Steffen Kutterolf

Hydrothermal systems in volcanic calderas are critical in signalling volcanic unrest, forming ore deposits, and sustaining chemosynthetic microorganisms. Analysis of a ~3500-year sequence of sediments collected from the Santorini caldera, Greece, during International Ocean Discovery Program (IODP) Expedition 398 reveals the behaviour of a prolonged paleo-hydrothermal system. Sediment geochemical and metagenomic data record vigorous hydrothermal activity and metal fluxes for ~1100 years, within a 2270-year window between two major eruptions. Sediment hydrothermally-derived trace metals are significantly enriched over background (~200-fold for As and Hg, and 10–50-fold for Mn, Sb, Mo, and V), with long-term metal fluxes (9 t yr ⁻¹ As, 2.5 t yr ⁻¹ Cu, 7 kg yr ⁻¹ Ag) comparable to fluxes from present-day geothermal fields in the Taupo Volcanic Zone. Metagenomic analysis identifies elevated metal resistance genes—signals of microbial adaptation to heightened hydrothermal stressors. Here we integrate geological and genomic evidence to decipher the paleoenvironmental and biogeochemical history of the past hydrothermal system at Santorini caldera.

Products of explosive volcanism can be transported into the oceans, where they form marine tephra layers. The processes responsible for their deposition are often complex, involving multiple transport mechanisms. During the RV Investigator voyage IN2022‐V02 (2022), a 35‐cm‐thick marine tephra unit was piston‐cored at 2,460 m water depth in the Havre Trough, north of New Zealand. The unit grades from planar laminated medium sand at the base to cross‐laminated fine sand and massive sandy silt at the top. It is composed predominantly of elongated (tube‐shaped), vesicular, curviplanar rhyolitic glass shards, with rare lithic clasts and pyroxene and feldspar fragments enriched at the base. Planktic foraminifera occur as intact bioclasts, increasing upward from 1 to 20 vol.%. The homogeneous major and trace element composition of glass shards throughout the sequence indicates a juvenile origin from a single volcanic event. Geochemical fingerprinting identified the Macauley Volcano, located ∼100 km from the core site, as the most likely source. The stratigraphy and vertical arrangement of the bedforms are consistent with a model of sedimentation by subaerial eruption plume fallout and/or pyroclastic density currents traveling over the ocean, followed by vertical density currents through the water column that eventually transformed into seafloor‐hugging turbidity currents upon impact on the seafloor. Our results demonstrate that the sedimentary history of primary marine tephra associated with large magnitude eruptions may be complex and include vertical density currents. This sedimentation regime may significantly contribute to the lateral variation in the thickness of marine marker tephra layers.

Gravitational volcanic flank collapses are recurrent processes producing large-scale landslides, commonly associated with secondary instabilities and destructive tsunamis. Ocean island volcanoes are particularly prone to such failures, yet the dynamics, emplacement mechanisms, and tsunamigenic potential of gravitational collapses remain poorly constrained due to the scarcity of direct observations. The ~ 68 ka Monte Amarelo flank collapse at Fogo, Cabo Verde, is one of the prominent examples of tsunamigenic gravitational collapses globally. But key parameters, including the collapse volume and the number of collapse stages, remain debated. We identify an extensive (914 km ² ) debris avalanche deposit associated with the Monte Amarelo volcanic flank collapse using high-resolution multibeam bathymetry and multichannel seismic reflection data. In addition, we find a smaller, previously unknown debris avalanche deposit superimposed on the northern half of the main deposit. Our results indicate that the Monte Amarelo collapse involved up to ~ 98 km ³ of material—the first volume estimate constrained by direct imaging of the submarine debris avalanche deposit through seismic data. The local morphology and internal structure of the main deposit suggest rapid emplacement and high tsunamigenic potential. The presence of a second deposit indicates multiple stages of collapse. Our results provide new constraints on the dynamics, volume, and sequence of events of one of the most recent gravitational collapses of a volcanic island in the Atlantic. These findings have important implications for tsunami generation and modelling and contribute to an improved understanding of hazards associated with gravitational collapses of volcanic islands.

