Millions of years ago, the Mediterranean Sea evaporated. It may have then been refilled by the largest flooding event ever experienced on Earth.
An international team of researchers has uncovered new evidence supporting the Zanclean megaflood, a theorized event that refilled the Mediterranean Sea after the Messinian Salinity Crisis had transformed it into a dry, salty landscape. As detailed in a December 28 study published in the journal Communications Earth & Environment, the researchers combined newly identified geological features in Sicily with geophysical data and computer models to potentially provide the most extensive look into the ancient megaflood known to date.
“The Zanclean megaflood was an awe-inspiring natural phenomenon, with discharge rates and flow velocities dwarfing any other known floods in Earth’s history,” Aaron Micallef of the Monterey Bay Aquarium Research Institute in California, who led the study, said in a University of Southampton statement. “Our research provides the most compelling evidence yet of this extraordinary event.”
Between 5.97 and 5.33 million years ago, the Messinian Salinity Crisis caused the Mediterranean Sea to be cut off from the Atlantic Ocean and evaporate into an expanse of salt deposits. Scientists previously theorized that, over a period of 10,000 years, the Mediterranean basin gradually refilled with water. However, the 2009 discovery of an erosion channel that stretches from the Gulf of Cadiz on Spain’s Atlantic coast to the Alboran Sea east of the Strait of Gibraltar challenged this theory, and instead led scientists to suggest a single flooding event.
“This megaflood is thought to have been caused by overtopping Atlantic waters through a Late Messinian isthmus near the modern Gibraltar Strait, which initially filled the western Mediterranean, and subsequently spilled over the intrabasinal Sicily Sill, filling the eastern Mediterranean,” the researchers wrote in the new study. Scientists estimate that the megaflood lasted between two and 16 years, and discharged between 2.4 and 3.5 billion cubic feet (68 and 100 million cubic meters) per second, according to the study.
The team identified more than 300 asymmetric, continuous ridges near the Sicily Sill, a now-underwater land bridge that once divided the western Mediterranean from the eastern Mediterranean. The ridges were layered in debris eroded from the ridge flanks and the surrounding area, which point to a rapid and intense deposition process. The layers date to between the Messinian (7.2 million to 5.3 million years ago) and Zanclean (5.3 to 3.60 million year ago) periods, aligning perfectly with the proposed timing of the Zanclean megaflood, around 5.3 million years ago.
“The morphology of these ridges is compatible with erosion by large-scale, turbulent water flow with a predominantly north easterly direction,” Paul Carling of the University of Southampton, who participated in the study, said in the statement. “They reveal the immense power of the Zanclean Megaflood and how it reshaped the landscape, leaving lasting imprints on the geological record.”
Carling and his colleagues also discovered a “W-shaped channel” in the seabed east of the Sicily Sill, connecting the ridges to an underwater valley in the eastern Mediterranean called the Noto Canyon. The researchers propose that when the Zanclean megaflood had filled the western Mediterranean and finally spilled over the Sicily Sill, the channel funneled water into the eastern parts of the sea.
The team also developed computer models to reconstruct this dynamic. The simulations suggest that the water changed directions and grew more intense over time, achieving a discharge of up to 72 miles per hour (116 kilometers per hour).
“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 added. “It opens the door to further research along the Mediterranean margins.”
Though the Zanclean megaflood remains just a theory, one thing is for sure—5.3 million years ago, the Mediterranean Sea probably wasn’t the idyllic travel destination it is today.
