Doctoral lecture in Geology -  Catherine Rachael Gallagher

Live stream: https://livestream.com/hi/catherinegallagher

Ph.D. student: Catherine Rachael Gallagher

Dissertation title: The timing and mechanisms of sulfur release by Icelandic flood lava eruptions: Holuhraun 2014–15 CE and Laki 1783–84 CE a case study

Opponents: Dr. Valentin Rudolf Troll, Professor at the Faculty of Earth Sciences at Uppsala University, Sweden.
Dr. Colin Macpherson, Professor at Durham University, UK

Advisor: Dr. Kevin W. Burton. Professor at Durham University, UK
Dr. Þorvaldur Þórðarson, Professor at the Faculty of Earth Sciences at the University of Iceland
Dr. Bruce Houghton, Gordon A. Macdonald Chair and Professor at SOEST, University of Hawai'i at Manoa, USA

Doctoral committee: 
Dr. Charlotte Vye-Brown, Senior Volcanologist at British Geological Survey, UK
Dr. Richard Brown, Senior Lecturer at Durham University, UK

Chair of Ceremony: Dr. Freysteinn Sigmundsson, Research Scientist at the Institute of Earth Sciences and the Head of the Faculty of Earth Sciences, University of Iceland

This is a joint degree between the University of Iceland and Durham University.  Catherine has already passed her PhD viva examination in Durham on the 10th of September 2021. This is open talk is in line with the requirements of the co-tutelle agreement between the two institutions.

Abstract: Flood lavas (FL), or high magnitude (1–100 km3) basaltic fissure eruptions have a recurrence interval of 250-500 years in Iceland. These events can produce atmospheric volcanic pollution at tropospheric–stratospheric levels via their sulfur (S) emissions. Current knowledge of the modulating role of shallow conduit processes on the vent activity, as well as the mechanisms and timing of peak S release into the atmosphere is limited.

This project has two key aims: First, to evaluate the influence of shallow conduit processes on eruption style and dynamics during peak intensities of explosive phases. Second, to produce a novel, chalcophile stable isotope proxy for the speciation of released S and the redox state of the system upon eruption. Two selected case studies for this project are: (i) the recent lower intensity and magnitude endmember, 2014–15 CE Holuhraun, and (ii) a high intensity and magnitude end-member, 1783–84 CE Laki, which is well-documented in detailed contemporary accounts.

Micro-textural analysis of the ‘frozen’ outer rinds of pyroclasts from both eruptions, which record the state of the magma prior to fragmentation, identified relative shifts in vesicle number density associated with changes in eruptive intensity. Whole pyroclast textural mapping and in-situ geochemical analysis constrain the modification of the interior of the clasts via post-fragmentation expansion. This process enhanced the contrasts between discrete pre-existing melt domains which mingled prior to eruption. These domains record different shallow conduit histories, in particular contrasting ascent rates, and therefore preserve evidence of equilibrium and disequilibrium vesiculation within the same clast. Zinc and copper stable isotope compositions of lava and tephra from distinct phases of eruptive activity were utilised to fingerprint the mechanisms of S loss. Changes in the efficiency of volatile loss of S can be linked to known changes in vent dynamics, as well as changes in S loss associated with both the evolving transport system, and redox conditions at the vent and in the flow field.

The textural and geochemical findings from these two eruptions will help further our understanding of shallow conduit, eruptive and emplacement processes during the many ill-constrained basaltic fissure eruptions of different intensities and magnitudes worldwide.

About the doctoral candidate:

Catherine Rachael Gallagher (1989) was born and raised in North West England in a small village in the Pennine Hills. She moved to Edinburgh, in Scotland, to attend University in 2008 where she got her taste for field geology, volcanology and petrology. There she did her BSc thesis mapping project in Eastern Iceland in Berufjörður in 2011. Catherine then completed her MEarthSci thesis in Geology at The University of Edinburgh in 2012, which focussed on the petrology and structural geology of Álftafjörður dyke swarm, in Eastern Iceland. After her masters studies Catherine decided to move to Iceland in

2013 and worked as a research assistant at Háskóli Íslands, before starting a dual PhD project between Durham University and Háskóli Íslands in 2015 funded by NERC and HÍ. Her PhD studies also included a Watanabe fund supported research visit to Okayama University in Japan, PLM Misasa in 2018.

During Catherine's time in Iceland she has worked as part of the Institute of Earth Sciences monitoring team for both the Holuhraun eruption in 2014, prior to starting her PhD, and during the recent Fagradalsfjall eruption in 2021.