Night shifts, drill cores, and sunrises: extending Santorini’s eruptive record on IODP Expedition 398

Ally Peccia – Columbia University, Lamont-Doherty Earth Observatory

Life on the R/V JOIDES Resolution

Before the winter of 2022, I’d only seen a handful of sunrises in my life and rarely on purpose. That winter, I would have the pleasure of witnessing 58 consecutive sunrises (from 14 December 2022 to 10 February 2023) each morning, from the upper deck of the R/V JOIDES Resolution. The first few took place while tied up in the Port de Tarragona just south of Barcelona, Spain as I was painfully adjusting to my new work schedule: 12 AM to 12 PM, every day, for the next two months.

I’d applied to sail on International Ocean Drilling Program (IODP) Expedition 398 to the Hellenic Arc just a year prior, in the “freshman fall” of my PhD. Having recently completed a project on the climate impact of the 43 BCE eruption of Okmok Volcano in Alaska, I was fascinated by the idea that volcanoes themselves might respond to changes in their environment. Santorini, an island arc volcano with a long history of explosive eruptions, seemed the perfect place to explore this idea, using ocean drilling to probe into the volcano’s deep past. The expedition organizers agreed, and invited me to sail as an Igneous Petrologist on the Core Description team (though, it did not mention I’d been assigned the night shift!). But as we set sail across the Mediterranean Sea we were blessed with a particularly breathtaking sunrise (Fig. 1), and my nocturnal grogginess eased. We continued east around Sicily and past the tip of Crete, towards a journey full of surprises, little sleep, and many more moments of awe.

The first “core on deck,” arrived several hours past my 1 PM bedtime. Still, we gathered excitedly to examine the contents of our very first sample: a few stray pieces of stark white pumice from the 1650 CE eruption of the submarine volcano Kolumbo, buried in the top meters of the underlying seafloor (Fig. 2). Over the following weeks, I would become so accustomed to seeing vast amounts and varieties of white pumice, that I began to dream of it. As a member of the core description team, I was responsible for characterizing every centimeter of material we recovered in our drilling efforts, which included information about the color, grain size, and most importantly, the lithology of the sediments we liberated from beneath the sea. Though tedious to make, our descriptions were important: they formed the basis for observations by other shipboard scientists (including Physical Properties, Biostratigraphy, Geochemistry, Microbiology, Paleomagnetism, Structural Geology, and Stratigraphic Correlation teams) and will serve as a guiding resource for any future scientists interested in studying Expedition 398 cores.

In the spirit of collaboration, the night shift core description and physical properties teams had developed a sacred tradition of making elaborate sandwiches together during our 3 AM “cookie break,” which often led to a full-belly crash directly after. The full brunt of exhaustion imparted by day after day of tedious work always hit me the hardest in these long hours, and I would begin to question why I had willingly subjected myself to such an experience.

With my fatigue soothed by a bespoke latte from the ship’s espresso machine, I was able to see the value of the experience I had been offered more clearly: though I had worked with drill cores in repositories prior to the expedition, seeing the entire process from expedition planning, shipboard collection, and eventual transport to a repository gave me a new appreciation for the efforts of cataloging such a geological library. In the seemingly unending stretch from 3 AM to sunrise, I came back time and time again to appreciate the legacy of expeditions like the one I was on: how the cores we collected would serve as an invaluable resource for many decades to come, being used to answer questions we couldn’t even dream of. I also began to appreciate the role that IODP and this expedition would play in my personal legacy. The expertise I was developing onboard was crucial to defining my own narrative as a novice scientist, and I was fascinated with the process unfolding before my eyes. Most importantly, I realized that the relationships I had formed over middle-of-the-night sandwich breaks would be what carried me through moments of uncertainty and discomfort. We were a team, and we were capable of far more than any of us on our own.

Discovering the Archaeos Tuff

As we drilled at numerous sites in the basins around Santorini (see Fig. 3 for map of sites), the fruits of our labor became apparent– in every basin, we had recovered a thick pumice deposit that did not correlate with any known eruption of Santorini from on land studies. Further, the density of the pumice and thick, graded nature of the deposits implied that it had largely been emplaced in submarine gravity flows, and the presence of certain foraminifera and microfossils suggest the eruption occurred around 520 ka. Now named the “Archaeos Tuff”, these findings were published in Nature Communications in January 2024. The entire ship buzzed with excitement as we realized just how much we might be missing from the geologic past of Santorini, and how much we might find buried in the seafloor.

Drilling inside Santorini Caldera – the 726 CE eruption

Another of these surprises came on the opposite end of Santorini’s volcanic past, with new insights about the nature of the 726 CE eruption from the intracaldera Kameni edifice. As a “multicyclic caldera,” Santorini has experienced several phases of edifice rebuilding and collapse, with the rebuilding phase thought to consist of effusive and small explosive eruptions in contrast to the massive and catastrophic, caldera-forming eruptions– the last of which occurred in ~1600 BCE, initiating a new caldera cycle. This line of thought came into direct relevance during a recent phase of unrest at Santorini in 2011-2012, when scientists, politicians, and local Santorini residents were forced to consider the possibility of an imminent eruption of Kameni Volcano. Hazard assessments suggested an eruption of Kameni would pose a relatively modest risk, based on the primarily effusive history deduced from historical descriptions and the exposed outcrops on Kameni. Thankfully, no eruption ensued. The crisis, however, prompted a renewed motivation for studying the recent eruptive past of Kameni in order to better understand present day threats to the heavily populated and touristed island. This was another charge of Expedition 398, and in order to fulfill this mission, we’d need to get a much closer look: from inside of the caldera.

