Abstract
The Martian outflow channels comprise some of the largest known channels in the Solar System. Remote-sensing investigations indicate that cataclysmic floods likely excavated the channels ~3.4 Ga. Previous studies show that, in the southern circum-Chryse region, their flooding pathways include hundreds of kilometers of channel floors with upward gradients. However, the impact of the reversed channel-floor topography on the cataclysmic floods remains uncertain. Here, we show that these channel floors occur within a vast basin, which separates the downstream reaches of numerous outflow channels from the northern plains. Consequently, floods propagating through these channels must have ponded, producing an inland sea, before reaching the northern plains as enormous spillover discharges. The resulting paleohydrological reconstruction reinterprets the 1997 Pathfinder landing site as part of a marine spillway, which connected the inland sea to a hypothesized northern plains ocean. Our flood simulation shows that the presence of the sea would have permitted the propagation of low-depth floods beyond the areas of reversed channel-floor topography. These results explain the formation at the landing site of possible fluvial features indicative of flow depths at least an order of magnitude lower than those apparent from the analyses of orbital remote-sensing observations.
Highlights
On July 4, 1997, the Mars Pathfinder touched down on the lower reaches of Tiu and Ares Valles[1,2] (Fig. 1), two of Mars’ largest outflow channels[3]
Detailed geological mapping shows that the youngest cataclysmic flood flows ensued from Tiu Valles, that they truncated the lowest reaches of Ares Vallis, and that their most recent manifestations resurfaced the Pathfinder site[3,14] (Fig. 1B; see supplementary methodology for mapping approach)
The presence of hundreds of kilometers of reversed gradient channel-floor areas leading to lower Simud and Tiu Valles[21,22,23,24,25] indicates that the previously proposed waning stages in a cataclysmic flood[11] cannot explain this www.nature.com/scientificreports discrepancy (Fig. 1B)
Summary
On July 4, 1997, the Mars Pathfinder touched down on the lower reaches of Tiu and Ares Valles[1,2] (Fig. 1), two of Mars’ largest outflow channels[3]. The presence of hundreds of kilometers of reversed gradient channel-floor areas leading to lower Simud and Tiu Valles[21,22,23,24,25] indicates that the previously proposed waning stages in a cataclysmic flood[11] cannot explain this www.nature.com/scientificreports discrepancy (Fig. 1B).
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