Effusion rates and rheology of lunar lavas

Abstract

Flow shapes in M are Imbrium, Copernicus, Tycho and Aristarchus have been related to lava properties by assuming that lavas have Bingham rheology. A universal formula which expresses flow dimensions in terms of fluid properties, flow rates and slopes has been derived theoretically and tested by means of experimental models and data from terrestrial lava flows. It is now possible to determine flow rates and yield stresses - both of which are related to the composition of lavas - from photographs of flow remnants. Results are presented for the lunar flows under study. Flow rates in Mare Imbrium are found to be very high by terrestrial standards. This is an important clue to the mechanism of formation of lunar sinuous rifles, which may be products of erosion by melting beneath turbulent lava flows.