Errita,

As you know, I'm highly skeptical that the gullies are actually evidence of discharge of liquid water on the surface of Mars. All the other evidence for the state of water on mars has it in an arid cold-trap, alternating between trace atmospheric water vapour and solid ice (generally in the subsurface).

All the evidence for geothermal gradients points to very cold conditions in the subsurface, with the depth for liquid water likely at several km to tens of km.

I favour a model of gas-supported density flows for the recent gullies on mars.

All the evidence for seasonal thaw and association with cold snowpack-filled gullies is equally valid as support for a CO2 avalanche model, in fact more so, because the gullies are demonstrably filled by CO2 snowpack.

I'm all in favour of Hi-Rise and other detailed imaging of the gullies, especially at the springtime thaw, because I think it WILL see things, but perhaps not what you have in mind...

I'd draw your attention to my 2002 paper on Sisyphi Cavi where I have suggested that there is already evidence for seasonal flows.

< a href="http://www.earthsci.unimelb.edu.au/mars/Polar.html">a summary of the paper. The full paper is in ASTROBIOLOGY, volume 2, number 3, pp313-323