An international research team led by a Maltese marine geologist has uncovered evidence that the largest flooding event in known history happened in the Mediterranean more than five million years ago.

The findings support the Zanclean megaflood theory, which posits that 5.33 million years ago the Messinian salinity crisis which effectively isolated the Mediterranean from the world’s oceans was brought to a quick and dramatic end by a massive flooding event.

Researchers have now published their findings in Communications Earth & Environment, an academic journal ranked among the world’s most impactful in the environmental sciences and geosciences sectors.

“The Zanclean megaflood was an awe-inspiring natural phenomenon, with discharge rates and flow velocities dwarfing any other known floods in Earth’s history,” said Aaron Micallef, lead author of the study. “Our research provides the most compelling evidence yet of this extraordinary event.”

Ridges shaped by the megaflood. Photo: Aaron Micallef

Micallef and other researchers found onshore and offshore indicators in south-east Sicily that confirm the cataclysmic event. By combining geological, geophysical, and numerical modelling techniques, they uncovered the impact of the megaflood on the landscape of south-eastern Sicily - where a shallow-water marine corridor, the Sicily Sill, existed at the time of the flood - and the adjacent Noto submarine canyon in the Ionian Sea.

Evidence includes over 300 streamlined ridges, breccia deposits, soft-sediment deformation features, and a 20-kilometer-wide buried channel on the seafloor east of Sicily.

Hydrodynamic modeling supported these findings, showing how the formation of Noto Canyon intensified water velocity and flow direction during the flood.

The research builds on previous research which Micallef and others have undertaken into the Zanclean megaflood theory.

“These findings not only shed light on a critical moment in Earth’s geological history but also demonstrate the persistence of landforms over five million years,” Micallef said. “It opens the door to further research along the Mediterranean margins.”

Micallef - a National Geographic explorer whose research was primarily funded by the global non-profit - is an alumni of the University of Malta.

Maltese marine geologist Aaron Micallef lead a team to find evidence of Mediterranean Zanclean megaflood. Photo: Aaron Micallef

The Zanclean megaflood is believed to have followed a dramatic drawdown of the Mediterranean Sea, which left it dry and full of vast salt deposits. Known as the Messinian salinity crisis, that event reshaped the entire region’s landscape and is believed to have lasted for roughly 600,000 years. Following the megaflood, the area transitioned back to being a maritime environment, with the Atlantic ocean filling the Mediterranean basin through what is now known as the Strait of Gibraltar.

The research was supported by the National Geographic Society, Deutsche Forschungsgemeinschaft, and the David and Lucile Packard Foundation.