Overview

Project Highlights:

  • Interpret the eruption styles and eruptive history of one of the most dangerous volcanoes on Earth
  • Research the pyroclastic succession of the spectacular Taal volcano, Philippines
  • Training in a variety of field and laboratory techniques to resolve the volcanic stratigraphy, eruptions, and emplacement mechanisms of unusual ignimbrites and tephras.

Flooded explosive caldera volcanoes present one of the largest geohazards on the planet, but the catastrophic eruption processes remain poorly understood. Fragmented silicic magma erupts vigorously through voluminous caldera lakewater, interacting with it. This may enhance the violence of the explosivity (‘fuel-coolant interaction’), while agglomeration and accretion of fine ash particles in water-saturated atmospheric conditions leads to premature fallout and deposition. This creates some unusual and intriguing fine-grained deposits with abundant accretionary lapilli2, and flash-quenched magma bombs5. Such deposits are preserved on the 600 m-high caldera walls, and pyroclastic shield around Taal caldera south of Manila in the Philippines1.

Taal was highlighted as a ‘Decade Volcano’1 in the 1990’s because of frequent historic explosive eruptions, the vast size (25 km across) of the caldera, and the potential threat to millions who live around it. However, the history of the major, caldera-forming eruptions is only sketchily resolved. Much evidence lies in the geological record: an extensive shield of fine-grained, accretionary lapilli -bearing ignimbrites, spectacular coarse-grained proximal deposits of enigmatic origin (breccias and agglomerates), and abundant phreatomagmatic cross-bedded tephras.

This project aims to re-assess the pyroclastic record using modern physical volcanology techniques to help quantify the styles, frequencies, and extent of the most-hazardous, large-scale eruptions at Taal.

Satellite view of Taal caldera volcano, with the younger, emergent Volcano Island in the middle of the caldera lake.

Methodology

This project will be a multi-faceted investigation into the large, caldera-forming phreato-magmatic eruptions of Taal caldera volcano. It will draw on techniques and approaches developed by our research group at explosive volcanoes in Tenerife, Mexico and the USA2,3.

  • Remote sensing and fieldwork will identify exposed sections of the pyroclastic stratigraphy.
  • Graphic sedimentary-style logs through the varied pyroclastic succession will be drawn-up at road cuttings, stream banks, and caldera walls, and interpreted in terms of latest understanding of eruption and emplacement processesg. 4.
  • Tephra and ignimbrite samples will be collected for textural analysis and 14C dating.
  • Pumice, scoria rags and crystals will be collected for geochemical analysis by XRF and LA-ICPMS at Leicester. Pumice and crystal compositions will characterise the basaltic andesite to rhyodacite magmas involved: some are mixed magmas.
  • Chemistry and mineralogy will be used with field evidence to define and characterise individual eruption-units and to correlate between exposures, and map out tephra distributions to shed light on hazards.
  • The processes and progression of individual large eruptions will be inferred from the new field, textural and chemical data, while ignimbrite and ashfall dispersals will be constrained by mapping.

Training and Skills

You will be trained in remote sensing, field and laboratory analysis of pyroclastic successions including clastic logging, granulometry, SEM training, and textural characterisation of phreatomagmatic and magmatic tephras. Training will be provided also, in geochemical analysis (LA-ICPMS, XRF and EMP), to characterise the magmas and aid the correlation of units regionally. By the end of the project you will be an expert physical volcanologist skilled in a variety of field and laboratory procedures, and in the interpretation of complex pyroclastic successions, with an emphasis on particularly hazardous, large explosive volcanoes. There will be the opportunity to undertake CAT-scan imaging, advanced computerised image-processing and morphometric analysis.

You will join a thriving research community within the Volcanoes, Tectonics and Mineral Resources Research Group at the University of Leicester, and gain a set of skills that will be useful for a career in physical volcanology, geohazards and research.

CENTA students benefit from 45 days training throughout their PhD including a 10 day placement. In the first year, students are trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to CENTA research themes.

Timeline

Year 1: The project will start in October 2017 with the student undertaking remote sensing of the volcano. Training on pyroclastic successions will begin in the field on Tenerife in December, with the emphasis on logging and using computer graphics packages. In late Spring of 2018, the student will conduct fieldwork in the Philippines (supervision provided), developing contacts with local volcanologists, documenting the pyroclastic successions, and collecting samples.

Year 2: Samples will be prepared for geochemical analysis, using the data to correlate units. The student will present preliminary results at a national conference, and there will be opportunity to draft a first publication. A second field season will follow.

Year 3: In the final year the student will complete the laboratory work, 14C dating, and develop interpretations of individual eruptions. The range of eruption styles, geographical extents of affected areas, and eruption frequency will be synthesised, and written-up for publication and thesis. Findings will be presented in the Philippines, and at an international conference.

Partners and collaboration (including CASE)

Professor Michael Branney has published extensively on large explosive eruptions around the world, and is a leading international expert in the interpretation of eruption and emplacement mechanisms of pyroclastic successions, with an emphasis on super-eruptions, calderas, phreatomagmatism and ignimbrite sedimentation. He has field experience at Taal, together with colleagues in the Philippines and USA.

Dr Dan Smith is an expert on hydrothermal systems in volcanoes, and has worked on arc volcanic rocks in the Philippines, and tropical South Pacific islands.

Dr Tiffany Barry is an igneous geochemist with 25 years experience of basaltic and evolved volcanic successions of ignimbrites and flood basalts from Antarctica to central Asia. She oversees the analytical laboratories at Leicester.

Further Details

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