International Ocean Discovery Program
Expedition 398 Scientific Prospectus

Hellenic Arc Volcanic Field

Volcanism and tectonics in an island arc rift environment (VolTecArc): Christiana-Santorini-Kolumbo marine volcanic field, Greece¹

¹Druitt, T., Kutterolf, S., and Höfig, T.W., 2022. Expedition 398 Scientific Prospectus: Hellenic Arc Volcanic Field. International Ocean Discovery Program. https://doi.org/10.14379/iodp.sp.398.2022

Abstract

The understanding of island arc volcanism and associated hazards requires study of the processes that drive such volcanism and how the volcanoes interact with their marine surroundings. What are the links and feedbacks between crustal tectonics, volcanic activity, and magma genesis? What are the dynamics and impacts of submarine explosive volcanism and caldera-forming eruptions? How do calderas collapse during explosive eruptions and then recover to enter new magmatic cycles? What are the reactions of marine ecosystems to volcanic eruptions? The Christiana-Santorini-Kolumbo (CSK) volcanic field on the Hellenic volcanic arc is a unique system for addressing these questions. It consists of three large volcanic centers (Christiana, Santorini, and Kolumbo), and a line of small submarine cones, founded on thinned continental crust in a 100 km long rift zone that cuts across the island arc. The marine rift basins around the CSK field, as well as the Santorini caldera, contain volcano-sedimentary fills up to several hundreds of meters thick, providing rich archives of CSK volcanic products, tectonic evolution, magma genesis and paleoenvironments accessible only by deep drilling backed up by seismic interpretations. We will drill four primary sites in the rift's basins and two additional primary sites inside the Santorini caldera. The expedition science has five main objectives, each with a leading testable hypothesis, and two secondary objectives. Deep ocean drilling will enable us to identify, characterize, and interpret depositional packages visible on seismic images, chemically correlate primary volcaniclastic layers in the rift fills with their source volcanoes, fill in the many gaps in the onshore volcanic records, provide a tight chronostratigraphic framework for rift tectonic and sedimentary histories, and sample deep subsurface microbial life.

Plain language summary

About 800 million people are threatened by volcanic eruptions around the globe: high plumes of ash, ground-hugging flows of hot ash and rock, earthquakes, and associated tsunamis. The Christiana, Santorini, and Kolumbo volcanic group in the Aegean Sea of Greece is particularly hazardous because the volcanoes have produced many eruptions in the past, and some of them were highly explosive. Santorini is an iconic volcano because of its well-known eruption in the Late Bronze Age, and it is a major tourist destination. Much has been learned about the eruption history of the Aegean volcanoes on land, but most of their volcanic products lie on the seafloor, requiring research to move offshore. During International Ocean Discovery Program (IODP) Expedition 398 we will drill the submarine sequences of muds and volcanic products that fill the marine basins around the volcanoes and inside the Santorini caldera. These will provide a rich record of volcanic activity much older than that known on the islands above sea level. The drilling will access sediments and volcanic layers to depths of several hundred meters below the seabed at six sites, enabling us to reconstruct the volcanic history of the region back to 3 million years or more. Postexpedition research will then be able to show the connection of the volcanic history and how the basins formed and whether major events of faulting of the Earth's crust or earthquakes coincided with switching on or shutting down the different volcanic centers and triggering any of their large eruptions in the past. Another aim will be to improve our knowledge and understanding of the Late Bronze Age eruption regarding the amount of magma erupted and possible effects of the eruption on the Minoan civilization on the island of Crete. We will also drill through and sample the products of the submarine volcanoes of Kameni inside the Santorini caldera and Kolumbo outside of it, allowing us to reconstruct their histories and better evaluate the hazards posed by underwater explosions and tsunamis. Moreover, the sediment layers of the marine basins have recorded sea level changes and the subsidence of the Aegean region over the last few million years, enabling us to reconstruct the change from continental to marine environments with time. Finally, drilling deep inside the Santorini caldera will seek evidence for microbial life below the seafloor and how it may have responded to repeated eruptions of the volcano in the past.