HYDROLOGY VERSUS CRATER RIMS: HOW TO FORM A LAKE ON MARS (Invited Presentation)

In contrast to Earth’s quasi-linear mountain belts, the surface topography of Mars is dominated by impact craters that divide the surface into separate intra- and inter-crater basins. Fresh impact craters are bowl-like basins surrounded by the topographic high of a crater rim, which can be hundreds of meters above the surrounding terrain (for craters 10s of kilometers in diameter). Despite their significant relief, on Mars (as well as on Earth) these obstacles were traversed by fluvial systems, as evidenced by the remnant crater inlet valleys that crossed drainage divides and brought water to the interior basins of impact craters.

Here we will discuss morphometric analysis of martian crater inlets and surrounding terrain that has revealed (1) by what mechanisms these inlet valleys formed, and (2) what factors controlled their formation on Mars. In many cases, early and widespread landscape degradation by numerous processes eliminated the obstacle of uplifted rim relief, and primed crater basins for inlet valley formation and integration into Valley Network (VN) systems. After landscape degradation quiesced (including VN activity), newly-formed crater rims persisted, with remnant relief on the order of 10s to 100s of meters. Yet, despite less widespread fluvial activity, fluvial erosion comparable to the VN-era must have occurred to establish inlet valleys across crater rims.

In contrast to the fact that removal of crater rim relief primed craters for inlet formation, not all degraded craters in proximity to VNs possess inlet valleys, suggesting additional factors controlled inlet valley formation. Morphometric analysis suggests that slope and surface roughness were not major controls, compared to how inset the basin is within the catchment, drainage density, and the potential contributing area available to a crater basin. These basin hydrology factors were likely more important because they surpassed inlet incision thresholds less frequently as compared to slope and roughness. Furthermore, the position of a crater within a wider catchment area is a first-order control on the amount of water that was available for fluvial incision (i.e., craters deeper within regional depressions receive more water), attesting to the significant affect Mars' crater-dominated topography has on its hydrology.