MODELING MARTIAN LAKE FORMATION BY INLET VALLEY BREACHING

In contrast to Earth’s mountain belts and drainage basins, the surface topography of Mars is dominated by impact craters that divide the surface into disconnected basins. Fresh impact craters include a high crater rim, which can be hundreds of meters above the surrounding terrain (for craters 10s of kilometers in diameter). Yet, on ancient Mars (and Earth), inlet valleys crossed many crater rim-drainage divides and supplied water to crater interiors, transforming them into lakes with greater habitable potential.

Here, we will present the results of numerical models of crater-inlet valley formation to inform on what environmental factors influenced the formation of inlet valleys. We first wrote a python code to generate crater topography on a 2D grid, after Howard (2007). The python crater-generating code is then used to generate initial grids for this work, with background craters and a central crater of interest for inlet valley formation. Available on github, the code is compatible with the open-source landscape model, LandLab. We use the LandLab formulation of the ‘fastscape’ implicit stream power erosion algorithm to simulate fluvial erosion on the artificial cratered terrain. Stream power refers to an empirical equation relating bedrock fluvial incision (E) to terrain erodibility (K), drainage area (A) to an exponent (m), and slope (S) to an exponent (n):

E = K A^m Sⁿ

In our modeling study K is kept constant at 0.0001, consistent with other martian landscape models. We vary the exponents m and n, which have been empirically linked to different environmental conditions. Other conditions are also varied, such as the presence, size range, rim height, and number of background craters, to better understand the role of terrain properties (e.g., terrain age as indicated by a greater number of craters) in crater-inlet valley formation. Since many components of LandLab exist, there are numerous other complexities to be investigated, such as variations in substrate properties (e.g., K) with depth, and the addition of other forms of erosion (e.g., diffuse mass wasting, landsliding) or use of different formulations of fluvial erosion (e.g., the SPACE model).