Ares Vallis Cataract
This Martian image shows a dry cataract within Ares Vallis. A cataract is a large waterfall where there is a high, steep drop. The presence of this large cataract in Ares Vallis confirms that this channel was carved by water, probably in one or many large catastrophic flooding events.
This feature has many of the same characteristics as the cataracts on Earth associated with the flood that carved the Channelled Scablands in Washington state, including horseshoe-shaped headcuts and longitudinal grooves. These grooves in the lower portion of the image lead up to the cataract, with the water flowing from the south to the north in this image. It then flowed down the cataract into the smaller incised channel.
The horseshoe-shaped headcut here is only part of a larger cataract system, and probably formed during the last stage of flooding. The inner channels are now filled with dunes formed by wind blowing along the channel floor.
Image PSP_003538_1885 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 29-Apr-2007. The complete image is centered at 8.4 degrees latitude, 335.6 degrees East longitude. The range to the target site was 276.0 km (172.5 miles). At this distance the image scale is 27.6 cm/pixel (with 1 x 1 binning) so objects ~83 cm across are resolved.
The image shown here has been map-projected to 25 cm/pixel and north is up. The image was taken at a local Mars time of 03:28 PM and the scene is illuminated from the west with a solar incidence angle of 58 degrees, thus the sun was about 32 degrees above the horizon. At a solar longitude of 228.1 degrees, the season on Mars is Northern Autumn.