Outcrops in Laplace A

Debris flows and outcrops exposed in the walls of Laplace A crater. Illumination from southwest, image is ~525 m across, down-slope is to the right, LROC NAC M137725771R  [NASA/GSFC/Arizona State University].

As with many mare deposit exposures when viewed at the Narrow Angle Camera imaging scale of 0.5 m/pixel, the bedrock outcrops in the walls of Laplace A appear as layered ledges. The layers are most noticeable in the north-northeast to south-southwest trending rocks visible in the northeast quadrant of the frame. Additional indications of layering can be found in the full NAC image (below). The prominent V-shaped outlines to some of the outcrops are suggestive of constructional deposition. Granular debris flows cascading down the crater walls following excavation appear to have encountered the obstructing ledges and "dammed up" behind them. Resistance to flow in such situations takes on a tapered shape in the direction of flow as the material becomes compacted. Minor occurrences of impact melt may be contributing to the smooth appearance of the flow deposits between the outcrops.

Laplace A is an approximately 9 km-diameter impact feature in the mare where Sinus Iridum meets Mare Imbrium. If you have access to a small telescope, it is a challenging target for the eyepiece!

The WAC mosaic shows the surrounding mare of Sinus Iridum and the whole of Laplace A. Image is ~ 80 km across, north is up [NASA/GSFC/Arizona State University].

Once again, the full NAC image can be found below. Additional examples of both layering and debris flow in crater wall exposures can be found in the following Featured Image posts: Dawes, Pytheas, and Layering in Messier A.

Published by James Ashley on 8 February 2012