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Terrain softening is a term describing martian terrain that has apparently undergone a reduction in topographic relief due to the downslope movement of surficial material. Softened terrain is included here because the wind may play a role in its formation. One type of terrain softening consisting of lobate debris aprons around older knobs is shown here. Whether the debris is derived from the knob itself or is the slumped remnant of an airfall deposit that once covered the entire area is under debate. The convex-upward profile of the debris, the presence of lobate flow margins (white arrows), and the deflection of the apron around obstacles (mixed arrows) are overwhelming evidence that flow has occurred. The mobility of the apron material is presumably enhanced by the lubrication caused by a high content of volatiles. Erosion, presumably wind-caused, has sculpted the upper surface of the apron since flow took place, forming moats (black arrows) around some of the knobs. Location: Latitude 46.4°, Longitude 311.4°. Viking orbiter photograph 338S31, NGF orthographic version, clear filter. Click here to view a high-resolution version of the image (2.05 MB)
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