Geologic/geomorphologic map of the Chryse Planitia region of Mars

Since the 1970's, when the Mariner 9 spacecraft revealed the geologic diversity of Mars, the Chryse Planitia region has been noted for its immense outflow channels and chaotic terrain (McCauley and others, 1972; Sharp and Malin, 1975; Baker, 1982, chap. 3; Mars Channel Working Group, 1983). Various proposals for the origin of these features have been offered; most workers have favored a mechanism in which ground water or water-rich debris was expelled from beneath a frozen crust, leading to catastrophic debris flows or floods that may have contained significant amounts of ice (Baker and Milton, 1974; Carr, 1979; Nummedal and Prior, 1981; Lucchitta, 1982; MacKinnon and Tanaka, 1989). The channels originated on or near the flanks of the volcanotectonic rises of Tharsis (whose east margin is the west edge of the map region) and Valles Marineris, which suggests that tectonic and igneous activity led to the conditions for discharge. Estimated discharge rates for some channels exceed those of prehistoric floods on Earth (Carr, 1979; Komar, 1979; Robinson and Tanaka, 1990). Some workers think that the discharges may have led to the development of temporary oceans that filled the northern lowlands (Parker and others, 1989; Baker and others, 1991). The Chryse basin (Chryse and southern Acidalia Planitiae), which is part of those lowlands, apparently has been the site of lava and sediment deposition (Greeley and others, 1977; Scott and Tanaka, 1986).