First, as to the movement / changes seen in the very first image posted:<br /><br />Well, you have to remember the following:<br /><br />There are trace amounts of Water Vapor, as well as CO2 in the Martian atmosphere. And the nighttime temperatures on Mars can go down as low as (IIRC) -170 or more degrees C at night. So it can freeze out of the atmosphere as a fine layer of frost.<br /><br />Or, there is the (Martian) yearly melting of the poles, which can release a great deal of water vapor and CO2 into the atmosphere.<br /><br />Or, the yearly Summer dust storms that occur.<br /><br />So, see, there's a whole range of conditions that could cause all of the changes we see in the imagery (including the frost / snow you think is there). <br /><br />Although, myself, I still think it's a simple change in reflectance, due to changes in the type and nature of the surface of windblown sand. That would fit the other changes we see in the image.<br /><br />********<br /><br />As to the catastrophic outflow channels: these are when subsurface pockets of ice or permafrost melt and their water flows, suddenly and catastropically (hence the name) out to the surface.<br /><br />As to where the ice / permafrost occurs is another matter. So why not more of these where the "bottom" of the river is, and less on the "banks?"<br /><br />Also, remember that these catastrophic outflows occur under the reduced gravity, temperatures, and atmospheric pressure of Mars.<br /><br />Better? <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis: </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>