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Re: More Seriously... LPSC abstracts
Posted by Robert Clark (64.9.8.60) on 8/29/2001 5:57:06 AM
In Reply to: Re: More Seriously... LPSC abstracts posted by Jill England on 8/28/2001 2:42:38 PM
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Re: More Seriously... LPSC abstracts
Posted by Jill England (64.24.187.135) on 8/28/2001 2:42:38 PM
In Reply to: More Seriously... LPSC abstracts posted by Justin Kelly on 8/27/2001 3:26:17 AM
I don't know if anyone thinks it's important or not but,
http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1698.pdf
Contains a rather serious graph labeling error;
Their Longitude scale goes from 0 to 360, in the wrong direction.
Their actual Map is the one with 0,0 in the center of the map and then moving out to 180 degrees on the edges, not the middle.
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Thanks for the catch. I had been thinking that the smaller concentration near the center of their fig. 4 was in Amazonis based on their coordinate labeling, rather than its actual location in Arabia Terra.
The latitudinal concentration might support the idea that water is involved with the origin of the dark streaks, as Bara and Hoagland suggest in their Tides report. Also, there was a recent report that there are active glaciers in Tharsis which might indicate a source for the water near surface. However, I don't see why there would need to be a concentration in Arabia.
Another possibility is that the volcanic activity in Tharsis is the cause. Recent research indicates that volcanism in the Tharsis region extends to geologically recent times, and perhaps currently. Then perhaps the supporting factor of the streaks is a gas release due to volcanic activity. Albin and King in their report "ORIGIN OF DARK SLOPE STREAKS WITHIN THE SCHIAPARELLI IMPACT BASIN, MARS.", http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1395.pdf , proposed a CO2 gas release to support the long flows of the streaks that can extend over a kilometer.
Why again in Arabia then? There was a paper in Science that suggested the Arabia uplift was due to Tharsis:
Ancient Geodynamics and Global-scale Hydrology on Mars
"Members of the MOLA Team used Mars Global Surveyor topography and gravity data to address loading of the lithosphere of Mars by the Tharsis rise. Tharsis is a BIG load on the surface of Mars and when it was emplaced it deformed the whole surface of the planet, just like what would happen if you punched a beach ball. By developing models, we showed that loading of Mars by Tharsis explains much of the global shape and long-wavelength gravity field of the planet. Loading by Tharsis also explains a ring of negative gravity anomalies and a topographic trough around Tharsis, as well as gravity-anomaly and topographic highs centered in the Arabia Terra region and extending northward toward the Utopia basin. We showed that the Tharsis-induced trough and antipodal high were largely in place by the end of the Noachian Epoch, the earliest stratigraphic epoch in Martian history (about 4 billion years ago)."
http://ltpwww.gsfc.nasa.gov/tharsis/tharsis_paper.html
There are some nice images from the Science paper and a link to the full text paper on this page.
Question: would you also expect ongoing volcanic activity or gas release from Arabia for this reason? If so then the low latitude concentration may only be an accident having to do with the location of the Tharsis volcanos.
Note also that this Science paper gives an alternative explanation of the Arabia rise to the one proposed by Bara and Hoagland. The authors suggest it is due to lithospheric deformation due to the Tharsis load.

Bob Clark
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Found this web page while doing a web search on periglacial processes:

Periglacial Form and Process:
"European geologists have long been aware that thick sheets of poorly sorted angular debris mantled their landscape beyond the limits of glaciation. The process of fluid motion of sheets of debris down gentle slopes to form deposits is solifluction. Gelifluction refers specifically to flow of the active layer (not permafrost) over a frozen substrate. Meltwater saturation greatly promotes gelifluction and enables it occur on miniscule gradients."

Fig. 2 shows dark streaks on slopes similar to those seen on Mars. Then perhaps a similar process in their formation requiring freeze-thaw cycles is involved in their formation.
Ferguson and Lucchitta suggested such a process in a earlier NASA report:

Dark streaks on talus slopes, Mars
In NASA. Washington Rept. of Planetary Geol. Programs p 188-190 (SEE N84-23431 13-91)
http://adsabs.harvard.edu/cgi-bin/bib_query?1984pggp.rept..188F [abstract]

The talus they mention is debris or sediment found at the bottom of slopes. Then the presence of talus at the bottom of the slopes with dark streaks on Mars may indicate the type of process seen in the periglacial slopes on Earth.
However, a key argument for the prevailing explanation that the streaks are due to dust flow down the slopes is that later streaks seem to avoid overflowing nearby earlier streaks. The Fig. 2 of the "Periglacial Form and Process" page does not appear to have this feature. It is possible that the viewpoint of the photo makes this difficult to see.
Note if this is a similar process occurring on Mars it would require liquid water or ice close to the surface. Then the research by Johann Helgason suggesting active glaciers in Tharsis beneath a sediment cover might give an explanation for the source of the water/ice and explain their concentration in Tharsis:

Does Mars Hide Vast Water Deposits?
http://spacedaily.com/news/mars-water-99b.html

Active Volcanism On Mars And The Search For Water
http://www.spacedaily.com/news/mars-volcano-01a1.html

As for the concentration in Arabia perhaps the ice that was expected to be kilometers subsurface at those latitudes was pushed close to the surface by the same deformation proposed to have created Arabia Terra.

Bob Clark