Peneus Patera shows what is termed "scalloped topography". Such topography displays depressions with scalloped edges. Sometimes the depressions seem to coalesce together. These features typically occur at about 55 degrees north and south latitude. They are believed to form from the removal of subsurface material, maybe interstitial ice by sublimation (change from solid to a gas). More gentle slopes face in the direction of the equator, while steep scarps face the pole. This is probably due to differences in solar heating. The process is believed to be ongoing.