Figure 19.

Inferred origin of the breccia zones in the inverted terrain study area, Mars. Outcropping rock includes thicker light-toned layers of Unit 4 composed of fine silty and clayey sediments and possibly thinner, probably granular, dark layers. Both are saturated with water ice. There is a permafrost substrate (surface indicated by dashed line) overlain by the lowest light-toned sediment and a capping layer of debris and regolith. Partial melting at the top of the permafrost results in destabilization of the overlying bedrock and surface debris, failure, and sliding. Progressive upslope stepping of the headward fractures exposes additional rocks to sublimation and possible melting, promoting additional downslope sliding. Downslope the size and proportion of light blocks diminishes due to block fracturing, melting, and sublimation. Displaced blocks are shown stippled; the finer matrix in gray.