The Hellenic arc – comprising the Santorini, Christiana, and Kolumbo volcanic centres in Greece’s Aegean Sea – is one of Europe’s most active volcanic centres. It is also particularly hazardous, producing many highly explosive eruptions with catastrophic impacts throughout Earth’s history.

IODP Expedition 398: Hellenic Arc Volcanic Field, onboard the JOIDES Resolution from 11 December 2022 until 10 February 2023, will drill deep into the sediments around these volcanoes and inside Santorini caldera to provide a rich record of volcanic activity extending back around three million years. Growing our understanding of island arc volcanism is crucial work, with roughly 800 million people across the globe threatened by volcanic eruptions. 

University of Tasmania PhD candidate Acacia Clark will represent ANZIC in the Onboard Science Party for the expedition, while Victoria University of Wellington Post Doctoral Research Fellow Dr Jenni Hopkins will join the Onshore Science Party. We spoke with Acacia as she prepared to fly out ahead of boarding.

Q&A with Acacia Clark, University of Tasmania

Tell us a little about your career and research to date.

I’m about 18 months into my PhD at UTas, where I’m investigating explosive silicic eruptions. I’ve divided my PhD into two parts; the first is focused on Mount Tarawera in the North Island of New Zealand, looking at the 1315 CE Kaharoa eruption which fluctuated in intensity over short time periods. This is unusually unsteady behaviour that isn’t well understood. I’m looking at what influenced that unsteadiness, and because it was quite a hazardous eruption. If something similar was to happen again, it would be devastating for New Zealand and probably also for Australia so it’s really important to understand as much as possible about this eruption. 

The second part is focused on the Hellenic arc in the Mediterranean, and that’s where the expedition comes into play. Silicic eruptions also occur underwater, but we don’t know much about silicic submarine eruptions – they’re hard to get to given they’re under a lot of water so we don’t have much data. On Expedition 398, we’ll be able to drill into the sediments that are surrounding these underwater volcanoes to gain high-resolution data from these eruptions and help us understand how these submarine eruptions can be quite different to those on land.


What is your specific role on the expedition?

My role is as a core describer, so I’ll be looking in high detail at the cores once they come onboard and describing and logging what I see. This includes looking at the different materials that the core is made up of, such as volcanic ash, pebble-sized volcanic products known as lapilli, or marine sediments. I was lucky enough to sail as a core describer on an expedition earlier this year on RV Investigator where we also drilled for sediments containing volcanic tephra, so I have some experience going in.


What are the key questions that Expedition 398 seeks to answer through the sediments that you’ll be examining?

Volcanic eruptions, particularly highly explosive ones, are very hazardous and life threatening. They produce huge ash plumes, very hot ground-hugging ash and rock flows, and even earthquakes and tsunamis. To understand how these hazards are linked to volcanic activity, we have to look at what’s driving that volcanism and how these volcanoes interact with their surroundings, whether these are terrestrial or marine environments. During the expedition, we’re going to explore questions around the links between the crustal tectonics, volcanic activity and magma genesis, the dynamics and impacts of explosive submarine volcanic and caldera forming activity, and how calderas collapse during explosive eruptions and recover to enter new magmatic cycles. We’ll also be touching on how the marine ecosystem reacts to volcanic eruptions, because that hasn’t really been explored in detail.


Why is the Hellenic volcanic arc system an ideal location to seek those answers?

It’s actually a really great place to try and answer these questions, because it consists of three large volcanic centres – Christiana, Santorini, and Colombo – along with several submarine volcanoes. Volcanoes in this region have erupted quite explosively in the past, and the deposits on land have been extensively studied but the majority of the erupted deposits lie on the sea floor within rift basins and the Santorini caldera itself. These deposits are hundreds of meters thick so hold a really great record of the volcanic history of the area. By drilling to sample these deposits we’ll be able to fill gaps in the onshore records, but we’ll also access much older deposits than those preserved on land. This will give us an extensive record of the past history that goes much further back than what we’ve already learned from the land deposits. 


What’s the significance of filling that gap in our knowledge, including in our region?

One important reason is that submarine volcanic activity can generate tsunamis and also earthquakes – which can also trigger a tsunami separately. Anyone who lives near the ocean probably wants to know how that might occur or when that might occur, including here in Australia. The Kermadec arc, which contains several active volcanoes, extends from the top of the North Island of New Zealand up to Tonga; there was a massive eruption earlier this year that produced a devastating tsunami for Tonga. It’s important for us to understand submarine volcanic activity and island arc volcanism because it can generate tsunami events, and they can have huge impacts.


What are you hoping to find in the sediments, and what will that bring to your research moving forward?

One of my key aims is to learn more about submarine volcanic processes. Hydrostatic pressure and water does influence a volcanic eruption and it changes the depth at which magma begins to degas and fragment and quench; that’s different to what we see on land. The majority of Earth’s volcanism happens under the ocean surface, so it’s vital for us to know how volcanic activity is influenced by this environment. I’ll also be looking at different ways we can distinguish primary eruption-fed deposits – those emplaced directly by a volcanic event – from those that have been transported from another location and resedimented; it’s not always easy to tell when looking at a core. Without knowing which deposit has come from which type of event we get a mixed or misleading view.


As a PhD candidate early in your research career, what does being part of an IODP expedition mean to you?

It’s a pretty amazing opportunity; I feel very lucky. Who wouldn’t want to go on a ship and experience cutting edge research as it’s happening? I’ll also get to meet and work with some of the best scientists in the world in these fields. As a young scientist, I’m looking forward to learning from everyone on board and collaborating with them, and making great connections that will continue into the future.


As you’re preparing to board, how are you feeling about life at sea for the next two months? What are you most looking forward to?

I’m quite excited to be heading off to sea. I have some idea of what to expect from my previous research voyage, and what excited me most there was when we would bring up the core and open it to see what was inside. It’s strange feeling to think that you’re looking at sediments that have been sitting on the ocean floor for years and years, and we’re the first people to look at them. You don’t know what you’ll find and there’s a story in every core, so I’m really looking forward to that. But I have to admit I’m also really looking forward to the food; I’m not a great cook but I love eating, so it’s just luxury having people make food for you every day!