Balme, M. R.; Gallagher, C. J.; Gupta, S. and Murray, J. B.
Fill and spill in Lethe Vallis: a recent flood-routing system in Elysium Planitia, Mars.
Geological Society, London, Special Publications, 356(1) pp. 203–227.
Lethe Vallis is an approximately 230 km-long and 1.5 km-wide channel connecting several shallow basins in the Elysium Planitia region of Mars. It sits within a distinctive morphological unit defined by a platy-ridged-polygonized texture. We have documented the geomorphology of the system, and constructed topographical long profiles of the channel thalweg and the contacts of the platy-ridged-polygonized material.
The Lethe thalweg is shallow (with a slope of about 0.0001) but contains steeper sections that match the locations of observed cataract systems. The contact profiles suggest that the small basins linked by Lethe progressively ponded and over-spilled as the system developed, the cataracts being associated with this over-spill. Other landforms observed in the system include streamlined islands, anastomosing distributary systems, fluvial hanging channels and terraces on the channel margins. There are also possible dunes and/or antidunes within the channel. These all point to catastrophic fluvial flooding. Estimates of formative discharge are of the order of 1×104–5×104 m3 s−1, similar to the discharge of the Mississippi River.
We infer that Lethe Vallis formed as a fluvial ‘fill and spill’ catastrophic flood system. This demonstrates that the main Western Elysium Basin, the upstream source of Lethe Vallis, contained a substantial transient lake.
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