This image was originally targeted on an interesting set of dark sand dunes on the floor of a 20-kilometer (12-mile) crater north of the Alba Patera region. The dune field contains an array of dune bedforms from large domes and linear ripples to barchanoid ridges forming complex ridges and interconnected ridge networks with about 25-meter spacing (about 27 yards). The complexity of these patterns reveals a likewise complexity of wind directions and speeds, reworking dune patterns over time.

But in addition to these sand dunes are at least two other networks of patterns. At this latitude subsurface water ice is prevalent just centimeters below the surface. Over time seasonal contraction of the ice-cemented soil will form a honeycomb-like network of evenly spaced fractures. Refracturing over thousands of years can work the surface into a network of visible troughs with 10 to 15-meter spacing (about 11 to 16 yards).

What’s more, the central peak of this crater, an uplifted region of light-toned bedrock, exhibits an array of long crisscrossing fractures. These fractures are apparent in HiRISE images due to dark sand outlining the fracture zones. The fractures often appear to cross at acute angles and are spaced apart from one another by a few meters to many tens of meters.

The shape and spacing of various network patterns can distinctly reveal the geologic origin of each pattern. As is often the case with HiRISE images, a single image can capture a wide assortment of geologic features formed by quite different processes.



Written by: Mike Mellon  (16 September 2026)