Yardangs - More Interesting Than I First Thought
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by Kitharode moderator
There's a good post about yardangs on the Blog: http://blog.planetfour.org/2013/01/15/you-have-asked/ with a nice image of yardangs included.
Slightly more detailed is this from Wiley Online Library...
A. Wesley Ward.
(Article first published online: 28 DEC 2012)"Yardangs are streamlined erosional wind forms, similar in form to inverted boat hulls, that in terrestrial deserts range from meters to kilometers in length. On Mars the best examples are seen in the equatorial region. In the Amazonis region, hundreds of ridges and sawtooth-edged mesas have been wind sculptured in layered rocks. Individual ridges are tens of kilometers long with intervening valleys nearly 1 km wide.
The wind-stripped surface seems to be relatively young and therefore must be easily erodible. Possible lithologies include ignimbrites, mudflows, or lithified regolith. Other wind-sculpted features occur in the Aeolis region, in Ares Valles, and in the Iapygia region. White Rock, a light-colored plateau inside a crater, is interpreted to be a yardang cluster eroded in a deposit inside the host crater. White Rock may be a jointed, wind-eroded pyroclastic deposit. Yardangs on Mars, especially when they are sculpted in young geologic units, demonstrate that much of the observed eolian erosion is recent. Yardang azimuths often are not parallel with wind streak directions, indicating that the yardangs were formed by different (older or weaker) winds from those that formed the streaks".
Fascinating stuff. I just need to find out what an ignimbrite is and where to find the lapygia region on Mars. White Rock sounds like a good place to visit, so I'll have to get an image or two of that if I can. Yes indeed, yardangs are far more interesting than I first thought.
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by Kitharode moderator
Hahaha ... Great NASA article with images titled 'White Rock: Not White, Not Rock.' http://themis.asu.edu/feature/21
It lives inside Pallas Crater located at 7.9° S and 334.8° W so it's outside of Planet4's area of study really, but it's association with yardang thinking makes it an interesting object.
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by Kitharode moderator
JellyMonster. If you could make time to rotate this 180deg and repost it as image, I'd be more than grateful. It's from somewhere else on here, but can't remember who's using it. But I know it's a different angle so shouldn't be a problem. Thanks to whomever...
My title may not be as off the wall as it first appears. Once I get the view right, with deep channels firmly in view, I see frost-filled channels 'flowing' through a somewhat darker area of 'boulder islands'. Although the frost channels cut through the islands in a gridlike fashion there appears to be a preference to the direction of flow.
This 'preferred flow' is emphasised even more by the 'channeling' (?) which cuts across the top of the islands in the same 'prefered' direction. Aeolian perhaps? Might this really be a wind-driven yardang spider object? Has someone asked same/similar question before and that's where image comes from? Maybe...
http://planetfour.org/subjects/standard/50e742b85e2ed211dc002aad.jpg
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by JellyMonster
Done. I am now progressing onto colour edits. Wax crayon glitch now on left hand side.
![Kitharode] (https://dl.dropbox.com/s/hb3bibzxhv5h453/Kitharode.jpg)
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by Kitharode moderator
Top Man JM, thanks muchly. What a difference. Grid effect still there but not as strong. Lost the 'flow' a bit but there's a directional element in there, for me. Yes, I can see that the channels on top of islands are not so much grooved, but rather they are sculpted. But I would still argue a left to right orientation of the sculpted channels. So...
Hopefully you'll pick out any good bits in that little outburst. Do you see my boulder islands? That'd be a starting point.
I've got about 90% of the way with Dropbox. That 'Share Link' box is a bit weird but might crack it tonight. Cheers again...
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by Kitharode moderator
I am absolutely MESMORISED by JM's image presentation above. There are some tricky questions lurking in there I can tell you. This is undoubtably one of the most interesting images I've seen and honestly, I can't get away. Gonna let someone else have a go first, or you'll never get a word in, but if you see 'the sculpted isles' I'd like to hear what you think about 'both sides of the story' ..... ooo ... strange end.
Anybody else notice that when your view goes 'wrong', you get a close-up of a woolly jumper?
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by JellyMonster in response to Kitharode's comment.
