A coupled model for dispersal of tephra during sustained explosive eruptions

We present a model for fallout of tephra based on approximate analytical solutions of the advection-diffusion transport equation. As usual, the model requires the distribution of mass throughout the eruptive column as a boundary condition, an input which is normally imposed ad hoc by means of analytical expressions. We propose an alternative way to assess this input based on coupling the model of fallout with already existing simple models for volcanic plumes, flow along the volcanic conduit and magma chamber withdrawal. The final outcome is a one-way coupled model that involves all the spatial domains simultaneously and has a good compromise between physical accuracy and computational efficiency. The coupled model outputs not only maps of isopachs but also several relevant eruptive parameters such as column height, mass eruption rate, or duration of the eruption. Time-dependency is introduced via a quasi-steady approach, that is, considering a succession of steady states. We apply the model to simulate the 2 ka subplinian eruption of Montaña Blanca, Tenerife Island.