Breaking Down Walls

Boulders on the rim of Moore F
Gravity is winning as boulders tumble down from the rim of Moore F (~24 km in diameter) in this LROC NAC mosaic (M1156517189) [NASA/GSFC/Arizona State University].

Moore F is located in the highlands of the lunar farside. Its well-defined rim, steep walls, and the predominance of boulders suggest that it is quite young. Over time, micrometeorite bombardment, the shock from more recent impacts, and other erosional processes break down the rock that composes the crater rim, walls, and floor. The result will eventually be a smoother, more subdued appearance.  The many large blocks suggest that Moore F has only just begun to break down.

The impact process left Moore F with exquisite impact melt, abundant terracing, and a stunning central uplift, but a closer look reveals subsequent modification courtesy of gravity that has yielded even more entrancing beauty in the flows streaming down its walls, as in the NAC image below. 

Granular flow in the wall of Moore F
LROC NAC image displaying granular flows in the wall of Moore F highlighted by the dramatic lighting of a low sun. Downhill is to the southeast (bottom left). Image width is approximately 8 km [NASA/GSFC/Arizona State University].

The streaks we see on the walls of Moore F in the image above are likely made of granular material  that acted like a fluid as it slid downslope. But how do we know if the flows formed by the downslope movement of dry, fine-grained material? The sources of the flows can be traced to specific locations and outcrops along the rim of the crater, suggesting that this is material from the rim that was disturbed and flowed downslope. The slightly braided appearance suggests multiple depositional episodes. These episodes could have been triggered by collapsing material from the rim or wall, boulders (like those in the opening image) knocking material loose as they hurtle downhill, or by shockwaves from nearby impacts.

WAC context image of Moore F
LROC WAC image of Moore F. The red box denotes the location of the NAC mosaic from which Today's Featured Image was taken. The yellow box shows the location of Today's Featured Image. Image width is approximately 94 km [NASA/GSFC/Arizona State University]. 

Investigate this incredible NAC mosaic below!

Related Posts:

Erosional Trough on Crater Wall

Moore F Crater DTM

Granular Flow

Tender Tendrils

Dry debris or liquid flow?

Fresh Copernican Crater


Published by H. Meyer on 24 June 2014