Towards scientific forecasting of magmatic eruptions

Forecasting eruptions is a fundamental goal of volcanology. However, difficulties in identifying eruptive precursors, fragmented approaches and lack of resources make eruption forecasting difficult to achieve. In this Review, we explore the first-order scientific approaches that are essential to progress towards forecasting the time and location of magmatic eruptions. Forecasting in time uses different monitoring techniques, depending on the conduit-opening mode. Ascending magma can create a new conduit (closed-conduit eruptions), use a previously open conduit (open-conduit eruptions) or flow below a solidified magma plug (semi-open-conduit eruptions). Closed-conduit eruptions provide stronger monitoring signals often detected months in advance, but they commonly occur at volcanoes with poorly known pre-eruptive behaviour. Open-conduit eruptions, associated with low-viscosity magmas, provide more subtle signals often detected only minutes in advance, although their higher eruption frequency promotes more testable approaches. Semi-open-conduit eruptions show intermediate behaviours, potentially displaying clear pre-eruptive signals days in advance and often recurring repeatedly. However, any given volcano can experience multiple conduit-opening modes, sometimes simultaneously, requiring combinations of forecasting approaches. Forecasting the location of vent opening relies on determining the stresses controlling magma propagation, deformation and seismic monitoring. The use of physics-based models to assimilate monitoring data and observations will substantially improve forecasting, but requires a deeper understanding of pre-eruptive processes and more extensive monitoring data.