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Lunar and Planetary Science XLVIII (2017) 1172.pdf

GEOMORPHOLOGICAL ANALYSES OF LANDSLIDE DEPOSITS IN HEBES (, ). O. Kromuszczyńska1* and K. T. Dębniak1**, 1Planetary Geology Lab, Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Wrocław, Podwale St. 75, PL-50449 Wrocław, Poland (*[email protected]; **[email protected]).

Introduction: Hebes Chasma, one of twelve 2.7 m/s2, caused by a fault of >1000 m length (within troughs constituting the Valles Marineris complex, is a disturbed rock mass), or 3.2 m/s2 induced by a fault of host of numerous landslides. Large-scale landslide 3.5 km length (for undisturbed rocks) [7]. scars are visible on both walls of Hebes Chasma and Landslides on Hebes slopes: There are at slopes of Interior Layered Deposits' (ILDs') mound, least five large collapse zones in Hebes Mensa slopes Hebes Mensa, located in the central part of the trough. (marked Li1-Li5 in Fig. 1). They are 6-23 km wide and The presented study was based on a creation of each of them removed up to ~290 km2 of the slope, landslide deposits' inventory. It was used for the what constitutes ~550 km2 of the total removal. The morphological classification and interpretation of run-outs and debris emplacements in front of the landslide deposits generation. collapse zones consist of extensive hummocky Hebes Chasma: Hebes Chasma is a closed terrains. Deposits of the landslide Li4 are mostly depression of an approximately elliptical shape, intact, with slight fluting on the toes suggesting measuring 315 by 126 km, covering an area of about insignificant eolian erosion. On the other hand, scarps 25 200 km2 (Fig. 1). It is located ~55 km from the of landslides Li1 and Li4 are heavily fluted, implying a northern margin of . Hebes Chasma is substantial erodibility [7]. The possible origin of one of the deepest trough on Mars with a maximum landslides are karstic processes related to groundwater depth of ~8 km. This large cavity originated in a action [2], or the landslide movement was initiated by removal of 105 km3 of material. However the process ground shaking under dry conditions [7,8]. responsible for the material vanishing is still an Methods: The study results were obtained through enigma – the hypotheses for Hebes Chasma origin geomorphological mapping of Hebes Chasma follow three major pathways: erosional excavation, landslide deposits conducted on the basis of CTX tectonic rifting, and karstic collapse [1]. The dataset. 20 CTX images with reduced spatial geomorphologic feature inside the chasma is Hebes resolution to 12 m/pxl were used to create a mosaic in Mensa following the chasma E-W elongation [1,2,3,4]. Integrated Software for Imagers and Spectrometers Landslides on Hebes Chasma walls: Ten large (ISIS). ArcGIS was used to perform the mapping landslides (marked L1-L10 in Fig. 1) emerged from the procedure. Hebes Chasma walls. Five of them (L1-L3, L5, L7) Preliminary results: Landslide scars in Hebes were characterized geometrically in [5] and for three Chasma are present on each wallslope of the trough, (L3-L5) the age was determined in [6]. among which those on the northern wall are the largest Wall landslides within the trough are entirely (L1-L3). There is a difference in scar shapes, i.e. L4-L6 chaotic. Among all large Valles Marineris landslides, scars are linear, while others are alcove-shaped. The these located in Hebes Chasma are characterized by evidences of structural control of mass-wasting medium mobility (M = Length/Vertical drop = 5.61) process are visible for L5 and L8-L10. Landslide and the highest material deficit (average material deposits in Hebes Chasma are spatially limited to scar balance here = 62.67%) [5]. This chasma is the only proximity which differ Hebes landslides from completely enclosed depression of the Valles landslides in other Valles Marineris chasmata. Marineris system, so material exportation after Landslide deposits display different morphologies, landslide is simply impossible. That is why the including coarse (disordered, large-scale material of reduced sediment volume after collapse might have numerous scarps; L1 near scar, L2, L4, L8), ridged been caused by high source sediment porosity and a (mountainous deposits arranged in parallel ridges; L5), deposit fluidization [5]. flat (plane, smooth material located adjacent to a scar; The modeled data [7] showed that these slope L1), and gentle (smooth material of mild hills failures might have been triggered by two processes: appearing as water-influenced; L4-L5). Other fluid influence or ground shaking. The disturbed and distinctive landslide deposits in Hebes Chasma are undisturbed basaltic rocks might have collapsed under located in: L6-L7 (where mass-wasted material is artesian fluid pressures equal to 66% and 82% of firmly chaotic and spatially impossible to distinguish overburden pressure, respectively. The failure might from deposit bulk), L2 (where deposits become more have been triggered also by ground acceleration of 2.3- degraded as the distance from the scar increases), L8 Lunar and Planetary Science XLVIII (2017) 1172.pdf

and L10 (which appear as hanging landslides). In The difference in morphology of landslide deposits addition, landslides L4-L5 display unique geometry between material derived from chasma walls and ILDs' indicating evolution in two large stages: first, parallel slopes is the consequence of their lithological to the chasma walls (meridional), and second, differences. The spatial arrangement of both landslide perpendicular (westward) to the major wall direction. deposit types allow to distinguish individual landslide The second group of landslides in Hebes Chasma materials in the northern part of Hebes Chasma, while are those related to the Hebes Mensa slopes (ILDs' landslide materials in the southern area are mixed and landslides: Li1-Li5). Scars of ILDs' landslides are greatly disrupted. rectangular and display fluted wall morphology. References: [1] Jackson M. P. A. et al (2011) GSA Deposits of these landslides are composed of two Bulletin, B30307, 1-32. [2] Grindrod P. M and Balme morphological zones, fluted near walls (imitating scar M. R. (2010) Geoph. Res. Lett. 37, L13202, 1-5. [3] morphology) and remnant located in further areas Hauber E. et al. (2006) LPSC XXXVII, Abstract #2022. (dark, fine-graded material). "Fresh" morphology of [4] Rossi A. P. et al. (2008) JGR, 113, E08016, 1-17. fluted deposits might indicate their younger age than [5] Quantin C. et al. (2004) Planet. Space Sci., 52, deposits of remnant morphology. Mass-wasting 1011-1022. [6] Quatnin C. et al. (2004) Icarus, 172, processes from Hebes Mensa are accompanied by 555-572. [7] Neuffer D. P. and Schultz R. A. (2006) accumulation of dark, fine-grained material (sand or QJEGH, 39, 227-240. [8] Neuffer D. P. and Schultz R. gravel) originated from the Mensa walls, the most A. (2005) LPSC XXXVI, Abstract #2076. impressive example is located west from the ILDs' mound (marked D1 in Fig. 1).

Fig. 1. Map of landslides in Hebes Chasma. L1-L10 - chasma wall derived landslides; Li1-Li5 - ILDs' slope derived landslides; D1 - the largest dark fine-grained material accumulation site in Hebes Chasma; lines - wall landslide scars; yellow lines - wall landslide deposits; blue lines - ILDs' landslide scars; purple line - ILDs' landslide deposits; red lines - main largest dark fine-grained material accumulation sites; dashed lines - uncertain extent of marked units. GoogleTM Earth, MRO/CTX mosaic, small box - MOLA topography.