Crater streaks in the Chryse Planitia region of Mars: Early Viking results

High-resolution images of Chryse Planitia and eastern Lunae Planum from the early revolutions of Viking Orbiter I permit detailed analyses of crater-associated streaks and interpretation of related eolian processes. A total of 614 light and dark streaks were studied and treated statistically in relation to: (1) morphology, morphometry, and orientation, (2) “parent” crater size and morphology, (3) terrain type in which they occured, (4) topographic elevation, and (5) meteorological data currently being acquired by Viking Lander I. Three factors are apparent: (1) light streaks predominate, (2) most streaks form in association with fresh bowl-shaped craters, and (3) most light streaks are of the “parallel” type, whereas dark streaks are approximately evenly divided between convergent and parallel forms; moreover, very few light or dark streaks are divergent or fan-shaped. Light streaks have an average azimuth of 218° (corresponding to winds from the northeast), which approximates the orientation of 197 ± 14° for eolian “drifts” observed by the Viking Lander imaging team (Binder et al., 1977). This lends support to the hypothesis that light streaks are deposits of windblown sediments. Dark streaks are oriented at an azimuth of 42° (approximately opposite that of light streaks) and are nearly in line with the dominant wind direction currently recorded by the Viking meteorology instruments (Hess et al., 1977). Although the size of the sample area is not uniform among the various terrain types, the highest frequency of streaks per unit area occurs in the knobby terrain. This is partly explained by the probable production of fine-grained material (weathered from the knobs) to form streaks and other eolian features, and the higher wind turbulence generated around the knobs. The lowest frequency of streaks occurs on the elevated plateaus. The light streaks in Chryse Planitia appear to be relatively stable and to result from deposition of windblown material during times of relatively high velocity northeasterly winds. Dark streaks are more variable and probably result from erosion by southwesterly winds. Both types will be monitored during the extended Viking mission and the results compared with lander data.