资源环境科技发展态势分析平台

The porosity at which a magma becomes permeable (i.e., the percolation threshold; phi(c)) 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 similar to 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.

Plain Language Summary Rates of gas escape from an ascending magma control volcanic eruption style. Gas transport along permeable connected bubble pathways is an important step in the degassing process as it allows pressurized gases to escape. The bubble concentration at which permeability develops (the percolation threshold) is poorly characterized in magmas with moderate to high crystallinities. In this study, we use decompression experiments with controlled crystal contents to address this knowledge gap. Our results show that the presence of at least 20-vol.% crystals reduces the percolation threshold in crystal-bearing magmas compared to crystal-free magmas. This suggests that the presence of crystals will enhance gas escape during magma ascent and has implications for transitions between explosive and effusive eruption styles.