Morphology and paleohydrology of intracrater alluvial fans north of Hellas Basin, Mars

Alluvial fans and sinuous ridges are both important records of the history fluvial activity on Mars, they often occur together. We present observations alluvial fans, many which exhibit inverted relief, in five craters region north Hellas basin. The observed ranged size from ~10 to 820 km2. identified three primary fan surface morphology classes (chute, degraded, Inverted) as well instances where transitions proximal chutes (or, rarely, a cratered degraded surface) distal corresponding increasing thermal inertia. Clear superposition relationships at contacts between adjacent rarely observed, suggesting interfingered deposits concurrent development across region. Localized factors appear influence there is no systematic trend azimuth range location, or catchment, degree crater filling. Water sediment availability may be controlled by lithology differences weather patterns. Many had mismatch catchment volume, significant amounts erosion perhaps due windblown stripping fine sediment. However, several notable exhibited volumes greater than their catchments. This reflect uncertainty accuracy estimated paleosurface, it indicate contributions outside mapped catchment. Ridges, inferred resistant remnants fluvially transported deposits, were used estimate flow magnitude construction with computed discharges 60–400 m3/s supply rate runoff values ~1–20 mm/h. Acknowledging that width-derived discharge overestimate conditions likelihood amalgamated channel this quantification provides climate constraints. upper rates quite high, would require either intense rain storms generate immediate runoff, longer-term snow accumulation subsequent melt-runoff, potentially enhanced rain-on-snow events. Minimum continuous formation time scales less century computed, but incompatible (e.g., relationships, embedded craters) mechanisms sustain flows. More realistic lower-limit times, accounting for modeled precipitation literature, tens hundreds thousands years. Fans active multiple events spanning Hesperian Amazonian periods, requiring transient support aggradation.