Structure of a recharging crustal magma plumbing system at the Santorini arc volcano

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

This project will improve the understanding of magma storage under volcanoes - a critical input for volcanic hazard assessments. Magma beneath a volcano can be detected using geophysical tools, but the shape of the magma plumbing systems that underlie volcanoes is still not known. For hazard analyses it is critical to know what fraction of a magma is molten rock (melt) and what fraction are crystals; this ratio controls how fluid the magma is and thus how easy it is for an eruption to occur. After a large, explosive eruption of the volcano, the subsurface magma system has to reassemble. To resolve the detailed structure of a recharging crustal magma plumbing system beneath an arc volcano, this project will use a unique seismic dataset, PROTEUS, from Santorini volcano in Greece. The PROTEUS dataset probed the volcano in unprecedented detail. The data reveal a column of broken rock that is narrowly confined beneath the northern caldera basin. Below this structure lies the uppermost part of the magma system. This project will further analyze the PROTEUS seismic data as well as model the stresses with the volcano to: (i) image the magma plumbing system of the volcano to great depths (the base of the crust); (ii) determine the melt content of magmas located in the mid- and upper-crust; (iii) explore how volcano internal structure and by regional setting control magma distribution within the volcano. When recruiting graduate and undergraduate students, diversity in STEM training will be prioritized. This project will build on existing international collaborations including with four different European scientific institutions and with an International Ocean Drilling expedition to Santorini. To most effectively bring the science results to the public and local decision makers, the project engages Greek collaborators and a science communications expert. This study will provide a framework for volcanic and seismic hazards assessment at Santorini, where the dramatic landscape draws over 2 million tourists per year. Current models of volcano plumbing systems predict vertically extensive magma systems dominated by low melt-fraction crystal mushes where differentiation occurs in the lower and mid crust and magma accumulation in the upper crust. However, the detailed geometry, distribution, and composition of melt throughout the crust remain poorly known. These conceptual models also predict that the existence of eruptible melt-rich magma chambers prior to Plinian events is short-lived. Of interest is how the magma system is reshaped after a caldera-forming eruption. This project will address two outstanding science questions: (1) What is the high-resolution structure of the magmatic system at an arc volcano and what are the melt contents throughout the crust? And (2) How is magma movement affected by caldera collapse structures and regional stresses? To resolve the detailed structure of a recharging crustal magma plumbing system at an arc volcano, this project leverages the unique PROTEUS active-source seismic dataset from the well-studied Santorini volcano. These data probed the volcano with unprecedented wavefield density and, to date, tomographic analysis of first arriving P-waves has resolved the structure of the uppermost crust at, and around, the volcanic edifice. The results reveal a low-velocity, porous column that is narrowly confined beneath the northern caldera basin beneath which is an upper-crustal magma system. Here the PROTEUS seismic dataset will be exploited further to model the stress state. The proposed analyses will: (i) determine the structure of the magmatic system below the currently-resolved upper-crustal reservoir through tomographic inversion of deeper turning rays and Moho reflections; (ii) better constrain the melt content of the mid- and upper- crust through joint Vp/Vs tomography and modeling of secondary arrivals; (iii) interpret the seismic results in terms of physical properties; and (iv) explore how the internal structure of the edifice and regional stresses affect magma accumulation within the volcano through modeling and seismicity analysis. This project will also build international collaborations including four different European institutions and synergies with an IODP proposal. Diversity in STEM training will be prioritized when recruiting graduate and undergraduate students. This study will provide a framework for volcanic and seismic hazards assessment at Santorini, where the dramatic landscape draws over 2 million tourists per year. To most effectively bring the results to the public and local decision makers, the project leverages Greek collaborators and a science communications expert. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.