Geography, Geology and the Environment

I studied MGeoscience at Keele University, graduating in 2010. I subsequently became a postgraduate research student, also at Keele. I am currently in my third year of my Ph.D, studying magmatic processes and their control on contrasting eruption styles in the Azores, Portugal.

Awards and Grants:

• International Association of Sedimentologists Postgraduate Grant 2013 (€1000)
• The Volcanic and Magmatic Studies Group Travel Fund 2013 (£250)
• The Geochemistry Group  Travel Bursary 2013 (£150)
• Keele University Postgraduate Association Bursary 2013 (£500)
• Volcanic and Magmatic Studies Group Cambridge 2011 – Geoff Brown Poster Prize (Runner-up)
• Keele University Postgraduate Association Bursary 2011 (£400)
• Research Institute for the Environment, Physical Sciences and Applied Mathematics (EPSAM), Keele University – Academic poster competition 2010 (1^st Place)
• North Staffordshire Group of the Geologists Association (NSGGA) – John Myers Award 2010 – For excellence in final year dissertation (Runner-up)
• The Micropalaeontological Society Student Award 2009 – For achievement in the course ‘Micropalaeontology: Principles and applications’

Affiliations:

• The Mineralogical Society of Great Britain and Ireland
• The Volcanic and Magmatic Studies Group
• The International Association of Sedimentologists
• The Geochemical Society
• International Association of Volcanology and Chemistry of the Earth’s Interior

Effusive versus explosive trachytic to rhyolitic volcanism in the Azores, Portugal

Explosive eruptions of evolved, silicic magmas are not typically associated with oceanic-island, intraplate settings, where effusive eruptions of basaltic magma dominate. However, many Atlantic islands exhibit ignimbrites, presumably due to the development of shallow magma chambers and the evolution of silicic magmas therein. The Azores archipelago provides one such example, where eruptions of silicic, and commonly peralkaline, magmas have been explosive (forming ignimbrites and pumice falls) and effusive (forming lava domes and flows).

This study aims to investigate the pre- and syn-eruptive processes occurring in the magma systems of the Azores, elucidating the controlling factors in the contrasting eruption styles of silicic magmas in oceanic island settings. Two case studies are utilised; the ignimbrites of Terceira Island and the products of Furnas volcano, São Miguel Island.

Terceira

With a surface area of approximately 382 km² and a population of 58,000, Terceira is the third largest island in the Azores archipelago. One of the five islands of the central group, it comprises four central volcanoes; Sánta Barbara, Pico Alto, Guilherme Moniz and Cinco Picos.

The island is bisected from NW-SE by a 2 km wide rift zone that cross-cuts Santa Bárbara, Guilherme Moniz and Cinco Picos. The rift is defined by various scoria cones and lava flow vents and is considered to be the surface expression of the large-scale geodynamic feature, the Terceira Rift (Self 1976; Gertisser et al. 2010).

Ignimbrites make up a significant proportion of the islands stratigraphy, attesting to multiple major ignimbrite-forming eruptions during the last 100 ka.

This study focuses upon the seven ignimbrite formations recognised by Self (1976) and Gertisser et al. (2010); the Lajes-Angra Ignimbrite (LAI), the Linhares-Matela Ignimbrite (LMI), the Vila Nova-Fanal Ignimbrite (VFI), the Caldeira-Castelinho Ignimbrite (CCI), the Pedras Negras Ignimbrite, the Groto do Vale Ignimbrite and Ignimbrite-i.

Furnas volcano

Furnas volcano is the youngest of the three active central volcanoes on São Miguel Island, Azores, and is widely considered to be one of the most active and dangerous in the archipelago (Booth et al. 1978; Guest et al. 1999).

Approximately 3,000 people live within the nested caldera, with several thousand more in the immediate vicinity. The volcano’s eruptive history ranges from effusive, dome-forming activity, to at least two explosive, caldera-forming events involving pyroclastic density currents (dated at ~30,000 and ~12,000 y B.P.).

The younger history of Furnas volcano, termed the Upper Furnas Group (UFG) (< 5,000 y B.P.), comprises ten sub-plinian eruptions of uniformly trachytic and often peralkaline material, at least three of which have produced lava domes after initial explosive phases. This study targets the UFG and the older, caldera-forming Povoação Ignimbrite (~30,000 y B.P.)

Methods:

The aims of this study will be addressed with the following objectives:

• Geochemical characterisation of the deposits, their crystal cargoes and melt inclusions, followed by thermobarometric determination of pre-eruptive intensive variables
• Quantitative textural analysis of pumice clasts, evaluation of conduit processes and conduit modelling
• Geochemical modelling of magma evolution and production of conceptual models for the temporal evolution of the Terceira and Furnas magma systems

Key References:

• Booth, B., Croasdale, R., Walker, G. P. L. (1978) A Quantitative Study of Five Thousand Years of Volcanism on São Miguel, Azores. Philos. T. R. Soc. Lond. S-A., 288, 271-319
• Gertisser, R., Self, S., Gaspar, J., Kelley, S., Pimentel, A., Eikenberg, J., Barry, T., Pacheco, J., Queiroz, G., Vespa, M. (2010) Ignimbrite stratigraphy and chronology on Terceira Island, Azores. Geol Soc Am, Special Paper 464
• Guest, J. E., Gaspar, J.L., Cole, P.D., Queiroz, G., Duncan, A. M., Wallenstein, N., Ferreira, T., Pacheco, J.-M. (1999) Volcanic Geology of Furnas Volcano, São Miguel, Azores. J. Volcanol. Geoth. Res., 92, 1-29
• Self, S. (1973) Recent Volcanism On Terceira, Azores. Unpublished PhD thesis, Imperial College, London, 250pp

Journal articles:

• Jeffery AJ, Gertisser R, Troll VR, Jolis EM, Dahren B, Harris C, Tindle A, Preece K, O’Driscoll B, Humaida H, Chadwick J (2013) The pre-eruptive magma plumbing system of the 2007-2008 dome-forming eruption of Kelut volcano, East Java, Indonesia. Contributions to Mineralogy and Petrology 166: 275-308

Conference abstracts:

• Jeffery AJ, Gertisser R, O’Driscoll B, Pimentel A, Pacheco JM, Self S (2013) Magmatic processes beneath Furnas volcano, São Miguel, Azores. Mineralogical Magazine 77 (5): 1381

• Jeffery AJ, Gertisser R, O’Driscoll B, Pimentel A, Pacheco JM, Self S (2013) Post-caldera explosive activity at Furnas volcano, São Miguel, Azores. VMSG 2013 poster presentation
• Jeffery A, Gertisser R, O’Driscoll B, Humaida H, Tindle A (2011) A petrological analysis of the 2007-2008 dome-forming eruption of Kelut volcano, Indonesia: insights into the pre-eruptive magma system. IUGG 2011 oral presentation
• Jeffery A, Gertisser R, O’Driscoll B, Humaida H, Tindle A (2011)The 2007-2008 dome-forming eruption of Kelut volcano, Indonesia: petrological insights into magma dynamics. VMSG 2011 poster presentation
• Jeffery A, Gertisser R, Humaida H, O’Driscoll B, Tindle A (2010) Lava dome extrusion into an active crater lake: the 2007-2008 eruption of Kelut volcano, Java, Indonesia. Cities on Volcanoes 6 poster presentation

Other:

• Jeffery A (2012) Introducing Volcanology: A Guide to Hot Rocks; by Dougal Jerram [Book Review] Geological Magazine 28: 197