The dynamics of lava flows

Lava flows are gravity currents of partially molten rock that cool as they flow, in some cases melting the surface over which they flow but in all cas es gradually solidifying until they come to rest. They present a wide range of flow regimes from turbulent channel flows at moderate Reynolds numbers to extremely viscous or plastic, creeping flows, and even brittle rheology may play a role once some solid has formed. The cooling is governed by the coupling of heat transport in the flowing lava with transfer from the lava surface into the surrounding atmosphere or water or into the underlying sol id, and it leads to large changes in rheology. Instabilities, mostly result ing from cooling, lead to flow branching, surface folding, rifting, and fra cturing, and they contribute to the distinctive styles and surface appearan ces of different classes of flows. Theoretical and laboratory models have c omplemented field studies in developing the current understanding of lava f lows, motivated by the extensive roles they play in the development of plan etary crusts and ore deposits and by the immediate hazards posed to people and property. However, much remains to be learned about the mechanics gover ning creeping, turbulent, and transitional flows in the presence of large r heology change on cooling and particularly about the advance of flow fronts , flow instabilities, and the development of flow morphology. I introduce t he dynamical problems involved in the study of lava flows and review modeli ng approaches.