Overview

Project Highlights:

  • A unique volcanological perspective gained from looking inside a super-volcano.
  • Combines physical volcanology with fieldwork and geochemical correlation in one of Britain’s most spectacular national parks
  • Develop expertise in a variety of field and laboratory techniques to resolve ignimbrite successions, and to trace tuffs to their source vents.

Overview:

How explosive caldera volcanoes erupt and collapse is essential to understand some of the most catastrophic events that affect the Earth’s surface. But research is hindered at modern volcanoes because most of the critical features, such as caldera faults, eruption conduits, vents, and caldera fill deposits are concealed1. However, in rare cases uplift and erosion has beautifully exhumed such features, allowing direct examination. Scafell caldera in the English Lake District is one of the best exposed, exhumed and dissected explosive caldera volcanoes in the world2. It has attracted interest internationally because it provides astonishing access to caldera fill ignimbrites, caldera floor faults, eruption vents and post-climactic lava extrusions2,3. It therefore offers unique insights into the internal workings of these complex systems. Of particular interest is how subsidence shifts with time, and how vents activate and migrate as caldera floor faults propagate and dilate.

Scafell is just one of a series of overlapping (nested) calderas that generated explosive super-eruptions in the Lake District. This project will clarify the relationship between the large eruptions and individual subsidence structures and their vent systems. Logging and sampling of sections will be followed by geochemical analysis to characterise outflow ignimbrites and relate them to their source to define and characterise individual eruption-units and to correlate between distal and near-source exposures.

  • Vent sites and silicic domes/intrusions will be mapped, described and chemically analysed to determine unit source locations.
  • Thickness variations of correlated units will be used to estimate density current runnout distances, successive eruption volumes and the related areas of subsidence.
Figure 1: Explosive volcanic caldera spectacularly exhumed by uplift and glacial incision, English Lake District

Methodology

The products of individual explosive eruptions will be characterised and correlated using fieldwork and analytical geochemistry, using an approach developed by the Leicester group for the Yellowstone-Snake River region of USA4. Whole-rock trace-element ratios will help distingush a number of super-eruptions. The utility of this method has been tested in the Lake District with promising results.

 

  • Graphic logging and will establish local pyroclastic successions and unit thicknesses.
  • Detailed geological mapping of selected hillsides will establish the geological relationships.
  • Sampling of ignimbrites and fallout layers for geochemical analysis and petrography.
  • Geochemical analysis by XRF and LA-ICPMS will help define and characterise individual eruption-units, and correlate them from proximal to distal and exposures.
  • Vent sites and silicic domes/intrusions will be mapped and chemically analysed to determine unit source locations.
  • Thickness variations of correlated units will be used to estimate runnout distances, successive eruption volumes and related areas of subsidence.

Training and Skills

You will be trained in field analysis of pyroclastic successions including geological mapping, logging, and sampling of ignimbrites, ashfall tuffs, and lavas. Training will be provided in chemical analysis (XRF, LA-ICPMS and EMP) to characterise and correlate units regionally. By the end of the project you will have expertise in physical volcanology, geological fieldwork, super-eruptions, and igneous geochemistry.

You will join a thriving research community within the Volcanoes, Tectonics and Mineral Resources Research Group at the University of Leicester. By the end of the project you will have gained a set of skills ideal for a career in geology, physical volcanology or igneous petrology.

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.

Timeline

Year 1: The project will start in 2019 with supervised fieldwork to familiarise with the well-exposed pyroclastic successions. Training (on Tenerife) on interpreting pyroclastic deposits. The student will undertake a second field season in early Summer, 2020, characterising a sampling successions, followed by sample preparation and XRF analysis. Participation at VMSG 

Year 2: Optical microscopy and interpretation of initial field data. Further fieldwork will be indertaken to identify, map-out and sample potential vent sites. Samples will be prepared for geochemical analysis, and the data used to correlate units. The student will present preliminary results at a national conference, and there will be opportunity to draft a first publication. Fieldwork will be undertaken to extend the correlations further into ‘unexplored’ regions.

Year 3: Complete the laboratory work, and develop interpretations of individual eruptions. Estimate the geographical extents and volumes of eruptions. Synthesis results to assess how vent positions migrated, and how areas of subsidence shifted with time. Write-up international publications and PhD thesis.Present findings at an international conference.

Further Details

Please contact Professor Mike Branney, University of Leicester (mjb26@le.ac.uk).

This project will suit an energetic geology student proficient in independent hillwalking, geological mapping, and camping in remote mountainous terrain. The student will be able to drive, have a facility for geochemistry and a keen interest in physical volcanology, stratigraphy and structural geology. Checkout: https://www2.le.ac.uk/departments/geology/research/vtmrg/volcanology-at-leicester

and https://www2.le.ac.uk/departments/geology/research/vtmrg