Dark streaks on slopes have been observed on Mars since the Viking
missions. The prevailing view is that they are dry slope flows.
However a new report to be given at this month's AGU meeting will
present evidence they are water related:

Title: Evidence for a water phase-transition at low latitudes on the
surface of present-day Mars
Authors: Aharonson,O.;Khatiwala,S.;Schorghofer,N.
Affiliation: AA(MIT, Bldg 54 Rm 521 77 Massachusetts Ave., Cambridge,
MA 02142 United States; oded@m...), AB(MIT, Bldg 54 Rm 521 77
Massachusetts Ave., Cambridge, MA 02142 United States;
spk@o...), AC(MIT, Bldg 54 Rm 521 77 Massachusetts Ave.,
Cambridge, MA 02142 United States; norbert@s...)
Journal: American Geophysical Union, Spring Meeting 2002, abstract
#P31A-11
Abstract
The Mars Orbiter Camera on the Mars Global Surveyor spacecraft has
returned images of numerous dark streaks that are the result of down-
slope mass movement occurring under present-day martian climatic
conditions. We systematically analyzed over 23,000 high-resolution
images and demonstrate that in addition to forming exclusively in
regions of low thermal inertia and steep slopes, streaks form only
where daily peak surface temperatures derived from TES data exceed
275 K. The northernmost streaks, which form in the coldest
environment, form preferentially on warmer south-facing slopes.
Repeat images of sites with slope streaks show changes only if
surface temperatures exceeded the melting point of water during the
time interval between the two images. These correlations suggest the
possibility that small amounts of water are transient and undergo
phase transitions at times of high insolation, providing a trigger
for the formation of the features.
http://adsabs.harvard.edu/cgi-bin/bib_query?2002AGUSM.P31A..11A

In a post to sci.astro below I suggested that the streaks may be
related to periglacial processes, which would require freeze-thaw
cycles on present-day Mars. This was prompted by the England and
Palermo report that the streaks origin was water-based.
Also if correct, it makes it quite likely that the Malin/Edgett
gullies are water carved and forming currently.

Bob Clark

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From: Robert Clark (rgclark@m...)
Subject: More on the dark streaks on Mars.
Newsgroups: sci.astro, alt.sci.planetary, alt.astronomy,
sci.geo.geology, sci.geo.meteorology
Date: 2001-09-09 06:54:22 PST

From the Habitablezone.com/space/ site:

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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
...
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.
=========================================

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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This discussion on the Habitablezone.com bbs was prompted by a new
examination of the dark streaks by England and Palermo:

"A Study of Mars Global Surveyor (MGS) Images Showing Probable Water
Seepages. Are They Dust Slides as NASA CLaims or Proof of Water on
Mars?"
www.users.qwest.net/~vtwild/webpage/Mars%20Society%20Seeps%20Paper.pdf

They made the apparently new observation of concentrations of the
dark streaks in Tharsis near the equator and 180° away in Arabia
Terra. (Note: I've been informed that their work is independent of
the Bara/Hoagland "Tides" report, rather Bara/Hoagland made reference
to the data in the England/Palermo work.)

I 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."
http://geomorphology.geo.arizona.edu//geos450/LECTURE23/lecture23.html

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 an 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 is expected
to be kilometers subsurface at such latitudes was pushed close to the
surface by the same deformation process proposed to have created
Arabia Terra.

Bob Clark
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