Ma'adim Vallis evolution: Geometry and models of discharge rate

Episodes of confined flows in Ma'adim Vallis are reconstructed by surveying the terraces in the valley. Three major levels and their associated tributary systems are identified and mapped. This study points out the evidence of the cessation of the valley activity between the formation of levels 1 and 2, characterized by degraded and large perched valleys, which floor are not adjusted to the following flow episode level. A strong asymmetry in the tributary distribution points toward a groundwater-supplied water origin of the valley. Potential source areas are demonstrated to be in volcano-tectonic regions, implying a hydrothermal origin of the water, that may include melted permafrost. Calculation of hydraulic radii, valley sections, and models of discharge rates associated with the morphologic and geologic survey shows that Ma'adim Vallis was an episodic channel, the lifetime of which spanned between the Noachian and Amazonian. (C) 1998 Academic Press.