Into a new caldera cycle: volcanic and magmatic evolution of Santorini volcano after the Late Bronze Age eruption

From December 2022 to February 2023, Expedition 398 of the International Ocean Discovery Program will carry out a drilling campaign in the Christiana-Santorini-Kolumbo (CSK) volcanic field in the Aegean Sea of Greece, a particularly hazardous area because its volcanoes have produced many and highly explosive eruptions in the past.

The proposed project focuses on Santorini, the largest volcanic centre of the CSK volcanic field and an iconic volcano because of its well-known eruption in the Late Bronze Age, also known as the Minoan eruption. This eruption was so powerful that it led to the collapse of the volcano, forming the flooded caldera, surrounded by the islands of Thera, Therasia and Aspronisi, and with the islands of Palaea and Nea Kameni - the surface expression of the Kameni volcano - in the centre, we see today.

The Late Bronze Age eruption was not the only caldera-forming eruption on Santorini. In total, at least four calderas existed on Santorini in the past ~ 360 thousand years, showing the cyclicity of caldera-forming eruptions.

Previous research led to considerable progress in our understanding of the assembly of magma and the timescales involved in the lead-up of these large-magnitude, caldera-forming eruptions at Santorini. By contrast, the transition from caldera-forming to post-caldera activity - or the renewed eruptive activity at the beginning of a caldera cycle - has remained largely unstudied. In case of the current caldera cycle, this is because the volcanic products from this activity are not exposed on land but lie beneath the seafloor within Santorini's caldera, therefore requiring research to move offshore.

The proposed project aims to investigate the onset of the latest caldera cycle of Santorini following the caldera-forming eruption in the Late Bronze Age, using samples from two Expedition 398 drill sites in the Santorini caldera, which, for the first time, provide the opportunity to recover previously inaccessible volcanic products from post-Late-Bronze-Age volcanic activity of the Kameni volcano. In particular, the research will characterise (1) the eruptive activity, (2) the styles and frequency of eruptions, (3) the magma storage conditions, and (4) the magmatic processes that occur at depth inside the volcano and their timescales, at the onset and during the early stages of the current caldera cycle of Santorini volcano.

The project aims will be achieved by macroscopic and microscopic drill core description, textural analysis of samples, and by characterising the geochemical composition, mineral content and other components of the magma(s) that fed the early, mainly submarine eruptions of the Kameni volcano, using a combination micro-textural analytical techniques, geochemical and petrological tools, and elemental diffusion chronometry applied to pyroxene, one of the main minerals in the eruptive products.

The results will then be used to develop a conceptual framework for the magmatic processes and their timescales at the transition from caldera-forming to post-caldera volcanic activity and the beginning of a new caldera cycle at Santorini volcano.