Insight Into Erosion and Lake-Filling Process from Crater Rim Fluvial Breaches on Mars

Abstract:

The identification and analysis of crater-hosted lakes on Mars have helped constrain early Mars’ hydrology. These lake basins are initially characterized by a high-standing crater rim that must be modified to allow water to reach the crater interior from its surroundings. The processes and timescales associated with lake filling have implications for lake level, sediment deposition in the basin, and overall lake evolution, yet they generally remain poorly constrained. We hypothesize Mars crater lake inlets may have formed via one of the following modes: (1) Rim relief degradation as part of wider landscape evolution through sediment infill upstream of the rim and/or direct topographic lowering of the rim, which would allow later fluvial valleys to flow directly into the crater; or (2) Fluvial activity that was sufficient to (a) erode headward through the rim and/or (b) overtop the rim and flood the crater interior. In terms of timescales, we expect that mode (1) requires landscape evolution over the most prolonged era, but provides no direct constraints on inlet formation timescales; mode (2a) is likely the next most prolonged, with consistent fluvial activity and/or mass wasting driving inlet incision; and mode (2b) could occur over much shorter, intense intervals of fluvial activity and implies at least temporary standing bodies of water.
To test the hypotheses for inlet formation, we have utilized CTX DEMs and images to map inlets associated with 34 martian crater-hosted paleolakes (48 total inlets; 21 inlets into 12 open basins, and 26 inlets into 22 closed basins) over a range of equatorial terrains and crater sizes. We use radial topographic profiles for each crater to assess the topographic relief associated with the crater rim in the vicinity of each inlet. Preliminary results suggest that the majority of inlets cut across topographically high crater rims, although some are associated with craters where the rim has been substantially degraded. We use topographic profiles across the inlet breach and longitudinal profiles of the inlet valley, supplemented with geologic context observations, to further constrain the degradation state of the craters. Finally, we map and analyze topographic contours exterior to the crater rims to identify whether any of these inlets may have been incised via overflow of an upstream lake.