ASSESSING THE CONTROLS OF OVERFLOW FLOOD TERMINATION FOR MARS PALEOLAKES (Invited Presentation)

Mars’ paleolake record includes more than 200 basins that were hydrologically open, with outlet canyons incised when water within the basin catastrophically overflowed the confining topography. The size of these outlet canyons scale with the volume of water drained such that larger basins carved larger outlet canyons. All of the previously identified hydrologically open lakes remain as local topographic lows, indicating they did not completely drain and the process of outlet canyon incision from lake overflow flooding self-arrested at some point after initiation. However, we note that the proportion of martian paleolakes that did completely drain is presently unconstrained, as such systems are difficult to distinguish from surface-runoff generated fluvial valleys.

Regardless, how completely a given basin drained can be simply quantified using a drained fraction (ratio of drained volume to initial lake volume), although which boundary conditions are important for controlling this drained fraction is unclear. Here we present work to address this question. Aside from the size of a given paleolake basin, other potential boundary conditions that we hypothesize as potential controls on drained fraction include: (1) the regional slope; (2) the height of the rim for crater-hosted lakes; (3) the shape of the basin; and (4) the erodibility of the terrain.

To test the relative importance of these five boundary conditions, we employ a suite of numerical experiments using a morphodynamic model of the crater lake overflow process. These numerical experiments use the ANUGA open-source finite volume solver for the shallow water equations coupled to morphodynamic operators for bedload and suspended load transport, and mass wasting of canyon walls. Numerical experiment results are also compared against observational data from 24 previously studied martian paleolake basins. Preliminary results indicate that rim height and regional slope provide the strongest controls on drained fraction, consistent between both numerical experiment and Mars observational results. Some outliers in the martian dataset also reveal potential influences of lithology and downstream lakes. Our results may be useful in the search for previously unidentified ancient martian lake basins that completely (or nearly completely) drained.