Transient magma permeability and gas flow: a combined experimental and theoretical model

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Magma ascends in the Earth's crust due to buoyancy - a property mainly controlled by the presence of gas bubbles. In fact, without the presence of gas bubbles, magma would not readily erupt; rather, it may be said that it is the presence of gas bubbles that drags magma to the Earth's surface. Understanding the relationship between gas and magma is thus central to understanding volcanic eruptions.As magma ascends through the crust, pressure decreases, which leads to the formation of gas bubbles (like uncorking a bottle of Champagne). As gas bubbles expand, they interact, creating a permeable, porous network, through which gas can escape. If sufficient gas is able to escape, the bubbly magma will either halt or will effuse out of the volcano, forming lava flows, but if gas pressure remains trapped in bubbles, the magma may fragment violently, causing an explosive eruption. Thus the development of permeability in flowing magma controls the release of gas from volcanoes, the style of volcanic eruptions and the severity of volcanic hazards.The permeability of volcanic rocks has been extensively studied in the past 3 decades. This work suggests that permeability generally increases with the fraction of pores in a rock. Yet, volcanic rocks are solids (as they cooled following eruption) and their study does not provide us with information about the permeability of deforming magma as it flows and erupts. Here, we will use state-of-the-art equipment recently developed at the University of Liverpool to replicate magmatic conditions in shallow volcanic conduits. We will conduct a series of novel experiments to measure the permeability of porous magma in its molten state and as it deforms. We will test a range of conditions relevant to gas flushing through (permeable) magma and see how the porous foam deforms as a function of different pressure conditions. Using this data we will develop, test, verify and refine a theoretical model to resolve fluid flow in porous magma subjected to volcanic conditions. The laboratory results constraining the permeability and compressibility of magma will be integrated into a database for future modelling efforts, and the model developed will be made available to help our understanding of gas emissions monitored during volcanic unrest. This experimentally validated model will be stepping-stone towards better forecasts of volcanic eruptions.