About six million years ago, the Mediterranean Sea transformed into a vast, isolated salt basin. It became a large salt lake that dried up after separating from the Atlantic Ocean, causing its level to drop by roughly 1.5 km. This dramatic event is known as the Messinian salinity crisis.
During that era, water input paused as the Strait of Gibraltar closed due to tectonic forces. Rivers fed water far more slowly than it evaporated, so the basin gradually built up a thick evaporite layer, dominated by gypsum and salt, spanning nearly the entire Mediterranean region.
It was a time of severe environmental stress across the area. The crisis culminated with the Zanclian megaflood, driven by a sudden surge of Atlantic water into the water-depleted Mediterranean basin.
Today, geologists from Utrecht University, University College London, and the University of Granada have pieced together clues about the once-magnificent flood. Their work portrays the megacele as the largest flood the Earth has ever experienced, as noted by Krijgsman and colleagues.
Top drained basin; down, underwater sedimentology
In a recent study published in Sedimentology, researchers examined sandstone exposed along Sicily’s southern coast and concluded that it records a powerful eastward flow from the western Mediterranean. They suggest that water flowed over a barrier that once separated the western and eastern Mediterranean basins.
The entire basin was flooded in a few short years
An article from 2009 in Nature highlighted how intense the Mediterranean flood was. Discharges reached up to 100 million cubic meters per second, roughly a thousand times the current Amazon’s average flow, occurring within just a few years. A later analysis by Daniel García-Castellanos of GEO3BCN-CSIC shed further light on this event, with attribution to the work of García-Castellanos. This phenomenon was described by researchers as catastrophic, potentially ranking among the most significant environmental upheavals since the dinosaur extinction 65 million years ago.
One enduring question for scientists was how waters eventually rose back to their former levels. It is believed that streams from the western side initially flooded the western basin and, through the Strait of Sicily, filled the eastern Mediterranean. The duration, estimated at a few months to two years, remains a topic of discussion, with attribution to García-Castellanos.
Mediterranean evolution sedimentology
Tracing the geology, researchers studied the southern Italian seas. In the Arenazzolo Formation of the Caltanissetta Basin in Sicily, a 5 to 7 meter thick sandy sequence preserves clues that link it to the sudden Mediterranean flood.
Through granulometric, petrographic, and paleocurrent analyses, the authors inferred the flanks and current types responsible for depositing Arenazzolo sands. Those currents reflect the renewed Western–Eastern Mediterranean exchange when basin margins overflowed, with attribution to Krijgsman and colleagues.
The lead author, a professor from Utrecht University, noted that rocks formed during the flood were found off Sicily’s southern coast. This work ties into long-running research on the Messinian crisis, sparked by meters of sandstone appearing where gypsum remnants met post-flood sediments near Sicily in 2020, inspiring a renewed field campaign in 2021 by an international team, with attribution to Krijgsman et al.
Current fluctuations
The team conducted careful examinations of the sands and observed that grain composition and size shifted every few centimeters. They noted fossilized stream undulations within the sand, a signature of rapid, high-energy flow conditions, with attribution to Van Dijk.
Photographs of these structures allowed researchers to reconstruct ancient flow directions and the conditions that shaped the sediment roughly 5.3 million years ago. The evidence points to a robust west-to-east undercurrent in deeper waters rather than a simple river deposition, with attribution to Van Dijk.
Ruins showing the history of the Mediterranean sedimentology
The findings suggest the sands were not merely washed in by rivers or local deltas but were moved by a strong undercurrent that cut through deeper waters, reshaping the basin from west to east as reconnection between the western and eastern Mediterranean unfolded, with attribution to Van Dijk.
Imprinted disasters
This study provides new physical evidence of a mega-flood propagating from the western to the eastern Mediterranean. Today, researchers can test and measure directly one of the planet’s most dramatic episodes of environmental change, which previously lived mainly in geophysical models, with attribution to Van Dijk.
Geologists emphasize that they use present-day Earth surface processes to interpret rock records, but in this instance they faced an unusual challenge because there were no closely analogous events in the past 100 million years, with attribution to Van Dijk.
The conditions surrounding these discoveries are precisely what make the results so intriguing for the scientific community, with attribution to Van Dijk.
Reference work: marked citation without link attributed to Krijgsman et al.
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