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  Physical and chemical signals of degassing and vesiculation during magma ascent at ocean island volcanoes

   Department of Earth and Environmental Sciences

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  Dr M Hartley, Dr M Polacci  Applications accepted all year round  Self-Funded PhD Students Only

About the Project

Magmatic volatiles provide the driving force for volcanic eruptions through the positive feedbacks between gas exsolution and bubble growth during magma ascent. However, volatile exsolution and degassing in magmatic conduits are not directly observable at the surface, and have proved difficult to understand from geophysical signals and geochemical studies of gases emitted at active volcanoes. Vesicles (gas-filled cavities) in erupted volcanic rocks preserve a textural record of volatile exsolution, and provide critical insights into the mechanisms of exsolution and degassing in volcanic conduits.

This project will investigate the processes of magma degassing, vesiculation and fragmentation operating during the 2021 Fagradalsfjall eruption in southwest Iceland, and the 2021 eruption at Cumbre Vieja on La Palma, Canary Islands. The Fagradalsfjall eruption underwent several changes in eruptive style. The earliest stages of the eruption were characterized by continuous, mild Hawaiian fire-fountaining, but after a month the activity became pulsatory, where periods of inactivity alternated with intense fire fountaining ejecting jets of magma up to 450 m in height. The Cumbre Vieja eruption likewise underwent several changes in eruptive style, with eruption intensity strongly correlated with increased gas fluxes measured at the surface. In both cases, the changes in eruption style are likely driven by the behaviour of magmatic volatiles in the volcanic conduit. This project aims to quantify the efficiency of volatile exsolution, vesiculation and gas escape that drove these different eruptive styles. What were the original dissolved volatile concentrations prior to eruption? At what pressures did volatile exsolution commence? How did vesiculation and fragmentation in the conduit affect degassing efficiency? What role did crystallization play in controlling vesiculation and gas escape? To what extent can an improved understanding of subsurface degassing in magmatic conduits be used to predict the local and global environmental impacts of eruptions at ocean island volcanoes?

The project will involve using a range of analytical techniques to examine the 3-dimensional (3D) properties of volcanic samples. A series of X-ray computed microtomography experiments will be conducted to reconstruct and visualise the textures of erupted tephra samples directly in 3D, and to quantify the vesicle proportions, shapes, size distributions and interconnected porosity. Permeability measurements on the tephra products will be used ascertain how gas was transported within and outside the magmatic conduit systems during the eruption. The dissolved volatile contents of the erupted products will be measured using electron microprobe analysis, FTIR and Raman spectroscopy. Diffused volatile concentrations measured in profiles perpendicular to the vesicle walls will be used to calculate timescales of volatile release, and investigate degassing efficiency under different eruptive regimes.

The broader impacts of this project are myriad. Depending on the student’s interest, the project could include an exploration of the links between textural and geochemical data with gas flux measurements from satellite and ground-based instruments; numerical modelling of crystallization and degassing during magma ascent; and/or reconstructions of the eruption styles and volatile emissions from large basaltic eruptions at ocean islands that pre-date human observations.


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Before you apply 

We strongly recommend that you contact the lead supervisor for this project before you apply. 

For application questions please email [Email Address Removed]

How to apply 

To be considered for this project you’ll need to complete a formal application through our online application portal

When applying, you’ll need to specify the full name of this project, the name of the PhD (Earth Science (academic programme) and  PhD Earth Science(academic plan), the name of your supervisor, how you’re planning on funding your research, details of your previous study, and names and contact details of two referees

Your application will not be processed without all of the required documents submitted at the time of application, and we cannot accept responsibility for late or missed deadlines. Incomplete applications will not be considered.  

If you have any questions about making an application, please contact our admissions team by emailing [Email Address Removed]

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Equality, diversity and inclusion is fundamental to the success of The University of Manchester and is at the heart of all of our activities. We know that diversity strengthens our research community, leading to enhanced research creativity, productivity and quality, and societal and economic impact.

We actively encourage applicants from diverse career paths and backgrounds and from all sections of the community, regardless of age, disability, ethnicity, gender, gender expression, sexual orientation and transgender status. 

We also support applications from those returning from a career break or other roles. We consider offering flexible study arrangements (including part-time: 50%, 60% or 80%, depending on the project/funder). 

Geology (18)

Funding Notes

This PhD project is for September 23/24 start, the tuition fee's have not yet been set for 23/24 year but will be band B.


• Polacci M, Baker CR, La Rue A, Mancini L, Allard P (2012) Degassing behaviour of vesiculated basaltic magmas: an example from Ambrym volcano, Vanuatu Arc. J Volcanol Geotherm Res 233-234:55-64, doi:10.1016/j.jvolgeores.2012.04.019
• Bai L, Baker DR, Polacci M, Hill RJ (2011) In-situ degassing study on crystal-bearing Stromboli basaltic magmas: Implications for Stromboli explosions. Geophys Res Lett 38:L17309, doi:10.1029/2011GL048540
• Degruyter W, Burgisser A, Bachmann O, Malaspinas O (2010) Synchrotron X-ray microtomography and lattice Boltzmann simulations of gas flow through volcanic pumices. Geopshere 6:470-481, doi:10.1130/GES00555.1
• Polacci M, Bouvet de Maisonneuve C, Giordano D, Piochi M, Mancini L, Degruyter W, Bachmann O (2014) Permeability measurements of Campi Flegrei pyroclastic products: An example from the Campanian Ignimbrite and Monte Nuovo eruptions. J Volcanol Geotherm Res 272:16-22, doi:10.1016/j.jvolgeores.2013.12.002

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