Current Research Issues for Lunar Sinuous Rilles: Vallis Schröteri, Aristarchus Plateau, the Moon

The formation of lunar sinuous rilles is an ongoing topic of debate. Field observations of Rima Hadley by Apollo 15 indicate that lunar rilles are volcanic in origin. However, eruption parameters and emplacement processes necessary for rille formation are not completely understood. Rilles often exhibit a meandering channel, u-shaped, v-shaped, or flat floors, and no levees or thickened flow margins. Channel widths tend to narrow downstream and lack well-defined lobes extending from the terminus. Based on the scarcity of thick flow margins on the lunar surface: Why do lunar eruptions preferentially form rilles? What are the eruption parameters, emplacement processes (erosion, construction, inflation), and flow dynamics of lunar lavas that result in observed rille morphologies? Here, we investigate Vallis Schröteri, the largest rille on the Moon, which originates toward the center of Aristarchus Plateau. Three key morphologic features define Vallis Schröteri: the cobra-head, primary rille, and inner-rille. Surrounded by a ~1000-m-high mound of material at the source vent, the primary rille extends for 125-km, with outcrops of lava flows exposed in the upper walls. An inner-rille, with tight, gooseneck meanders, carves into the flat floor, cross cuts the distal wall of the primary rille and extends for an additional 40-km towards Oceanus Procellarum. These complex stratigraphic and morphologic relationships are not well explained by a single, existing model of rille formation and yield several questions to consider. How did the cobra-head mound originate? Was the primary rille's path influenced by pre-flow topography? Why does the inner-rille have tight gooseneck meanders? We will present scenarios involving both volcanic erosion and volcanic construction processes to explain the morphology of Vallis Schröteri based on observations of terrestrial volcanic eruptions. A renewed study of Vallis Schröteri and rilles in general using data from current and upcoming missions will provide insight to their origin.