Evidence of Combined Erosive and Constructional Formation Mechanisms for a Lunar Sinuous Rille

We have identified a sinuous rille in the northern Aristarchus region that displays an evolution of erosional to constructional formation mechanisms through multiple proposed flow regimes. The first flow regime, down the side of the Plateau, is interpreted to be erosional and contains characteristic features such as plunge pools at the base of lava cascades. The rille moves off of the Plateau in the second regime and into the flat, low-lying mare, where it becomes a constructional channel. At its distal end, the rille is interpreted to spread into an inflated sheet flow, becoming indistinct within the mare. These interpretations were made using morphological comparisons between this sinuous rille, referred to as the northern Aristarchus Rimae (NAR), and terrestrial analogs from Kīlauea volcano in Hawai'i. Morphologic zones within the NAR were identified and correlated to flow regimes observed in the formation of the Fissure 8 lava channel during Kīlauea's 2018 eruption. The comparison between the terrestrial analog and NAR was done using cross-sectional and profile comparisons along the channel as well as the evolution of channel morphology and specific features within it. The interpretations of erosional features were based on previously published work on terrestrial lava tube formation and observations from erosional features within the Kazumura lava tube. The strong similarities between actively observed volcanic processes on Earth and ancient volcanic features on the Moon, as identified in this paper, provide insight into the emplacement behavior of lunar lavas.