LRO image of the Moon: Alphonsus Crater Mantled Floor Fracture
LROC NAC closeup of a fracture in the floor of Alphonsus crater. Dark pyroclastic materials are intermixed with lighter rocks and boulders from the fracture walls and all appear to have moved in streamers toward the fracture floor at upper right. A NASA Constellation site is centered just to the southeast of this view. Image width is 538 m, NAC image M111606491L [NASA/GSFC/Arizona State University].
Many fractures on the Moon are seen in the floors of ancient, flat-floored highlands craters. Such fracture networks often encircle all or part of the crater floor, and in some areas they show accumulated deposits of dark volcanic material. This NAC image above (538 m across) shows a portion of one such fracture, located in the northeastern floor of Alphonsus crater. The fracture has been mantled by a dark, fine-grained pyroclastic deposit that appears to have moved down the wall of the fracture (at left) toward the floor (out of view to the upper right).
The wall of the fracture is composed of light-colored rocks that are typical of the lunar highlands (mostly composed of anorthosite). Rocks and boulders of this bright material have also moved down the fracture wall; the largest one (near the top, center of the image) is about 8 meters across in its longest dimension. In some areas near the top of the fracture wall, dark boulders and mantling materials are seen. It is likely that this dark volcanic material came from a nearby volcanic vent located along this fracture network.
