Importance of surface crust strength during the flow of the 1988–1990 andesite lava of Lonquimay Volcano, Chile

The emplacement of the 1988–1990 andesite lava of Lonquimay Volcano, Chile is examined using theoretical expressions for the relevant dynamical flow regimes. The surface crust regime, where the flow is controlled by the growth of a surface crust rather than by the rheology of the fluid interior, is found to predict accurately the entire propagation of the Lonquimay lava flow. This discovery offers the exciting prospect of being able to predict the propagation of future blocky lavas, simply from early observations of both the volume erupted and the flow length as functions of time, without the need to know anything about the rheology of the interior lava.