The objectives of International Ocean Discovery Program Expedition 398, Hellenic Arc Volcanic Field (11 December 2022 to 10 February 2023), were to study the volcanic record of the central Hellenic island arc; document the links and feedbacks between volcanism/magmatism, crustal tectonics, and sea level; investigate the processes and products of shallow submarine eruptions of silicic magma; and groundtruth the seismic stratigraphy of Santorini caldera. Reconstructing the subsidence history of the southern Aegean Sea and searching for deep life inside and outside of Santorini caldera were additional objectives.
During the expedition, 10 primary and alternate sites that were originally proposed were drilled, in addition to 2 extra sites that were requested during the expedition. Outside of Santorini caldera, drilling penetrated the thick basin fills of the crustal rift system hosting the Christiana-Santorini-Kolumbo volcanic field, identifying numerous pumice and ash layers, some known from on land and others hitherto unknown, pushing back the onset of volcanism in the area into the Early Pleistocene or even Pliocene. Significant events of mass wasting into the basins, accompanied by very high sedimentation rates, were also documented. These basin sites served to groundtruth the seismic stratigraphy of the basins and open the way to unraveling relationships between volcanic activity and crustal rift pulses. Two sites of condensed sequences served to sample many volcanic layers within the detailed age-depth constraints provided mainly by biostratigraphy, as diagenetic effects complicated the magnetic reversal record significantly. Drilling penetrated the Alpine basement at three basin sites northeast of Santorini, whereas in the Christiana Basin to the southwest it penetrated a thick sequence of Messinian evaporites. Drilling inside Santorini caldera penetrated to ~120 meters below seafloor, less than planned due to hole instability issues but deep enough to groundtruth the seismic stratigraphy and sample the different layers. One intracaldera hole yielded a detailed tephra record of the history of the Kameni Islands, as well as possible evidence for deep bacterial colonies within the caldera. Despite variable recovery in the unstable pumice and ash deposits, the expedition was a significant success that may address almost all the scientific objectives once the laboratory work has been done.
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Expedition 398 Preliminary Report: Hellenic Arc Volcanic Field
The objectives of International Ocean Discovery Program (IODP) Expedition 398, Hellenic Arc Volcanic Field (11 December 2022 to 10 February 2023), were to study the volcanic record of the central Hellenic island arc; document the links and feedbacks between volcanism/magmatism, crustal tectonics, and sea level; investigate the processes and products of shallow submarine eruptions of silicic magma; and groundtruth the seismic stratigraphy of Santorini caldera. Reconstructing the subsidence history of the southern Aegean Sea and searching for deep life inside and outside of Santorini caldera were additional objectives.
The expedition drilled 10 primary and alternate sites that were originally proposed, in addition to 2 extra sites that were requested during the expedition. Outside of Santorini caldera, drilling penetrated the thick basin fills of the crustal rift system hosting the Christiana-Santorini-Kolumbo volcanic field, identifying numerous pumice and ash layers, some known from on land and others hitherto unknown, pushing back the onset of volcanism in the area into the Early Pleistocene or even Pliocene. Significant events of mass wasting into the basins, accompanied by very high sedimentation rates, were also documented. These basin sites served to groundtruth the seismic stratigraphy of the basins and to open the way to unraveling relationships between volcanic activity and crustal rift pulses. Two sites of condensed sequences on the basin margins served to sample many volcanic layers within the detailed age-depth constraints provided mainly by biostratigraphy, as diagenetic effects complicated the magnetic reversal record significantly. Drilling penetrated the Alpine basement at three basin sites northeast of Santorini, whereas in the Christiana Basin to the southwest it penetrated a thick sequence of Messinian evaporites. Drilling inside Santorini caldera penetrated to ~120 meters below seafloor (mbsf), less than planned due to hole instability issues but deep enough to groundtruth the seismic stratigraphy and to sample the different layers. One intracaldera hole yielded a detailed tephra record of the history of the Kameni Islands, as well as possible evidence for deep bacterial colonies within the caldera. Despite variable recovery in the unstable pumice and ash deposits, the expedition was a significant success that may address almost all the science objectives once the laboratory work has been done.
A dense program of preexpedition and shipboard outreach during the expedition gave rise to 59 live ship-to-shore tours, reaching 6,400 people in 7 countries including many school children. A total of 51 journalists were contacted and 9 stories were written about the expedition, with a readership of almost 200,000 people. While in Santorini caldera, the ship hosted 12 documentarians and journalists, the future products of whom should include a 1.5 h documentary and a four-part TV series about Expedition 398. The expedition social media pages were active. Prior to the expedition, an exhibition, “In Search of Earth’s Secrets,” ran for a week on Santorini and was visited by more than 1,800 school children.
