By Anna Katsigera

Evidence from a marine research mission has revealed the history of Aegean volcanoes. An international team led by the GEOMAR Helmholtz-Center for Ocean Research in Germany and the participation of the University of Athens, located the traces of 20 volcanic eruptions in the Aegean Sea and almost completely recounted the eruptions of the last 200,000 years in the journal G-Cubed.

According to the researchers, the Aegean has a very active volcanic past, but the recording of the frequencies and magnitudes of the eruptions remained incomplete due to the absence of data from the seafloor.

The researchers examined 47 sediment cores up to 7.4 meters long that were acquired during a research mission with the ship “RV Poseidon” in 2017. More than 220 different layers of ash were identified by “geochemical footprints” as deposits from 19 explosions in the Aegean as well as an Italian explosion from the Phlegraean Fields in Italy.

“Just as in fingerprinting, the fingerprint helps us identify someone, so in volcanology the geochemical fingerprint corresponds to a unique volcanic eruption,” said Dr. Steffen Kutterolf, a volcanologist at GEOMAR and the Helmholtz-Centre GEOMAR and co-author of the study. “The imprint results from the chemical composition of the eruption products – in our case the composition of volcanic glass – which are characteristic of each eruption. With this we can match the unknown layers of ash from the sea to their explosion from the land.”

The study also found previously unknown explosions. The already known eruption of Milos turned out to have happened earlier than we originally knew, 37,000 years ago. The two new eruptions found in Nisyros were in between two known explosions between 57,000 and 76,000 years ago. Although the dense ash on the islands is impressive, most of the eruption data is stored in the sea ash.

“On land, erosion by wind and rain affects the deposits and vegetation can make it difficult to find the fine ash deposits away from the source of the explosion,” explains Dr Caterloff. “In the marine environment, land deposits are almost completely preserved.”

According to new data, ash volumes place 80% of eruptions in very large eruptions, comparable to the Cracatoa eruption in 1883, while the remaining 20% ​​still represent large size eruptions, such as the eruption of Vesuvius in 79 AD which buried and destroyed Pompeii.

The next step

The research completes the archive of major volcanic events on which the risk assessment for possible future events in the Aegean is based. “The next step is to apply the method for the entire life cycle of volcanoes,” said Dr Paraskevi Nomikou, associate professor at the Department of Geology and Geoenvironment of the University of Athens.

Going back in time, researchers will investigate whether “external control factors such as earthquakes or even sea level changes have affected volcanic activity.” The deeper drilling cores to be collected at the end of 2022 by the research vessel “RV JOIDES Resolution” in the Santorini caldera and around the island by the International Ocean Drilling Program (IODP) were designed to reveal the evolution of the volcanic eruption and, possibly, its birth.

This article was previously published in Greek at kathimerini.gr.