Hey Marcia... Something tells me you're on to what may be the answer. There's still a tendency to automatically characterize all circular formations on the Martian surface as impact craters, but I've noticed a hestitation lately, referring to "pits" rather than craters, and otherwise letting alternative options be considered.

The Opportunity site outcrop is so broken up, it almost shouts "impact" and yet... sections of it seem to have broken up and collapsed into the pit -- or started to. It seems to me an internal energy source could be just as likely as an external one -- if not more so -- and it can help explain the deposit as well. Thanks for those pictures from Iceland. They are evocative, aren't they?

I notice, too, that the exposed outcrop we see on the distant crater appears to be almost like a frozen wave. There are signs all around that crater that suggest an impact origin, but the wave form -- if it is real, and not one of those visual tricks we see on Mars all the time -- suggest that the "white" material may be quite pliable. And that crater too may have formed from internal rather than external forces.

Hard to say.

I'm just thrilled with all of it!

Cheers, BRFelix