A geomorphological analysis of Ares Vallis, , using HRSC data: new constrains about catastrophic floods and ice-related morphologies. A. Pacifici, G. G. Ori, G. Komatsu, and M. Pondrelli International Research School of Planetary Sciences, Universita’ “G. d’Annunzio”, Pescara, Italy. (pacifi[email protected]) Ares Vallis is one of the greatest outflow channels of Mars: it was extensively inves- tigated in the past decades, also to support landing site analysis of the 1997 NASA Pathfinder Mission. Using high-resolution images of last Martian missions (MGS, Mars Odyssey, and MEX), we investigated Ares Vallis and its tributaries, taking also advantage of 3D analysis performed using the MEX HRSC stereo capability. Ares Vallis appears to be characterized by different morphological associations along its path. We ob- serve and investigate grooved terrains, streamlined uplands, pendant bars and several thermokarstic features: detailed measurements of such features are performed, and their geological properties are suggested. Observed morphologies give new constrains about catastrophic floods, and concur to provide a possible geologic history of the trough. Our investigations revealed that Ares Vallis and its tributary were sculpted by several catastrophic floods, well spaced in time, and originating from Iani, Hydaspis and . Floods were responsible for sculpting of grooved terrains and streamlined uplands. During these catastrophic events, climatic conditions of the planet are assumed to be similar to those of today, and ice probably formed on top of the floods. Consequently, at the end of each flood, ice masses grounded and joined to each other and formed a thick stagnant dead-ice body. Floods of lower magnitudes and possibly different in origin were responsible for the emplacement of ice contact deposits. Several pieces of evidence for sub and/or intra-glacial floods are observed. Finally, we observe associations of pitted surfaces and high values of emittance on Infra-Red Thermal images. This association is proposed as an indicator of the exis- tence of buried ice bodies today or in the past.

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