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Geomorphology of Gale Crater, Rock on!
Eyesonmars
post Jan 2 2013, 01:06 AM
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If "true polar wander" did occur in the past that means GALE crater could have been at a higher latitude when some of these fluvial features were created. Are there any constraints on this imposed by the formation of the tharsis bulge ( which wants to be on the equator i assume)? Do we even know if Gale and/or its fluvial geomorphology formed before, during, or after Tharsis?
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chuckclark
post Jan 2 2013, 01:18 AM
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QUOTE (elakdawalla @ Jan 1 2013, 06:15 PM) *
check the direction of tilt and how that relates to long-term changes in Mars' shape due to, say, the construction of the Tharsis volcanic complex. Mars' shape has changed in the past, and it's been suggested that the entire crust has reoriented (true polar wander). I'd love to see if the tilting observed here is consistent with geophysical work on Mars' tectonics -- or inconsistent, which would be just as interesting.


Sound like a puzzle that might be unscramble-able with constant-scale natural boundary mapping. If the tilting blocks can be identified (say by constructing the medial axis of all the surface that is not the Tharsis complex, and using that topological skeleton to form the edge of the CSNB map (same as, or similar to, the way the foldable asteroid maps were laid out), then we'd have, perhaps (I'm just making this up as I go along), an ideal map in which to contemplate all the data and speculations about tilt.

And then again, the inverse map, the one that uses critical boundaries within Tharsis complex as the CSNB map edge may be better to project the stresses to the antipodes, which would then by in the middle of the Tharsis-edged map. See some tilting scenarios may be seen as more likely than others.

The nice point is that the two topological skeletons would be complementary to each other, so all sorts of analysis by numerical and (with the handy constant-scale critical boundary format) geometrical, i.e., waterlines, (the old Victorian mapmaking treatment of watery shorelines) which would project stresses (and carry second order stresses) onto the other skeleton.
May not even be necessary to have the map, but then a picture's worth, what? I forget the math . . .
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serpens
post Jan 2 2013, 03:38 AM
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Since Edwin Kite's article generated this discussion it is interesting that he (and others) also wrote a paper on true polar wander a few years ago.

www-eaps.mit.edu/faculty/perron/files/Kite09.pdf
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serpens
post Jan 2 2013, 10:06 PM
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QUOTE (Eyesonmars @ Jan 2 2013, 01:06 AM) *
If "true polar wander" did occur in the past that means GALE crater could have been at a higher latitude when some of these fluvial features were created.


Based on analysis of tectonic structures,topography and gravity as well as crustal magnetism Zhong Migration of Tharsis volcanism on Mars caused by differential rotation of the lithosphere concludes that that the main Tharis Bulge had migrated to its current location by the end of the Noachian. I think Gale is assessed as being formed in the late Noachian/early Hesperian and if Zhong is correct then Gale has always been equatorial and the tilt in layers would not be attributable to polar wander although I guess that gradual change to the equatorial bulge following the Tharsis realignment could have some influence.

Emily has an impressive ability to generate, with few words, an incentive to research topics that were previously of minor interest.
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Gerald
post Jan 10 2013, 03:15 PM
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Several of the rocks near the border of Yellowknife Bay look to me like creeping.
Seasonal temperature cycling might lead to a creeping of the top layer in the direction of the net force, if the top layer consists of material sufficiently different from the layer below.
Might it be, that slope winds exert a force to the top-layer rocks strong enough to result in a net movement towards the crater rim?
An annual creeping of 1mm will be sufficient to exceed aeolian abrasion (0.01 to 0.05 mm per year estimated) twenty- to one hundredfold.

A rough sample calculation, assuming one creeping step per (Earth) year, i.e. two per Marsian year, a difference of the linear thermal expansion coefficients of the two layers of 10 ppm per Kelvin, a seasonal temperature difference of 20 Kelvin, and a length of a rock fragment of five meters yields
0.00001/K x 20 K x 5000mm x 0.5 = 0.5 mm
annual creeping. (Factor one half, because I have to look at the center of the rock.)

For small and thin rocks, even diurnal creeping may occur.
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JRehling
post Jan 10 2013, 06:14 PM
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This may touch only tangentially on the case of Gale, but I was struck recently upon learning that a 100 km lunar crater, Icarus, also has a central peak that is higher than its rim. Because, obviously, the Moon lacks many of the mechanisms that act on Mars, it offers a far narrower set of possible explanations. In fact, I'm not sure if anyone has explained the case of Icarus. I see a citation of one article I can't read without disbursing some cash:

http://www.sciencedirect.com/science/artic...019103573900237

That said, it is certain that Mt. Sharp has undergone a lot of phenomena that could not be shared between the two cases, but it's interesting to note the lunar case when trying to piece together the logic of Mt. Sharp.
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Phil Stooke
post Jan 10 2013, 06:27 PM
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Save your cash! There's nothing in that paper about the crater Icarus - it was published in the journal Icarus! (is that where a search led you astray?) There is also absolutely nothing in that paper about any central peak higher than the rim of its crater. LOLA data will allow this topic to be explored much better than any past studies have done.

