A team led by researchers at the Australian National University (ANU) examines the ancient Mediterranean as it was five million years ago, when a dramatic event reshaped the region and set the stage for the sea’s modern order. In this scenario, a colossal waterfall nearly 1.5 kilometers high is thought to have formed in what is now Sicily, initiating a flood that inundated the eastern half of the basin.
Known as the Zanclean Mega-Flood, this event stands as the largest flood identified in geological history. It is believed to have transformed the Mediterranean from a desiccated saltwater basin into the vibrant marine ecosystem observed today. ANU’s research, published in Nature Geology, sheds light on the sequence of changes that accompanied this transformation.
Today, seashells can be found in the Troodos Mountains, the largest range on the island, illustrating the region’s turbulent history of tectonic movement, island subduction and emergence, and periodic flooding.
Udara Amarathunga, the lead author and ANU PhD researcher in paleoenvironments, notes that the Zanclean flood ranks among the most abrupt global environmental shifts since the mass extinction that ended the era of the dinosaurs. He refers to this event as a kind of “Mediterranean rebirth.”
Gibraltar’s second gate starts to close
The mega-flood marked the end of the Messinian Salinity Crisis (MSC). The Mediterranean basin partially dried as the Atlantic–Mediterranean gateway near the Strait of Gibraltar closed, leaving large salt deposits and posing severe challenges to life, according to Cosmos magazine.
Amarathunga explains that the MSC began around six million years ago, when European and African tectonic plates collided, separating the Mediterranean Sea from the Atlantic at the site of present-day Gibraltar.
He stresses that the “gate” was not completely shut for long. Access narrowed over millions of years and finally closed fully about 5.6 million years ago, reaching the peak of the salinity crisis.
Although the exact extent of the drying remains a topic of study, the team suggests the sea level dropped by roughly 1–2 kilometers, creating eastern and western basins now separated by Sicily.
A giant waterfall 1.5 kilometers high
What caused the Mediterranean to shift from a lifeless salt lake to a thriving sea? Amarathunga describes a gradual process: erosion at Gibraltar allowed small amounts of Atlantic water to seep into the Mediterranean. The mega-flood hypothesis, first proposed in 2009 by Spanish scientist Daniel García-Castellanos, posits that initial modest flows eventually overwhelmed a natural dam, unleashing a massive influx of freshwater and saltwater into the basin.
This would have produced a dramatic waterfall towering 1.5 kilometers at Sicily’s height, flooding the eastern portion of the basin and altering the sea’s circulation and chemistry. The energy of the flood would have been enormous, with daily movement potentially matching hundreds of times the annual output of Niagara Falls. The Mediterranean would have risen by more than 10 meters per day at the flood’s peak.
The western basin filled first, followed by a rupture of the land barrier at Sicily that released a then-giant cataract to the east. This event carried significant salt into the eastern basin, prompting researchers to explore how long it took for the salt to disperse back into the Atlantic and the basin to settle into a normal marine state.
Amarathunga notes that the analysis suggests about 26,000 years were required to remove the excess salt and restore normal ocean conditions in the Mediterranean.
While the mega-flood theory has sparked some debate, the latest ANU study adds weight to the idea that a rapid, large-scale transformation reshaped global marine environments. The team argues that such a swift change is rare and serves as a striking example of how entire ecosystems can reorganize in a geological blink.
Notes from the research emphasize that this work engages with established data and previously proposed ideas while offering new modeling to trace salt transfer and the timeline of the flood and its aftermath. The findings appear in Nature Geology, with citations attributed to the study by ANU researchers.
Overall, the Zanclean flood illustrates a dramatic episode in Earth’s history, highlighting how tectonics, hydrology, and ocean chemistry intersect to reimagine a sea that hosts life today. It also demonstrates how modern scientists use multiple lines of evidence and computational models to reconstruct ancient environments, test competing hypotheses, and push the boundaries of what is known about the world’s largest seas.
This synthesis of evidence, while still under discussion in some scientific circles, strengthens the view that the Mediterranean’s re-emergence was driven by a sequence of abrupt and powerful events that reshaped continents, land bridges, and ocean pathways. The research invites ongoing inquiry into the precise dynamics and durations of these transitions, underscoring the value of interdisciplinary approaches in paleogeography.
There is no public release of author contact details here; the discussion remains anchored in published peer-reviewed work and the collaborative efforts of researchers examining ancient marine basins. The study continues to inspire curiosity about how planetary-scale floods influence climate, biodiversity, and ocean circulation across millions of years.