Steve has spoken. Let no mere mortal question...

-the other Doug

I don't see any way to prove that by what we see.
The dust that is present below the surface could be from a windless period
when no clearing of dust or deposition of sand was taking place, only deposition
of dust. When the seasonal wind is present there could easily be deposition
of sand from the crater and removal of dust by wind too weak to hold onto
the sand but still strong enough to carry dust away.

edit: When the winds start up again, some of the dust buildup is removed
but some is covered by deposited sand and preserved as a layer beneath,
waiting to be exposed by some roving rover.

This post has been edited by centsworth_II: May 1 2007, 07:19 PM

I wonder what you think he has said.

Mere mortals parse the phrases of the
Bible all the time to support their views.

No need to "Poor Stu" me; my idea was a long shot and I put it forward as such. I'm happy to have my unconventional bubble burst when it has been shown that the basic idea it bubbled up from was basically right:

crater + wind + dark material = streak.

With the recent statement, I revived these quotes from the thread. It sorta all fits together:

When deposition>removal, you get a layer.
Dark sand out of crater blows out from crater/dark streak on annulus and goes all over plain = dark zone in sequence.
Light dust from all over Mars filters down from atmosphere = light dust buildup makes light zone in sequence.



There's probably a pretty tiger stripe sequence of altenating dark layers and light layers as you dig down in the streaks. I'd expect dark streaks when more wind is present, and light streaks all other times.
Just like tree rings. Everybody wins.

Any imagemeisters got any patterns from image analysis of dunes near the annulus? Might give a clue as to the seasonality....

-Mike

Stu: I think you've discovered a burst bubble... And it's not yours, either!

I take Steve Squyres' comments to mean that there is nothing special
about the sand being blown out of Victoria onto the streak. It is the
same as the sand laying all around on Meridiani. In fact, the same blowing
out of Victoria once was laying on Meridiani, before it was blown into
Victoria were it lay until being blown out back onto the plains.

The dark layers in the dunes did not come from Victoria, but are due to
some Meridiani wide process.

Hmmm. So how come the layering gets more distinct as you approach the annulus (as WindyT noticed)?



-Mike

I don't think the gusts that carry sand out of the crater drop so quickly in energy that
they dump their sand load and have no power to sweep away dust. I think the fanned
out, feather edged pattern of the streaks indicates a wind which loses strength over the
length of the streak. The wind could not have carried some sand all the way to the end
of the streak while not removing any dust along the way.

Steve is making fun of us!
It looks like Spirit is winning this round.

Ok, just to show I can have an open mind, I thought of a way this could happen.
Perhaps you all have thought of this before. The wind blows up over the rim and
does not stay on the surface and causes no turbulence on the surface, so no
dust is removed. As the wind loses energy, sand drops to the surface, more at the
beginning of the streak and less toward the end.

It doesn't necessarily happen this way though.

That's the only reason you're saying this? It doesn't have anything to do with figuring out what is really happening?



Actually, it is exactly what is happening...

And, I might add, it's been explained that way many times in this thread already.

And it's what S S has said (twice) already...

But thanks for coming up with that indendantly.

The same strong winds that carry the heavier sand out the crater will also be keeping it clean of the dust that falls everywhere surely?. If it was ALWAYS deposition and nothing else- then it would be a huge big pile would it not? A big pile built up at the lip of the crater.

The dust falls everywhere - it's why the sky is the colour it is.. In light winds it forms dunes of its own. In heavy winds, it is blown away totally. Only stronger winds carry the sand. So - for this to be a place of all sand and little dust - both deposition AND erosion have to be occuring. Not only because we see no dust that we know to be falling everywhere, but also because if there were no erosion at all - we would have a sand mountain to see.

Doug

Can you blame him, though? This has gotten quite silly...

I disagree. El Dorado is a trap. The grains are being blown up the hill and roll back down. They have nowhere to go.

The streaks are not a deadend. The grains are being lofted out of the crater by the wind funneling thru the bay. Once on the apron, the streak is subjected to the same (weaker) winds as the rest of the apron. If the streak was being swept of dust, the rest of the apron would be as well. The reason that the sand is being deposited is that the wind is weak in the streak zone.