[X] My Assistant

[Guest_AlexBlackwell_*]

Water May Not Have Formed Mars' Recent Gullies
By Lori Stiles
University of Arizona News Services
March 16, 2006

[ljk4-1]

"Are Martian Gullies Generated by Granular Flows?" by Dr. Troy Shinbrot of Rutgers University.

An Associate Professor of Biomedical Engineering at the New Jersey institution, Shinbrot's regular area of study is how various pharmaceutical products flow and interact with each other.

At a conference he co-organized with Cornell Professor Michel Louge in 2002, Shinbrot was discussing the "beautiful pictures" he saw of the Martian gullies. To Shinbrot, these surface features looked like they were made by the sandy particles themselves moving down the sides of banks, canyons, and craters, and not by liquid water.

...

From his previous granular flow research, Shinbrot knew that very light particles in a lower gravity environment act like a liquid before they eventually settle together to behave as regular solids.

Full article here:

http://www.zwire.com/site/index.cfm?newsid...id=216620&rfi=8

Dr. Shinbrot's Web site:

http://sol.rutgers.edu/~shinbrot/NewHome2006/index.html

[Guest_AlexBlackwell_*]

"Are Martian Gullies Generated by Granular Flows?" by Dr. Troy Shinbrot of Rutgers University.

Note that Shinbrot et al. published their work in 2004 in the Proceedings of the National Academy of Sciences.

See also

Treiman, Allan H.
Geologic settings of Martian gullies: Implications for their origins
J. Geophys. Res. Vol. 108 No. E4
10.1029/2002JE001900
08 March 2003
Abstract

Alex had some interesting answers to my points, which I won't insert here without permission.

No problem, John. Go ahead. If I don't like it, I can always plead lack of memory (à la Moomaw).

[JRehling]

No problem, John. Go ahead. If I don't like it, I can always plead lack of memory (à la Moomaw).

I'll repost the info in two installments in this post, each of which includes another post by quotation:

I wrote, quoting Alex:
--- In planetary_sciences@y..., "alexblackwell_2000" <ablackwell@c...>
wrote:
> --- In planetary_sciences@y..., "jarehling" <rehling@c...> wrote:
>
> > The morphology was also interesting.
>
> Did you by chance notice any anastomosis or channel piracy, which is
> observed at the Malin and Edgett gully sites and which is also a
> characteristic of subaerial fluid flow (as opposed to a dry mass
> movement) moving down a topographical gradient under the influence of
> gravity?

No, I didn't. In the case of the dunes, the flows I was looking at
were too small (decimeters wide, a meter long) to show some of the
phenomena that might have shown up on a larger scale.
You seem to suggest that the observed morphology of martian
gullies is incompatible with dry mass movement (with the following
caveat:)

> FWIW, though, Allan Treiman of LPI posits in an abstract
> ("Dry Mars: Parched Rocks and Fallen Dust") from the NASA
> Astrobiology Institute General Meeting, Washington, D.C., April
> 10-12, 2001 (in the latest issue of journal Astrobiology) that the
> Malin and Edgett gullies could represent "debris flows [from] large
> avalanches from thick dust deposits, analagous to climax snow
> avalanches." Treiman bases his model on the latitudinal distribution
> of the gully sites, which correlates to the large abundance of dust
> observed in the southern highlands, as well as to the dessicated
> nature of the Martian surface.

It seems highly reasonable that dry mass collapses would not show
the branching of channel piracy (which, if the flow were spreading
upwards, would not branch in that way for any obvious reason, and would
lead, instead, to a broader upslope collapse -- more alcove). Still, it
would be interesting to see simulations using martian parameters
instead of relying upon earth-condition analogues.


AND THEN
Alex wrote, quoting me:
--- In planetary_sciences@y..., "jarehling" <rehling@c...> wrote:

> You seem to suggest that the observed morphology of martian
> gullies is incompatible with dry mass movement...

Just to be clear, I am not referring soley to the
alcove-channel-apron morphology, which, especially for a wide array
of equatorward-facing examples, are attributed to dry mass movements.
However, with respect to the Malin and Edgett seepage sites, which
are observed finer scales, "the observed morpholog[ies]" (e.g.,
sinuosity, anastomosis, incision, streamlining, presence of levees,
channel/stream piracy, etc.) are indeed "incompatible with dry mass
movement."

For example, take a look at the dust avalanche scars reported by
Sullivan et al. and note the absence of these distinctive
characteristics. At any rate, it is not merely the observed
morphologies that suggest fluid flow, but also their spatial
distribution and preferential orientations.

> It seems highly reasonable that dry mass collapses would not
> show the branching of channel piracy...

Agreed.