The role of fractures in lava dome instability

Lead supervisor: Claire Harnett, UCD School of Earth Sciences, University College Dublin, Dublin, Ireland.

Co-supervisors: Eoghan Holohan, UCD School of Earth Sciences, University College Dublin, Dublin, Ireland. Mike Heap, Institut de Physique de Globe de Strasbourg, Université de Strasbourg, Strasbourg, France. Thomas Walter, GFZ German Research Center for Geosciences, Potsdam, Germany.

Project description

Lava domes form when lava is too viscous to flow away from a volcanic vent and instead forms ‘mounds’. Such domes sit atop some of the world’s most active volcanoes and are often located close to large population centres. If a lava dome becomes unstable, its collapse can generate rockfalls, debris avalanches, and pyroclastic flows. Despite the significant hazard, the dynamic relationship between dome growth and dome collapse is still not fully understood.

Factors hypothesised to trigger lava dome collapse include oversteepening, internal gas overpressures, intense rainfall, a switch in extrusion direction, and seismicity. The stability of a dome is also affected by the nature of the volcanic rock, for example its strength and elastic properties, as well as its alteration state and its fracture state. In particular, it is hypothesised that small scale but high frequency fracturing may generally weaken a dome rock mass, whereas larger scale, lower frequency fractures may act as planes for major dome failure.

This fully funded, four-year PhD project will explore the role of fractures at varying scales on lava dome instability. The PhD candidate will work with a team of international researchers to develop a multidisciplinary project. The candidate will learn attain cutting-edge skills in field methods, geomechanical testing, and numerical modelling, as well as having access to transferable skills training as part of the UCD research community. They will also have the opportunity to take taught modules as part of the structured PhD program at UCD. This training will help the candidate develop a strong and varied set of skills to prepare them for a scientific career following their doctoral study. Objectives

The project is flexible and can be tailored to the student’s interests and/or strengths. Considering the supervisory expertise available to the candidate, possible project approaches and related objectives include:

1. Quantitatively establishing the fracture state of a lava dome. A range of high resolution, near- field observations (e.g., drone-based photogrammetry and thermal imaging, LiDAR) will be used to assess a ‘typical’ fracture state of a dome. This will be done in collaboration with GFZ. 2. Investigating the mechanical properties of volcanic rock and its fractures. This will involve laboratory experiments conducted at the University of Strasbourg on fractured and non- fractured samples to establish up-scaled rock-mass properties. There is also potential for fieldwork in order to collect rock samples for laboratory testing. 3. Numerical modelling of a fractured lava dome. Modelling will be undertaken to investigate how the nature of fracture networks (i.e., geometry, size, distribution) can influence large-scale dome stability.

Further reading

Harnett, C. E., Thomas, M. E., Purvance, M. D., & Neuberg, J. (2018). Using a discrete element approach to model lava dome emplacement and collapse. Journal of Volcanology and Geothermal Research, 359, 68-77.

Walter, T. R., Subandriyo, J., Kirbani, S., Bathke, H., Suryanto, W., Aisyah, N., ... & Dahm, T. (2015). Volcano-tectonic control of Merapi's lava dome splitting: The November 2013 fracture observed from high resolution TerraSAR-X data. Tectonophysics, 639, 23-33.

Voight, B., & Elsworth, D. (2000). Instability and collapse of hazardous gas‐pressurized lava domes. Geophysical Research Letters, 27(1), 1-4.

Student profile

The candidate should have an interest in volcanology, and a strong background in a quantitative science (earth sciences, physical geography, geophysics, geology, geotechnics, engineering, physics), with a degree in a related discipline. An MSc is desirable, but not required. This project would best suit a candidate with experience and interest in scientific computing, and some coding knowledge (e.g., MATLAB and/or Python). An interest in rock mechanics would be advantageous, but full training will be provided for any laboratory work. The candidate should be enthusiastic about international collaboration and overseas travel.

How to apply

For informal queries, or to discuss your interest in the project, please contact Dr Claire Harnett ([email protected]) before applying. To apply, please send a CV (including details of two academic references) and cover letter to Dr Claire Harnett before 02/03/2020.

Funding notes

This 4-year award will provide tuition fees, a tax-free stipend of €18,000 per year, and a research grant of €4000 per year. This funding is open to both EU and non-EU students. The project is due to start in September 2020.