FLOWGO - a Thermo-Rheological Model for Determining the Lengths of Channelized Lava Flows

FLOWGO is a kinematic, self-adaptive, thermo-rheological model that determines the distance that an element of lava in an open channel can flow before it stops due to cooling-induced rheological changes. The processes that affect cooling are interrelated in the model, and include heat loss (radiative, conductive, convective), heat gain (latent heat of crystallization, viscous dissipation), crustal growth as a function of velocity, entrainment of crust, etc. For each step down the length of the lava channel, the model determines the temperature change resulting from these heat terms, and uses this to calculate the bulk viscosity and yield strength. These, along with the underlying slope, determine the velocity in the channel; when this approaches zero, the maximum length has been achieved. FLOWGO is essentially 1-d, but it becomes somewhat 2-d by using a DEM to determine the flow path. Comparison with flows for which rheological and eruptive parameters are known shows good results. Applications have included determining the parts of Mauna Loa and Etna that are likely to be impacted by eruptions of given effusion rates, and determining the lengths of channel fed flows on Mars. Our two most recent adaptations have been to apply a stochastic approach to determining downslope flow paths to replicate lava flow fields, and to use satellite-derived effusion rates to help constrain at-vent model parameters. In an ongoing-eruption situation, our mode of operation is to provide FLOWGO results to the relevant volcano observatories. In combination with all their other geological and geophysical data, it is these observatories who will advise civil protection agencies, who in turn make decisions about immediate risks, evacuations, etc.