Erosional trough on crater wall

Erosional trough (400 m long x 100-200 m wide) on the eastern inner wall of the farside crater Moore F. Morphologically it resembles a martian sapping feature, suggested to form due to erosion by water flowing out of the subsurface. LROC NAC image M128075293R, image width is 500 m, Sun is coming from the lower right. [NASA/GSFC/Arizona State University].

A number of erosional troughs are observed on the inner wall of Moore F on the lunar farside. The crater is 23.7 km in diameter and is relatively fresh, as evidenced by bright ejecta and its pristine morphology. Numerous troughs are observed extending down the inner crater wall. The feature shown here is the freshest with a smooth floor composed of bright material. The trough is about 810 m long; it is ~140 m wide near its head, narrows slightly to about 105 m in the middle, and then widens to some 200 m.

Several other older troughs occur along the crater wall to the north and south of this feature. They all appear to begin at about the same level of the crater wall, an area marked by what appears to be discontinuous outcrops of bedrock. The older features are darker, with an albedo similar to the surrounding terrain, as opposed to this feature, which has a considerably higher albedo.

These features resemble so-called sapping features observed on Mars. The martian features are suggested to be formed by the release of ground-water along a cliff face causing headward erosion of the trough. In these lunar examples, it is highly unlikely that ground water occurs. Presumably the features are the result of dry debris flows of fine-grained, unstable material. Once mobilized, the dry granular flow broadened into a fan-shaped deposit. Here the material extends more than 1 km downslope from the mouth of the trough.

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Published by Jeff Plescia on 24 November 2010