Permeability evolution during non-isothermal compaction in volcanic conduits and tuffisite veins: Implications for pressure monitoring of volcanic edifices

Explosive volcanic eruptions are destructive geological phenomena that pose hazards of significant socioeconomic impact and potential loss of life. Effective risk mitigation and decision making prior to and during volcanic crises require real-time monitoring of gas overpressure – the single most important driving force for explosive eruptions. Development and release of gas overpressure are regulated by gas loss through permeable pathways that are inherently transient. Here, we use geometry-dependent conductive cooling models, in concert with the most up-to-date welding and permeability models, to assess the potential for “freezing in” permeability within (1) conduit-filling pyroclastic deposits and (2) tuffisite veins within the edifice. We find that both geometry and dimension of each deposit dictate its thermal evolution and, with that, its transient outgassing capacity. Rapid cooling of thin sheet-like tuffisite veins preserves high porosities and permeabilities. In contrast, wide cylindrical conduit-filling deposits cool slowly and permeability is annihilated over a period of minutes to hours. This highlights that conduit-filling deposits lose their outgassing capacity through welding, while tuffisite veins (previously thought to rapidly seal) can form long-lived outgassing features. We use the model results to calculate the time dependent gas flow partitioning between both degassing lithologies. Based on the reconstructed outgassing pattern we outline the potential to use the gas flow balance between the central conduit and distal fumaroles fed by tuffisite veins as a simple tool to monitor gas overpressure within a volcanic edifice.