MORPHOMETRIC ANALYSES OF TERRESTRIAL-MARTIAN ANALOG CHANNELS AND POINT BARS: IMPLICATIONS FOR THE USE OF RADII OF CURVATURE IN PALEOHYDRAULIC ANALYSES

Regions on Mars (e.g., Meridiani Planum, NW Hellas, Aeolis Dorsa) and some candidate landing sites (e.g., Eberswalde, Jezero Craters) preserve diverse fluvial deposits that can yield important paleohydraulic information. Deriving such information requires morphometric relationships. For example, the relationship between channel radius of curvature and channel width may be coupled with width-discharge relationships to estimate paleodischarge. On Mars, paleochannel width and radius of curvature may not be preserved in negative-relief and therefore, these dimensions must be inferred from deposits, such as point bars. Here, we analyze the relationship between point bar radius of curvature (R_c) and bankfull channel width (W_b) in two fluvial systems – rivers on the North Slope, AK, and the Quinn River, NV – that were previously examined as terrestrial analogs for fluvial deposits in the Aeolis Dorsa region, Mars. We measured point bar radii of curvature by delineating circle arcs over point bar ridges in high-resolution visual images and topography. Radii were calculated from chord lengths between the ends of ridge arcs, the distance between chords and arcs, and rearrangement of the theorem of intersecting chords. Radii were coupled with a commonly used morphometric relationship (W_b=0.71*R_c^0.89) to estimate bankfull width. We find that this technique approximates actual width for Alaskan rivers, but overestimates width for the Quinn River by ~400%. These Alaskan rivers flow through vegetated, permafrost, and sand-rich floodplains that are sufficiently stable to promote meandering. The Quinn River flows through cohesive, paleo-lacustrine clays and silts, which promote meandering in the absence of vegetation. However, limited bank erosion along the Quinn River may enhance downstream migration and enlarge point bar radii of curvature relative to channel width, although for us the causality of these fundamental relationships is under investigation. These results suggest that applications of morphometric relationships to Martian meander deposits should consider downstream migration, preserved as enlarged or asymmetric point bars, as the morphodynamic effect of resistant channel banks. Misrecognition of this effect may lead to overestimation of paleochannel width and therefore paleodischarge.