VOLUMETRIC ANALYSIS OF THE REULL VALLIS FLUVIAL SYSTEM IN THE EASTERN HELLAS REGION OF MARS: INVESTIGATION INTO THE CONTRIBUTIONS OF WATER

This study evaluates the fluvial and erosional history of the eastern Hellas region of Mars by investigating the sources of water that carved the Reull Vallis outflow system. Reull Vallis is located east of Hellas Basin in the Hesperia Planum and Promethei Terra regions of Mars. We estimate the volumes of the morphologically distinct segments of the Reull Vallis system in order to determine the contributions of water to the system. Its source area (segment 1) is believed to have provided the water for the main canyon (segments 2 and 3). Teviot Vallis is identified as an additional source area that is believed to have enlarged segment 3 downstream. A large topographic depression, the Morpheos Basin, separates segments 1 and 2, and is believed to have stored the effluents of segment 1 until it breached its divide and carved segment 2. Previous researchers define the extent of the Morpheos Basin by the 650 m contour level, which we estimate could have contained 17,138 km³ of water. Our estimates of segments 1 (2,377.2 km³) and 2 (2,320.5 km³) suggest that water expelled from segment 1 could not have filled the basin to this level, and this volume of water would have formed a much larger segment 2 than is currently observed. Therefore, we chose to measure the volume of the basin at several additional contour levels (600, 550, 500, and 450 m), which suggests only the western side of the basin may have contained water. Volumes were estimated using the MOLA 64 pixels/degree DEM with the IDL-based module GRIDVIEW. Our results indicate that segment 1 was likely the sole source for the water that carved segment 2, and that the Morpheos Basin was likely filled to one of the lower contour levels. Our results also show that segment 3 is significantly greater than its source areas (segment 2 and Teviot Vallis). Several possible factors may explain this: 1) a second release of water from Teviot Vallis; 2) the presence of a pre-existing aquifer in the area around segment 3; 3) the drastic slope increase in the lower part of segment 2 may have increased eroding power of the water as it approached segment 3; 4) sediment buildup on the floors of the source channels could be underestimating their volumes; and/or 5) a blocked connection between the terminus of Reull Vallis and the head of Harmakhis Vallis may have resulted in backcutting of segment 3.