An international expedition led by Dr. Steffen Kutterolf of GEOMAR Helmholtz Centre for Ocean Research Kiel has found evidence of one of the largest eruptions ever recorded in southern Aegean Arc of Greece. The expedition was conducted aboard the JOIDES Resolution research vessel as part of the International Ocean Discovery Program (IODP).

The Greek island of Santorini consists of the remnants of a massive underwater volcano. Members of the IODP ‘Hellenic Arc Volcanic Field’ expedition have discovered evidence of an incredibly powerful eruption in the area from long ago.

In a recent paper in Communications Earth & Environment, they describe a huge newly discovered deposit of pumice stone sampled from the seafloor around Santorini island. This indicates the Christiana-Santorini-Kolumbo volcanic field was much more explosive in the distant past than previously thought.

IODP drill sites are shown as red dots and land sites as yellow dots. Drill sites are labeled with their IODP site numbers. No Archaean tuff was recovered in the U1590 reservoir, but its presence is apparent in the seismic profiles. The inset shows the location in the South Aegean Volcanic Arc. See Methods for bathymetric data sources
IODP drill sites are shown as red dots and land sites as yellow dots. Drill sites are labeled with their IODP site numbers. No Archaean tuff was recovered in the U1590 reservoir, but its presence is apparent in the seismic profiles. The inset shows the location in the South Aegean Volcanic Arc. See Methods for bathymetric data sources | photo Tim Druitt et al. / Communications Earth & Environment

The Aegean volcanic arc consists of over 20 volcanoes stretching 60 kilometers underwater. It is considered highly dangerous as the volcanoes have a history of eruptions, some of which were extremely explosive. For example, the Santorini eruption around 3,600 years ago at the end of the Bronze Age likely caused the downfall of the Minoan civilization on Crete – a major event in both volcanology and archaeology.

The international team of scientists discovered a new deposit around the island, pointing to a much larger submarine eruption approximately 520,000 years ago. According to Dr. Kutterolf, the newly discovered pumice deposit has a volume of over 90 cubic kilometers and a thickness of up to 150 meters. This makes it six times larger than deposits from the Minoan eruption and ten times larger than the 2022 Hunga Tonga-Hunga Ha’apai eruption.

Pyroclastic flows, which are fast-moving currents of hot ash, rock and gas, originated from an underwater volcano during this recently mapped Santorini event. As the flows interacted with water, they transformed into turbulent mudflows. These carried vast amounts of volcanic material as far as 70 kilometers into surrounding seabasin areas. Layers from this eruption were also found on three neighboring islands.

The eruption was produced from one or more shallow submarine vents of the ancient Akrotiri volcano in the Santorini-Christiana area. The vent was located in water shallow enough for magma fragmentation to occur primarily by exsolution and expansion of magmatic gases. The orange colors of the jet denote higher temperatures. As the mixture of gases and particles from the eruptive jet ascended the water column, it ingested water and partially collapsed to form submarine pyroclastic flows. These currents in turn entrained more water and transformed into turbidity and mudflows that spread across the seafloor depositing a volcaniclastic megaturbidite up to 150 m thick. The breaking of the sea surface by the eruptive column also generated subaerial pyroclastic currents that moved across the sea surface and pumice rafts, and deposited thin layers of ignimbrite on the islands (not shown) of Christiani, early Santorini, and Anafi. The cartoon is vertically exaggerated, several km in diameter and about one km high | photo Tim Druitt et al. / Communications Earth & Environment

Various methods helped decipher details of the eruption. Microfossils found immediately above and below the pumice deposits onboard allowed determining the eruption’s initial age and water depth using their known geological age and preferred depth range. Physical parameters like density and porosity were also measured onboard. Back in the lab, a GEOMAR electron microprobe – a specialized scanning electron microscope – was used to chemically analyze drilled samples.

Bombarding samples with a 0.01 millimeter electron beam provides information on which chemical elements like silicon, iron or magnesium the now solidified magma contained. This precisely linked deposits to their seafloor locations, ultimately helping determine the eruption’s size using seismic images of the seafloor topography and thickness measurements of the deposits.

While this region has an explosive past, researchers agree another eruption of this scale is very unlikely in the near future. However, as Dr. Kutterolf states, understanding the past is also essential for predicting the future. Further studies may help improve monitoring and preparedness for this potentially hazardous volcanic system.

Sources

GEOMAR Helmholtz Centre for Ocean Research Kiel | 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). doi.org/10.1038/s43247-023-01171-z

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