Assessing Controls on the Incomplete Draining of Martian Open-Basin Lakes

Abstract

Over 250 hydrologically open paleolakes, which filled with water before catastrophically breaching, have been identified on Mars. These open-basin lakes are recognized by the topographic geometry of a closed contour below the elevation of the outlet, indicating that the lake was incompletely drained by the breach flood. Here, we explore factors that controlled how completely a given open-basin lake on Mars drained using (a) observations of 24 open-basin lakes on Mars and (b) numerical modeling experiments of lake breach flooding. Observational results suggest that the key parameters for promoting more complete draining in open-basin lakes on Mars were steeper regional slopes and taller crater rims. From a suite of 303 numerical experiments, we find that more complete draining is accomplished with larger basins, steeper regional slopes, basins with steeper walls, taller crater rims, and a more erodible substrate (parameterized by grain size in our model). Outliers in the observational results suggest that complete draining was inhibited by the presence of another lake immediately downstream of the breach as well as a less erodible substrate relative to other basins. We observe no correlation between open-basin lake area and drained fraction on Mars, contrary to the strong trend in our numerical experiments. We hypothesize that this is the result of increasing resistance to erosion with depth in the Martian crust, which is not incorporated into our model. Our results provide new insights into controls on the fluvial integration of the early Mars landscape as well as the spatially variable erodibility of the shallow Martian crust.