Phil



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elakdawalla
post Jan 10 2013, 06:54 PM
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Sorry, Gerald, what you're describing makes no physical sense, and multiplying a couple of numbers together doesn't make it any more sensible. I encourage you to read a physical geology textbook and then ideally a geophysics textbook -- or take some classes -- before trying to do quantitative geophysics. I like both Press & Siever (Earth) and Monroe & Wicander (Physical Geology) as introductory texts, though my textbooks are aging now and there may be better ones out there.

As Phil has said before this forum is better at image processing than geology.


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JRehling
post Jan 10 2013, 07:31 PM
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Thanks for the tip, Phil. Actually, it was not an errant search, but a comment online by the author of the article who cited it in reference to that crater, but the relevance he inferred to the case of the crater Icarus may have been largely (or entirely) overstated. There may be no scholarly work at all on the case of the lunar crater Icarus.
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Gerald
post Jan 10 2013, 08:32 PM
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Thanks Emily, for the hints to appropriate literature! It's difficult to find literature, that is not based on conditions observed on Earth.

I looked for investigations of soil creeping on Earth in the web, before I wrote the post. Unfortunately on Earth there is almost always water involved, which leads to additional expansion and shrinking by binding and releasing water to rock containing clay minerals, so that those processes may lead to an estimated soil creeping of about 1cm per year, less than solifluction, so it is mostly negligible on Earth. This may not be obvious for Mars. Therefore I redid the calculations based purely on temperature cycling. Normally such creeping occurs on slightly inclined layers or even within a layer. So the creeping will per se be a valid physical process. The question to me is, whether the thin atmosphere of Mars can exert a net force.

If the creeping as a valid process looks questionable, I may describe the mechanics behind that. In literature it is mostly sketched very briefly, because it's rather easy.

The idea of soil creeping on Mars is not quite new, see Paper on soil ceeping on Mars

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drz1111
post Jan 10 2013, 09:37 PM
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QUOTE (elakdawalla @ Jan 10 2013, 01:54 PM) *
Sorry, Gerald, what you're describing makes no physical sense, and multiplying a couple of numbers together doesn't make it any more sensible. I encourage you to read a physical geology textbook and then ideally a geophysics textbook -- or take some classes -- before trying to do quantitative geophysics. I like both Press & Siever (Earth) and Monroe & Wicander (Physical Geology) as introductory texts, though my textbooks are aging now and there may be better ones out there.

As Phil has said before this forum is better at image processing than geology.



QFT. Sigh.
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Gerald
post Jan 10 2013, 09:56 PM
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Thanks JRehling, thanks Phil, thanks Emily, thanks drz1111 for your assessments, and for being honest!
The idea is either too brilliant, or nonsensical, probably the second.
I'll return to image processing.

EDIT: Luckily, I came across the literature, where I originally found an explanation of soil creeping, including quantitative estimates:
David John Briggs, Peter Smithson: "Fundamentals of Physical Geography", p. 325.
Just in case, someone is interested.
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ngunn
post Jan 10 2013, 11:18 PM
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Speculating about processes on other planets is a better way to spend your time than many others. I do it a lot and in the case of Mars I know I'm 'getting warm' when one or more of the real geologists here responds. There have on many occasions been good geological discussions on this forum even if it isn't what we're best at.

On another tack: crowd sourcing is becoming fashionable in science, mainly for searching through large data sets. I think it can apply also to ideas if similar filtering processes are employed. This forum is perhaps a precursor for what could be done more generally. In the meantime the admins have to keep judging their interventions. It's hard work done for free and I respect them greatly for it.
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SFJCody
post Jan 11 2013, 03:57 AM
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QUOTE (ngunn @ Jan 11 2013, 09:18 AM) *
Speculating about processes on other planets is a better way to spend your time than many others. I do it a lot and in the case of Mars I know I'm 'getting warm' when one or more of the real geologists here responds. There have on many occasions been good geological discussions on this forum even if it isn't what we're best at.


I'm with ngunn. I enjoy sticking my oar into areas I have no strong specialist knowledge of (hey, it's a fun mission, sometimes one can get a little over-excited!) but I'm even happier to be corrected by the better read among us.
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TheAnt
post Jan 11 2013, 10:58 AM
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QUOTE (Gerald @ Jan 10 2013, 09:32 PM) *
The idea of soil creeping on Mars is not quite new, see Paper on soil ceeping on Mars


A good find there, and you're right it takes humidity in the soil for creeping, in the lower arctic forests the trunks of birch trees get a funny bent shape in such areas. With the temperature as low as they are, and frozen in subsurface layers I thought creeping would not occur, I am all happy again to be proven wrong. =)
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