“…Permeability results from the combination of various conduit processes related to magma vesiculation and crystallization that accompany magma rise from chamber/dykes along the conduit to the surface and/or to the formation of fractures due to shear fragmentation (Gonnermann and Manga, 2003;Tuffen and Dingwell, 2005). It is a key parameter in the transition from effusive to explosive volcanism (Eichelberger et al, 1986;Jaupart and Allegre, 1991;Woods and Koyaguchi, 1994;Kozono and Koyaguchi, 2009a,b;Degruyter et al, 2012), for example in the catastrophic failure from dome-forming eruptions to Vulcanian/Plinian behaviour (Lipman and Mullineaux, 1981;Herd et al, 2005). Permeability is also responsible for the quiescent gas loss from persistently degassing volcanoes (Oppenheimer et al, 2003), through formation of networks of continuously connected vesicles , where gas percolates and can exit the volcanic system non-explosively (Burton et al, 2007).…”