Alex Blackwell writes: [[Interestingly, no reference to this earlier work is given by Palermo et al.; I'll assume that they are unaware of this as well.]]

Why would that be interesting? These people are amateure researchers working in their spare time. It's not interesting, that they didn't have a vast collection of references; it's irrelevant.

[[(1) The MOC NA imagery of the dark streaks, assuming a "wet" origin, show no pooling where the streaks descend across craters or other topographical lows.]]

What are the frame numbers that show this? I haven't seen such streaks passing through any craters wider than the streaks themselves in the images I've looked at.

[[(2) Many slope streaks are observed to display a high degree of widening downslope. A model incorporating across-slope dispersion of fluid operating under the influence of gravity to produce the widening is problematic, to say the least, especially in the many areas where slopes do not possess cone-shaped morphologies.]]

It's not at all problematic for a liquid to spread out from the point of origin in all directions until the surface tension and the pressure of the liquid layer balance as the layer thins out. Try releasing a small stream of water from an eye dropper on the side of a sink basin. The water streak is the diameter of the dropper tip at the beginning of the flow and widens out quickly and maintains a relatively constant width for most of its length.

[[3) Since the vast majority of the dark streaks are observed on slopes, if their origin is "wet" presumably this is due to intersecting or even perched aquifers (near surface gound ice is implausible given the temperatures and the probability that the near surface is is in diffusive contact with the atmosphere). In this setting the putative liquid (water) would be subject to considerable hydraulic head pressures and/or lithostatic overburden. Assuming a breach, one would suspect that the liquid would erupt catastrophically (a la the Malin and Edgett seepage gullies) and shatter or collapse the overlying host rock.]]

The explosiveness of the release would be in part related to the thickness of whatever is blocking the flow. I don't see any reason off-hand why all water releases would have to be violent.

[[Further, and paradoxically, this "wet" flow would have to "seep" at a slow enough rate to not produce relief at the margins and yet fast enough to run out long distances in the ambient temperature/pressure regimes, which, to me, is implausible.]]

To the contrary, the lack of evidence for any relief is one of the characteristics that indicate a slow "seepage" of liquid that does not carry away large quantities of debris like a raging flood would do. A slow seepage could flow a very long way, given a surface that is not very absorbent and a liquid that isn't very viscous.

The lack of relief is far more a problem for the dust slide interpretation, as Malin himself states repeatedly in the LPS papers he's written. For that exact reason, in the LPS XXX 1809 paper, he favors a mechanism by which individual debris elements move only a short distance, with the disturbed area extending for long distances by a sort of domino effect. That would have gotten around problem of the missing relief.

But in the LPS XXXI paper 1911, he abandons this idea completely and switches his preferences to a more traditional landslide mechanism, a mechanism with which he found "problems" in the previous paper. One of those problems was the lack of any indication of relief associated with debris elements moving long disances. I saw no indication that he solved this problem in the second paper. It appeared only that further research rendered the previously more favored theory less tenable but really showed nothing to make the previously less favored theory more tenable. Changing theories in the middle of the stream (no pun intended) is not a very good sign, really.

[[Even assuming this hurdle can be overcome, why would two different mechanisms for fluid flow (the Malin and Edgett seepage sites and the "dark stains") that produce two different morphologies be operating during the same geologic epoch when one is sufficient?]]

Malin's interpretation of the gullies as water related was criticized because there were no indications of water flow elsewhere. Maybe there are such indications of water in these streaks at equatorial latitudes. The mechanism might be different at different latitudes.