Thanks Kitharode but I'm trying to understand what all the fuss is about. All I see is a woolly jumper (not the sort of thing I would wear), oh, and a fan of sorts. Hold on a bit longer though, as I need a bit more time to work out your cryptic message. Don't suppose you have the APF number for it?
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by Kitharode moderator
JellyMonster. You might just have it with fan!! Depends whether the 'fan' (hand/paw print) is quite large, made up of 'islands', and covers a lot of the right hand side of your inverted image. For now, I'm ignoring the top of the image where the tadpole blotch is and using the bottom 4/5ths of the image (ish). Thanks for feedback.
APF numbers. No, can't help. I think it might be useful to get a grip with them, though? New thread soon.
Late Edit: 'New' thread is here http://talk.planetfour.org/#/boards/BPF0000005/discussions/DPF0000cjr
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by JellyMonster
This is the same image as the 'planetfour' link that Kitharode put up, except, that it has been spun round. Unusually, what were channels now become ridges. What are those hairlines... they're all over the place?
![Yardang] (https://dl.dropbox.com/s/nw8eb0fi7ply9y5/Yardangs.jpg)
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by Kitharode moderator
How would I get along without you JM? Brill, as usual.
Two things I need someone to confirm: The direction of light in the blog image, which will also tell me the direction in JM's image (it'll be opposite). Are the 'yardang ridges' the thin lines or the wider lines?
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by JellyMonster in response to Kitharode's comment.
Muchas gracias senor. I thought the 'yardang ridges' were the thinner lines?
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by Kitharode moderator
Oh goody, because I thought the same. They could well be ridges, but now I'm not quite clear about what I mean by 'ridge' and how they are structured. I'm a real 'newbie' when it comes to yardangs, so I'd like to move slowly at first.
Without looking at them properly I'd formed the impression that the ridges were like a long linear triangle of hard rock, sticking up out of the 'red' landscape, with wide (if shallow) depressions between them where the wind had taken away the more friable material. 'Ridge and furrow' if you will, but with harder ridges and wider furrows.
I'm trying hard not to see the thin lines as channels, so I make sure to try and get ridges. Best I can manage though is to get the ridge to appear like a thin linear slice standing apart from the 'furrows'. Hope you can see why I need to get a basic understanding of what's what here. What bits are higher, what bits are lower, what height difference are we talking, is dust taken away or does it help form the ridge? Blimey, I really am a newbie on this - I don't know anything! Am gonna reread the blog entry and other stuff to see if that helps.
Hair lines. Well spotted. I've not seen these before and I've no idea. Might come up with something hairbrained later on when I've got my head around the ridge thing. (Late edit: just noticed that's a joke) 😉
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by JellyMonster in response to Kitharode's comment.
I have noticed that these hairlines appear on quite a few images. Take a look at the new post 'Mini craters' in Science.
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by wassock moderator
I asked either Meg or Anyway about the fine lines a while back. They have them down as cracks/not there in summer images. But they are on EVERY one of the 'red yardang' images. To mymind if you were looking at aerial earth photos you'd say they were animal pathways and I am sceptical of them as cracks cost they don't have many fans
There are 2 things that trouble me, one is the you get spiders running across the ridges and the other is that there are straight line vents which also lie across the ridgelines. Can't see how either of those work
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by Kitharode moderator
I'll read Anya for Anyway, but correct me if I'm wrong. 😉 I've asked Meg if she can find us a height for the ridges, or a depth for the depressions, and if she does I've asked her to drop the numbers in here.
If you say the lines are on every red yardang, I'll take it as fact. I've certainly seen the thicker ones before, but now I'm looking more carefully I see them everywhere. You're right also about rarity of fans. Generally small if you do find one.
I'm most surprised to hear that the lines do not appear in summer, or summer images at least. I'd got them down as thin spider channels and was about to incorporate them into a 'story' elsewhere. Won't go into it here, it'll break the thread. So if they aren't there in summer then they aren't channels in the surface, as I thought, so they come and go. If that's true then I need to get away from regolith and move above the non-existant channels.
So am I looking at an area of yardangs covered in a very thin, very transparent layer of ice, and the lines are thin cracks in this icecover? Could be I suppose....
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by wassock moderator
Felting very thin Ice doesn't fit the theory for getting fans which are there. There's one image with a standard type fan in it a fine line which skirts the up wind side of the vent. Will go seek.
