R. E. Arvidson

Wind-blown streaks, splotches, and associated craters on Mars - Statistical analysis of Mariner 9 photographs

Abstract Crater morphology and size play a major role in determining whether wind-blown streaks emanating from craters or dark splotches within craters will form. Both bright and dark streaks emanate almost exclusively from bowl-shaped craters. Dark splotches are found mainly in flat-floored craters, especially those that are deep and have high rim relief. Trends of dark splotches in the northern to southern midlatitudes closely follow those of bright streaks, suggesting both were formed by similar winds. In the high southern latitudes, on the other hand, dark splotch trends closely follow those of dark streaks. Qualitative models of streak and splotch formation have been derived from these data and results of Sagan et al. (1972, 1973). Bright streaks probably form by trapping and simultaneous streaming of bright dust downwind. Dark splotched craters in regions with bright streaks usually have upwind bright patches, suggesting these features form by dumping of bright dust over crater rims with some minor redistribution of dark materials toward the downwind sides of craters. Data are consistent with dark streaks forming by erosion or nondeposition of bright material or by trapping of dark material. Dark splotches in these regions are probably mainly the result of trapping of dark sand in the downwind sides of crater floors. Craters with dark splotches and dark streaks are usually rimless and shallow. This is consistent with ponded dark sands easily washing over crater walls and extending downwind. Plots of streak length versus crater diameter suggest a complex history of streak formation for most regions. Bright streak trends and latitudinal distributions are consistent with return flow of dust to the southern hemisphere. Some dark streaks may be direct relics of passing sand and dust storms. Trends of dark streaks and splotches away from the south pole are consistent with the spreading of a debris mantle from the polar regions toward the equator.

Craters and associated aeolian features on Mariner 9 photographs - An automated data gathering and handling system and some preliminary results

Craters and associated aeolian features visible on Mariner 9 photographs have been examined. An automated system used to gather, reduce, and store data may have application to other types of planet-wide geological studies. A brief description of the method used to accumulate data is presented, along with some preliminary results for A-frames.

Sedimentary Patterns in and around Craters from the Pinacate Volcanic Field, Sonora, Mexico: Some Comparisons with Mars

We present results of a reconnaissance study of sedimentary patterns around the Pinacate volcanic field and adjacent Sonora dunes. A cinder cone located in the dunes west of the Pinacates has acted as a sand-migration barrier and has formed a sand-free shadow downwind. This may be analogous to the manner in which dark streaks form downwind of Martian craters. Orbital and aerial photography of the Pinacates suggest that maars adjacent to the Sonora dunes are being infilled by dune sand. However, petrographic data suggest that erosion of friable tuffs and tuff breccias from crater walls is the dominant process filling in all of the craters. The Martian situation is presently less complex than terrestrial examples, such as the Pinacates, since wind seems to be the dominant agent. Water erosion, however, may have been active in past history, and Martian craters may have been modified in a manner analogous to the Pinacate maars.