Latent outflow activity for western Tharsis, Mars: Significant flood record exposed

Observations permitted by the newly acquired Mars Observer Laser Altimeter data have revealed a system of gigantic valleys northwest of the huge Marti an shield volcano, Arsia Mons, in the western hemisphere of Mars (northwest ern slope valleys (NSVs)). These features, which generally correspond spati ally to gravity lows, are obscured by veneers of materials including volcan ic lava flows, air fall deposits, and eolian materials. Geologic investigat ions of the Tharsis region suggest that the system of gigantic valleys pred ates the construction of Arsia Mons and its extensive associated lava flows of mainly late Hesperian and Amazonian age and coincides stratigraphically with the early development of the outflow channels that debouch into Chrys e Planitia. Similar to the previously identified outflow channels, which is sued tremendous volumes of water into topographic lows such as Chryse Plani tia, the NSVs potentially represent flooding of immense magnitude and, as s uch, a source of water for a northern plains ocean.