A massive volcanic eruption on Greece's Kos Island hundreds of thousands of years ago sent a huge wave of volcanic ash deep into the Aegean Sea, reaching areas near Santorini more than 120 kilometers (75 miles) away, according to new research.
The study, led by Abigail Metcalfe of Clermont Auvergne University in France, along with Greek scientists, reports the discovery of a 200-meter-thick (656-foot) underwater ash deposit -- one of the thickest ever found from a single eruption. The findings were published in the journal Science Advances.
The ash layer, known as a "megabed," was uncovered during deep-sea drilling by the International Ocean Discovery Program (IODP). Drilling sites were located in marine rift basins northeast of Santorini.
Until now, only small traces of this eruption had been found offshore. The discovery reveals that the eruption's reach and strength were much greater than previously thought.
The source of the ash is the Kos Plateau Tuff eruption, which occurred about 161,000 years ago. Scientists matched the chemical makeup of the ash in the seafloor cores to material from the eruption on Kos.
Unlike thin ash layers deposited by wind, this megabed was built by fast-moving underwater currents that carried heavy volcanic material across the seafloor.
The researchers say these ash-rich flows, called turbidity currents, formed when hot pyroclastic currents from the eruption entered the sea.
As they mixed with seawater, they cooled and transformed into dense, gravity-driven flows that swept along the seafloor, trapping volcanic material in deep basins. These flows moved fast and carried enough force to destroy marine life in their path.
The thick ash deposit is largely undisturbed and lacks signs of marine burrowing. This suggests it settled quickly, likely within hours or days, giving sea life no chance to recover.
The deposit contains not only volcanic ash and pumice but also broken remains of corals, shells, and other marine organisms -- signs of widespread damage to ocean ecosystems.
Researchers estimate the volume of this underwater deposit to be approximately 73 cubic kilometers (17.5 cubic miles).
When combined with earlier onland and atmospheric fallout estimates, the total eruption volume reaches at least 210 cubic kilometers (50.4 cubic miles). This places the Kos eruption among the largest known in the region, suggesting that previous estimates of its size were too low.
The study also highlights how deep-sea drilling can uncover volcanic impacts that are invisible from land.
Without the IODP cores, most of the Kos eruption's reach would have remained unknown. The findings reveal how island volcanoes can unleash powerful events that not only reshape landscapes but also the seafloor.
The research provides scientists with new insight into how explosive island eruptions interact with the ocean and transport ash across large distances.