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Investigating the abundance and origin of magmatic volatiles at Rabaul volcano, Papua New Guinea


Department of Earth and Environmental Sciences

About the Project

Around our planet, hundreds of volcanoes are constantly emitting gas into the atmosphere. Over geological time, this volcanic outgassing is a key control on atmospheric composition, climate change, and planetary habitability, but how does volcanic outgassing vary, in chemical composition, in flux, and over what spatial or temporal scales? Measurements of gas emissions at active volcanoes suggest (i) a variable balance in the planetary reservoirs (e.g. mantle, subducting slab, crustal rocks) feeding outgassing, and (ii) wide disparities in outgassing flux between volcanoes. Are certain volcanoes or arcs inherently major contributors to planetary outgassing, due to the efficiency of volatile recycling in the adjacent subduction zone, unusually volatile-rich magmas, or persistent mafic recharge from depth? To address these questions, we need to combine studies of active outgassing today with analysis of volatiles in magmas sampled by past eruptions.

In this project, we will study the abundance and origin of volatiles at Rabaul, a caldera in Papua New Guinea that has been among Earth’s major outgassing sources in recent decades. Rabaul has a long history of activity, ranging from caldera-forming eruptions associated with dacitic ignimbrite and airfall deposits, to andesitic–dacitic intra-caldera vulcanian to subplinian explosive eruptions and lava flows, to basaltic eruptions from nearby extra-caldera stratocones. Recent petrological and geochemical studies suggest that the majority of Rabaul magmas originate by fractional crystallization from a parental basaltic melt, though mafic recharge and magma mingling and mixing is important in sustaining long-term volcanism, triggering eruptions and potentially feeding outgassing. Future eruptions at Rabaul pose a significant threat to regional populations and infrastructure, and further investigation of magma volatile contents, the present state of unrest, and possible signs warning of imminent eruptions are all important for monitoring and risk management.

We will analyse rocks, minerals, and melt and fluid inclusions sampled from a diverse suite of eruptions at Rabaul. Our objective is to place constraint on the abundance and origins of volatiles in magmas sampled by eruptions of different styles, from different vents, and from different intervals in the caldera cycle. We seek to determine if recent high outgassing fluxes at Rabaul are characteristic of the volcano’s long-term behaviour or an artefact of our short period of modern observations. The student will initially work with rocks from the supervisors’ collections, though there may be opportunity (COVID permitting) to conduct fieldwork in Rabaul. Full training will be provided in Manchester in the necessary analytical methods, including SEM, EPMA, LA–ICP–MS and noble gas mass spectrometry. All outputs and interpretations will be shared with in-country partners (Rabaul Volcanological Observatory) to support ongoing monitoring and hazard assessment.

We seek a motivated individual with a strong background (MSc, MSci, or BSc) in Earth or physical sciences. No specific programming or laboratory experience is necessary, as the successful candidate will be offered training in required methods, but some prior knowledge of coding, data manipulation, or lab-based microanalytical methods (e.g., SEM, EPMA, ICP-MS) would be helpful. For enquiries, please contact Dr Brendan McCormick Kilbride,



Funding Notes

This is a funded studentship open to UK/EU applicants only.

We have start dates available in July 2021 or September 2021.

References


- Aiuppa, A. et al. (2019) CO2 flux emissions from the Earth’s most actively degassing volcanoes, 2005-2015, Scientific Reports.
- Fabbro, G. et al. (2020) Variable mafic recharge across a caldera cycle at Rabaul, Papua New Guinea, Journal of Volcanology and Geothermal Research.
- Roggensack, K. et al. (1994) Volatiles from the 1994 eruptions of Rabaul: understanding large caldera systems, Science.

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