FLOW OR BLOW? UNDERSTANDING MAGMA FLOW IN CONDUITS DURING VESICULATION

The ability of silicic magma to erupt explosively depends on the retention of exsolved volatiles in the magma prior to eruption. If volatiles escape before an eruption, effusive lava flows are likely to occur; if gas is retained in magma and helps increase its internal pressuriza tion, then magma might be fated to erupt explosively. Lipari Island, off the northern coast of Sic ily, has been characterized by explosive-effusive events occurring in the same eruptive cycle, such as the explosive phase of Monte Pilato followed by the effusive lava flow of Rocche Rosse ~450 years later. Using glassy obsidian and spherulite-bearing obsidian samples collected from the deposits of the Rocche Rosse unit, this study tested the influence of minor changes in H2O concentration in the style of vesiculation and flow of material in conduits at temperatures rele vant to magmatic conditions. This study presents a nano- and micro-scale analysis of the experi mental products undergoing 950-1150 °C at atmospheric pressure, along with thermodynamic estimations of crystallization and associated potential chemical changes contributing to differing volcanic textures in these high-viscosity systems at equivalent temperatures. Results show vesic ulation primarily occurred at the microscale, and plug flow dominated ascent in experimentally generated conduits.