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- Award ID(s):
- 1326927
- PAR ID:
- 10486076
- Publisher / Repository:
- International Ocean Discovery Program
- Date Published:
- Journal Name:
- Preliminary report
- Volume:
- 398
- ISSN:
- 2372-9562
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The objectives of International Ocean Discovery Program Expedition 398, Hellenic Arc Volcanic Field (11 December 2022 to 10 February 2023), were to study the volcanic record of the central Hellenic island arc; document the links and feedbacks between volcanism/magmatism, crustal tectonics, and sea level; investigate the processes and products of shallow submarine eruptions of silicic magma; and groundtruth the seismic stratigraphy of Santorini caldera. Reconstructing the subsidence history of the southern Aegean Sea and searching for deep life inside and outside of Santorini caldera were additional objectives. During the expedition, 10 primary and alternate sites that were originally proposed were drilled, in addition to 2 extra sites that were requested during the expedition. Outside of Santorini caldera, drilling penetrated the thick basin fills of the crustal rift system hosting the Christiana-Santorini-Kolumbo volcanic field, identifying numerous pumice and ash layers, some known from on land and others hitherto unknown, pushing back the onset of volcanism in the area into the Early Pleistocene or even Pliocene. Significant events of mass wasting into the basins, accompanied by very high sedimentation rates, were also documented. These basin sites served to groundtruth the seismic stratigraphy of the basins and open the way to unraveling relationships between volcanic activity and crustal rift pulses. Two sites of condensed sequences served to sample many volcanic layers within the detailed age-depth constraints provided mainly by biostratigraphy, as diagenetic effects complicated the magnetic reversal record significantly. Drilling penetrated the Alpine basement at three basin sites northeast of Santorini, whereas in the Christiana Basin to the southwest it penetrated a thick sequence of Messinian evaporites. Drilling inside Santorini caldera penetrated to ~120 meters below seafloor, less than planned due to hole instability issues but deep enough to groundtruth the seismic stratigraphy and sample the different layers. One intracaldera hole yielded a detailed tephra record of the history of the Kameni Islands, as well as possible evidence for deep bacterial colonies within the caldera. Despite variable recovery in the unstable pumice and ash deposits, the expedition was a significant success that may address almost all the scientific objectives once the laboratory work has been done.more » « less
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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.more » « less
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Site U1599 is located ~6 km north of Anafi Island within the upper reaches of the Anafi Basin at a water depth of 592 meters below sea level (mbsl) (Figure F1). Permission to drill in this location was granted by the International Ocean Discovery Program (IODP) Environmental Protection and Safety Panel during the expedition (proposed Site CSK-22A). Three holes (U1599A–U1599C) were drilled to a maximum recovery depth of 698.1 meters below seafloor (mbsf) (all depths below seafloor are given using the core depth below seafloor, Method A [CSF-A] scale, except in Operations, where the drilling depth below seafloor [DSF] scale is used), with average hole core recoveries ranging 51%–83% (Figure F2). Whereas Site U1592 is situated on the axis of the Anafi Basin and penetrated a thick basin fill including mass-transported material, Site U1599 is located on the southeast margin of the basin. It was chosen to offer a condensed sequence of tephra without quantities of mass-wasting debris. As such, it provided a complete stratigraphy of volcanic tephra from Santorini and Kolumbo. The same six seismic units (U1–U6, from the bottom up; Preine et al., 2022a, 2022b) present at Site U1592 are present at Site U1599. Site U1599 is located within the area of the 2015 PROTEUS seismic tomography experiment, during which subbottom profiling, gravity, and magnetic data were also recorded (Hooft et al., 2017). Drilling at Site U1599 enabled us to reconstruct a near-complete volcanic stratigraphy consistent with both onshore and offshore constraints and pinned by chronological markers from biostratigraphy, magnetostratigraphy, and sapropel records. Benthic foraminifera from fine-grained sediments provided estimates of paleowater depths and, via integration with seismic profiles and chronologic data, of time-integrated basin subsidence rates. Drilling in the Anafi Basin addressed scientific Objectives 1–4 and 6 of the Expedition 398 Scientific Prospectus (Druitt et al., 2022). It was complemented by Site U1589 in the Anhydros Basin because each basin tapped a different sediment distributary branch of the Christiana-Santorini-Kolumbo volcanic system.more » « less
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Site U1598 (proposed Site 14A) is located ~8 km northwest of Christiana Island and ~20 km southwest of Santorini (Figure F1) at 521.5 meters below sea level (mbsl). The drill site targeted the volcano-sedimentary fill of the Christiana Basin in two holes (U1598A and U1598B), with a maximum recovery depth of 95.7 meters below seafloor (mbsf) (all depths below seafloor are given using the core depth below seafloor, Method A [CSF-A], scale, except in Operations where the drilling depth below seafloor [DSF] scale is used) and core recoveries of 69% and 34%, respectively. The drill site targeted the volcano-sedimentary fill of the Christiana Basin. This basin was believed to have formed by subsidence along an ENE–WSW fault system before the changing tectonic regime activated the current northeast–southwest rift system in which the Christiana-Santorini-Kolumbo (CSK) volcanic field lies (Tsampouraki-Kraounaki and Sakellariou, 2018; Preine et al., 2022a, 2022b). The Christiana Basin is deeper than the Anhydros and Anafi Basins; its volcano-sedimentary fill potentially recorded the earlier volcanic history of the CSK volcanic field (including the products of Christiana and early Santorini), as well as the younger Santorini and possibly the Milos Volcano to the west along the Hellenic volcanic arc. The now-extinct Christiana Volcano produced lavas and tuffs of unknown ages (Aarburg and Frechen, 1999). An ignimbrite found on Christiani Island (one of the two small islands of the Christiana Volcano), Santorini, and the nonvolcanic island of Anaphi, called the Christiani Ignimbrite, was identified (Keller et al., 2010). Site U1598 was chosen to complement the previously drilled Site U1591. The aim was to retarget a thick pumice layer found at Site U1591 (uppermost ~65 mbsf; Figure F2), for which we had insufficient samples for our scientific aims, to increase our recovery of the interval. The site addresses scientific Objectives 1–4 and 6 of the Expedition 398 Scientific Prospectus (Druitt et al., 2022).more » « less
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