Pluvial shorelines in Nevada and Oregon as analogs for features in crater lakes on Mars

Depositional and erosional landforms were examined within enclosed basins in Nevada and central Oregon in order to assess the detectability of possible pluvial features within crater lakes on Mars. A Trimble R8 Differential Global Positioning System (DGPS) was used to survey both shoreline sequences and erosional scarps (at the highstand level), all tied to USGS elevation controls. The studied features were developed during the latest pluvial episodes within the southern portions of Surprise and Long Valleys (western and eastern Nevada, respectively) and within Christmas Valley (central Oregon). The precision available from DGPS surveys (<2 cm horizontal and <4 cm vertical) demonstrated that elevations of both prominent shorelines (within a shoreline sequence) and erosional scarps at the highstand level (when present) could be correlated across horizontal distances of 5 km. The highstand level provided the strongest topographic signal in all three basins; 1533.4 m in Surprise Valley, 1908.7 m in Long Valley, and 1350.8 m (at Fort Rock) in Christmas Valley. Highstand level in Christmas Valley was more variable than those measured in the Nevada basins, most likely because some surveyed locations within Christmas Valley were separated by more than 60 km. Adherence of both depositional and erosional landforms to a geopotential elevation over length scales on the order of 5 km appears to be the best indicator that a feature is likely the result of pluvial processes. Shoreline profile shape, even at DGPS precision, was not diagnostic of a pluvial origin for these features. The results obtained from this study indicate that well-controlled elevations (<0.2 m vertical precision) of candidate pluvial features would be the most useful measurements for testing a pluvial origin for features within impact crater basins on Mars. This work was supported by Mars Fundamental Research Program grant NNX07AQ71G from NASA.