Re: Circular formations on Mars, their origin(s)
Some of the craters seen on Mars are probably maars, rather than impact craters.
Some examples of maars:
Espenberg Maars.
http://www.gi.alaska.edu/ScienceForum/ASF2/245.html
Crater Elegante from the southwest.
http://jgutmann.web.wesleyan.edu/images/crater1.html
Bob Clark
