Flow-to-fracture transition in a volcanic mush plug may govern normal eruptions at Stromboli

Stromboli is a model volcano for studying eruptions driven by degassing. The current paradigm posits that Strombolian eruptions represent the bursting of gas slugs ascending through melt-filled conduits, but petrological observations show that magma at shallow depth is crystalline enough to form a three-phase plug consisting of crystals, bubbles, and melt. We combine a 1-D model of gas flushing a crystalline mush with a 3-D stress model. Our results suggest that localized gas segregation establishes hot conduits of mobile magma within a stagnant plug. The plug is prone to tensile failure controlled by gas overpressure and tectonic stress, with failure most likely beneath the observed vent locations. We hence argue that Strombolian eruptions are related to plug failure rather than flow. Our proposed three-phase model of the shallow plumbing system may provide a promising framework for integrating geophysical, petrological, and morphological observations at Stromboli and in open-system volcanism more generally.