Middlebrook, William David (2015-07). Three-Dimensional and Multi-Temporal Dune-Field Pattern Analysis in the Olympia Undae Dune Field, Mars. Master's Thesis.
Thesis
Fields of sand dunes are ubiquitous in the north polar region of Mars and provide a record of sand transport processes influenced by Mars' polar climate. Spatial and temporal variations in dunes, ripples, coarse-grained ripples, and exposed dune cross-strata were analyzed in two areas of the Olympia Undae Dune Field in order to assess the influence of the Martian polar boundary conditions on ripple and dune activity and on pattern development. Two- and three-dimensional parameters, including dune crest length, spacing, width, slope, and height, were statistically assessed using regression analysis and descriptive statistics. Sediment fluxes were calculated using Co-registration of Optically Sensed Imagery and Correlation (COSICorr), a program that precisely co-registers and correlates imagery, and by measuring dune displacement. Two-dimensional pattern analysis indicates the co-existence of two populations of dunes that can be interpreted as two generations or as forming simultaneously under sediment availability limited conditions. Three-dimensional pattern analysis shows an asymmetry in slope profiles of the primary dunes and is consistent with primary dunes forming transversely to constructional winds. Four different types of ripple crestline patterns are identified and likely arise due to differences in grain size and dune-modified wind speeds and secondary flow directions. Maximum measured ripple displacement in the center of Olympia Undae study area is ~1.4 m yr^-1 +- 0.13 m. Assuming a mean ripple height of 0.11 m and a 4:1 saltation to reptation ratio, the sediment flux is ~0.42 m3 m^-1 yr^-1. Adjacent to the polar ice cap, barchan dune crest displacements range between 0.25 m yr-1 and 2.80 m yr-1 and dune heights between 11 m and 31 m. Mean sediment flux is 3.5 m3 m-1 yr-1. Results indicate that there is a spatial decay in sediment transport across the field and that fluxes near the cap are comparable to those found in Nili Patera, Mars and Victoria Valley, Antarctica. Overall the polar boundary conditions seasonally limit sand availability by seasonal frost cover and subsurface ice. The polar boundary conditions are most influential at the dune pattern scale, but appear to have little influence on the ripple pattern or ripple mobility.
