Now that we're finally about to do a detailed inspection of the darkest of the dark streaks emanating from the north-northeast portion of the crater rim, it's time for final speculations before we know the truth of the matter.

I'm in the clean-sweep camp. The large-scale orbital observations make these streaks appear almost definitely of aeolian origin -- the manner in which the streaks feather along the edges, and the way in which they curve off as they extend out from the crater, are all consistent with wind/ground interactions.

Observations of the lighter, western streak seem to show more visible concretions right up on the surface. If this holds true of the darker streak, I think that proves the clean-sweep theory.

Think of it this way -- if you packed pebbles and dry dust as a pavement and then let the wind strip away at this surface, the dust would blow off and the pebbles would remain. What dust remained would sit in the lee of the pebbles.

This seems to be exactly what we're seeing in the first dark streak -- the lighter soil component has been blown away entirely, and the darker component (probably eroded concretion material) has been mostly blown away but its remnants sit in the lee of the concretions.

I would expect that any depositional streak would appear as dust or fine-grained soils which cover over the materials we see on the surface outside of the streaks. That's *not* what we're seeing.

In addition, I'd have to treat any suggestion that the blueberries themselves are being blown out of the crater to form the streaks with an awful lot of skepticism. Martian winds aren't strong enough to move the relatively large-and-heavy concretions along level ground -- it would be absolutely impossible for these thin-air winds to have blown them entirely out of the crater and up to a crater diameter's distance away.

Now, if the MIs in the darker streak show that dark dust is consistently filleted on the upwind side of the concretions, and shadowed with less dust downwind of the concretions, *that* would be an indication that the streaks are depositional. But, so far, that's not what we're seeing.

-the other Doug

Ooh, I love adding my completely geologically untrained, marginally informed opinion to any question that divides us into camps. I anxiously await the appearance of the mascots.

Bad news for you, Doug. I'm adding the clean sweep camp to my already dodgy resume that includes being a member of the far side through the keyhole beacon camp, the Oppy should lay down and die at Victoria camp, and the (admittedly unannounced) gosh homeplate is really kind of boring let's get on to the promised land camp.

On the plus side, I've never been in the abyss camp.

Brian

I certainly hope the plan codes show an MI sequence of the surface at this location, so that we will be able to make side-by-side comparisons with MIs taken in the streak ahead. Some overhead pans will also be useful for close comparisons of berry abundance and distribution. Codebreakers? What's the plan?

Me too!

Actually, ("I'm glad you asked me that, Brian"), my view of this controversy is clear and unequivocal. I believe I can say, without fear of contradiction, that I don't know enough to decide yet, and that further research is indicated. "Send pictures!"

This one's a no-brainer. The dark streaks are caused by a steady removal of the finer ambient dust/silt in the region (indeed coating the entire planet).

What do you think is particularly special about the dark streak areas?

Is the local windspeed slower (due to turbulence effects?) or do you think the local windspeed is faster in the dark streak area?(again due to turbulence effects?).

Why are the dark streaks on the North side of the crater, but not on the South side? Where would you expect to find other localized dark streaks in Victoria crater?

For that matter, do other craters nearby show a similar dark streak pattern?

-Mike

They extend from bays that act as turbulence causing funnels given the predominantly ~SSE to ~NNW prevailing wind direction.

Faster and more turbulent. Like wind in urban canyon zones.The reason only some exhibit this is because the effect depends strongly on the shape of the specific bay ramps and their surrounding cape bluffs.
If this was dark material being lofted out of Victoria then my gut feeling is that there would be streaks emanating from many more of the bays and in more directions. Bays like Bahia Blanca and the Bay of Toil in particular.

Prevailing wind direction.

Nowhere.

Yes

I'll buy that.

So...the faster windspeeds are picking up lighter colored material and leaving behind the darker material (from the "gray" sands around the apron of Victoria). We would then expect to see deposition of the lighter stuff around the darker streaks - which we do.

Would this explanation also work for the lighter dark streaks seen in the SE corner of Victoria trending towards the SE?
And the even lighter dark streaks seen in the W?