Situated in the Cabo Verde Archipelago, Fogo is among the most active oceanic volcanoes in the Atlantic, hosting frequent eruptions some of which were highly explosive and at least one gravitational flank collapse in the last 100 kyr. This study presents new volcanic glass shard geochemical data with high spatial distribution from 54 sites comprising samples from both pre- and post-collapse times. The analyzed glasses comprise basanites, tephrites, and foidites with a subset extending into the phonolite field. The glass compositions complement bulk rock data particularly in the range between 6 and 1 wt.% MgO, thus enabling more detailed inter-dataset comparison. Major and trace element data reveal five geochemical Groups characterized by incompatible element contents partly delineating rock series. Compositional diversity is primarily controlled by fractional crystallization, and to lesser extents by mantle-source heterogeneity and degrees of partial melting. A geochemical framework is established for investigating provenance of ash and volcaniclastics in the Cabo Verde region and beyond by integrating new glass data with published bulk rock and tephra records. We validate the classification scheme through comparison with primary marine tephra deposits, demonstrating robust sample assignment to the observed compositional Groups. The new provenance data go beyond simple attribution to Fogo by resolving distinct compositional Groups, enabling improved discrimination within Fogo-derived material. Group assignment and characterization of differentiation trends provide a useful first-order indication of pre- versus post-collapse affinity. The glass dataset serves as a reference for future provenance and source correlation studies across the Cabo Verde Archipelago.

Volcanism in continental rifts, rifted volcanic arcs, and back‐arc basins is fundamentally coupled with crustal extension. However, the precise geometry and timing of the fault systems that facilitate magma transport and accommodate extension remain poorly constrained. The Christiana–Santorini–Kolumbo volcanic field lies within the Santorini–Amorgos Tectonic Zone, an actively extending back‐arc rift where volcanism transitioned from dominantly effusive and moderately explosive andesitic activity (∼570–250 ka) to repeated caldera‐forming silicic eruptions after ∼250 ka. Here we integrate scientific drilling results from IODP Expedition 398 with a dense grid of high‐resolution seismic profiles and identify a previously unrecognized rift structure, the Kolumbo Graben, bounded by the NE–SW–striking Kolumbo Fault and hosting Kolumbo Volcano and the Kolumbo Volcanic Chain. Subsidence and fault throw rates across the rift system accelerated between ∼330 and ∼160 ka, with the Kolumbo Fault accommodating ∼220 m of displacement. This phase of accelerated extension preceded the emergence of Kolumbo and the onset of repeated caldera‐forming silicic eruptions at Santorini. Volcanic edifices of the Kolumbo Volcanic Chain cluster within the graben interior rather than along the master fault, indicating that distributed intra‐graben deformation and locally reduced horizontal stresses provided preferred pathways for magma ascent. Structural continuity further suggest that the Kolumbo Graben extends beneath Santorini. We conclude that accelerated rifting and strain localization exerted first‐order control on magma ascent and the transition to highly explosive volcanism over the past ∼250 kyr, while magma intrusion and associated thermal weakening likely provided a positive feedback that further localized deformation during periods of peak activity.

Extensional tectonic regimes often host volcanoes that produce highly hazardous, caldera-forming explosive eruptions. An example is the Santorini-Kolumbo volcanic centre on the continental South Aegean Volcanic Arc. The volcanic centre includes Santorini caldera, the submarine polygenetic Kolumbo Volcano to the northeast of Santorini, and the linear zone of more than 20 smaller volcanic cones making up the Kolumbo Volcanic Chain. It is one of the most active eruptive centres on the South Aegean Volcanic Arc and experienced a period of unrest in 2024-2025. IODP Expedition 398 deep-drilled the volcano-sedimentary infills of submarine half-grabens around Santorini and on the western flank of Kolumbo in order to produce a high-resolution eruptive chronostratigraphy for the volcanic field, ground-truth seismic stratigraphy, and to extract an integrated timeline of interactions between the neighbouring volcanoes and volcano-tectonic couplings. In the new, more complete volcanic record, we: (1) recognise a transition of Santorini from moderately explosive, arc stratovolcano behaviour (~570 – 250 ka) to repeated caldera-forming behaviour (

