HYDROTHERMAL CONTROLS ON CALDERA EXPLOSIVITY

Almost all active caldera volcanoes host hydrothermal systems that circulate a mixture of seawater, meteoric water and magmatic fluids through the subsurface geology to seeps or vents on the seafloor. These fluids can explosively interact with magma in volcanic eruptions and can change the physical properties of their host rocks, influencing both the likelihood of eruptions occurring and their explosivity. The nature of these interactions is poorly understood, including how fluid flow changes during periods of magmatic intrusion, how the hydrothermal system connects magmatic fluids to the surface and the spatial distribution and extent of alteration/mineralisation. While we know hydrothermal fluid flow plays an important role in modulating eruption dynamics, as long as these fundamental knowledge gaps exist it is impossible to forecast, with any degree of accuracy, what this effect will be which makes understanding hazards and impacts in eruption scenarios difficult.

In this proposal we will combine novel controlled source electromagnetic mapping of porosity and permeability, with passive seismic mapping of hydrothermal fluid flow in the shallow subsurface, constrained by heat flow measurements and surface and subsurface sampling to characterise the porosity and permeability of the Santorini hydrothermal system. Santorini has been selected as the ideal natural laboratory to test these relationships because it is exceptionally well characterised geophysically and geologically, has a diversity of hydrothermal vents and has experienced recent activity which can be used to test modelling. We will quantify how magmatic fluids are partitioned between vents to identify the primary pathways for magmatic volatile escape, and quantify the impact hydrothermal mineralisation has had on the physical strength of the seafloor. Once we have a full picture of the system in its current state we will use mapping, fluid inclusions, mineralogy and the sedimentary record to establish how vent locations, subsurface fluid pathways, and fluid fluxes, temperatures and chemistries responded to the 2011/12 period of unrest. These data will be used to constrain the boundary conditions for a hydrothermal system model, which can be used to predict how the system will respond to future periods of intrusion both at Santorini and at other caldera systems around the world.

This project will provide a step change in our understanding of hydrothermal interactions with volcanoes and our ability to predict their response to changes in the magmatic system. This has implications not just for understanding volcanic eruptions, but also for understanding metal and volatile fluxes from the mantle to the ocean and atmosphere, the development of economic metal deposits in these systems, the impact on ecological communities of intrusive and extrusive volcanic events, geothermal energy production, and for hazard forecasting and mitigation. The project will push the frontiers of knowledge by combining cutting edge geophysical and geochemical techniques to produce a model of a caldera hydrothermal system at a resolution previously not possible, and by developing modelling tools that would allow the application of these findings to other systems. The project is ambitious but achievable and benefits from a large team of international expert proponents, partnerships with other large international projects and high-quality pre-existing data upon which to build.