Observations of the 1975 subterminal lava flows and sections through the larger flank lavas on Mount Etna show that there are four principal types of levees formed in Etnean lavas: initial, accretionary, rubble, and overflow. Initial levees are formed because of the yield strength of these non-Newtonian lavas and are thought to determine channel width. The other types of levees are formed subsequently and are built up over the rarely preserved initial levees. Mechanisms of formation of each levee type vary; most levees are hybrids of two or more of the four types. We also discuss the prospects of deducing lava rheology from morphology and the application of this technique to surfaces of other planets.