The Permeability of Porous Volcanic Rock Through the Brittle‐Ductile Transition

Abstract

Bubbles form and grow as volatiles dissolved in magma exsolve in response to depressurization during magma ascent in the crust (Coumans et al., 2020;Gardner et al., 1999;Sparks, 1978;Toramaru, 1995). If magma ascent is sufficiently rapid, and if these exsolved volatiles cannot escape the system through permeable networks of bubbles and cracks, the gas pressure within the bubbles can increase (Melnik et al., 2005). In that scenario, magma can fragment if the gas overpressure exceeds a critical threshold value (Koyaguchi et al., 2008;Spieler et al., 2004;Zhang, 1999), a process that is thought to be the origin of explosive eruptive behavior. As a result, the permeability of a volcanic system (the magma and the surrounding host-rock) is thought to exert influence on eruption style, effusive or explosive. High pore pressures associated with permeability reductions in the volcanic edifice and lava dome are also thought to promote volcanic instability (