Stripes by wind and gravity
Windy windows
April 11, 2016Old ripples
April 25, 2016
A Piece of Mars: This scene (800×450 m or 0.5×0.28 mi) is a steep slope, with high rocky outcrops on the upper right and both gullies and ripples heading downslope to the lower left. The wider, brighter stripes are gullies that were carved by stuff eroding from the outcrops and falling downhill, just like on Earth. Beneath that are some finer stripes: this time the straight lines are made by a combination of wind blowing sand into ripples (from upper left to lower right) and gravity elongating the ripples downslope (stretching them from upper right to lower left). (HiRISE ESP_044997_1755 NASA/JPL/Univ. of Arizona)
1 Comment
Dr Fenton, Thanks very much for your response to my comment back in March to “How Far Does the Wind Blow Stuff”.
You interpret this slope that is gullied and rippled as something like a scree or talus deposit at the top and a wind-rippled surface further down. I have trouble accepting that the gullied top of the slope is talus because it appears uniformly fine grained. Granted we might not be able to see the individual rocks on a scree slope from space, which should be sorted larger toward the bottom, but the material below this “scree” is apparently even finer grained being wind-rippled, and there are triangular slide scars on the slope that apparently cross the boundary into the wind-rippled area. I’m pushed toward seeing the entire slope, except the bedrock, as originally a wind deposit because only wind could accomplish this sorting. Also, if there has been relatively recent mass-wasting, it seems too active to match the erosion rate of the bedrock, which is likely to be extremely slow compared with aeolian movements of material.
I’ve been interested in mass wasting imaged by the rovers since Opportunity reached Santa Maria Crater, and I’ve been thrilled after collecting all examples at Gusev and Meridiani to see so many more appear at Gale. There’s been some real science published on this now, in this year’s LPSC: Dickson, Head and Kulowski of Brown University. “Active Flows at the MSL Landing Site: Results from a Survey of Mastcam Imagery Through Sol 971.” (Sorry, I’d place a link here but I’m not sure how the blog software might interpret it.)
These authors interpret the hundreds of examples of this very active recent process as basically a wind-driven system. It has no obvious analog on Earth. I know Dr. Head has also published papers about the slope streaks visible from space, so now I have high hopes that the connection will be made between all the ground-truthed slope activity in the rover archives and the bigger activity visible from space. At this point they are equally mysterious, but any scientist interested in aeolian processes on Mars should be interested in this paper. Thanks again.