In reply 5, mcoony asks:
i wondered if there is any evidence of sinkholes or slumping?
The answer is yes, lots of evidence. Go to the MOC page and search "sinkholes"--there are over a doen good images of large Martian sinkholes, both singly and in chains, that are NOT impact features. Some of these seem to show clear fluid alteration.
Of course, there are also at this point many hundreds of pictures of gullies on crater walls. Penny Boston has published several papers theorizing that there are warm "microenvironments" on Mars associated with both natural geothermal activity (to a small degree), and imapct sites (to a large degree). The temporary energy from a big impact can trigger local geothermal heating that lasts 10,000 years or longer, melting ground ice creating karst-like cave and sinkhole formation, not only in the crater, but impact fissures radiating from the crater, sometimes over long distances. These new caves themselves become heat sinks that may last long after the primary geothermal energy has subsided.
Boston may get to test her theories, as she is currently on development teams for two different possible future missions. She also has a nice website on "Caves of Mars" (sorry, don't have URL handy).
Good thread, btw, mcoont--glad you stopped lurking. ALthough I mostly lurk myself, and can't even do much of that during the summer.