Experimental analysis of bubble-driven mixing in a volcanic conduit and how it affects lava lake sustainability
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The effects of bubble ascent dynamics on magma motions in a conduit have not been well studied. An investigation of bubble dynamics is accomplished using an analogue model for magma convection in a volcanic conduit, which represents the top-most section of the conduit, where large bubbles exist. In the experiments, bubbles rise through a stagnant medium in a tube and the resulting liquid descent velocity (liquid flux) is measured using various gas flow rates (gas flux) and liquid viscosities. It is determined that the rate of liquid flux depends on the rate of gas flux and on the flow regime of the gas phase. The induced liquid flux is an order of magnitude higher when the gas is in the turbulent regime than in the laminar regime. Two best-fit, numerical models are derived to describe how the liquid flux changes with gas flux, one for each flow regime, using experimentally-derived data. The liquid flux is roughly 15% of the gas flux in the turbulent regime and 1% of the gas flux in the laminar regime. These models are then applied to data from selected volcanoes to determine how the magma flux estimation changes with the introduction of bubble dynamics. Bubble-driven liquid motions can have a significant effect on magma convection in low-viscosity systems (less than 10 3 Pa*s), affecting the shallowest tens of meters of magma in the conduit. As viscosity increases, these effects become more suppressed, which leads to laminar flow proportions of magma flux.