This observation 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.
Photo credit: NASA/JPL/University of Arizona
2 comments:
Hmmm ... having just returned from a 2 week geo-tour in the Washington Scablands (Aug-Sept 2014), I really cannot identify the elements you describe. Exactly where is the cataract/headcut in this image - and where is the incised channel ? I feel that this is important given the very few examples of such features known on Mars ... yet the purported analogy with WA Scablands is all over the literature.
Simon (PhD, Geology)
Simon:
First, thanks for visiting.
Second, the original caption (which I merely copied-and-pasted from the HiRise site) was written by an Alexandra Davatzes (http://www.uahirise.org/PSP_003538_1885). She (if she's still affiliated with HiRise; the commentary was written four years ago) might be reached through HiRise's contact page (http://www.uahirise.org/contact/).
Lastly, and this is purely a guess on my part, but perhaps Alexandra had based her caption upon the larger contextual images (see the "Image Products" section of the page) as opposed to the featured image that shows up on my blog.
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