Groundwater Sapping in Hack Crater (Mars): Geologic Evidence and Geophysical Modeling of Groundwater Stability

This study investigates Hack crater in Arabia Terra on Mars, which exhibits remarkable water-related landforms, suggesting a period of intense water activity despite lacking a connection with large-scale fluvial networks. Instead, short valleys within its walls display morphologies indicative of mass-wasting processes driven by groundwater seepage. These valley heads located at approximately −2,900 m provide insights into the groundwater table during landform development, and suggest sustained groundwater supply after the crater's formation at 3.5 Ga. For the first time, we combine geological analyses and geophysical models to investigate the depth of groundwater at this location using two independent approaches. By analyzing the locations and the topography of water-related features, we identify key events that shaped the area, from the appearance of a closed lake due to groundwater influx to its eventual disappearance. After crater excavation, groundwater influx from subsurface sources started driven by sapping processes, filled the basin, and created valleys and depositional features. The system likely persisted until groundwater reservoir exhaustion or until top-down freezing of the groundwater conduits into the crater. The basin dry-out led to the exposure of water-related morphologies to subaerial erosion. Our study provides insights into the multi-stage evolution of a Martian lake formed through groundwater sapping, offering an alternative hypothesis to surface runoff-dominated scenarios. Despite possible regional implications due to the basin's water levels matching the hypothesized global shoreline levels, caution is warranted in extrapolating these findings on a planetary scale, as surrounding craters do not exhibit comparable water-related features indicating a possibly localized phenomenon.