The porosity at which a magma becomes permeable (i.e., the percolation threshold; ϕc) is important for magma degassing; it is also poorly constrained in crystal‐bearing systems. To address this, we conduct high pressure‐temperature decompression experiments on water‐saturated rhyolitic melts with variable crystal contents. We find that crystal‐bearing run products become permeable at ~55‐vol.% vesicularity (crystal free), a value that is similar to that found in decompression‐crystallization experiments using basaltic andesite compositions. Our results provide insight into controls on the eruption styles of hydrous, crystal‐bearing magmas in general and controls on pulsatory Vulcanian behavior, in particular.

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Volcanic eruption style is modulated by the process of volatile (e.g., H 2 O, CO 2 ) exsolution from ascending magma. Volatile exsolution efficiency strongly depends on composition, namely the degree of melt polymerization (e.g., Cassidy et al., 2018;Mangan et al., 2004). Highly polymerized melts, such as rhyolites, can inhibit volatile exsolution, a phenomenon typically not observed in less polymerized melts, such as basalts. However, kinetic processes can impact volatile exsolution and impact eruption style. For example, fast decompression rates can promote Plinian basaltic eruptions (e.g., Lloyd et al., 2014;Sable et al., 2006), while slow decompression rates can result in effusive rhyolitic eruptions (e.g., Castro et al., 2013;

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