Unravelling the behaviour of basaltic volcanoes by combining field observations, 4Dimaging of HPHT basaltic magma kinetics experiments and analytical investigations

Basaltic volcanism is the most widespread volcanic activity on Earth. Basaltic eruptions can manifest
through different types of eruptive styles, from quiet lava emissions, to mild/moderate Strombolian
explosions, to more violent fire fountaining events and paroxysmal activity. Understanding basaltic
volcanism and its eruptive styles is therefore key to forecasting the impacts of eruptions. A crucial
limitation of previous work is that it has been predicated almost exclusively on the assumption of
equilibrium between melt, crystals and volatiles. The volcanological community has traditionally assumed that the processes of basaltic magma degassing and solidification/crystallisation occur nearly instantaneously in response to depressurisation associated with magma ascent and eruption. However, it is now recognised that the timescales required to achieve equilibrium for both crystal growth (Vona and Romano, 2013) and volatile exsolution (Pichavant et al. 2013; Lloyd et al. 2004) are longer than the timescales of magma ascent in low viscosity basaltic magmas, meaning that basaltic eruptions are particularly prone to disequilibrium processes. The impact of disequilibrium is profound because gas and crystal content control magma viscosity, density, ascent rate, and the fragmentation process. These are the dominant factors controlling the eruption style, which ultimately dictates the nature and scale of the hazard posed. Quantifying disequilibrium processes in volcanic systems remains an enormous challenge: the P, T, volatile content, melt composition and rate-of-ascent parameter space is huge, and, until now, laborious experiments requiring interruption and quenching were required to capture each individual data point. In addition, experimental work (Brugger and Hammer 2010; Arzilli and Carroll 2013)] on crystallisation kinetics has been mostly done through the study of 2D textures. However, the texture of a volcanic rock is the final product of a dynamic process, which is difficult to quantify with 2D measurements. Magmatic crystallisation is generally considered as the growth of single crystals from the melt, but growth could be related to a sequence of processes, from Ostwald ripening, to crystal aggregation (Schiavi et al. 2009) or dissolution/formation of new phases, which significantly complicates the understanding of crystal texture evolution in both space and time. This PhD project proposal will make a breakthrough in understanding disequilibrium crystal kinetics in basaltic magmas by integrating volcanological observations of basaltic eruptions with analytical work on basaltic erupted products and 4D (space+time) X-ray microtomography imaging of HPHT crystallisation experiments in basaltic magmas.

The PhD project is directly linked to the recently awarded NERC Large Grant ‘Quantifying disequilibrium processes in basaltic volcanism’ (DisEqm), based in the Schools of Earth and Environmental Sciences and Materials in Manchester and led by Prof Mike Burton.

The project will integrate field, experimental and analytical work. The PhD candidate will first review the existing literature on the dynamics of basaltic eruptions and on crystallisation in basaltic magmas. The student will be involved in at least one field trip to Italy or Iceland to study basaltic tephra deposits directly in the field and collect samples of basaltic products from Mount Etna and/or Laki eruptions. The student will then be engaged in performing 4D X-ray microtomography imaging of basaltic sample textures produced during HPHT experiments of crystallisation kinetics at Diamond Light Source, the UK Synchrotron in Harwell. The aim of such work will be to be able to visualise and quantify time sequences of crystal (and vesicle) textures directly in 3D and link these features to disequilibrium processes in basaltic conduits and the eruption dynamics. The X-ray microtomography experimental work will be complemented by petrological and geochemical analyses of natural and experimental basaltic samples. Results from field observations, 4D imaging and analytical work will be combined to produce an improved holistic model of the dynamics of basaltic eruptions.

The student will be involved in a dynamic, international research group based in Manchester and Harwell (Oxfordshire), and will travel abroad for conferences and fieldwork to an active, hazardous basaltic volcano together with the other project partners.

We seek an able and enthusiastic individual with a strong background in geoscience or physical science to join our volcanology research group. The project will suit a numerate candidate with enthusiasm for field studies and analytical/experimental work. At the end of the project, the student will have gained a broad range of practical, intellectual and interpersonal skills, opening multiple career opportunities, from academia to industry or government roles.