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.