Evidence for very recent melt-water and debris flow activity in Istok crater, Mars A. Johnsson (1), D. Reiss (2), E. Hauber (3), H. Hiesinger (2), M. Zanetti (4). (1) Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden (2) Institut für Planetologie, Westfälische Wilhelms-Universität, Münster, Germany. (3) Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany. (4) Earth and Planetary Sciences, Washington University in St. Louis, McDonnell Center for Space Sciences, St. Louis, MO, United States (andreasj@gvc.gu.se /Fax: +46-31-786 19 86). Abstract We report on very young (~0.2 Ma) and well- preserved deposits of water bearing debris flows in Istok crater, Mars. Debris flows postdate the latest dust-ice mantle emplacement. A model of melting of recent snow packs is proposed as a water source in Istok crater. Asymmetry in slope degradation demonstrates that insolation-controlled slope processes (including gully formation by debris flows) are surprisingly efficient on Mars under very recent climate conditions. 1. Introduction Gullies on Mars are known to display a range of different morphologies but typically include an alcove, channel and apron [1]. Several processes have been invoked to explain their genesis ranging from dry granular flows [2], debris flows [3] to fluvial erosion with alluvial deposition [4]. Albeit there is a general consensus that the medium involved is water, more attention is now drawn towards the dominant depositional processes of the gully fan formation. The observed range of fan morphologies asks for several depositional mechanisms which likely vary at different sites due to regional and local differences in climate and source material. Studies indicate that the common mechanism is fluvial deposition [5] in contrast to debris flow-like deposits which have only been documented at three sites [5,6,7]. These sites formed deposits of seemingly fine dusty mantle material. Here we report on unusually well preserved Martian debris flows in Istok crater which is rich in clastic material that forms pristine debris lobes, debris plugs and lateral levees. It also displays numerous fresh looking rock falls with distinct boulder tracks. This raises the following questions: Why does so well- developed debris flows occur here and not in other nearby craters? What role does the clastic material play in debris flow initiation and development? 2. Observations and results The Istok crater is a well preserved 4.7 km-diameter crater located in the Aonia Terra region (centered at 45.11°S; 274.2°E). Istok is superposed on the ejecta blanket of a much larger 17 km-diameter rampart crater. The nighttime THEMIS-image of Istok’s ejecta point to a surface of either blocky or consolidated sediments (Fig 1). Figure 1. Nighttime THEMIS-IR (I31123004RDR) highlights the rayed ejecta which suggest unconsolidated, blocky material with limited aeolian deposition and reworking. Image credit: NASA/JPL Caltech/Arizona State University. Due to the underlying unconsolidated ejecta the former is favored. Numerous debris flow deposits are present at the pole facing inner wall of the crater (Fig. 2A) forming a bajada. Distinct, meters high levees are seen (Fig 2B), overlapping lobe fronts (Fig. 2C), and more recent fan structures (Fig 2D). Within debris flow channels debris plugs with rounded termini are clearly visible (Fig. 2E). The crater floor display numerous fresh appearing rock falls, with sizes ranging from less than a meter to ~2.5 m. The pole facing deposits display a high fraction of clastic material. EPSC Abstracts Vol. 9, EPSC2014-491-1, 2014 European Planetary Science Congress 2014 c  Author(s) 2014 E P S C European Planetary Science Congress