The current Mediterranean landscape results from a violent geological history that science only begins to reconstruct. One of the most brutal stages in this story was the end of the Messinian salinity crisis, 5.3 million years ago, when the Mediterranean Sea, then dried up, suddenly filled. An international team of researchers from the University of Southampton, Monterey Bay Aquarium Research Institute and the University of Catania highlighted the terrestrial and submarine traces of this event, known as Zanclean Megaflood.
An ocean in free fall
5.3 million years ago, at the end of the Messinian salinity crisis, the Mediterranean was nothing like what we know today. Deprived of her link with the Atlantic Ocean because of tectonic movements, she had emptied under the effect of an intense evaporation, caused by a warm and arid climate. The water level had dropped by more than 1,500 meters, exposing the seabed and transforming the basin into a huge bowl of salt and hypersaline lakes, witnesses of an extreme hydrological imbalance.
When the Atlantic connection was restored at the Strait of Gibraltar, a cataclysmic event has started. The water flow, precipitated by a difference in dizzying height between the Atlantic and the Mediterranean, generated a flow comparable to a planetary waterfall. This drop of approximately 1,400 meters produced sufficient gravitational acceleration for the water to cross the strange threshold at speeds greater than 40 m/s.
© © Micallef, A., et al., 2024Model for formation of ridges, channels and breach linked to the megaflot of Zancleen on the Sicily threshold. © Micallef, A., et al., 2024
This phenomenon, now described as Zanclean Megafloodwas accompanied by spectacular erosion. The water, compressed in the neck of the Strait, dug a gigantic underwater channel and moved massive quantities of sediments. On this scale, it is no longer simply a progressive invasion, but a hydraulic collapse. In just a few years, the sea reformed, first to the west, then later to the east. This brutal tilting of the marine system has left sustainable imprints in ocean funds, witnesses to one of the largest known floods in geological history.
Sicily, the Storm Carrefour
THE SICILY SILLBathymmetrical threshold located between Sicily and Tunisia, represents the geographical rocking point between the western and eastern basins of the Mediterranean. At 430 meters from the current sea level, this threshold formed, at the end of the Messinian crisis, a submerged, but essential natural barrier. Understanding how the Zanclean Megaflood crossed it to reach the east of the Mediterranean basin remained a major enigma.
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Aerial photograph of a crest eroded by megainundation in southeast of Sicily. © Aaron Micallef
The study led by Antonio Caruso in 2024 provided the first Earth-Mer-Mer-Mer-Merjugation evidence of the flood at this location. On almost 10 km wide, the researchers have identified more than 300 elongated ridges in Sicily South Oriental, north of the Hybléen plateau. Their orientation (around 40 ° northeast) and their asymmetrical profile are compatible with a large-scale turbulent flow. Their morphology varies from northwest to the southeast. Higher and less profiled upstream, lower and tapered downstream, they indicate a strengthening of the current as it advances.
The buried proof at the bottom of the sea
But it is under the sea that confirmation is decisive. Seismic profiles have revealed a buried channel, 8 to 20 km wide and deep up to 270 meters, extending from the coast to the Canyon of Noto, located off the south-eastern coast of Sicily. This erosive conduit, interpreted as a Erosional Margin Surfacecorresponds to the expected layout of a flood flow.
Hydrodynamic models show that this relief has intensified the current. Speeds of 32 m/s, for a flow of 13 Sverdrups – an Sverdrup is equivalent to one million cubic meters per second. The shear exceeds the erosion thresholds of limestone rocks. The breach found at the top of the ridges contains blocks torn from Messinian formations, transported by suspension, and even injected by overpressure into the lower layers, signs of a brutal passage of water. These observations, now correlated with marine dynamics, attest that the Sicily Sill was indeed the central crossroads of the largest flood known on earth.
The sediments as the memory of the history of the Mediterranean
Beyond the terrestrial reliefs, it is in the sea basement of the Ionian basin that the most imposing trace of the flood is found. The researchers identified, thanks to high -resolution seismic profiles, geological training called “Unit 2”. It is buried between Messinian evaporites and recent marine sediments. This sedimentary body covers 15,000 km². It can even reach a thickness of 860 meters. Its internal, disordered and acoustically chaotic structure, contrasts strongly with typical, more regular marine deposits.
Researchers have shown that neither an underwater collapse nor a conventional river system can explain this accumulation. The propagation speeds of seismic waves through unit 2, between 2.3 and 2.6 km/s, are too low to correspond to layers of compacted gypsum or massive carbonates. On the other hand, they agree with furniture deposits, quickly deposited, probably from an extreme turbulent flow.
Hydrodynamic models show that at the time when the water has crossed the Sicily threshold, it has engulfed in the Noto canyon, whose slope reaches locally 70 °, and whose head forms an amphitheater 6 km wide. This canyon, unique on the escarpment of Malta, would have acted as a natural duct, causing the sediments towards the bottom of the basin. The massive deposit thus formed would be the largest ever attributed to a flood on earth. It testifies to a brutal transfer of matter, comparable to the effects of a river a thousand times more powerful than the Amazon, sustainably carving the Mediterranean funds.
A redefinition of geological history
What these discoveries reveal is that an event as massive as a flood capable of filling the Mediterranean in a few years has really taken place – and that its traces are still visible today. This forces scientists to deeply review the geological history of this region. No, the sea did not reform slowly by slowly infiltrating Gibraltar. It was suddenly overwhelmed, at a speed and a powerless power known on earth.
It is a paradigm shift. The Mediterranean, which is often considered as an old, stable basin, was in reality the scene of a dazzling upheaval. “” Water has returned to a speed comparable to that of a continuous hurricane Summates the geologist Daniel Garcia-Castellanos. And this is not a detail. This changes the understanding of ecosystems, salt cycles, and current underwater geography.
This new reading also makes it possible to identify, elsewhere in the world, other traces of massive floods which have so far been misunderstood or poorly dated. It shows how much the landscapes can be transformed into a very short time. By accurately reconstructing such a scenario, the researchers are not content to correct the past: they also provide keys to understanding the risks of brutal collapse in other sensitive regions of the globe, such as certain Deltas or strategic marine passages.
Source: Micallef, A., Barreca, G., Hübscher, C. et al. “Land-to-Sea Indicators of the Zanclean Megaflood”. Common Earth approximately 5794 (2024).
