HYDRAULIC AND TOPOGRAPHIC CONSTRAINTS ON WATER LEVELS AND LONGEVITY OF A SEA WITHIN ELYSIUM PLANITIA, MARS

Flood lavas and water flow have been key resurfacing processes throughout much of terrestrial and martian history. Recent Mars missions have returned copious images and topography of geologically young-appearing channels on width scales of meters to hundreds of kilometers on Mars. Some of these channels are suggested as sources of possible extant frozen seas or sites of water-based mud or slurry type flows, or as locations for very large fluvial flood events. More recently, the Elysium Basin region at the outflow of Athabasca Valles has been suggested to be the location of remnants of a frozen sea on the basis of platy terrain attributes and distribution, and two spillway or exit flow locations have been proposed. For determining both channel origin processes and the potential water level and longevity of the proposed Elysium sea or ocean, estimating flow velocities and flow rates is key. These velocities and rates will aid in constraining the source processes, are a controlling factor in the effects of the flow on the local and global climate, and are also a major rate-controlling parameter for assessing the eventual fate or end state of the liquid water. Clearly, the sources, rates, and destinations of water on such a large scale in the recent martian geologic past are of great interest when we consider: 1) Where to search for past or present accessible water for possible life ecosystems; 2) What types of catastrophic loading on the atmosphere and climate such flooding might have had; or 3) How possible ecosystems between the deep subsurface and the surface or near surface might be linked through the associated flood source vents of the channels. In this study, we use topographic and image data to determine channel shapes and slopes and hydraulic diameters, as well as spillway elevations and possible levels prior to overtopping. Basin volumes, areas, and entrance and exit flow rates then constrain the water level and range of estimated duration times for the proposed sea at original and downcut spillway levels.