Nilosyrtis Mensae - Erosion on a large scale
The northern and southern hemisphere of Mars are fundamentally different with respect to their surface topography, age, and morphology. The northern hemisphere is smooth and has lower elevations compared to the heavily cratered high-standing southern hemisphere. An escarpment that marks a topographic difference of several kilometers characterizes the transition zone between both. The landscape in this region has been deeply dissected through the action of water, wind, and ice.
The region Nilosyrtis Mensae is delineated fretted terrain, because of its numerous labyrinth-like valleys that often exhibit viscous flow features. Dissection by water and ice left rounded hills and mesas. Many landforms throughout the image have a softened appearance attributed to extensive degradation. The former impact crater to the right of the image was flattened and widened over time due to fluvial erosion and infilling with sediments, so that the crater relief nearly disappeared.
The valley floors especially in the northern part of the image show linear ridges and grooves that can be traced along the course of flow. These textures suggest that icy material once slowly flowed down the valleys, possibly in the form of debris-covered glaciers similar to rock glaciers found on Earth. Rock glaciers are bodies of ice interspersed with boulders and rocky debris found primarily in regions of permafrost on high mountain ranges or at polar latitudes. The glacier-like deposits could represent leftovers of a retreating ice sheet that has covered the region during recent Martian ice ages. Former climatic conditions on Mars obviously allowed for the accumulation of significant amounts of snow and ice on the plateaus and in the valleys.