M. Carr, P. Masson, B. Foing, H. Hoffmann, M. Kreslavsky, S. Werner, S. Milkovich, S. van Gasselt, and The HRSC Co-Investigator Team, Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars, Nature, 434, 346-351, doi: 10.1038/nature03359, 2005. [Abstract]
Head, J. W., D. R. Marchant, M. C. Agnew, C. I. Fassett, and M. A. Kreslavsky, Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change, Earth Planet. Sci. Lett., 241, Issue 3-4, 663-671, 2006. [Abstract]
Li, H., M. S. Robinson, and D. M. Jurdy, Origin of martian northern hemisphere mid-latitude lobate debris aprons, Icarus, 176(2), 382-394, doi: 10.1016/j.icarus.2005.02.011, 2005. [Abstract]
Lucchitta, B. K., Ice and debris in the fretted terrain, Mars, J. Geophys. Res., 89(B1), B409-B419, 1984. [Abstract]
Mangold, N., Geomorphic analysis of lobate debris aprons on Mars at Mars Orbiter Camera scale: Evidence for ice sublimation initiated by fractures, J. Geophys. Res., 108(E4), GDS 2-1, CiteID 8021, doi: 10.1029/2002JE001885, 2003. [Abstract]
Mangold, N. and P. Allemand, Topographic analysis of features related to ice on Mars, Geophys. Res. Lett., 28(3), 407-410, doi: 10.1029/2000GL008491, 2001. [Abstract]
Mellon, M. T. and B. M. Jakosky, The distribution and behavior of Martian ground ice during past and present epochs, J. Geophys. Res., 100(E6), doi: 10.1029/95JE01027, 11781-11799, 1995. [Abstract]
Milliken, R. E., J. F. Mustard, and D. L. Goldsby, Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images, J. Geophys. Res., 108(E06), 5057, doi: 10.1029/2002JE002005, 2003. [Abstract]
Paterson, W. S. B., The physics of glaciers, 3rd edition, Pergamon, Oxford, ix + 480 pages, 1994.
Squyres, S. W., Martian fretted terrain – Flow of erosional debris, Icarus, 34, 600- 613, doi: 10.1016/0019-1035(78)90048-9, 1978. [Abstract]
Squyres, S. W., The distribution of lobate debris aprons and similar flows on Mars, J. Geophys. Res., 84, 8087-8096, 1979. [Abstract]
Squyres, S. W. and Carr, M. H., Geomorphic evidence for the distribution of ground ice on Mars, Science, 231, 249-252, 1986. [Abstract]
Squyres, S. W., Urey prize lecture – Water on Mars, Icarus, 79, 229-288, doi: 10.1016/0019-1035(89)90078-X, 1989. [Abstract]
Vialov, S. S., Regularities of glacial shields movements and the theory of plastic viscous flow, in: Physics of the movements of ice, Int. Assoc. Hydr. Sci., 47, 266-275, 1958.