The establishment of continuous volcanic time series is a key to understanding the volcanic evolution and behaviour of arc systems and volcanic complexes. Yet the establishment of continuous records is often hindered by incomplete volcanic archives on land due to erosion or inaccessibility of volcanic deposits. Growing steadily over the past decades, the field of marine tephra studies has shown great potential in overcoming these issues. As marine drilling techniques advance, they now enable the recovery of continuous and undisturbed marine sediment records, often even extending the volcanic onland records significantly further back in time. Drilling close to volcanically active environments, like volcanic arcs, provides the most complete eruptive archive possible and therefore allows us to unravel the volcanic and magmatic behaviour of volcanic systems over geologically long periods of time. Furthermore these long and continuous records enable multi-disciplinary studies, such as the establishment of volcano-tectonic or volcano-climate relationships.IODP Expedition 398 drilled the marine sediments in the basins of the Christiana-Santorini-Kolumbo Volcanic Field (CSKVF) with the aim of expanding our knowledge of its volcanic evolution, and its interaction with tectonics and climate. The CSKVF belongs to the South Aegean Volcanic Arc (Greece), and particularly Santorini has been known for its highly explosive volcanism and caldera-forming eruptions since c. 250 ka that laid down the Thera Pyroclastic Formation (TPF). Before that, Santorini’s volcanic activity has been described as mainly effusive to weakly explosive forming the Peristeria stratocone (c. 530-430 ka) and the Early Centres of Akrotiri (c. 650-550 ka). However, IODP Expedition 398 identified a large submarine rhyolite deposit, the Archaeos Tuff (AT), interpreted as the product of a highly explosive submarine eruption of Santorini occurring at c. 765 ka, clearly pushing the boundaries of the unkown.Here, we present the revised

Over the last two decades, tephrochronology has become a fundamental tool for high-resolution stratigraphy, providing constraints for dating, correlation, and synchronization applicable to various Earth sciences disciplines. In coastal and island volcanic settings, the analysis of the texture, mineralogy, and geochemistry of volcanic particles allows the identification of the source volcanoes and the reconstruction of eruptive histories, also providing crucial information on associated hazards, such as slope collapse and tsunamis.In this study, we applied an integrated tephrochronological, sedimentological, and geochemical approach to three marine sediment cores collected ~30–43 km northwest of Stromboli volcano (southern Tyrrhenian Sea). Marine sedimentary sequences are particularly valuable in this context because they preserve both turbidite sequences produced by past volcanic flank collapses and tephra deposits from nearby volcanoes, providing essential chronological constraints. The cores consist of epiclastic sediments and hemipelagic muds intercalated with volcaniclastic deposits, which were divided into three main types: (a) primary tephra (and cryptotephra) layers, representing direct fallout deposits from explosive eruptions; (b) mono-magmatic volcaniclastic turbidites that were directly linked to collapse events of the north flank of Stromboli; (c) multi-magmatic volcaniclastic turbidites resulting from the mixing of materials from multiple volcanic sources during transport through the Stromboli channel. We focused on the upper 2 m of the cores, representing the Holocene period, where sedimentological and geochemical analysis allowed the identification of three primary tephra layers, which could be correlated with well-known eruptions on land. These include the Vallone Gabellotto rhyolitic tephra (~9–8.7 ka) at the base of the investigated sections and which constrains the record to the last ~10 kyr, a high-K trachyandesitic tephra related to Neostromboli explosive activity (~8.7–6 ka), and the Monte Pilato rhyolitic tephra (~1.2 ka BP) near the top of the cores. Together, these markers provide a solid time frame for constraining the ages of the intercalated volcaniclastic deposits. Within this framework, at least 8 mono-magmatic volcaniclastic turbidites were identified that are geochemically correlated with the main eruptive periods of Stromboli. Due to their homogeneous compositions, we interpreted these turbidites as genetically related to collapse events at the flank of Stromboli, implying that at least 8 large-scale landslide events have occurred at Stromboli during the Holocene. Compared with the 2002 tsunamigenic landslide (~30 × 10⁶ m³), the landslide volumes estimated from the turbidite thicknesses (~45 × 10⁶ to ~58.5 × 107 m³) suggest that all were of higher magnitude and potentially tsunamigenic.This study highlights how marine tephrochronology represents an effective tool to reconstruct volcanic events and associated risks, providing crucial data for hazard assessment and mitigation strategy development in the southern Tyrrhenian Sea.

