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

Abstract

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.

Grain‐Displacive Gas Migration in Fine‐Grained Sediments

“…Gas migration mechanisms in soft sediments control gas release events (Dupre et al, 2015;Scandella et al, 2017), determine the formation of craters and pockmarks (Andreassen et al, 2017;de Prunele et al, 2017;Riboulot et al, 2016), and constrain the potential gas recovery strategies from methane hydrate accumulations in shallow marine sediments (Fauria & Rempel, 2011;Jang, 2014;Moridis et al, 2011). Gas migration pathways are also relevant to other degassing processes such as subsurface CO 2 leakage (Bang et al, 2013;Cevatoglu et al, 2015;Lewicki et al, 2007) and gas-driven volcanic eruptions (Suckale et al, 2016).…”

Oscillatory rheology measurements of particle‐ and bubble‐bearing fluids: Solid‐like behavior of a crystal‐rich basaltic magma

“…If the conduit oscillates horizontally with a width of 3 m [ Burton et al , ], the resonance frequency becomes V s /(2 L )∼1 Hz, which is the same order of frequencies of tremors generally observed [e.g., Chouet et al , ; Falsaperla et al , ]. If a plug with an effective length of several 100 m [e.g., Suckale et al , ] oscillates vertically, lower frequency tremor or VLP may result [e.g., De Lauro et al , ; Chouet et al , ].…”

“…The slow shear wave velocity may explain the low‐frequency seismic signals observed as tremors and VLP events in various volcanoes. Observed crystallinity in clasts from Stromboli is ϕ p >40 vol % [ Métrich et al , ; Francalanci et al , ; Landi et al , ; Corsaro et al , ; Gurioli et al , ], suggesting that the crystal‐rich magma filling the shallow conduit behaves as a solid‐like medium [e.g., Suckale et al , ]. If the conduit oscillates horizontally with a width of 3 m [ Burton et al , ], the resonance frequency becomes V s /(2 L )∼1 Hz, which is the same order of frequencies of tremors generally observed [e.g., Chouet et al , ; Falsaperla et al , ].…”

“…Indeed, some basaltic clasts fractured in a brittle manner from Stromboli show a high crystallinity [e.g., Métrich et al , ; Francalanci et al , ; Landi et al , ; Corsaro et al , ; Gurioli et al , ]. Crystallinity typically varies with eruption styles [ Pioli et al , ], and fracturing of highly crystalline plug has been suggested as a mechanism of explosions [ Suckale et al , ], based on the fracture textures observed in a dense suspension [ Oppenheimer et al , ] (Figure a). Such a high‐crystallinity plug may become a resonator to be a source of volcanic tremors and very long period (VLP) events [e.g., Chouet et al , ; Ripepe et al , ].…”

“…typically varies with eruption styles [Pioli et al, 2014], and fracturing of highly crystalline plug has been suggested as a mechanism of explosions [Suckale et al, 2016], based on the fracture textures observed in a dense suspension [Oppenheimer et al, 2015] (Figure 1a). Such a high-crystallinity plug may become a resonator to be a source of volcanic tremors and very long period (VLP) events [e.g., Chouet et al, 2003;Ripepe et al, 2005].…”