Drilling inside the caldera was exhilarating. Having lived in New York City for 8 years, I was not accustomed to having even a single day absent the presence of strangers, let alone 58 in a row. And though I greatly enjoyed the company of my shipmates, we were admittedly going a bit sea crazy by the time we entered the caldera. Seeing and smelling land so close after spending weeks at sea gave me a fresh bout of homesickness, and I swore I could make out intrepid February vacationers sipping Aperol from the luxurious white terraces overhead. I felt affronted by the sheer normality of the daily activities of the islanders, as so much of my life for the past weeks had involved inspecting the remnants of the destructive forces that lay just beneath the surface. The two realities harshly abutted one another, and I began to truly understand the relevance of our work beyond pure scientific curiosity– although many moments on the ship felt isolated or in a vacuum, the work we were doing was intimately connected to people past, present, and future.

On our first day drilling inside the caldera, it quickly became clear that we’d have to contend with challenges outside of those purely volcanic in nature. As we’d already experienced several times, thick deposits of unconsolidated pumice made drilling quite difficult. Not only was the drill hole vulnerable to collapsing in on itself, the finer ash mixed with seawater and nannofossil ooze formed a sticky, “Oobleck”-like substance (as Project Manager Thomas Ronge later identified, all the ingredients necessary to form Roman concrete) that inhibited the removal of the drill string. This exact instance had necessitated “severing” of the drill string two times already, which involved the detonation of explosive cutting charges within the pipe to free the drill string. The drilling challenges we’d faced at previous sites left us low on supplies, and another misstep could put an early end to our expedition. We felt the high stakes as we began our activities in the center stage of the caldera, the cliffs above us rising like an amphitheater.

Quick thinking and expertise on behalf of the drilling crew allowed us to avoid expedition-ending difficulties in such uncertain circumstances, while also recovering cores that would hold vital information about Kameni’s past. We discovered that the 726 CE eruption of Kameni Volcano was significantly larger and more explosive than previously thought, similar in size to the VEI 5 eruption of Mt. St. Helens in 1980. Further, the integration of the lithologies determined in our cores with seismic imaging efforts shows that the Kameni edifice is built upon unconsolidated pumice deposits and may be at risk of a flank collapse: another potential hazard to the residents of Santorini and the greater Aegean region. Recently published in Nature Geoscience, these findings change the picture of hazard assessment should future unrest of Santorini occur and rework our understanding of the types of eruptions that characterize interplinian or caldera building phases.

Perspectives on submarine volcanism

The discovery of both the Archaeos Tuff and the explosive deposits from the 726 CE Kameni eruption highlight the gaping blindspot in our knowledge of island arc volcanoes: submarine eruptions. Because these eruptions occurred at least partially in the submarine realm, their deposits are largely hidden from the eyes of land-bound geological observers. In the case of Santorini, deep sea drilling has allowed us to fill in the submarine record, where it might otherwise be missed– my future research intends to understand how Santorini’s magma system responds to external tectonic and climate-driven forcing, utilizing the more complete marine record of its past eruptions. However, the global picture of submarine volcanism remains underdeveloped. The submarine eruption of Hunga Tonga–Hunga Haʻapai in 2022 occurred with little warning and jettisoned a plume 58 km high, demonstrating the power of an eruption that could easily be missed in the continental record. Only through the study of submarine deposits from eruptions past can we resolve this gap in our understanding.

References

Druitt, T., Kutterolf, S., Ronge, T.A. et al. Giant offshore pumice deposit records a shallow submarine explosive eruption of ancestral Santorini. Commun Earth Environ 5, 24 (2024). https://doi.org/10.1038/s43247-023-01171-z

Preine, J., Karstens, J., Hübscher, C. et al. Hazardous explosive eruptions of a recharging multi-cyclic island arc caldera. Nat. Geosci. 17, 323–331 (2024). https://doi.org/10.1038/s41561-024-01392-7

About the author

Her time on IODP Expedition 398 prompted her to think about volcano-climate interactions on longer timescales: she aims to characterize the volatile content of Santorini magmas over the lifetime of the volcanic arc, and evaluate whether external forcing such as tectonic and sea level changes influence the subsurface magmatic system.

You can get in contact with Ally via email or connect with her on X @asapeccia .

Would you like to be featured on our blog?

We’re on the hunt for fellow VIPS enthusiasts to share their stories, whether you’re a student, an early career researcher (ECR) or more experienced researcher – we want to hear from you!

Do you have a new paper to tell the world about? Or have you been involved in some exciting fieldwork recently? Get in touch at info@vipscommission.org to tell us what’s going on in your field of VIPS.