Voyager observations of Ganymede show broad, high-albedo, topographic domes situated within the central pits of some impact craters, referred to in this study as ''dome craters''. Of 56 dome craters identified on Ganymede, all but two can be placed into one of two classes, based on the ratio of dome diameter to crater rim diameter. Two new hypotheses for the origin of the domes involving diapirism as an agent of dome formation are offered. Implicit in both hypotheses are possible regional heat flux variations. Under these scenarios, ''relaxation'' of crater relief may not be homogeneous in space and/or time, and crater morphology may not be a consistent indicator of crater age. Plutonic intrusions within the upper lithospheres of Ganymede (and Callisto) may have played a far more important role in heat transport on these satellites than previously noted. ¿ American Geophysical Union 1988