Formation of Olympus Mons and the aureole-escarpment problem on Mars

Abstract

Based on morphologic interpretation of Viking Orbiter images, it is postulated that on the summit area of Arsia Mons, Mars, there is a several kilometer thick ice cover. In addition, numerous linear striae on the flanks of Arsia Mons resemble terrestrial “washboard moraines,” behind which there may be substantial dead-ice deposits. This implies that glacier phenomena are active in the Tharsis region. These features may have bearing on the formation of the aureole deposits of Olympus Mons. Olympus Mons has been the cause of dispute among geologists for years, and several contrasting models have been proposed to explain the up to 10-km-high distal escarpment and broad lobate aureole deposits below. One model by Hodges and Moore (1979) assumed 2–3-km-thick ice under which volcanism proceeded at an early stage to build Olympus Mons, thereby leading to the growth of the high cliff section. It has been argued that the origin of the aureole has not been satisfactorily explained. Modifications of the Hodges and Moore hypothesis are proposed to explain some aspects of both the aureole formation and the escarpment at the lava-aureole boundary. The assumption is made that volcanism that persisted was mostly localized on the Olympus Mons massif throughout the aureole development, and that a blanket of ice and wind-blown dust covered the lower flanks of the volcano. Deposition of volcanic products on the flank blanket led to faulting and sliding of material away from the summit area, thereby creating the aureole deposits and scarp. Further eruptions of lavas in the summit area substantially elevated the cliff segment, and additions of lavas off the cliffs into the wing area led to further creeping of the lower flank region, thus generating the vast aureoles. Therefore, the aureole formation succeeded and resulted from Olympus Mons volcanic activity, and is one of the youngest features of Olympus Mons and not older, as has been postulated.