Fractured Melt Rock

A portion of western crater wall inside Jackson crater (72 km diameter). LROC NAC M182253065R. Image center is 22.534°N, 195.59°E, image width is 2130 m. Illumination is from left side of this image, incidence angle is 57° [NASA/GSFC/Arizona State University].

The opening image highlights a fractured pond of impact melt rock inside Jackson crater (72 km diameter). This prominent farside crater is known by its prominent ray system and large amount of impact deposits. Melt pooled not only at the bottom of the crater floor, but also on terraces of the interior wall. 

The fractured melt sheet in the opening image is found amongst a grouping of melt lakes on a western crater wall terrace (see WAC context image below). Detached fragments from the main body of melt sheet look like a jigsaw puzzle (upper smooth surfaced portion of the image). These fragments give an impression of the thin and brittle nature of solidified impact melt. Shadow lengths show these fractured pieces to be 5 to 8 m thick. What caused the once level and smooth ponded surface to fracture? We don't know for sure, but by looking at the whole area a plausible story can be imagined. The south part of the melt lake with the fractured plates is connected to another melt lake at a lower elevation. Perhaps drainage of subsurface unsolidified melt might have dragged a crust toward the south and broken the it into many blocky pieces. Tectonic deformation of the crater wall, perhaps consisting of whole terraces deforming, also might have occurred which could deform the brittle crust of melt ponds.

Western part of Jackson crater and surrounding areas in LROC WAC monochrome mosaic (100 m/pix). The NAC footprint (blue box) and the location of opening image (yellow arrow) are indicated [NASA/GSFC/Arizona State University].

Explore this mosaic of fractured melt rock and surroundings to unravel the complex history of Jackson crater below!

Related posts:

Fragmented Impact Melt


Melt Fractures in Jackson Crater

Cracked mound

Polygonal fractures on Tycho ejecta deposits

More Impact Melt!

Published by Hiroyuki Sato on 22 October 2013