So the streaks around Victoria are telling the preferred wind vectors: from SSE dominant, then from NW, and finally from E as the minor component?

-Mike

I've been leaning into the dark deposit camp. Another point just occured to me, and I think I've now toppled head first and completely into Deposit Camp. Why are the streaks emerging from bays D2 and VwP much darker than any others?

Look at the orbital view. I hope we can all agree that the winds in the streaks are roughly from the SSE. Why don't the other bays on the north rim, such as Blanca, Toil, and Bottomless, have similarly dark streaks to the two darkest? If anything, I'd expect a darker streak from Bottomless, eg, since the winds should approach and funnel through it more directly than D2 and VwP. See attached image:
Click to view attachment
Basically, if the streaks were due to clean sweep, I can't see why the other northern bays wouldn't produce dark streaks. If instead the streaks are depositional, it's easy to imagine compositional differences between east and west sides of Victoria that result in dark material eroding out preferentially on the east side. Indeed, looking at the orbital view again, there does appear to be different material inside the NE rim in the form of dunes similarly dark in appearance to the streaks.

The winds are amplified as they funnel through the bays, and then slow down again as they spread across the plains. As they slow down, first the heaviest, then lighter and lighter dark particles settle out.

Edit: I see that while writing this helvick posted making the same point but coming to a different conclusion! Intriguing.

Could the effect really be so sensitive to the shape of the bays that none of the bays between and including Matias and Duck show streaks nearly as dark as the two darkest? Doesn't it seem more likely, since the few darkest streaks are clumped together, that the clumping is due to compositional differences across the crater?

I think it can be argued either way. _If_ cleaning by turbulent air is the explanation then the shape of the funnel is absolutely relevant. If it is some darker zonal material only present on the eastern side of Victoria then then that could work too but apart from the Blueberries have we seen any material that is dark enough to produce this? Personally I'm unconvinced by the black dust idea but we'll find out soon enough I hope.

There was the dark dust piled up beside rocks on the edge of VwP that I mentioned in the VwP thread:
http://marsrovers.jpl.nasa.gov/gallery/all...90P2395L2M1.JPG
(see bottom of frame.) And there's the dark dune material inside the NE rim.

I don't buy it completely, because of the preponderance of dark dust directly below the cliffs of Tierra del Fuego. The prevailing wind direction doesn't explain these clearly depositional dune like features. This dark material is trapped just below the cliffs. A wind direction from the North instead would explain such a trap. But the wind direction is not generally from the North, is it? If it came from the North, then that would destroy the wind channeling idea.

I doubt that the current prevailing wind has remained the same over these hundreds of million of years. There should have been a lot more mixing than appears evident given enough time involved. So these features must be fairly young. Also, the dark nature of the material suggests they are probably related. The dark material below the cliffs and inside the crater is probably debris from the erosion of blueberries (just a guess that would need to be confirmed). That would suggest that the whole area where the streaks are is saturated with blueberries beyond normal concentration for Meridiani. That means there is a much higher concentration both above and below ground at these locations. I wonder if the streaks maybe related to underground fractures of the type SS talked about near Soup Dragon. If water plays a role, it could help explain things nicely because of the higher concentration of the berries. Wind directions change with time. I would expect it to do so on Mars too, especially with the time frames we are talking about. So the wind channeling process might have helped clear the surface with the streaked areas. Yet, with probable change in wind direction over large time frames--why are they situated in one general direction? Fractures might help explain them with subsequent seeping (if they are deep below ground)--just a thought.

Yes, wind must have had some role to play here. But it cannot be as simple some have explained so far. There must be a lot more to the story. It's the 'a lot more to the story' that I'm interested in.

Hmmm. Both very good hypotheses. There's no way I'd put hard money down on either.

If you look very closely at the boundary of the dunes vs. apron to the N of Victoria, it "seems" that the dunes/apron boundary is closer to the crater in the dark area and further out in the brighter zones. The dark ray coming off "the bay 4 to the E of Valley without Peril" seems the shortest of all. The dunes are more visible closer to Victoria. The dark stuff appears to obscure less of the dune field. (At least when I stare at it).



