As for the "dark" streaks this zoom of the high resolution colour Victoria crater TIF file suggests the dark material has moved come from / been blown from Victoria crater and overlayered lighter material. Victoria crater is below and to the right (about 5 o'clock) of these small craters.

This streak debate seems to have legs and might become the next near-rim, far-rim brouhaha! Either way there could be wind blasting through there.

Yes, that's fascinating. Those craters could be candidates for a visit later on. I've often wondered about the petrified figure at the southeast rim. A lost sightseer perhaps?

This is true, of course, Tom, but why not grab the very top of the section when it's sitting there waiting for you to RAT it. And we have risk-free access to the exposed edge of the layer, as well as the top, without having to reach over the brink and risk a tumble down to the dunes. If the edge reveals laminae, and there is no discontinuity with the underlying layers, we have strong evidence that the beacon is in situ, and therefore points directly at an ancient (Noachian/Hesperian) formation of Victoria, followed by burial and recent exhumation.


But if the evaporite is in situ, then it indicates that ground water existed both below and above the berry-free strata.

But Tom, those of us in the "Ancient Victoria" school of thought, don't believe that we are seeing, driving over, or ratting Victoria's ejecta. We hold that ejecta is nowhere to be seen. What we are seeing is sandstone that roofed over Victoria back in the Noachian/Hesperian, was subsequently indurated and leached by ground water to produce concretions, and finally eroded and collapsed.

I am frantically awaiting close-up views of the uppermost exposures in the capes to see if they are primarily intact, in situ, more or less horizontal sandstones. The latest pancam of "Hoy" looks remarkably in situ right to the top. If close examination confirms this all around Vikky, then I will hold my hypothesis to be supported. I cannot emphasize too strongly that a hypervelocity impact shatters the target rocks near the crater, transforms some into exotic forms, hurls them high into the air and deposits them around the crater with a more or less random orientation of chunks (OK, clasts) in an impact breccia. We saw some of this around Beagle, though that was such a tiny crater that regular impact models may apply imperfectly.
I have not yet seen anything around Victoria that I would call impact breccia. Close-up views may reveal it, if we ever get any. Hence my disappointment when Beacon was bypassed.

I agree with you on this. I don't see any source of dark material down in Vikky. The only dark things in this area are the concretions, perhaps, and the basalt sand grains when they are cleaned of dust. It depends upon lighting and viewing angles, of course, but in general, what looks darker on Mars is more dust-free.

Yeah, I'll let other, more tidy minds decide whether to leave these posts here, or put them in the stratigraphy thread.

There are dark dunes in the eastern quadrant of the crater that could be the source of the plumes of (relatively) dark dust. The colour doesn't match the average colour of the mantle over this region so I'm on the dust plume side of the debate.

I would reply, Mark, that those dunes have been swept free of light dust by the same winds that funnel up through the bays to sweep the annulus beyond. I think it's unlikely, and unparsimonious, to postulate a source of dark mineral existing in Victoria, other than the basalt sands and blueberries that are everywhere else.
Of course anything is possible, but the likelihood is that the whole deposit making up the Planitia Meridiani is about 800 meters of more or less uniform, laminated basalt sandstone, more or less indurated by sulfates, and containing varying concentrations of hematite concretions. Victoria's formation almost certainly did not excavate below these sandstones, and so I would not bet the farm that we will find anything else in the crater.
One can hope, but...

P.S. "Cry, Havoc!, and let slip the Dogs..."

Err, not Phobos and Deimos - It's the sun.

Rats. I so wanted it to be.
So what's the little oval to lower left? Nothing but an artifact? Why can't modern science invent an imaging device that is free of artifacts? Hell, if they can put a man on the moon....

Yep, an artifact, go and look at the right eye image taken at the same time, it's not there in that one. It's always worth checking the filter for images like this, 8 (in either eye) is the solar filter and will never be of anything except the sun.

This image is part of an observation of the atmospheric tau at sunset and you can actually see the horizon across the image.

James

If I had a nickel for every time someone made that mistake in this forum... I'd have several nickels.

I thought it was an artifact of parallax that Diemos wasn't there!

Good tip! Actually I haven't managed to penetrate the MER image labels much farther than the time stamp, without losing my place.

Hi Mark,

I suggest the dark plume material may be originating from inside the crater as suggested in this marked up image:



There are two other clearly visible spots around the rim where darker material is also seen:



Victoria may have more untold secrets to learn

The usual interpretation of dark streaks etc. like these is not that they are dark material, but that they are places where the regular dark surface of Mars is freshly exposed because bright dust has been removed. The orange-pink dust in the sky of Mars is always settling onto the surface - and constantly replenished by dust devils and occasional large dust storms. So the surface is usually covered with dust as a matter or course.

Dust devil tracks - the DD removes bright dust leaving a dark streak.

Steep slope streaks - a small landslide or "dust avalanche" sliding down the slope causes enough motion to expose darker stuff under the surface dust layer.

So here in Victoria, the streaks and patches in the post above are caused by small downslope movements, recent small landslides etc. They are not patches of dark material - everything is dark everywhere. But most of it has a veneer of bright dust.

And the plumes are places where the dust is removed by wind focussed up the "ramps" - and made more turbulent in the process. The crater higher up the posts does indeed look as if darker dust was deposited over most of it, leaving bright dust exposed only in the sheltered areas. But the reality is still probably the other way around. The wind blows bright dust away everywhere except where it's sheltered.

I'm not saying it couldn't occasionally work the other way, but this is the generally accepted explanation. If it's true that in some areas dark dust is being blown around, keeping it from becoming intimately mixed with the bright dust would be very tricky. Incidentally, dark sand dunes are seen in some areas, but sand grains would be hard to get out of a deep depression. That's another issue.

Phil

Bonneville definitely had dark matterial that was forming dunes on the crater floor. And it was blowing up and over the crater rim to leave a dark streak on the plains down wind... It seems plausible to me that there could be a layer of darker matterial that is exposed in the wall of Victoria. That this matterial is eroding and being swept up and out of the crater.

I agree with Phil's points. I think our position represents one pole of a "streak hypothesis", wherein the dark streaks are formed by cleaning winds. The opposing hypothesis implies that the streaks are "dirtied" by some unusually dark, exotic material eroded from the walls of the crater and scattered across the annulus. Presumably this debate will be soon settled by MIs of the surface outside and inside the plumes.
We could call these two schools of thought, the "Clean Streakers" and the "Dirty Streakers"!
I'm sure Ustrax could devise some appropriate mascots.
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