Linking surface deformation to magma emplacement

Overview

Migration of magma often drives small-scale movement of Earth’s surface, which we can monitor using satellites (Interferometric Synthetic Aperture Radar: InSAR, Fig. 1). By modelling how this observed ground movement relates to magma migration, we can assess potential hazards at active volcanoes. A fundamental and critical question is thus, how does magma migration translate to ground movement?

Figure 1: Workflow showing how satellite-derived ground deformation maps can be modelled using analytical and numerical methods to estimate properties such as magma volume, pressure, and depth (Masterlark et al. 2010).

Although we have recorded many magma injection events using InSAR, these data have only been collected for <50 years. Yet we know from the rock record that magma intrusions are commonly built through the accumulation of many discrete magma pulses over 10’s to 1000’s of years (or more). Even coupled with geophysical images of active volcano plumbing systems, it is difficult to test intrusion shapes and volumes modelled from ground deformation data, or know how much magma is already present. These limitations restrict our ability to assess eruption hazards.

We can study final intrusion forms exposed at Earth’s surface or imaged in geophysical data to determine how magma is emplaced and drives deformation in the crust over long timespans (Fig. 2). Yet it is difficult to isolate discrete magma injection and host rock deformation events from these records that have timescales comparable to those we can examine with InSAR. This problem means we cannot easily take all our knowledge on ancient intrusions and apply it to understanding active volcano systems.

To help bridge the gap between satellite-based ground deformation analyses and studies of ancient intrusions, this project will focus on: (1) establishing the duration of discrete magma injection events in ancient sills and laccoliths using a novel palaeomagnetic technique; (2) using seismic reflection data to reconstruct multiple uplift and subsidence events associated with ancient sills offshore New Zealand, and simulating their InSAR response; and (3) numerically modelling the ground deformation signals produced by different magma injection configurations over varying timescales.

 

Aim

To understand how magma intrusion translates into ground deformation over different timescales.

 

Objectives

Fieldwork

You will conduct one or two field seasons to an area where the host rock above an exposed sill or laccolith has been uplifted. This uplift of the overburden is driven by intrusion and is referred to as forced folding. Possible field areas include the Henry Mountains in Utah, USA and Sandfell, Iceland (Fig. 2). Fieldwork will involve structural measurements and sample collection for palaeomagnetic and petrological analyses.

Figure 2: Forced folds above intrusions in the field and seismic reflection data.

Palaeomagnetism

The remnant magnetisation of a rock records the orientation of Earth’s magnetic field when it is deposited or cools below the Curie Point (~500 °C). When magma intrudes it can heat up the host rock to temperatures above the Curie Point, locally changing the host rocks remanent magnetisation. Because magma intrusion can also uplift and fold the host rock, we can examine the palaeomagnetism of the deformed strata to try and establish intrusion duration. For palaeomagnetism, samples collected from fieldwork will be processed and analysed at the University of St Andrews, in collaboration with Dr William McCarthy.

Seismic interpretation

Reflection seismology can image entire intrusions and their surrounding host rock deformation in 3D (Fig. 2). Numerous studies have shown that sills imaged in seismic reflection data are commonly overlain by forced folds. In many cases, we can see strata onlapping onto the tops of these folds, which indicate they created relief at the surface. By dating onlapping strata we can date magma emplacement. You will work on a 3D seismic reflection dataset where we recognise multiple onlap events within a single forced fold. You will reconstruct the ground deformation at each onlap event and compute how ground deformation changes through time; this will be equivalent to analysing ground deformation signals captured via satellites over timescales of 10’s – 100’s years.

Modelling

You will use state-of-the-art numerical models to establish how the ground deformation signals above different intrusions may vary depending on how they are constructed through time.

 

Impact

Satellite monitoring of ground deformation is vital to many volcano observatories globally. Understanding how magma movement translates into ground deformation is critical to making the most of this data. By integrating geological, geophysical, and modelling techniques, this project will help advance volcano monitoring. The work conducted as part of this project will also improve our understanding of how deformation around intrusions influences fluid flow (e.g., mineralising fluids, water, etc…), and will thus contribute towards enhancing the efficiency of exploration and extraction of volcano-related economic resources. To communicate project findings you will be given opportunities and support to write and publish academic papers, present your work at national and international conferences, and involve yourself with outreach activities.

 

Applicant suitability

This PhD project would suit candidates who are passionate about volcanoes, enjoy fieldwork, and have (some) undergraduate training in Earth Science topics.

 

Training

You will be a key member of a team of researchers across the School of Earth and Environment tackling fundamental problems in volcanology. As a member of the Volcanology and Tectonics research groups in the Institutes of Geophysics and Tectonics, and Applied Geosciences, you will interact daily with not only your supervisors, but other senior colleagues, postdoctoral researchers, and fellow PhD researchers. You will also work with Dr McCarthy at the University of St Andrews and travel there to conduct palaeomagnetic analyses. Through the Panorama Doctoral Training Programme, you will received tailored training alongside a cohort of other postgraduate researchers.

You will receive extensive training in: (1) field mapping, using both traditional (i.e. pen and paper) and digital (i.e. tablet-based) techniques (Magee, McCarthy); (2) rock magnetic techniques (McCarthy, Magee); (3) interpreting seismic reflection data (Magee); and (4) modelling of satellite-derived ground deformation data (Ebmeier). Training will be largely one-to-one, working closely with supervisors. Through training in scientific writing, statistics and data analysis, problem-solving, time management, and developing independent research planning skills), you will become a confident and independent researcher with transferable skills applicable to both academic and non-academic jobs.

 

Further reading

Reeves, J., Magee, C. and Jackson, C.A.L., 2018. Unravelling intrusion-induced forced fold kinematics and ground deformation using 3D seismic reflection data. Volcanica1(1), pp.1-17.

Ebmeier, S.K., Andrews, B.J., Araya, M.C., Arnold, D.W.D., Biggs, J., Cooper, C., Cottrell, E., Furtney, M., Hickey, J., Jay, J.J.J.A.V. and Lloyd, R., 2018. Synthesis of global satellite observations of magmatic and volcanic deformation: implications for volcano monitoring & the lateral extent of magmatic domains. Journal of Applied Volcanology7(1), pp.1-26.

Biggs, J., Ebmeier, S.K., Aspinall, W.P., Lu, Z., Pritchard, M.E., Sparks, R.S.J. and Mather, T.A., 2014. Global link between deformation and volcanic eruption quantified by satellite imagery. Nature communications5(1), pp.1-7.

Magee, C., Bastow, I.D., van Wyk de Vries, B., Jackson, C.A.L., Hetherington, R., Hagos, M. and Hoggett, M., 2017. Structure and dynamics of surface uplift induced by incremental sill emplacement. Geology45(5), pp.431-434.