This makes me suspect that the dark rays are not deposited or if they are they don't go very far, but that the "regular" whitish stuff goes further. So I go with the dark stuff being darker and heavier component and left behind.

Throw me in the "swept clean" camp, but a good shred of evidence to the contrary would flip me in a heartbeat.


So why no streaks near Bottomless Bay? Great question. Local topography? Could the topography from deposits from a SSE wind cause a new deposition pattern when the wind shifts to a NW wind? Could this erase the effect on the W side first, but set up larger turbulences when it finally reaches the NE part of Victoria? The effect could be real subtle, but just might be enough to make an effect.

(Man, I need a sandbox, dark volcanic sand, light sugar sand, and a fan and a few hours to play).

-Mike

- There IS dark matterial at the base of the cliffs below the streaks. In fact, the entire floor of victoria is much darker than the planes. But the stuff at the base of the streak cliffs are forming dunes and are darker than the rest of VC.
- The streaks are all grouped together. There are two bays that don't have streaks in the middle of the group. But these clearly have very steep walls. Much harder to blow stuff out of.
- The bays on the other side of the crater display the same variety of shape as the streak bays. Don't see why they would be different, wind wise.
- faster, not turbulent, air will clean most effectively. The bays along the line of the wind should have the darkest streaks.

Clearly, I'm in the depositional camp.

I've searched in vain for a nice clear discussion (with diagrams) of the effect on prevailing winds by impact craters. No doubt the effects would vary significantly with a wide assortment of variables: The diameter and depth of the crater, the height of the rim, its profile and planview shape, the prevailing wind direction and speed, its seasonal and longer term variations, the sediment substrate, its grain sizes, density etc. etc.
Somebody should write one. It's not what I would term a "no-brainer" (as the beacon was ), but a lot of brain power has already been devoted to the issue (Search at adsabs.harvard.edu for crater wind trails Mars .)
There is a fairly broad consensus that wind streaks are downwind of the crater, that they are light or dark in albedo depending whether they are depositional or erosional in nature, that one crater can produce both types of tail, and that the local wind speed across the surface will govern whether deposition or erosion of dust occurs. We may be confident of the prevailing winds in this area of Meridiani (and there are lots of MSSS images showing dark trails extending NNW from Meridiani craters, but we know much less about what the unique topography of Victoria Crater (no raised rim, cape-and-bay planview) will do to the velocities of those winds. Both the pattern of ripples on the bottom, and the traces of trails around the crater show that the wind patterns are complex over the short to medium term.

What we learn here at VC will comprise an important contribution to the field.

Since the dark streaks only seem to be emanating from the steepest cliffs, which also happen to have the most boulders at their base, the dark streaks must be evidence of erosion, and thats why there are no streaks coming out of the other downwind bays (simply because there isnt much erosion there due to either compositional or prevailing wind factors). So we have the dark dust having blown up and out (with some of it getting stuck behind at the base of the cliff) and the dust deposits in the streak pattern as the dust-lofting turbulence subsides.
This can be seen in the attachment by fredk:
Click to view attachment
(its odd that i can see the image when i 'Preview Post' this attachemnt in the message composer but it doesnt display when i 'Submit Modified Post', so heres a link to his post)

It all seems that simple, but then theres the tentative observation that the dark streaks are actually composed of the blueberries themselves, which is the only thing that is threatening to make me bail out of the dark-dirt camp. So if thats true i'll be camping on clean-streaks, if not im stuck in the dust, even though its where i wanted to camp all along. so i guess i have to commit now or it would be cheating, so im officially camping in the dirt.

O.K., Atom, this is possibly a very astute observation, but I would like to see your data on the steepness of all the Victoria bays so I can convince myself that steepness correlates with streak darkness.
If this is true, however, I don't see how it follows that the streaks are therefore dustier. I could as easily conclude that greater erosion and steepness correlate with wind strength through the bays, and thus greater likelihood that light dust will be removed from both the bays and the streaks beyond.
Why the bays to the northeast of the prevailing area wind axis have the greatest wind velocity may result from a complex rotary eddy set up within the crater as a function of its complex topography. (Who is going to be first to set up a model of VC with dark sand and light dust and hit it with a hair dryer? )


Suit yourself, but please wipe your feet before you come in the house .

This kind of thing occured to me too. But then you still have to explain why the mirror image of the effect doesn't happen with the bays on the opposite side of the wind axis from VwP, such as Duck Bay and it's neighbours. In fact we see no dark streaks at all from Duck bay and neighbours.

Do not resist, Luke. Come over to the Dark Side...

Notice how the whole area north and east of Victoria is darker, beginning with those streaks. It's not just about the streaks when we talk about the dark material! Tierra del Fuego has the dark material accumulating under the cliffs there, but it doesn't appear to accumulate under others. Why? (I don't think it has anything to do with how steep they are).

Although there is a tendancy for us to see what we want in these images, IMO we must be looking at slight compositional differences in the ground itself, not just the surface. So when Tierra Del Fuego erodes, it creates a lot of dark material dust. It then is blown out over the surface from the bays where the streaks start. Yet, the erosion of those particular cliffs are creating the dark dust faster than it can be blown away.

My guess is that the accumulation under Tierra del Fuego could be from erosion of the higher concentration of blueberries from within those cliffs. So that might be a source from which the darkness of the streaks is enhanced because of the winds. But since the whole northeast side is much darker (not just the streaks), then there probably are other processes involved.

Notice also, that the top of St. Vincent is very clean. There may be a combination of clean-sweep and depositional processes at work in this area of the crater. We should not look at this in isolation. If you look closer at other bays, there are fainter streaks in other areas of the crater. These on the northside are merely much darker. I hope I'm not just seeing what I want to see.

The fun thing about this discussion is that I think I could make some good arguments in favor of each of the two prevailing theories. But I had previously cast my vote on this phenomenon a year or maybe two ago, and I remain in the clean sweep camp. If for no other reason, Occam's razor is pretty convincing. Light-colored, lee deposits are usually depositional, dark-colored streaks on the lee side are usually due to the removal of the ubiquitous light-colored dust. The wind flow through this crater is surely a complex subject. My intuitive suspicions lead me to expect a more laminar flow through the center, but interactions with the roughness on the east and west sides might create turbulent vortices that would exit the NNE and NNW bays. You could use that to support either argument, though. I see some patchy dark dunes inside the SSW side. The only way we'll likely be able to convincingly conclude the debate is with empirical observations of the surface.

You really should consider a career in politics, if you haven't already.
The problem I see with the dark dune material inside the crater is that it may simply be dark material that has had the coating of light-colored dust removed from it. It might also be a reworked accumulation of dark sediment that fell from a layer above. I've speculated earlier about a pre-impact residual soil that might exist in patches between the bedrock and the ejecta layer, to explain the unexpected dark stuff that was observed in some of the bays.
I don't know where this idea of supersaturated blueberries came from, but I went back and looked at the surface all around Victoria and I pretty much saw the same concentration of concretions everywhere. They looked pretty dusty on the west side, and less so as Opportunity moved to the north side.
There's no doubt in my mind about that.

I see a huge difference in concentration. But perhaps we should replace the word blueberry for dark material. Blueberries may only be one kind of dark material. Here are some images from different time periods representing vastly different locations.

The first one was taken in July while still on the plain approaching Victoria.
Click to view attachment
There is some dark material, but the distribution is vastly different than this image taken in December.
Click to view attachment
And yet that distribution is very different from this recent image on the edge of one of the streak features. Look in the foreground at the base of the images, to get an idea of what I'm talking about.
Click to view attachment
You could easily take a shovel and grab nothing but concretions on that last image. They are piled together as if somebody was storing them. Granted, the appearance of the concretions is different, but so is the concentration of them.

I'm in the deposit camp (as opposed to clean sweep)

I've spent some time wondering about these streaks, and a couple weeks ago someone pointed out the loose dark material just under the NNE cliffs (such as Tierra del Fuego). It occurred to me at it could be that prior to the event that formed Victoria Crater, during the depositing of the salt layer, that this particular area had some feature that lead to an increased density of blueberries (or other hematite concretions) compared to the rest of the area that is now this crater.

While it IS possible that the clean sweep model is part of the process (if the crater formation threw out extra blueberries at these NNE locations), I imagine that the slumping of the material leading to the hematite drapes under the cliff also resulted in abrasions creating enough hematite dust to create the streaks.

Side note: if the wind is really amplified at the bays, perhaps Opportunity should loiter at one for a Spring cleaning of the solar panels.

Impact deposit could very well be part of the explanation. In the last image that I showed in my previous post, there are a lot of sparkle like features--specks everywhere. I first thought that they might be some sort of image artifact; but soon realized that they are pretty evenly distributed with NONE in the sky. A look at the base of the image suggests that some of the concretions are split open. Perhaps the splitting of the blueberries on impact created reflective surfaces, and those are the sparkles we see in that image!

MII: You really can't compare the rippled plains to Victoria's annulus. According to the hypothesis SS has described, the annulus is a special case. Downward looking pancams are the best images to use for these kinds of comparisons.

I agree with both Antoniseb and MarsIsImportant. The simpler explanation is that there is a slight compositional difference across Victoria crater, with a larger concentration of blueberries (or other dark concretion) in the NE.

But this also fits the "clean sweep" hypothesis. The darker concretion-bearing material was blown out during impact in a smaller tighter annulus. Over time, prevailing winds have blown out lighter colored (and physically lighter also) material from the crater to form the brighter streaks which are covering the darker material.

This should be fairly easy to check. By going slightly to the E of one of the darker rays and doing a few wheel scuffs, we should get down to an area that would have more darker concretions than a corresponding are in the NW.

Has anybody got MI images from set locations around Victoria that they could easily post for comparison?
('Course this would only be the surface pix, we would need to dig to provide more evidence for the "clean sweep" vs. depositional theory.)

-Mike

I'm not comparing the rippled plains to Victoria's annulus. I simply put that there to show there are all kinds of different distributions of the dark material. Maybe I did not make that clear.

The comparison is with the last two images. That is a very fair comparison. And the concentration difference is Huge. I hope that clears up any misunderstanding.

Antoniseb makes a good point. I've thought that the biggest nail in the coffin of the clean sweep idea was the existence of a clump of a few very dark streaks in the NNE and essentially none in the NW. It would require a very contrived and sensitive dependence of strength of turbulence (or whatever) on local topography to explain the complete lack of dark streak from Duck Bay and neighbours. This is the kind of explanation that could make Occam roll over in his grave, CosmicRocker!

This I see as very strong evidence of compositional differences from Victoria's west to east side. This idea has support in the morphological differences we see across the crater, for example with the "linear fracture" features inside the NE to E rim.

However, as antoniseb pointed out, this could still be consistent with clean sweep. If there are many more blueberries outside the NNE rim than the NW rim, then it's possible that the winds are equally strong out of Duck Bay and VwP, eg, but that outside of VwP there are many more blueberries to be cleaned of light dust, so that area looks darker.

This is possible, but already we have evidence against it. Compare this pancam view from sol 1128, very close to the first dark streak:
http://marsrovers.jpl.nasa.gov/gallery/all...00P2588L7M1.JPG
with this pancam from sol 995, near the Beacon:
http://marsrovers.jpl.nasa.gov/gallery/all...WUP2461L7M1.JPG
The concentration of blueberries is similar.

It's still possible that it's not the blueberries that vary in concentration from east to west and make the dark streaks dark after clean sweep, but another finer dust/sand component.

Regardless, we should know soon. Notice this sol 1135 MI taken from tosol's between-streak location. I suspect with one more drive (anyone know the plans?) we'll be sitting on the darkest streak and then take another MI for comparison with today's image. Hopefully the answer will be clear then!

MII, those specks are noise in the CCDs. The noise tends to be more noticeable in the L7 images, since they need long exposures with that deep blue filter. You can see the specks in other images, like this one where you can see it's not split berries:
http://marsrovers.jpl.nasa.gov/gallery/all...LOP2587L7M1.JPG

Well then, my first guess was correct. The specks are artifacts. Thanks for pointing that out.

Like I said before, sometimes we see what we want to see. Split berries would explained a lot of things. Now we still have a great deal of mystery here! Yet some of the berries could still be split--we just need a closer look.

Well, the color of the depositional dust would depend upon its source. Perhaps the compositional differences within Victoria create different sources of the dust deposited over the surrounding area. If the dust in the east is the same basic color as the blueberries, then it would be difficult to distinguish the two from a distance. So you have light colored dust deposits in the west covering the berries, and dark colored deposits covering the east. So the difference would only be the east to west difference in the composition of the underlying rock or soil, in which the impact that created Victoria occurred.

This all adds up to something...more things for Oppy to investigate. HURRY up Oppy! I'm getting impatient.

Does anybody know what day this image was taken? It must be fairly recent because it was posted today. It's important because it shows split and mangled blueberries along with sand or dust particles. If this is from within that first dark streak, then it supports an impact deposit origin. If not, then I'd still like to know exactly where it was taken.

http://qt.exploratorium.edu/mars/opportuni...D2P2936M2M1.JPG

As I just posted, that's 1135, between streaks.

Ever notice how the only area in Victoria with the dark streaks is also associated with what is pretty much a linear feature that is the cliff boundary layer.
again, here is Fredk's linked image

I'm not sure if anyone here has already pointed this out, but this might be a very important detail, as it could be that this is a fault boundary, meaning one (or perhaps both (or neither)) of two things:

1) being a fault, its is composed of compositionally different (that is, water-modified) materials.

2) it could have experienced more geologically recent rockfall so there is relatively new dark material to blow out of the cliff face. elsewhere in the crater these exposures have long depleted.

I've mentioned that...not nearly as well put as you though.

Sorry, I guess I didn't click on all of your link in that post.

I just wonder if a CRISM image wouldn't tell us a lot about the characteristics of the dark streaks. Given CRISM's 19m/pixel (38m resolution) they should be able to get a nice spectrum of the streaks.

On an off-topic tangent, it just seems unlikely that there are no CRISM images of Gusev or Meridiani in the system somewhere. (in mild conspiratorial mode)

Steve

Put me in the deposit camp. El Dorado was also a dark region, and it was clearly deposition. True, this could be an entirely different material, but it just seems to me like it'd be deposition. The wind could come in, hit the cliff faces, cleaning them off, and bringing dust along with. It loses energy as it climbs the crater wall, but maintains some speed because it's being constricted by the funnel-like shapes in the scalloped edge. When the wind finally makes it over the edge and into the open, its speed drops as it dissipates, and it's no longer able to keep the dust airborne. Plop, down it falls = dark streaks.

Just a reminder to people (like myself!) who thought they had the streaks all figured out, that things are perhaps more complicated than you thought:
Click to view attachment
It looks like there's a broad light coloured streak trailing to the SE of Victoria. That's consistent with light streaks from other craters in the area, such as Endurance. I'm guessing that's due to bright dust eroding off of the bright evaporite along the rim. We're obviously dealing with varying wind directions and distinct processes.

That's interesting, isn't it? I've played with various stretches of the HiRise imagery, too. I am not yet certain what to make of that. I have been concentrating on the ground with Opportunity's eyes.

There is a series of foreground pancams taken on many sols that gives a nice sampling of the near surface views. Setting MMB panoramas to a rover relative view and skimming through the sites, one can quickly notice the places where useful imagery exists. I really don't think complicated theories are needed.

Here is one of the quite early images from a relatively light area from sols 1016-1019. To me, it looks like berries buried in dust. You really need to look through the whole series of such images to notice the changes. If some of you don't look at all the images, you might not see the larger picture. I'm sticking with that razor guy.
Click to view attachment

It doesn't strike me as possible to have such a long thin jet of air coming off of a feature that has virtually no relief above the plain.

On the other hand...

If a small "fountain" of dark dust were being thown into an otherwise laminar flow, this is the effect you would see. The "fountain" would be a jet of air coming up one of the bays carrying dust particals from those dunes at the base of the cliff.

