So a 'complex crater' involves a certain degree of subsidence of the uplifted outer rim, and the forces involved in this subsidence, spreading the underlying ro

So a 'complex crater' involves a certain degree of subsidence of the uplifted outer rim, and the forces involved in this subsidence, spreading the underlying rock, combine at the center to push material upwards into a small solitary peak. I always assumed this happened due to a continuous pressure of magma or something in volcanoes, but it turns out the effect happens regardless of and in addition to any underlying geothermal activity: it's a feature of gravity and long-term settling of annular structures. http://en.wikipedia.org/wiki/Complex_crater#mediaviewer/File:Craterstructure.gif http://en.wikipedia.org/wiki/Complex_crater#mediaviewer/File... It looks like this is a crater which has ice(water ice? CO2 ice?) underlying a thick, mobile dust layer. When Ceres suffered an impact at some point in the past, it excavated a crater in the ice and dust, then the dust settled back down, covering everything. Over the following millennia / eons, the crater rim subsided and the center entered a long period of slow uplift, pushing through the dust layer and exposing the ice. It's possible something more novel could be at work here involving phase changes and maybe cyclical patterns; Unpredicted seasonal geysers have been observed on Mars, as an example. A complex crater filled with dust over underlying ice, though, is probably the default assumption.