HR: 1340h
AN: P13A-0990    [Abstracts]
TI: New Results from Topographic Studies of Martian Debris Aprons
AU: * Li, H
EM: han@earth.northwestern.edu
AF: Northwestern University, Department of Geological Sciences, 1850 Campus Dr., Evanston, IL 60201 United States
AU: Robinson, M S
EM: robinson@earth.northwestern.edu
AF: Northwestern University, Department of Geological Sciences, 1850 Campus Dr., Evanston, IL 60201 United States
AB: Lobate debris aprons in the mid- to high latitudes for Mars' northern and southern hemispheres have been interpreted as ice-related features [e.g. 1, 2, 3]. Using MOLA topographic profiles perpendicular to apron flow fronts, we surveyed 45 debris aprons in the 35-$55\deg$N›¦ latitude range of both the northern and hemispheres, specifically Mareotis, Protonilus, and Deuteronilus Mensae and Acheron Fossae, Argyre and eastern Hellas Basin. The profiles of these aprons were compared with predictions from idealized simple plastic and viscous power law models for ice-rock mixtures. All aprons studied exhibit convex profiles that closely match or follow the overall trend of a simple plastic model. This result is consistent with previous interpretations [1, 2, 3, 4] that debris aprons are ice-rich mixtures with rheologies similar to stagnant ice sheets and furthermore requires high ice concentration ($>$40 percent by volume) in apron deposits. About 60 percent of the surveyed debris apron population deviates from the idealized simple plastic model profile, which may be due to locally reduced ice content, with ice content likely being the primary control on apron topography. Although post-emplacement modification due to near-surface ice sublimation may play a secondary role in defining the overall shape of aprons, it causes conspicuous surface textures. Degradation by ice sublimation results in pitted and ridge-and-furrow surface textures revealed by high resolution MOC images. Such textures may indicate decreased near-surface ice stability since the formation of the aprons, consistent with a recently proposed interglacial period after their emplacement [5]. Despite their elevation difference, northern and southern hemisphere debris aprons have essentially identical profile shape and exhibit similar surface texture and surface age. These similarities suggest two groups of aprons share same origin and degradation processes and their most recent reactivation likely occurred around the same time. Our crater counts(limited areal extent) suggest that debris aprons are young features with an age constrained to be $<$100 Myr. Since current climate at mid to high latitudes of Mars is not conducive to the formation of ice-related flows the climate ~100 Myr ago must have been wetter than today, and was probably similar to that of the terrestrial periglacial regions. High ice content, inferred from morphology, suggests some debris aprons have ice cores, which are potentially exploitable water resources for future robotic/human operations that could prove invaluable for missions remote from polar regions. {[1]} Squyres, S.W., Icarus, 34, 600-613, 1978. {[2]} Lucchitta, J. Geophys. Res, 89, 409-418, 1984. {[3]} Crown, D.A. et al., Icarus, 100, 1-25, 1992. {[4]} Mangold, N. and Allemand, P., Geophys. Res. Lett., 28, 3,407-3,410, 2001. {[5]} Head, J.W. et al., Nature, 426, 797-802, 2003.
DE: 5400 PLANETOLOGY: SOLID SURFACE PLANETS
DE: 5416 Glaciation
DE: 5470 Surface materials and properties
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting