GEOLOGICALLY RECENT MARTIAN VOLCANISM AND FLOODING IN ELYSIUM PLANITIA AND CEBERUS RUPES: PLAINS-STYLE ERUPTIONS AND RELATED WATER RELEASE?

Recent Mars Orbiter Camera (MOC) images and Mars Orbiter Laser Altimeter (MOLA) topography from the Mars Global Surveyor (MGS) Spacecraft have led several research teams to suggest geologically recent (10-100 m.y. ago) volcanism within Elysium Planitia and Amazonis Planitia that--in some areas-- may have been emplaced over ice-rich ground. Other work has pointed to the possibility that the same rifts serve as a source for both the volcanism and the water. MOLA data provides us with new abilities to 1) provide recognition of low relief, low albedo variation volcanic or fluvial features not apparent in available images, 2) constrain estimated flow rates from edifice geometry or channel geometry and regional slope measurements, and 3) topographically track these volcanic and fluvial features to their apparent sources. We find that the volcanism in this region is well-expressed in a series of topographically fresh rift and low shield eruptions. Shield and regional slopes are quite low, with shield flank slopes ranging from 0.14 to 0.3 degrees and regional slopes of 0.01 to 0.04 degrees. Some shields have extensive associated flows, and several are constructed over rift segments. In general, the volcanism appears to be a relatively topographically fresh expression of plains style volcanism. Our edifice and channel models provide evidence for lower volcanic production rates than would be derived for flood-type basaltic provinces. Model calculations for typical basaltic or basaltic andesite rheologies yield very plausible volcanic flow rates (e.g. 1000 cubic meters/second). Rift and small shield sources are evident in the topographic data for much of the youngest volcanism, and we concur with prior suggestions that some of the volcanic and fluvial features appear to originate at common rift sources. Given the apparent youth from both topographic freshness and from existing crater dating work for the fluvial and the volcanism features, this region provides compelling evidence for the overlap of volcanic and hydrologic domains for the martian near-surface and surface environments in the recent geologic past. From the apparent age range of flows within the region, this is clearly a long-lived volcanic province, and future hydrologic and/or volcanic events are still conceivable.