A new study has provided compelling new evidence that a huge “megaflood” refilled the Mediterranean Sea around 5 million years ago.
This surge of water – the Zanclean Megaflood – is said to have ended a period during which the Mediterranean was a vast expanse of salt flats, known as the Messinian Salinity Crisis, which lasted for hundreds of thousand years.
An international team of scientists, including the University of Southampton, has identified a series of geological features around southeast Sicily that suggest a massive flood occurred across the region.
“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 Dr Aaron Micallef, lead author of the study and researcher at the Monterey Bay Aquarium Research Institute in California.
“Our research [published in the journal Communications Earth & Environment] provides the most compelling evidence yet of this extraordinary event.”
During the Messinian Salinity Crisis the Med became isolated from the Atlantic Ocean and evaporated, completely reshaping the region’s landscape.
For years, scientists thought that this dry period had ended gradually, with the Mediterranean refilling over 10,000 years. However, this theory was challenged by the discovery of an erosion channel stretching from the Gulf of Cadiz to the Alboran Sea in 2009. This pointed to a single, massive flooding event, lasting between two and 16 years, which became known as the Zanclean Megaflood.
The researchers investigated over 300 asymmetric, streamlined ridges in a corridor across the Sicily Sill – a submerged land bridge that once separated the western and eastern Mediterranean basins.
“The morphology of these ridges is compatible with erosion by large-scale, turbulent water flow with a predominantly north-easterly direction,” says Professor Paul Carling, from the School of Geography and Environmental Science at the University of Southampton and a co-author of the study.
“They reveal the immense power of the Zanclean Megaflood and how it reshaped the landscape, leaving lasting imprints on the geological record.”
They found that these ridges were topped with rocky material eroded from the ridge flanks and the surrounding region, indicating it was deposited there quickly and with immense force.
This layer is found at the boundary between the Messinian and Zanclean periods – when the megaflood is believed to have occurred.
Using geological ultrasound, the researchers discovered a “W-shaped channel” on the continental shelf east of the Sicily Sill, which connects the ridges to the Noto Canyon – a deep underwater valley in the eastern Mediterranean.
The channel’s shape and location suggest that it acted like a massive funnel, meaning that the megaflood poured over the Sicily Sill, this channel likely carried the water toward the Noto Canyon and into the eastern Mediterranean.
The team developed a computer model of the megaflood to simulate how the water might have behaved. The model suggests that the flood would have reached speeds of up to 72mph.
“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,” Dr Micallef added. “It opens the door to further research along the Mediterranean margins.”