Utilising the co-analysis of EDM and GPS data in modelling surface deformation at the Soufrière Hills Volcano, Montserrat

Abstract

Greater understanding of volcanoes through monitoring and modelling of magmatic processes can help protect lives, communities, and economies at risk from volcanic activity. Ground deformation offers vital insight into the activity of volcanoes and associated magmatic systems, and can be monitored via geodetic methods. Each geodetic method has limitations, thus utilising multiple techniques provides better coverage of a volcano, but requires an understanding of how different methods respond to different changes in the magmatic system. This thesis investigates how EDM and GPS can be used in tandem to distinguish between shallow and mid-crustal magmatic processes. I focus on the Soufrière Hills Volcano (SHV), using ground deformation data collected by the Montserrat Volcano Observatory from 2010-2019. The SHV has been in an extended intra-eruptive pause since 2010, following 15 years of discontinuous effusive activity, and has a well-developed GPS and EDM monitoring network. I investigate how the two networks record ground deformation at the SHV, which parts of the magmatic system they respond to, and what they can tell us in tandem about the current status of the magmatic system. I also relate these investigations to the unusual behaviour of the GPS site HERM, relative to the rest of the GPS network. This study finds that the EDM network responds predominantly to changes in the shallow magmatic system, while the GPS network primarily responds to changes in the mid-crustal system. EDM line length change is mostly dictated by the relative horizontal movement of the reflector and base station; relative vertical displacement is less significant. I find that the behaviour of the EDM network from 2010-2019 can be explained by negative pressurisation in a shallow dyke conduit orientated NNW-SSE, while the deeper system is still undergoing pressurisation. The behaviour of HERM is also partially tied to the behaviour of the shallow system. Ultimately, monitoring multiple flanks of the volcano close to the vent is vital for both monitoring and modelling the shallow aspects of volcanic systems.