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by Kitharode moderator in response to wassock's comment.
With 'F' and 'M' not being neighbours on my querty I have to ask the question in case you mean something I've missed. By 'Felting' ice do you mean 'Melting' ice? Assuming you do, then yes, the theory begins to look as thin as the ice when it comes to getting fans in yardang country.
At the same time though, fans seem rare and small. Only need a small hole in thin ice? Only small pockets of gas space available, enough to break through thin ice but not enough to create big fans? Few spits of loose grust but doesn't scrape surface so no channels in summer? All guesswork.....
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by Kitharode moderator
Just to be clear. When I say lines I'm talking 'hair' lines. The thin lines that often meander about the place. The other wider-spaced 'tram' lines are my ridges with the wide 'depressions' between them. The ridges and depressions together are yardang (or so I've read). It was the thin meandering hair lines that I'd seen as channels, perhaps thin spider channels. But the can't see them in summer thing muddies that idea.
Found some numbers from wikipedia that are useful:
Mega-yardangs, meso-yardangs, and micro-yardangs. Mega-yardangs can be several kilometers long and hundreds of meters high and are found in arid regions with strong winds;
Meso-yardangs are generally a few meters high and 10 to 15 meters long and are commonly found carved in semiconsolidated playa sediments and other soft granular materials;
Micro-yardangs are only a few centimeters high.
I'm posting the above elsewhere, along with more wiki yardang stuff, but it's a very different thread. I'm hoping that this thread can stay leaning towards the 'stripey' yardangs and hair lines, with the other place leaning towards the 'sculpted island' idea. In both places we're talking yardangs (of this I'm sure) but if I'm right in my thinking, then we're talking recent yardangs here and earlier yardangs in the other place. I hope you'll see the distinction if/when you visit and that you'll help me prove my 'theory'. Oh yeh, the other place is 'Yarders and Spidangs' thread.
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by Kitharode moderator
Yardangs on Mars demonstrate that much of the eolian erosion is recent since they are sculpted in young geologic units. (Wikipedia)
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by JellyMonster
The 'hairline cracks' seem to be raised? Part image zoom from the one above.
![Cracks] (https://dl.dropbox.com/s/5ld8v7k2s44yxb3/YardangsZoom.jpg)
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by Kitharode moderator
I have to agree that the hair lines looked raised. My spider channels are doomed here so rethink required.
But I reckon they're only just raised. I'm guessing they will eventually 'blend' into the background. I've a feeling that we're looking at the end of a process here. In the wider view, the 'red' landscape appears somewhat stipled (I use sculpted elsewhere) but in this closer view I clearly see a 'golf ball' effect where the stipled surface itself is densely pitted.
Some of the hair lines appear continuous, but others tend towards a 'string of beads' effect where they appear to be broken. Creeping in from the lower right corner I easily see a hair line that is now all 'beads'. It's difficult for me to imagine these ridge hairs growing from the surface to stand proud (although we are on mars), but with smooth lines, and broken lines, and beads of lines on a pitted surface I've no difficulty at all with seeing the lines blending into the background. Please don't ask me how (yet).
Good wizardry again JM.
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by JellyMonster in response to Kitharode's comment.
I wouldn't take too much notice of the stippling effect, as I think it has been caused by the method used to enlarge the image. I go up in steps of 10% (called step interpolation).
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by Kitharode moderator
"A yardang is formed in cohesive material. Depending upon the winds and the composition of the weakly indurated deposits of silt and sand from which they are carved, yardangs may form very unusual shapes — some resemble various objects or even people". Wikipedia
I see lots of that in the image above. But you need to see the 'red islands' as raised blobs. Yeah, got this sorted I think (the pride before the fall) but I'm not sure how to put it into words. It's coming together nicely though. Now if someone could find an image just like the one above, with just a few more definate spider channels involved, well....now then....that'd be good. Maybe I'll get lucky..... 😉
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by Kitharode moderator
I've got info scattered all over the place but I'm sure I've got something that confirms the stipling is real. Can't remember exact wording so I'll try and find it to post here. All to do with old layered deposits being exposed after newer ones eroded, or similar. Hmmm ... it's a time thing, change, evolution, gotta be.
