Surface deformation from stalled magma

The movement of magma through the Earth’s crust can result in broad, distinctive patterns of surface deformation. However, after it has stalled, processes acting within a body of magma and the surrounding crust are also capable of generating measurable displacements. Knowing which post-emplacement processes are capable of causing deformation once magma stops moving is important for interpreting inter-eruptive deformation and understanding the growth of magmatic zones.

This PhD will investigate the magnitude and prevalence of post-emplacement deformation processes in magmatic zones. This will involve examining satellite radar measurements of deformation, modelling the volume changes during the evolution of different magmas and performing analogue experiments to understand how deformation is generated by a body of magma in the upper crust.

Background

We know from the crystal cargo of erupted rocks, the characteristics of volcanic eruptions and from thermal modelling, that the storage of magma in the Earth’s crust is complicated. Magma consists of three phases – crystals, melt and volatiles – and resides in extensive storages zones in the Earth’s crust with heterogeneous thermal histories4. The crust surrounding magmatic intrusions may behave elastically, viscoelastically at higher temperatures or experience brittle failure near the Earth’s surface. Linking the complexity of this understanding to geodetic measurements is a major challenge.

Deformation at volcanoes is most often attributed to the movement of magma: the ascent of a new intrusion, loss of volume during an eruption or transport through the crust1. However, some processes that affect a body of magma after its emplacement also have the potential to cause displacements at the Earth’s surface. For example, deformation has been attributed to phase changes associated with cooling (or reheating)2, the escape of mobile fluids and the response of the surrounding country rock to the presence of magma3.

The advent of satellite radar data in the field of geodesy has increased the volume and diversity of observations of volcanic deformation around the world. Recent research has also begun to demonstrate that a range of magmatic processes beyond juvenile intrusion can cause deformation. This PhD will advance our understanding of what it is possible to infer from geodesy about the characteristics of magma storage and in particular, how magmatic zones develop.

Objectives

The primary aim of this project is to advance our understanding of when the evolution of a magmatic intrusion can cause measurable deformation. The candidate will have the opportunity to adapt the project to follow their own interests, but avenues of investigation open to them will include:

• Analysing patterns in the spatial and temporal distribution of post-intrusion deformation detected by satellite radar (Interferometric Synthetic Aperture Radar). The European Space Agency’s (ESA) Sentinel-1 instruments provide global coverage of the world’s volcanoes with an optimal repeat time of 6 to 12 days, and in combination with access to the ESA archives, will allow the candidate to investigate post-intrusion time series in a range of settings.

• Forward thermodynamic modelling of phase equilibria (e.g., MELTS) following a number of thermal scenarios. This will allow the candidate to estimate the magnitudes of volume changes2 and use them to predict deformation patterns for selected source geometries. We will use magmatic compositions from well-studied systems as constraints, including end-member magmas from Hekla (Iceland) and the Taupo Volcanic Zone (New Zealand) as starting points for this analysis.

• Design and run analogue experiments (at GFZ, Potsdam)5 to examine how post-intrusion processes can cause deformation. For example, this could involve investigating (1) the conditions under which gas exsolution and accumulation can cause deformation, and (2) the impact of surrounding rock properties (e.g. a subsiding lid) on the development of an intrusion.

The first year of the PhD project will focus on (1) assessing the magnitude and temporal development of deformation attributable to stalled magma in the geodetic record, and (2) mapping out the parameter space for ambient deformation processes using simple forward modelling. This will inform the design of analogue experiments to be carried out in the second year of the project.