Surface characteristics and degradational history of debris aprons in the Tempe Terra/Mareotis fossae region of Mars

We have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the Tempe Terra/Mareotis fossae region of Mars. These aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations, which can provide insight into the dominant controls on apron development. Tempe/Mareotis debris aprons, found at the bases of isolated or clustered massifs, escarpments, and crater interior walls, were studied using Viking Orbiter, Mars Global Surveyor, and Mars Odyssey datasets in a GIS database. Six textures related to degradation of apron surfaces are identified in MOC images, and they are divided into two groups: an upper-surface group and a lower-surface group. Degradation occurs within an inferred smooth, upper surface mantle of ice and debris, producing a sequence of pitted, ridge and valley, and knobby textures of the upper-surface group. Where upper-surface materials have been removed, smooth and ridged textures of the lower-surface group are exposed. Degradation to various depths may expose lower-surface materials, which may consist of the main apron mass, remnants of mantling deposits, or both. A combination of geologic processes may have caused the degradation, including ice sublimation, ice melt, and eolian activity. Apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces, which may be explained by the trapping of unconsolidated materials in low-lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces. One feature observed only on Tempe/Mareotis debris aprons are broad ridges, which mimic the shape of massif bases for tens of kilometers. We propose these to be constructional features that could have formed during cycles of increased debris production. Apron morphometric parameters including area, volume, slope, thickness, relief, and H/L, were compiled and the results show that Tempe/Mareotis aprons have average surface areas, volumes, and frontal thicknesses that are ∼2-3 times smaller than eastern Hellas aprons. Within the Tempe/Mareotis population escarpment-related aprons are larger than massif-related aprons, suggesting that aprons with larger source areas have potentially greater volatile accumulation, translating into longer apron travel distances and lower H/L values.