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by Kitharode moderator
Test for Dropbox: https://www.dropbox.com/s/4y40wmnmwp5q5zj/Yardangs in Tsaidam Desert.jpg
Image from wikipedia, so v small on my screen. These are yardangs on Earth from ground level. Imagine this area is packed with these yardangs, leaving just enough room to meander around and between them. Then imagine looking down on that packed yardang area. It'll be something like your image above. The Earth yardangs may be a little taller than ours, and they taper at the top, but hopefully you'll get what I'm trying to describe.
These are my 'islands' in your image, with their stipled tops. But if you can't see islands....Does image work?
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by JellyMonster
Thought you might like this one... mini spider top right? Original image here - APF0000o6g. Mine has been spun etc.
![Yardang] (https://dl.dropbox.com/s/13x5x72l3b5ybnh/R-50e7405a5e2ed211dc001dbd.jpg)
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by JellyMonster in response to Kitharode's comment.
I've looked for more of these type of images but can't find any... must be a one-off 😃
Kitharode, this is not the same stippling effect as was mentioned in your other yardang post. If you have a look at some of the other image enlargements I have done, the effect will be noticeable on them too.
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by Kitharode moderator
Thought it might get easier to read these images with practice - How wrong can yer be?
Tough for me to see a thin spider in there. The hair lines are there again, very thin. The rustgrust can't be a glitch this time, can it? 😉
Found the Sculpted Islands yet? (PS. Think Dropbox sorted, got irfanview now)
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by Kitharode moderator in response to JellyMonster's comment.
Just got Irfanview downloaded. Can't do wizdardry stuff yet, but did get a look at the 'zoom stipling' so I know what you're saying now. If you can see my dropbox effort in previous post, then is the effect seen where sky meets yardangs what we're talking about? A kind of stipled halo following tops of yardangs when you zoom in?
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by wassock moderator
Here is one I saved earlier APF0000970 - straight line vent across the ridges,fine lines and a proper baby spider in the middle.
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by Kitharode moderator in response to wassock's comment.
Nice one. A few hairs in there. I'd go with baby spider in middle. And, it reminds me to look in my linear venting collection (nice example in your image) to see if there's anymore clues to be found. Those hairs are strange.
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by Kitharode moderator
Concerning the yardangs; I can tell you one thing for sure. There's more to them than just stripes. Blimey.
I've just started having a look at the 'history' and variety of yardangs via HiRise pages. Unbelievable. There's so much to be had from every image that I've had to drag myself away.
(Gonna be fun when a certain guy gets his own board to play with). 😉
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by JellyMonster in response to Kitharode's comment.
Tough for me to see a thin spider in there.
I should have said, on the right hand side, near the top. If it is not a spider then what is it?
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by Kitharode moderator in response to JellyMonster's comment.
My problem is: If zoomed out I don't see it, but zoomed in I see too much. Lots of stuff I 'don't know what it is' so I might have seen your spidery thing, or might not. Even if I have, I'm guessing I don't know what it is. I'll make a brew and see if that helps...
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by JellyMonster
Maybe it's me? But how come you can see tiny spiders (the width of a human hair) but not small ones 😃.
Hint - divide the image up into 9 equal parts. Use your numerical keypad (numbers 1-9) as a guide. Spider is in box 9, bottom right.
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by Kitharode moderator
Not you methinks, but my eyes. These images certainly play tricks with your brain, eh? One day I'll see it and then wonder how I ever missed it. Sorry, but today ain't that day. Love the 'keypad 1-9' zoom in thingy - I'm nicking that.
We seem to be making some good progress though on understanding the images and some of the stuff in them. Also getting some vague idea of where things are - near pole, near equator, with ice, no ice, etc. Should have it all sorted in a decade or two 😉
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by JellyMonster in response to Kitharode's comment.
Should have it all sorted in a decade or two 😃
Hahaha (not in dictionary).
Re 'yardang with small spider' image - are we actually looking at the same pic?
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by Kitharode moderator
What about Hohoho then. That in there? 😃
Back to page 3, halfway up (or down) is what I'm looking at...
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by JellyMonster
Yes, that's the one - how strange. Maybe wassock can see the spider (instructions four threads back).
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