Evidence of one of the largest explosive eruptions ever recorded in the Aegean Sea

The Greek archipelago of Santorini is made up of the remains of a powerful volcano. Members of the international IODP “Hellenic Arc Volcanic Field” expedition have now found evidence of one of the largest eruptions ever recorded in the southern Aegean Arc.

In their article published today in the journal Earth and Environment Communications, they describe a recently discovered giant deposit of pumice, taken from the seafloor of seven coastal sites around the island of Santorini. This shows that the Christiana-Santorini-Kolumbo volcanic field was much more explosive in the distant past than previously thought.

The Greek Aegean volcanic field consists of a 60-kilometer chain of more than 20 volcanoes, most of which are underwater. It is considered particularly dangerous because the volcanoes there have experienced eruptions, some of which have been highly explosive.

“For example, the eruption of Santorini in the Late Bronze Age, around 3,600 years ago, likely triggered the fall of the Minoan civilization on Crete, an event important to both volcanology and archeology “, explains Dr. Steffen Kutterolf, volcanologist at the GEOMAR Helmholtz Center for the Ocean. Search in Kiel.

With Dr. Timothy Druitt of the University of Clermont-Auvergne, he led the expedition to Santorini. The international team of scientists discovered a new deposit around the island, indicating a much larger underwater eruption around 520,000 years ago.

Dr Kutterolf says: “The recently discovered tuff deposit has a volume of more than 90 cubic kilometers and can be up to 150 meters thick. This makes it six times larger than the pyroclastic flow deposits from the Minoan eruption and ten times larger than those from the Minoan eruption. Hunga Tonga-Hunga Ha’apai volcanic eruption of January 22, 2022.”

Pyroclastic flows are streams of hot ash, rock and gas that, in the case of the recently mapped Santorini event, originated from an underwater volcano at the time and transformed with water into cloudy and mud flows. These flows transported large quantities of volcanic material up to 70 kilometers into surrounding marine basins. Layers of rock from this eruption have also been discovered on three neighboring islands.

Various methods have been used to decipher the eruption. Dr Kutterolf explains: “The first dating and estimation of the water depth at which the eruption took place was possible directly on board thanks to micropalaeontology.” Microfossils (foraminifera), of known geological age and preferred water depths, have been discovered directly above and below the pumice deposits.

Physical parameters such as density and porosity were also determined on board. The chemical composition of the drilled samples was then analyzed using GEOMAR’s Electron Microprobe, a special scanning electron microscope.

“The sample is bombarded by an electron beam with a diameter of 0.01 millimeter. This provides information about the number of chemical elements, such as silicon, iron or magnesium, contained in the extinguished magma .” This allowed the deposits to be precisely linked to their location on the seafloor, allowing their extent and thickness, and ultimately the size of the eruption, to be determined using seismic images of the seafloor.

Despite this explosive history, researchers agree that it is very unlikely that the volcanic field will experience another eruption of this magnitude in the near future. “But knowing the past is also an essential part of predicting the future,” says Dr. Kutterolf.