Revealing Elysium Planitia's Young Geologic History: Constraints on Lava Emplacement, Areas, and Volumes

Elysium Planitia includes several outflow channels that were likely carved by aqueous erosion and subsequently infilled by younger lava flows, making Elysium Planitia the youngest volcanic terrain on Mars. Studying this region is critical for constraining the recent hydrological and thermal evolution of the planet. Here, we investigate the lava flow areas, thicknesses, and volumes in Elysium Planitia using Context (CTX) camera images in combination with SHAllow RADar (SHARAD) sounder data. Compiling 1,777 reflectors over an area of 9,126,790 km 2 allows us to reconstruct the subsurface landscape evolution over time. Our findings show that Elysium Planitia is composed of about 40 episodes of effusive volcanic activity. We report volumes for individual eruptions of 4,000 ± 1,600 km 3 infilling Athabasca Valles, 12,200 ± 2,500 km 3 in Marte Vallis, and 16,000 ± 4,000 km 3 in Rahway Valles for the major flow units and volumes as small as 100 ± 50 km 3 in Cerberus Plains. The surface morphologies and inferred dielectric properties of lobe interfaces suggests that the regions consists of basaltic lava. The region also experienced multiple aqueous flooding events. However, while we found evidence of past lava–water interactions, present-day ground-ice, if present, is likely limited to local patches. Further, the pre-eruption landscape reveals that the aqueously carved Marte Vallis is more areal extensive, but shallower than previously suggested, with a likely paleo-flow direction from northwest to southeast. The channel is most likely sourced from a segment in the northwestern portion of Cerberus Fossae, and is now buried by multiple Late Amazonian lavas with the same lava flow direction.