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V.R. Baker (Dept. of Hydrology and Water Resources, University of Arizona, Tucson)
Recent results from the Mars Pathfinder and Global Surveyor Missions corroborate the hypothesis, first presented in 1991, that episodes of cataclysmic outburst flooding temporarily produced extensive ponded water and associated climate change on Mars. This hypothesis colligates numerous diverse facts concerning the Martian landscape and its history into a single, unified genetic system. The elements of the hypothesis are given by the name MEGAOUTFLO - ``Mars Episodic Glacial Atmospheric Oceanic Upwelling by Thermotectonic Flood Outburst". The hypothesis explains long periods (~108 years) in which Mars had a stable atmospheric state of cold, dry conditions, similar to those prevailing today at the planet's surface. These long periods of quiescence and extremely slow surficial erosion were punctuated by short-duration (~104 to 105 year) episodes of quasi-stable conditions, considerably warmer and wetter than those prevailing today at the planet's surface. The transition from the long-persistent cold-dry state was induced by the cataclysmic outburst of huge flood discharges from the Martian outflow channels. The energy for these immense floods was supplied by the thermotectonic effects of immense mantle plumes. Gas that had accumulated beneath the ice-rich permafrost served to propel the great floods. Additional radiatively active gas was released by the associated volcanism. The result was a transient greenhouse that coincided with immense pondings of water that accumulated from the outburst floods. This produced glaciation on portions of the Martian surface. Features consistent with the above hypothesis are the great smooth expanses of the northern plains, documented by the Mars Global Surveyor's laser altimeter; the extensive thermokarstic disruption of the northern plains and other areas of sedimentary accumulation; glacial landforms; the abundance of relatively young valley networks; and the general preservation of heavily cratered uplands on Mars.