Katharina Pank

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.

Long‐term tephrostratigraphies of volcanic islands such as the Azores are often limited to young and incomplete subaerial records. Here, we present a Pleistocene‐Holocene marine tephra archive around the eastern islands of the Azores based on 22 marine gravity cores. We provide a new extensive data set comprising major element glass compositions of 350 marine tephra layers and 26 tephra samples collected from subaerial outcrops on São Miguel Island. The marine tephra record is dominated by trachytic glass compositions with lesser amounts of trachy‐basaltic/basaltic materials. We categorize the marine deposits into four facies: primary fall (F1), primary flow (F2), eruption‐related secondary flow (F3), and non‐eruption‐related secondary flow deposits (F4). Cores collected close to the islands contain a high proportion (>50%) of volcaniclastic material deposited during secondary processes. Using machine‐learning algorithms, we assign potential volcanic sources to individual tephra layers. Furthermore, our spatial characterization of primary/secondary deposits demonstrates the importance of carefully selecting core locations during sea‐going campaigns, as the preservation and distribution of primary and reworked tephras considerably differ depending on several factors (e.g., on paleo‐wind directions, island topography, seafloor bathymetry, and distance from source volcanoes). We also report the occurrence of mafic primary fall tephras tens to hundreds kilometers away from the closest island, indicating a potential hazard from mafic Plinian eruptions in the Azores. This study aims to improve the estimation of the eruptive frequency of the archipelago and opens new pathways for more detailed studies concerning long‐term volcanic cyclicity in the region.

Data report: visible to shortwave infrared (VSWIR) spectroscopic scanning of selected core sections from Holes U1589A and U1591C, IODP Expedition 398, Hellenic Arc Volcanic Field

Large explosive volcanic eruptions from island volcanoes deliver vast quantities of ash to the marine environment. While many of the transport pathways are understood, those from shoreline-crossing or submarine pyroclastic currents, and their transformation into water-supported gravity flows, remain poorly constrained. We report the discovery by International Ocean Discovery Program (IODP) deep drilling of a 200-meter-thick ash megabed buried in rift basins of the South Aegean Volcanic Arc. The >73–cubic kilometer ash deposit originates from the Kos Plateau Tuff caldera-forming eruption, which occurred 161 thousand years ago, >120 kilometers to the east. The ash forms a chemically uniform, graded megabed lacking bioturbation, interpreted as having been emplaced by a stream of eruption-fed turbidity currents. Bioclastic debris within the ash provides evidence of widespread destruction of marine ecosystems. Large volcanic eruptions can remodel the seafloor landscape, deposit thick ash turbidites, and destroy marine biota on island arc–wide scales in short-lived, catastrophic events.

Subseafloor in situ temperatures in a drilled hole in the Anhydros Basin, Aegean Sea, measured during International Ocean Discovery Program (IODP) Expedition 398, yielded a low heat flow (2) despite active magmatism and rifting in the region. The coldest and highest temperatures were 13.9°C at 52.5 m below seafloor (mbsf) and 15.5°C for the deepest measurement at 360.4 mbsf, respectively. Comparison of a heat transfer model with measurements suggests that sea bottom temperatures during the last glacial period were up to 10°C cooler than Holocene temperatures. The magnitude of Holocene warming co‐varies with the geothermal heat flow: if the former goes up the latter goes up. Low heat flow may arise from lateral removal of heat through deeper formations by gravity driven advection of fluids. Tectonic separation of the northwestern Anhydros Basin from the Christiana‐Santorini‐Kolumbo volcanic field may lead to minimal magmatic influences on heat flow.

Data report: core-seismic integration and time-depth relationships at IODP Expedition 398 Hellenic Arc Volcanic Field sites

Data report: X-ray fluorescence scanning of Sites U1591 and U1599, IODP Expedition 398, Hellenic Arc Volcanic Field