Massive flood refilled an empty Mediterranean Sea millions of years ago

Five million years ago, one of the most spectacular events in Earth’s history unfolded as a massive flood refilled the Mediterranean Sea. This wasn’t a typical flood – it was a colossal surge of water that transformed a vast salt desert into the blue waters we know today.

The Zanclean Megaflood, a massive influx of water, ended the Messinian Salinity Crisis, a period during which the Mediterranean Sea had largely evaporated, leaving behind vast salt flats.

This transformative flood, occurring between 5.97 and 5.33 million years ago, refilled the basin in a dramatic and rapid event, challenging long-held scientific theories.

An international team of researchers, including scientists from the University of Southampton, has now identified a series of geological features in Southeast Sicily that point to the reality of this megaflood.

The findings offer the most detailed and convincing evidence yet of one of the largest floods in Earth’s history.

End of the Messinian Salinity Crisis

Before the Zanclean Megaflood, the Mediterranean was unrecognizable compared to today. During the Messinian Salinity Crisis, the Mediterranean Sea became isolated from the Atlantic Ocean.

Without a constant influx of water, it began to evaporate under the intense heat, leaving behind thick salt deposits and transforming the region into an arid wasteland. The loss of water reshaped the entire landscape, creating vast salt plains and deep canyons.

For years, scientists believed that the Mediterranean refilled gradually over approximately 10,000 years. This view suggested that small, sustained breaches in natural barriers allowed water to trickle back into the basin, slowly restoring the sea.

However, in 2009, researchers discovered an erosion channel stretching from the Gulf of Cadiz to the Alboran Sea. This discovery suggested that the refilling was not a slow process but rather a single, massive flood event lasting between two and sixteen years.

The latest research, published in the journal Communications Earth & Environment, provides further confirmation that the refilling of the Mediterranean was anything but gradual. Instead, it was a catastrophic event of unimaginable scale, reshaping the Mediterranean landscape in a matter of years.

Massive flood in the Mediterranean

“The Zanclean megaflood was an awe-inspiring natural phenomenon, with discharge rates and flow velocities dwarfing any other known floods in Earth’s history. Our research provides the most compelling evidence yet of this extraordinary event,” noted Dr. Aaron Micallef, lead author of the study and a researcher at the Monterey Bay Aquarium Research Institute.

To understand just how enormous this flood was, researchers estimate that it had a discharge rate of between 68 and 100 Sverdrups (Sv), with one Sv equal to one million cubic meters of water per second.

By comparison, the combined discharge of all modern rivers on Earth is approximately one Sverdrup. This means the Zanclean Megaflood involved an amount of water far exceeding anything seen in recorded history.

The force of this flood was enough to carve deep channels, erode solid rock formations, and transport vast amounts of sediment across the region. Scientists now believe that this event fundamentally altered the geography of the Mediterranean, leaving behind geological scars that persist to this day.

Flood clues beneath the Mediterranean

To uncover the full impact of the Zanclean Megaflood, researchers examined over 300 streamlined ridges across the Sicily Sill, a submerged land bridge that once divided the Mediterranean’s western and eastern basins. These ridges provide clear evidence of large-scale, turbulent water flow.

“The morphology of these ridges is compatible with erosion by large-scale, turbulent water flow with a predominantly north easterly direction. They reveal the immense power of the Zanclean Megaflood and how it reshaped the landscape, leaving lasting imprints on the geological record,” explained study co-author Professor Paul Carling of the University of Southampton.

By studying these ridges, scientists found that they were topped with a layer of rocky debris. This debris consisted of material eroded from the ridge flanks and surrounding regions, indicating it had been deposited suddenly and with immense force.

Importantly, this sediment layer aligns with the transition from the Messinian to the Zanclean period, providing further confirmation that the flood occurred at this critical juncture.

Role of W-shaped channel

A crucial piece of evidence came from seismic reflection data, a technique that uses sound waves to create images of subsurface geological formations. This method revealed a previously unknown “W-shaped channel” on the continental shelf east of the Sicily Sill.

This channel, carved deep into the seabed, appears to have played a vital role in directing floodwaters toward the Noto Canyon, a deep underwater valley in the eastern Mediterranean.

The shape and location of the channel suggest it functioned like a giant funnel, helping to transport the enormous volume of water into the deeper sections of the sea.

Computer models developed by the research team simulated the likely behavior of the floodwaters. The results showed that as the flood progressed, water flow intensified, reaching speeds of up to 32 meters per second (72 miles per hour).

This powerful current deepened channels, eroded rock formations, and transported sediment over vast distances.

Lasting impact of the megaflood

Dr. Micallef highlights the significance of these findings, not just for understanding the Mediterranean’s past but for studying large-scale floods on Earth and other planets.

“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. It opens the door to further research along the Mediterranean margins.”

The research highlights the long-lasting impact of the Zanclean Megaflood. Even millions of years later, its effects remain visible in the Mediterranean’s underwater topography.

Understanding how such catastrophic floods shape landscapes can provide valuable insights into similar events that may have occurred on Mars or other planetary bodies.

New chapter in Earth’s history

The Zanclean Megaflood is now recognized as one of the most significant flooding events in Earth’s history.

This research, supported by the National Geographic Society, Deutsche Forschungsgemeinschaft, and the David and Lucile Packard Foundation, redefines how scientists understand the Mediterranean’s transformation.

By combining geological surveys, numerical modeling, and seismic imaging, researchers have reconstructed a detailed picture of this catastrophic event.

The findings challenge previous assumptions and open new avenues for exploring past megafloods and their role in shaping the planet.

The study is published in Communications Earth & Environment and is available online.

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