The role of pre-existing topography in modulating lunar lava flow widths, depths and channel structure

Lunar volcanism is one of the most important endogenic processes on the Moon. The final morphology of a lava flow depends on (a) the composition of the magma, which determines its rheology, (b) the effusion rate, controlled by the geometry of the dike transferring the magma to the surface and the overpressure in the magma source, (c) the lava cooling behavior influenced by whether the flow is laminar or turbulent, (d) the total volume of magma erupted, and the topography of the surface onto which the lava flows. Thus, studying the morphology of flows sheds light on their eruption conditions, and has implications for the nature of the magma source region. In this study, we document the effects of topography on a well-preserved Eratosthenian-aged lava flow that most likely originated from the volcanic complex around Euler Crater in Mare Imbrium. We assess how the observations can improve our understanding of previous models of lunar lava flow emplacement and cooling behavior. We find that: 1) the pre-existing topography significantly affected the morphology of the flow; 2) several low wrinkle ridges predating the eruption and controlling the flow path underwent significant tectonic modification after lava emplacement; 3) variations in the extent of lava channel/levee structures along the flow are linked to turbulent/laminar flow modes; 4) the emplacement of the lava flow investigated here was probably completed in about a week, occurring in the very early period of regional wrinkle ridge formation. This lava flow history provides new insight into the interplay of regional volcanism and tectonism in Mare Imbrium and late-stage lunar thermal evolution in general. • The geometric and morphological features of lava flows can be significantly affected by pre-existing topography. • The observed channel within a well-preserved Imbrium lava flow is interpreted to imply a transformation of flow mode from turbulent to laminar. • We deduced the paleo-geological sequence of processes forming this Imbrium lava flow. • Topography quantitatively influenced lunar lava flow emplacement. • Flow morphology suggests initial turbulent, then laminar lava motion. • Evidence implies proximal channel drainage and distal flow inflation. • The central part of Mare Imbrium may have subsided 200 m since 3.0 Ga.