What controlled the explosivity and sulfur release of the largest recent explosive eruption on Earth?

Supervisory Team  Mike Cassidy www.earth.ox.ac.uk/people/michael-cassidy  David Pyle www.earth.ox.ac.uk/people/pyle  Jonathan Castro www.geowiss.uni-mainz.de/1732_ENG_HTML.php  Tamsin Mather www.earth.ox.ac.uk/people/mather/

Key Words Volcanology, Petrology, Experiments, Explosivity Overview

Intermediate alkaline magmas (e.g. trachyandesite) have been responsible for some of the most explosive and highest sulfur emitting eruptions in the Holocene, including Tambora (1815), El Chichon (1982) and Samalas (1257). These trachyandesite magmas are commonly much more enriched in sulfur compared to their rhyolitic counterparts, and their potential for global climatic impact is thus far greater. A major puzzle with these events is why these alkaline The 6.5 km diameter crater of Rinjani, Lombok intermediate magmas erupt so explosively, in spite Indonesia and site of the 1257 eruption. The of their low viscosity, and how they can active Baru Jari cone in the middle is the site of accumulate such high S concentrations. The eruptions as recent as 2016. answer to this apparent inconsistency may lie in how the magma is stored, its ascent speed and style, and how the volatiles behave during storage Methodology and ascent. To assess this, this project will focus on the Plinian Samalas eruption of 1257 AD from Rinjani volcano (Indonesia), which has only Phase equilibrium and decompression recently been associated with the highest sulfur experiments will be conducted on the products peak in ice core records in the past 2000 years from this particularly explosive eruption to and the consequential Little Ice Age (e.g. Lavigne determine its bubble nucleation and degassing et al., 2013; Vidal et al., 2016). An experimental behaviour, as well as pre-eruption storage and approach will be used to simulate the different ascent conditions (Martel et al., 2017). Sulfur conditions experienced by the magma during addition experiments will aim to quantify sulfur storage and ascent, to elucidate the behaviour of partitioning between the melt, fluid and mineral sulfur and the controls on volcano explosivity. phases during pre-eruptive storage and during ascent. These experiments will provide new insights into how sulfur behaves in trachyandesite magmas and thus how eruptions (such as Samalas) can be capable of such high sulfur fluxes (Webster and Botcharnikov, 2011).

Experimental products will be analysed using a suite of state-of-the-art techniques, including: electron probe microanalysis (EPMA, for major and minor elements, in Oxford), Raman spectroscopy (Mainz), and X-ray micro- fluorescence and X-ray near-edge spectroscopy References & Further Reading (XANES; for sulfur-oxidation state, at the Diamond Light Source, Oxfordshire). Bubble size distributions will be measured by micro-computed Webster, J.D., and Botcharnikov, R.E., 2011, tomography in Durham. Distribution of Sulfur between Melt and Fluid in S- O-H-C-Cl-Bearing Magmatic Systems at Shallow Crustal Pressures and Temperatures: Reviews in Timeline Mineralogy and Geochemistry, v. 73, p. 247–283, doi: 10.2138/rmg.2011.73.9.

Year 1: Literature review, laboratory training, Lavigne, F., Degeai, J.-P., Komorowski, J.-C., analytical training, experiments in Germany and Guillet, S., Robert, V., Lahitte, P., Oppenheimer, Oxford, micro-CT analysis. C., Stoffel, M., Vidal, C.M., Surono, Pratomo, I., Wassmer, P., Hajdas, I., Hadmoko, D.S., et al., Years 2 and 3: Sulfur solubility experiments, 2013, Source of the great A.D. 1257 mystery decompression experiments, sample analysis eruption unveiled, Samalas volcano, Rinjani (EMPA, Raman etc). Volcanic Complex, Indonesia: Proceedings of the National Academy of Sciences, v. 110, p. 16742– Year 4: Data integration, thesis completion, papers 16747, doi: 10.1073/pnas.1307520110. for international journals/conference presentation. Vidal, C.M., Métrich, N., Komorowski, J.-C., Pratomo, I., Michel, A., Kartadinata, N., Robert, V., Training & Skills and Lavigne, F., 2016, The 1257 Samalas eruption (Lombok, Indonesia): the single greatest stratospheric gas release of the Common Era: The student will be registered at the University of Scientific Reports, v. 6, p. 34868, doi: Oxford, and will have the option of participating in 10.1038/srep34868. the formal training provided by the Doctoral Training Partnership in Environmental Research. Martel, C., Brooker, R.A., Andújar, J., Pichavant, M., Scaillet, B., and Blundy, J.D., 2017, This project is partly funded through the German Experimental Simulations of Magma Storage and research council, and will be in collaboration with Ascent, in Springer, Berlin, Heidelberg, p. 1–10, several European institutions, most notably, the doi: 10.1007/11157_2017_20. University of Mainz, where the student will conduct some of the experiments within the Experimental Petrology Lab, managed by Castro and Helo Further Information (funded by the VAMOS research center) during 2- 3 month-long stays. The majority of the Contact: Dr Michael Cassidy experiments will be performed in the newly ([email protected]) constructed cold-seal pressure vessels in Oxford. The project will include volcano fieldwork training in either Indonesia, Mexico or Greece. Collaborating partners

The project will require a student with a degree in geology; a background in petrology, geochemistry Christoph Helo and Roman Botcharnikov or volcanology would be helpful. Excellent (Johannes Gutenberg University, Mainz, Germany) communication skills in English are essential. The student will receive training in a range of Marie Edmonds and Celine Vidal (University of petrological and geochemical techniques, including Cambridge) electron microscopy, Fourier transform infrared spectroscopy and conducting high pressure and Katherine Dobson (University of Durham) temperature experiments. The student will be Sebastian Watt (University of Birmingham) expected to present their research at leading international conferences and to publish results in leading scientific journals.