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

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.

Understanding the permeability of hot rocks and magmas is essential to our models of (1) fluid flow in reservoirs (incl. hydrothermal fluids, gas, oil and ore deposition), (2) fault propagation, (3) magma transport, and (4) volcanic eruptions. This study will directly impact the current state of understanding of these geological processes. The work planned will benefit the academic, industrial and public sectors alike.

Volcano Monitoring and Policy Makers. The volcano monitoring/modelling community will gain from the proposed project as they will be provided with an improved model of volcano permeability (incl. hot rocks and the magmatic column) to constrain gas emission data and the state of magma in conduits; this dataset will help quantify monitored data to improve probabilistic models of volcanic eruption scenarios, used by volcano monitoring agencies around the World. This work will help answer questions about the state of magma in active volcanoes - a challenge which will improve our ability to forecast switch in eruptive behaviour from effusions to explosions.

Science and Engineering. The wider scientific community (geoscientists, engineers, metallurgists, chemists) will further benefit from a better understanding of the permeability of material under a range of temperature and stress conditions (including an understanding of porous material deformation); for example, the temperature-dependent permeability data will contribute to the refinement of models of fluid flow in fault zones as much as it will contribute to a better understanding of the permeability of concrete casing employed in borehole during geothermal exploration. The data will also contribute to a better understanding of gas loss during densification of porous liquids in a range of industrial applications in metallurgy and glass making.

Industry. Understanding the permeability of hydrothermal systems is fundamental to the optimisation of geothermal energy productivity, and the high-temperature permeability data will impact the geothermal sector who demands a better understanding of the poorly constrained effects of temperature on the efficiency of fluid flows in hot rocks (as there are very few high-temperature permeability data available in the literature). An increased understanding of fluid flow in hot rocks and magmas will thus improve the exploitation of geothermal resources, ultimately reducing costs and increasing the use of this sustainable, environmentally-safe energy resource.

Public. Volcanic eruptions are amongst the most spectacular natural phenomena and they often inspire public imagination. This multi-disciplinary investigation will help provide a better description of fluid flow and volcanic processes necessary to reach the public, especially communities living in those areas affected by volcanic activity. Public engagement will be sought by designing materials to present the goals and outcomes of this project in relatable terms; including building an educational website as well as hard copies of information to disseminate in schools locally; materials will also be used in Continuing Professional Development (CPD) Training (incl. an Introduction to Volcanology module open to the public and a geology module open to A-level teachers). Public engagement will also be done locally, visiting schools and presenting at the Science Café in Liverpool as well as other public outreach events (e.g., The Royal Society Summer Science Exhibition, which the PI recently participated following a competitive section process).