Overview

Project Highlights:

  • Investigate how shifts in volcanic behaviour are driven by major edifice collapses
  • Participate in a marine research expedition and use marine core datasets (Ritter Island and Montserrat) and samples to reconstruct volcanism across different timescales
  • Determine how magma storage and ascent processes are affected by surface unloading

 

Overview:

Sector collapses are among the largest volume events to affect volcanic systems, potentially involving the rapid displacement of tens of cubic kilometres of rock. There is growing evidence that such substantial changes in surface loading can have profound effects on the stability of an underlying magma reservoir, potentially manifested through shifts in eruption rate or composition and dominant eruptive behaviour. Nevertheless, a detailed understanding of how and why collapses perturb a magma system is lacking, both because of an absence of historical observations of large sector collapses, and because of the challenges involved in generating high resolution reconstructions of past eruptive activity that span the periods before and after collapse. This project will take advantage of two unusual marine sediment sample sets collected offshore the volcanic islands of Montserrat (Lesser Antilles) and Ritter Island (Papua New Guinea). These samples and cores preserve a record of activity at these volcanoes before and after major collapse events, and can advance our understanding of how volcanism at arc-volcanic systems responds to sudden changes in surface loading.

Ritter Island was the site of the largest historical sector collapse (around twice the size of the Mount St. Helens event in 1980), in 1888, and recent analysis of samples collected in 2016 indicate that unusually evolved magmas were erupted immediately following collapse, and that subsequent rebuilding of the submarine cone has produced rocks that are compositionally distinct from those erupted before collapse. The event provides an ideal opportunity to better understand the nature of post-collapse changes in activity, but inaccessibility means that the volcano has been little studied previously. The 2016 samples were the first collected from the 1888 collapse. More will be collected on a planned research ship expedition in 2020, in which the PhD student would participate.

Montserrat has been subject to multiple large scale sector collapses throughout its history, and provides an opportunity to investigate the impacts of collapse on volcanic behaviour over longer (103-5 year) timescales, thus complementing the higher-resolution, shorter timescale study of Ritter. The student would work with extensive core samples from IODP 340, potentially alongside new samples planned for collection in 2019.

Figure 1: The RV Sonne collecting data and samples at Ritter Island in 2016. The crescent-shaped remnant of Ritter is all that remains of the subaerial island. The cone has been rebuilding beneath sea-level, with results indicating a shift in magma compositions following collapse.

Methodology

The project student would work with marine volcaniclastic sediment and core samples, applying a range of sedimentological, geochemical and petrographic approaches to investigate the nature pre- and post-collapse volcanism at Montserrat and Ritter. Work will be undertaken at the University of Birmingham (general stratigraphy, sediment properties, SEM imaging) and the University of Oxford (electron microprobe and laser ablation ICP-MS, analysing glass and mineral compositions). In developing the stratigraphy offshore Montserrat and Ritter Island, the student will also work with seismic reflection datasets to map the extent of sector collapse deposits and their bounding units.

From this variety of approaches, the student will acquire evidence for changes in magma chemistry, mineral contents, eruptive style and frequency in both pre- and post-collapse periods, and develop an eruptive chronology (particularly for the Montserrat core datasets) from existing age data, with the potential for additional constraints using 40Ar/39Ar methods.

Using the combined dataset, the student will address whether and how the magmatic plumbing system that previously existed was affected and potentially reorganised following collapse. To develop this interpretation, the student will combine approaches including thermobarometry, textural analyses and diffusion chronometry, using further electron microprobe analyses and working directly with co-supervisors and facilities at the Natural History Museum and University of Oxford.

Training and Skills

The project student will receive training in core sampling and sedimentological analysis, and the preparation and geochemical analysis of volcaniclastic samples (optical microscopy, SEM analysis, electron probe micro-analysis) and techniques used to investigate and quantify magmatic processes (e.g., diffusion chronometry). There is a potential opportunity to experience marine research through participation in a ship expedition to Ritter, and through this to experience working as part of a major cross-disciplinary international project. The student will work with co-supervisors at facilities across the UK (including the Natural History Museum, London, and the University of Oxford), with the potential to also gain experience with 40Ar/39Ar dating methods. The project thus provides the opportunity to obtain a wide range of analytical experience and work with varied facilities and several research groups.

Timeline

Year 1: Sampling of Montserrat IODP 340 cores; sedimentological analysis; production of stratigraphy; tephra sample preparation. Additional work on existing Ritter dataset. Planning for further sample collection in 2020. Attendance and presentation at a national volcanology conference.

Year 2: Geochemical and textural analyses of Montserrat samples; participation in Ritter expedition and development of subsequent stratigraphy; continuing geochemical analyses.

Year 3: Analysis of magmatic processes and plumbing system structure under pre- and post-collapse conditions, drawing on reconstructions across different timescales. Writing up of project results for publication; presentation at an international conference.

Partners and collaboration (including CASE)

The project student will be based at Birmingham but would work closely with the co-supervisors at Oxford and the Natural History Museum (a CENTA2 Level 1 partner), making use of laboratory facilities at a number of UK institutions. The student will also have the opportunity to build relationships with international collaborators at GEOMAR (Germany) and with international participants in the wider marine research project (including collaborators in Papua New Guinea for the Ritter Island component of the project).

Further Details

Please contact Dr Sebastian Watt - s.watt@bham.ac.uk

This project will suit a student with an interest and facility for detailed laboratory work, an enthusiasm for volcanology and an interest in working within a collaborative, interdisciplinary project.