Farewell Beacon..., The next cape beckons... |
Farewell Beacon..., The next cape beckons... |
Nov 26 2006, 03:58 AM
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Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
Wow! If I live to be a hundred, I'll never understand why we've sailed right on past the Beacon toward "Boat Ramp". I agree that the deepest exposures are the most important, but Beacon is the highest! It's sitting right there waiting for us. It's the top of the section. Whether it's composed of impact breccia or undisturbed laminated evaporite determines whether Victoria formed after or before the deposition of the upper Planitia Meridiani. I can't believe that is a trivial issue. It is a fundamental fact of Victoria's history.
-------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
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Nov 28 2006, 01:56 AM
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Solar System Cartographer Group: Members Posts: 10229 Joined: 5-April 05 From: Canada Member No.: 227 |
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 -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PDF: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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