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Evidence for a Hydrothermal Event in Santorini's Caldera Preceding a Large Volcanic Eruption

Sofia Della Sala 1, Joost Frieling1, David Pyle1, Tamsin Mather1, Tim Druitt2, Steffen Kutterolf3, Thomas Ronge4 & Expedition 398 scientists

  • Affiliations: 1Department of Earth Sciences, University of Oxford, UK; 2Laboratoire Magmas et Volcans, Université Clermont Auvergne, F-63000 Clermont-Ferrand, France; 3Research Division 4: Dynamics of the Ocean Floor, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany; 4JRSO-IODP at Texas A&M University, College Station, Texas, USA 

  • Presentation type: Talk

  • Presentation time: Tuesday 09:00 - 09:15, Room R290

  • Programme No: 6.2.3

  • Theme 6 > Session 2

Abstract

Santorini is a mature volcanic system located in the South Aegean volcanic arc. Though its eruptive history is well-studied, the post-caldera evolution of the volcanic and hydrothermal systems remains poorly understood. Our objective is to understand the relationship between volcanic eruptions and hydrothermal activity within the caldera. This study focuses on the chemical analysis of samples from seafloor sediment cores collected from the Santorini caldera during International Ocean Discovery Program (IODP) Expedition 398 in 2023. Samples from four sites (U1594-U1597), which penetrated between depths 45 and 130 meters below the sea floor (mbsf), were selected to obtain a comprehensive record of volcanic and sedimentary activity since the last caldera-forming eruption 3600 years ago. The sediment record is hypothesized to include both subaerial and submarine eruptive products from the young, intra-caldera edifice (Kameni Islands) that has progressively grown. The aim of our study is to detect past episodes of hydrothermal activity by examining trace metal enrichment patterns in accumulating sediments. Our hypothesis is that sedimentary units show enrichments in elements that are typically elevated in hydrothermal fluids, indicating heightened activity. We present results for down-core concentrations of strongly enriched elements, in particular Hg, Sb, Mo and Mn, where a key horizon between 55 and 60mbsf shows particularly elevated concentrations of these elements---consistent with a period of strong hydrothermal activity prior to a large eruption of Kameni in 726 CE. We draw comparisons with the present-day hydrothermal fields, and explore ways to constrain the extent and significance of this ancient hydrothermal event.