In the sci.astro post copied below I speculated that an image from Mars Express might show a recent or active volcanic vent:

Portion of Valles Marineris.
http://sci.esa.int/science-e/www/obj...objectid=34528

The reason for this was that the dark deposit showed the material being spread out in a fan shape. You would expect just wind blown dust to blow straight out from the origin point. In other words the wind-blown material should be no wider that the deposit it originates from. When the wind-blown material grows significantly wider than its origin, that suggests material is being ejected from the origin.

I was able to get a high resolution MGS image of the crater where the dark material emanates from from the imaging public request site on Msss.com:

Mesa with dark-toned material in chaotic terrain region.
http://www.msss.com/mars_images/moc/...R22-00522p.gif

But this doesn't seem to resolve the issue of whether or not this is an example of venting.

However, I found another example that might provide a stronger case for venting:

Southern rim of Isidis Planitia basin (Released 11 April 2002)
http://themis.asu.edu/print-20020411a.html

Notice again the wind-blown material is fan shaped, which I argue is suggestive of material being ejected from the surface. But what is really suggestive of venting is the curved shape of the fan deposit. This is strongly suggestive of material being ejected in the air then swirling around due to high winds.
Anyone know of any high resolution MGS images of this area?


Bob Clark



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From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: Active volcanic vent on Mars?
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.geology
Date: 2004-03-13 20:31:21 PST


Another similarity between the two images is that there appears to be
two separate streaks that are emanating from opposite sides of the
crater. That again could be due to light colored dust being blown to
cover the area nearest the crater. However, there is a separate
instance that suggests this is in fact due to venting of some kind.
In the southern polar regions there have been observed strange
spider-like forms in the region covered by a seasonal CO2 cover. These
branching spider-like ravines have been attributed by Kieffer et.al.
to venting of CO2 gas beneath a CO2 ice cover. Interestingly, in
support of this interpretation there were given some images of dark
fan-like spots emanating from craters that are seen in association
with the spiders. Many of these fan-like spots have that same
charactertic of two separate streaks emanating from opposite sides of
the crater. But they are interpreted as due to the CO2 jets venting to
the surface.

Example of the "spiders":

MOC narrow-angle image M11-00396
South Chasma Australe scarp
http://www.msss.com/moc_gallery/m07_.../M1100396.html

Example of the fan-like deposits:

MOC narrow-angle image M07-03150
sample
http://www.msss.com/moc_gallery/m07_.../M0703150.html

Discussions of the spiders and fan-like deposits:

BEHAVIOR OF SOLID CO2 ON MARS: A REAL ZOO. Hugh H. Kieffer, U. S.
Geological Survey [Emeritus], Flagstaff, AZ
86001, USA, (hkieffer@******.net).
Sixth International Conference on Mars (2003) 3158.pdf
http://www.lpi.usra.edu/meetings/six...3/pdf/3158.pdf

ANNUAL PUNCTUATED CO2 SLAB-ICE AND JETS ON MARS. H. H. Kieffer, U.S.
Geological Survey,
2255 N. Gemini Dr., Flagstaff, AZ 86001
Mars Polar Science 2000 4095.pdf
http://www.lpi.usra.edu/meetings/polar2000/pdf/4095.pdf

Sublimation of Mars's southern seasonal CO2 ice cap and the
formation of spiders.
Sylvain Piqueux, Shane Byrne, and Mark I. Richardson
Division of Geological and Planetary Sciences, California Institute of
Technology, Pasadena, California, USA
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. E8, 5084,
doi:10.1029/2002JE002007, 2003
http://www.gps.caltech.edu/~shane/2002JE002007.pdf



Bob Clark



rgregoryclark@yahoo.com (Robert Clark) wrote in message news:<832ea96d.0402212306.324b99c@posting.googl e.com>...
> Here's an analogous image in a different area taken by Mars Odyssey.
> The color combinations were done by Keith Laney:
>
> http://www.keithlaney.com/colormars/V04437003color.jpg
>
> The individual THEMIS filter images are here:
>
> http://themis-data.asu.edu/img/V04437003.html
>
> This image raises another possible explanation for why there is a gap
> between the dark material and the crater. In this Mars Odyssey image
> it looks like lighter dust has been blown from the crater to cover the
> area immediately adjacent to it.
> The same may be the case in the Mars Express image. However, in both
> these cases the dark material still appears to emanate from the
> crater. And there is a widening of the dark material away from the
> crater. For a case of simple wind blown dust, the width of the dark
> streak should stay about the same.
>
>
> Bob Clark
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