- Physical volcanology of a newly-discovered giant super-eruption
- Fieldwork in the Yellowstone hotspot track of southern Idaho and Nevada, USA
- Uses changing glass geochemistry to track what happens during a catastophic event,
- Hands-on training in modern micro-analytic and fieldwork techniques within a dynamic volcanological/impact research teamv
Much recent attention has been given to the identification of giant explosive volcanic eruptions in the geological record, mainly to determine their size and frequency. Less attention has been given to what actually happens during one of these eruptions: what are the physical processes, how long do they last (minutes, days, months?) and how do they evolve with time? It is becoming clear that the style of the largest eruptions differ fundamentally from the largest (e.g. Plinian) historic eruptions1,2,3. Resolving these issues is critical if we are to understand the wider effects of giant events.
This PhD project aims to develop new understanding of what happened during a particularly large explosive eruption in the western USA. The full size of the eruption has just been discovered, last year4. In the track of the Yellowstone hotspot, along Idaho’s Snake River Plain, a single welded ignimbrite covers ≥23,000 km2 – an area larger than Wales. The 8.8 magnitude super-eruption has an estimated volume of ≥2800 km3 and is the largest and hottest eruption from the Yellowstone hotspot yet documented4. The student will record the tephra-stratigraphy of the eruption deposit in the field, followed by micro-analysis of the ash textures and glass compositions at different heights in order to deduce the processes of eruption and emplacement, and to track how these evolved with time. The unit is well-exposed5, and allows good access to unusual ashfall layers associated with the ignimbrite, both proximally and distally, and will be of particular interest. Results of the investigation will be used to develop a new model of how the largest eruptions on Earth begin, wax to a peak and then wane, and how the ash from them is dispersed during the different stages. The project will draw from recent advances in understanding of large explosive eruptions, and the results should inform our understanding about some of the largest events on Earth.
HostUniversity of Leicester
- Dynamic Earth
- Prof. Michael Branney
- Dr Tiffany Barry
This project will use geochemical analysis of individual glass shards6 at different levels in the deposit to track changes during the eruption. The deposit record of the eruption will be logged in detail and sampled at different sites, including into neighbouring states. Chemical variations within the deposit will be used to define time-lines (entrachrons7) to distinguish individual time-slices through the eruption and thereby deduce the order of processes that rapidly unfolded during the eruption. New, robust techniques being developed by the research group will be employed to quantify the grainsize and sorting characteristics of the deposit at different stratigraphic levels, where conventional sieving is precluded by welding. The project will, for the first time, produce a time-series of data through the proximal and more distal sites that will provide the basis for inferring the various emplacement mechanisms, and how these waxed and waned with time. This will shed new light on the origin of the various ash fall deposits and their geographic extents, and how the geographic footprint of the radial pyroclastic density currents varied with time.
Training and skills
The student will gain hands-on training in physical volcanology field and laboratory techniques, including granulometry and shape analysis, optical and SEM microscopy, analytical SEM, EMP and LA-ICP-MS analysis of volcanic glasses6. Training will be provided in the sedimentology of fine ashes, and in analytical and interpretative geochemistry. There will be opportunities for practical training in the field, and in the latest techniques to document and interpret field relations. By the end of the project the student will have leading expertise in the interpretation of explosive eruption deposits and in a wide variety of state-of-art laboratory techniques, ideal to launch a career in academic research or industrial-based research. Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.
Partners and collaboration
The student will benefit from collaboration with experts in a dynamic international research group at Leicester investigating extreme events, large volcanic eruptions and asteroid impacts. The project also will involve collaborators in the western USA, including at University California at Santa Cruz.
For informal enquiries please contact Professor Mike Branney ( [email protected] ) at the University of Leicester. Or Google ‘Volcanology at Leicester’.
To apply to this project please visit: https://le.ac.uk/study/research-degrees/funded-opportunities/centa-phd-studentships
Development of methods followed by initial fieldwork. Field training in logging and interpreting pyroclastic deposits will be provided in UK or Canary islands prior to the first field-season in USA. Directed reading and optical microscopy, followed by SEM and LA-ICP-MS analysis of glass shard and crystal populations in rock thin-sections to determine the best ways to characterise chemical and textural variations with stratigraphic height. Conference participation. Fieldwork in late Spring to Idaho, to log and collect key sections.
Geochemical and shard textural micro-analysis of samples collected in 1st field season, data analysis, developing discriminate plots to track temporal changes during the eruption. Quantitative analysis of ash granulometry, and initial interpretations. Conference presentation of initial findings. Second field season to document and sample more distal successions, exploration of new distal sites.
Working-up data from second field season, to allow comparison between the proximal with distal data sets. Discussion with eruption modellers and development of a field-constrained interpretation of the evolving progress of a large super-eruption. Presentation of findings at an international conference. Writing-up thesis and publications.
1Branney, M.J., Bonnichsen, B., Andrews, G.D.M., Ellis, B., Barry, T.L., McCurry, M. 2008. ‘Snake River (SR)–type’ volcanism at the Yellowstone hotspot track: distinctive products from unusual high-temperature silicic super-eruptions’. In: Leeman, B., and McCurry (eds). 2008. Volcanism and petrogenesis of the anorogenic rhyolites, Bulletin of Volcanology 70: pp. 293-314.
2Branney, M.J., Brown, R.J., Calder, E. (2021) Pyroclastic rocks. In: Encyclopedia of Geology. 2nd Ed. Elsevier.
3Costa, A., Suzuki, Y.J. and Koyaguchi, T (2018) Understanding the plume dynamics of Explosive super-eruptions. Nature Communications(2018) 9:654 doi: 10.1038/s41467-018-02901-0
4Knott, T.R., Branney, M.J., Reichow, M.K., Finn, D.R., Tapster, S., Coe, R.S. 2020. ‘Discovery of two new superuptions from the Yellowstone hotspot: Is Yellowstone hotspot waning?’ Geology 48, pp. 93-98. https://doi.org/10.1130/G47384.1
5Andrews, G.D. M., Branney, M.J. 2011. ‘Emplacement and rheomorphic deformation of a large rhyolitic ignimbrite: Grey’s Landing, southern Idaho’. Geological Society of America, Bulletin 123: 725-743. doi: 10.1130/B30167.
6Pearce, N.J.G. Westgate, J.A., Perkins, W.T., Preece, S.J. 2003, ‘The application of ICP-MS methods to tephrochronological problems’. Applied Geochemistry 19: pp. 289-322.
7Branney, M.J. and Kokelaar, B.P., 2002. ‘Pyroclastic density currents and the sedimentation of ignimbrites’. Geological Society of London, Memoirs 27. pp. 152.
This project can start without an initial sampling visit to the USA as we already hold a large collection of ignimbrite and tephra samples from the province. The student should, thereafter undertake their own fieldwork and sampling (Leicester has a pandemic protocol for safe fieldwork). However, our research group includes local geologists, so if need be samples could be collected and shipped to the UK. Analytical work can be done safely in-house at the University of Leicester. International conference attendence could proceed on-line.