Magmatic overpressure: controlling factors and links to volcano monitoring

Overpressure is thought to be a major control on volcanic explosivity, yet it is poorly understood.The explosivity of an eruption influences the scale and type of volcanic hazards, which in turn impact human populations. The ever-increasing use of satellite radar (InSAR) to observe volcanoes means that estimates of overpressure are readily available, so this is a good time to refine our understanding of this parameter.One of the long-term goals of this research is to understand how the different controls on magmatic overpressure affect the explosivity of volcanic eruptions.A second goal is to use this knowledge to improve physical models linked to InSAR observations of volcanic deformation, and improve our eruption forecasting capabilities.This study aims to examine the different factors affecting magmatic overpressure, and to determine how these factors may vary between volcanoes. More specifically, the study will examine the accommodation of stress both within magma itself, and within the rocks surrounding the magma reservoir.This information will be integrated in to a physical model, to see how these variations may affect InSAR estimates of overpressure.By pursuing the aims described above, this study will address the following questions: How do different magma types accommodate overpressure?How do different volcanic wall rocks accommodate overpressure?How does this accommodation affect the deformation profile observed using InSAR?In order to assess how magma accommodates overpressure we will heat and pressurise real volcanic samples inside cold seal pressure vessels, where parameters can be varied to simulate sub-volcanic magmatic conditions.We can then increase pressure conditions towards the end of the experiment, and examine the resulting sample for deformation signatures using electron backscatter diffraction (EBSD).Using this method, it may be possible to calibrate crystal deformation intensity to overpressure(although other variables may also be involved).In order to assess how different wall rocks accommodate overpressure we can take wall rock samples and place them in high-temperature uniaxial creep apparatus.We can then examine the deformed samples using EBSD, to determine how they respond to overpressure.These experimental results can be integrated with InSAR observations of volcano deformation in a physical model.The experimental work may help to refine the overpressure estimates used in physical models, with links to InSAR monitoring.InSAR does not require any ground-based monitoring equipment (which the majority of volcanoes do not have) so it has huge potential for global volcano monitoring and eruption forecasting.The analysis of magmatic crystal and wall rock deformation using EBSD is a relatively new field of study.By incorporating these results in to physical models which link overpressure and deformation, it may be possible to refine these models and improve their utility.The laboratory facilities at the University of Oxford provide an excellent opportunity to undertake this research, as they host three cold seal pressure vessels and high-temperature uniaxial creep apparatus.The University of Oxford is also part of COMET(the centre for observation and modelling of earthquakes, volcanoes and tectonics)which integrates satellite and ground-based data to monitor volcanoes.Depending on the volcanic samples used in this study, this project presents the opportunity to collaborate with researchers and volcano observatories in other countries, and to develop international links.