NSFGEO-NERC Quantifying disequilibrium processes in basaltic volcanism (DisEqm)

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Although most basaltic eruptions erupt lava, they can also be explosive. An understanding of what controls the eruptive style will lead to better assessment of hazards, such as those to aviation (explosive ash) and to the environment around the volcano (effusive). Most previous work on the controls of explosive versus effusive eruption assumed that crystals and gas are in equilibrium with the melt as it travels from deep within the Earth. This assumption is faulty, however, because crystals and bubbles grow so fast that they are commonly out of equilibrium. A novel x-ray imaging technique will be used to measure the compositions and growth rates of crystals and bubbles under realistic eruption conditions. The project involves an international team of investigators, each of whom will tackle a different part of this integrative project. The United States investigators will integrate the experimental results into computational models to assess how the magma fragments as it is erupting and how ash is transported in the atmosphere.NSF funding is being provided to U.S. investigators who are part of an international team that will assess the importance of disequilibrium processes during basaltic eruptions. X-ray tomography will be performed on decompressing and cooling natural magmas using a diamond light source synchrotron. These measurements will quantify the growth rates, distribution, and compositions of crystal, gas, and melt phases under conditions that are close to those of a natural eruption. The role of the U.S. investigator is to incorporate these parameters into a computational code that simulates magma transport through an eruptive conduit. The truly novel aspect is that previous models assume equilibrium between the phases, but the measurements made as part of this project will provide the necessary parameters to model disequilibrium bubble and crystal growth. The conduit model will then be coupled to a model of an atmospheric eruptive column. These models predict textures and modal contents of the eruptive products, as well as the deposits' distributions, permitting field tests of the numerical models.