Fred's enhansement seals it for me. There are streaks off of ever bay (some more than one). They're all about the same length. That indicates that the phenomenon is effecting the whole crater. There is simply more dust on that one side.

I should apologize up front for posting a montage that is kind of a mess, but I am tired of adjusting the layers to make it prettier. I've assembled a sampling of 10 false color pancam images from light and dark areas around the crater and then drew arrows to their approximate locations on Tesheiner's route map. It seems to me, at least qualitatively, that the surface appears generally dustier in the light areas, and generally cleaner in the dark areas.
Click to view attachment

That's a nice start at organizing the data for systematic comparison, Tom. But with only one view from a truly dark streak, it's still a bit early to draw conclusions. The next few days of pans and MIs should tell the tale. I for one need the close-ups to be confident of what I'm seeing.

Thanks for the post, Rocker. I think it's very hard to judge dustiness based on uncalibrated colour images, though. Different channels may have been stretched differently at different times.

I am really looking forward to an MI from the dark streak to compare with the sol 1135 one. Without access to minites data that'll be about the best we can do ourselves. I'm afraid we may have to wait till after the long weekend, though.

That's right, guys. I wasn't trying to say anything too definitive; that's why I used words like qualitatively and generally, etc. Apparently I find the trend displayed by this set of images more convincing than you. We should get other imagery in the darkest streak eventually, but I'm not sure that uncalibrated imagery is a huge problem. The colors may be wrong, but dust can usually be identified by its texture. Anyway, I have some other stuff in the works, but I'm still waiting for a few images.

That's good work Rocker. Thank you very much.

But my interpretation of those same images is very different. What you show is that the light colored areas are dusty with light colored dust; and the dark colored areas appear to have dark colored dust mixed in with the blueberries. IMO, this suggests the depositional theory is more correct--the one that takes into account the possibility of slightly different composition of the soil layer underneath different parts of Victoria.

I don't see the darker areas any cleaner at all; they are simply darker because of the dark dust. The fact that they are darker can create an illusion that they are somehow cleaner, but they are not. So, there appears to be deposition across the entire annulus of Victoria. Some streaks are light colored, while others are dark or darker still.

...and gosh i hate it how quoting removes the image attachments, so here is the link to the above quote

yeah, wow, is that a 'contrast enhanced' image? regardless, i'm stumped again, confusing the issue could also be the possibility that the dark streaks are laid down in episodic periods and are now dormant... the light streaks go against the current wind direction, whatever that is im no longer sure, did we rush to judgement and infer that by looking at the dark streaks? who knows what the wind direction is lately?

That image I posted was straight from this MOC image; I did no processing of my own.

My guess is that there may be seasonal wind direction changes, or temporary changes associated with major dust storms.

That's interesting, fredk. If I had looked at your image a bit more carefully I might have realized it was from the MOC. I had been playing with some contrast enhancements of HiRise imagery and that MOC resembled one of those.

You encouraged me to look again at some of the other orbital imagery available. I'm not certain I appreciate all of the differences that are taking place over time and between the various cameras. I think I'll stick with the close-up views from the rover's eyes that I am more familiar with.

I think the wind direction has been said to reverse every year, with the seasons.

To add one more layer of complexity, here's an animated gif with two MOC frames: The first was taken Febuary 1st, 2004, and the second October 11th, 2004:
Click to view attachment
In the second frame the dark streaks in the NNE of Victoria appear much darker. The images may differ in their calibration, but clearly there's a real change since the darkest streaks darken substantially relative to the fainter dark streaks. Eg, look at the east-most of the 3 darkest streaks, which comes out of Bay D5. There's a much fainter and shorter dark streak coming out of the same bay towards the ENE. The main, NNW directed streak gets much darker relative to the shorter streak between the two frames.

The illumination and imaging angles are different, but why would that cause a difference between the two streaks emerging from D5?

I don't think this is surprizing, since I could certainly imagine seasonal wind differences, and while the wind is blowing towards the SE, the main dark streaks should get covered in the ubiquitous light dust. It does mean though that the darkness of the streaks may have changed even since the hirise images.