Mars Express has released the results of a gravity mapping program, done in conjunction with MRO, looking at volcano formation. There are two pages now on-line:

General Interest:
http://www.esa.int/esaSC/SEM6HJNW91H_index_0.html

Science and Technology pages, with more slightly technical detail:
http://sci.esa.int/science-e/www/object/in...fobjectid=50299

Is there a global map somewhere? It is edifying to know that there probably is, but it would be neat to see it after reading about it. Perhaps this:
http://ars.els-cdn.com/content/image/1-s2....003830-gr13.jpg

Interesting that the found evidence to support a mantle plume for those three volcanoes in a line. Wonder if that means the mantle moved, but the crust didn't.

Or the other way around (or a bit of both). I recall reading some time back that the redistribution of mass associated with the bulge could have caused the surface to do a 'polar flop' and that this might account for the putative northern ocean shorelines being off-level today.