The polycyclic Santorini caldera (Greece) has entered a new caldera cycle following the large-magnitude Late Bronze Age (Minoan) eruption1. In this new caldera cycle, low-magnitude effusive and mildly explosive eruptions have built up the Kameni islands inside the flooded Minoan caldera. However, an eruption deposit up to 34 m thick was recovered during the International Ocean Discovery Program (IODP) Expedition 398 to the South Aegean Volcanic Arc2 at various sites inside the Santorini caldera (U1594-U1597) and has been interpreted as produced by an explosive (VEI 5) eruption in 726 CE3. Such explosive eruptions are uncommon in the early stages of caldera cycles when the plumbing system is recharging, and the shallow magma reservoir is recovering from caldera collapse. The indication that Santorini can produce explosive eruptions early in a new caldera cycle elevates the hazard potential of future eruptions for Santorini and neighbouring islands in the eastern Mediterranean.This study presents a petrological and geochemical investigation of juvenile material from the 726 CE eruption deposit at IODP Site U1595, encompassing the full thickness of the deposit, including light and dark grey pumice, banded pumice, scoria, mafic enclaves, dark cognate lithics and glomerocrysts. We also report the results of diffusion chronometry on the primary crystal phases, including Fe-Mg diffusion in orthopyroxene and clinopyroxene, and Mg diffusion in plagioclase. Crystal chemistry reveals the presence of mafic (Mg# 84-73 and An 86-82), intermediate (Mg# 71-69 and An 67-57), and more silicic (Mg# 67-54 and An 53-37) crystal assemblages derived from compositionally distinct magmatic sources beneath the volcano, as well as a crystal mush zone, with evidence of crystal exchange between these reservoirs. By modelling reverse-, normally- and oscillatory-zoned core-rim profiles using diffusion chronology, we constrain mafic and silicic magma recharge timescales, revealing the complex recharge dynamics of the plumbing system associated with the 726 CE eruption. Plagioclase-, clinopyroxene-, and orthopyroxene-hosted melt inclusions of dacitic composition record water concentrations between 3.1-6.1 wt% H2O (average of 4.5 wt% H2O and CO2 concentrations below detection limits (

Santorini-Kolumbo is one of the most hazardous volcanic centres in Europe, as highlighted by its VEI-5 explosive eruptions of 726 CE and 1650 CE, and its bradyseismic crises of 2011-12 and 2024-2025. IODP Expedition 398 deep-drilled the volcano-sedimentary infills of marine rift basins at eight sites around Santorini to depths of up to 900 m below the sea floor, and integrated the core stratigraphies with a dense array of seismic profiles from eight expeditions to construct a high-resolution timeline of volcanic activity and to relate it to the basin-fill architecture and tectonic history. In this overview we show that the four drill sites analyzed to date reveal >200 Santorini and 19 Kolumbo tephra layers intercalated in marine sediments. The tephras were correlated chemically between sites, either as the products of individual eruptions or as packages of layers, with the onset of explosive activity at ~1 Ma. The rift basins contain several submarine volcaniclastic megabeds from the caldera-forming eruptions of Santorini and one from the Kos caldera. The megabeds formed when pyroclastic flows poured into the sea and transformed into subaqueous gravity flows. The thickest megabed succession is < 250 ky old and lies on a seismic reflection onlap surface that records a phase of rapid rifting. Sedimentation lagged behind subsidence during rapid rifting, creating bathymetric troughs that served as depocenters for the megabeds. Reconstruction of the basin subsidence history shows that the rift extension rate accelerated markedly about 350 ky ago. This increase in rifting rate preceded, and may have driven, the transition of Santorini from a prolonged state of effusive and moderate explosive activity (~550 – 250 ka) typical of arc stratovolcanoes to one of repeated caldera-forming eruptions (