The Flood To End All Floods: The Dramatic History Of The Middle Sea

Ah, the Mediterranean!

In later 2022 and beyond, Wheel & Anchor will be spending a lot of time on the shores of this near-landlocked sea often described as the cradle of Western civilization. For thousands of years, it’s served as the breadbasket (or more correctly fish-net) & multi-lane superhighway of the European, Middle Eastern and North African countries directly or indirectly bordering upon it…

And, of course, it’s been a source of immense pleasure to beachgoers, sailors and international tourists of all kinds. Just ask everyone who enjoyed the recent Wheel & Anchor trip to Madeira, or everyone with us in Cyprus right now – and it’s why we’re taking long stays in Malta and Madeira next year, alongside other Mediterranean destinations.  

It’s a reassuringly timeless place. The coastline may change a little here and there, the politics of each country may ebb and flow, but the sea itself is just as it’s always been, as reliably as a Japanese railway timetable.


This is certainly true within human timescales. But let’s go on a journey to a time before humans – to an event of almost unimaginable drama. Hold onto your hat – this might change how you see the Mediterranean forever.

*Scene change*.

Now it’s six million years ago – and the view looks very different. In place of the 1,000,000 cubic miles of modern seawater that stretches 2,500 miles (4000 km) from Gibraltar to the Gulf of İskenderun (Turkey), there’s…something else entirely.

A big problem here is how unimaginably distant 6 million years is. But there are clues to help us. In the 1960s, a seismic survey (think “geological ultrasound”) of the floor of the Mediterranean uncovered a continuous feature a few hundred metres down. Further investigations by the crew of the research vessel Glomar Challenger in the ‘70s confirmed both its existence and composition.

It was salt. Lots and lots of salt.

Some of these layers of salt were two miles thick. As National Geographic science writer Maya Wei-Haas puts it: “enough to give each of the world’s 7.7 billion people nearly 50 Great Pyramids of Giza filled with the stuff.”

Salt comes from evaporated seawater – so, salt on this scale? It must have been the mother of all dessications. 

Scientists now refer to this as the Messinian Salinity Crisis, after the geological age it took place in. In some presumed tectonic upheaval, the sea floor of what’s now the Strait of Gibraltar was thrust upwards, forming a bridge that cut the Mediterranean off from the Atlantic, its main replenishing source of water – and the Med started drying out. 

After some amount of time – certainly more than all recorded human history, probably even longer than the 300,000 years that anatomically modern humans have existed on Earth – the bowl of the Mediterranean was a deep, empty desert, save for a few huge, super-salty lakes of unknown size. 

A desert up to 900 miles across, with sloping cliffs over a mile deep – shallower in the west of the Mediterranean bowl where the seabed is former of continental crust, much deeper in the east (and at its extreme eastern end, an incredible “Egyptian Grand Canyon,” formed from the foundations of the Nile)… 

And at its Western end, a plug – a strip of land just a few miles wide – with the force of the whole Atlantic behind it.

Maybe you can see where all this is going.

A few decades ago, Daniel Garcia-Castellanos, a geophysicist at Geosciences Barcelona, grew curious about what happened next. How quickly could a whole sea be refilled?


It’s easy to imagine centuries of streams and rivers trickling water back in, nibbling away at that land-bridge, a little stronger every year. A uniformitarian model, based on the rate of gradual change we can see at work today. I mean, all this geology didn’t happen overnight, did it?

But the gradualistic model didn’t tally with the work Garcia-Castellanos had previously done around tectonic lakes:  

“In the models we were running in Amsterdam, this transition was very fast.”

It seemed more likely that while a stream or river maybe have taken hundreds or thousands of years to cut back to the Atlantic side and form a breach, when that critical tipping-point was reached, 90% of the floodwater powered through according to a human timescale.

“When we got the first predictions, I was very surprised and thought maybe something was wrong with the formulations,” Garcia-Castellanos later told the journal Nature. “If the model was correct, we would expect to find traces of the flood erosion preserved under the sedimentary layers in the strait.”

So he and his team went looking – and found the marks of a cataclysm.

There on the floor of the Strait of Gibraltar was a massive channel, carved through sediment and rock, hundreds of meters deep and running from the Gulf of Cadiz to the Algerian Basin – a distance of nearly 390 km. If this did indeed happen quickly, and this was the result…can you imagine the violence at work here?

This is a silly question. Nobody can, so we have to resort to using numbers.

Ever seen the Niagara Falls, on the border between Ontario and New York? Or even better, have you felt them, standing there in person, with all that water roaring past, feeling the spray against your face and the thunder of it shivering through your knees?

Every second, around 2,400 cubic metres of water tumble over the Falls, representing a total weight of around 3,100 tons, smashing the base of the waterfall with a force of 2,509 tons. That’s every second, remember.

It’s very hard to put any of this into a meaningful human perspective – so I’ll just say that the weight of an Airbus A380, currently the world’s largest passenger airliner, is a touch under 620 tons.

In contrast, the flood Garcia-Castellanos and his team were modelling seemed to require a peak flow of a hundred million cubic metres of water a second.

This wasn’t a waterfall, but a catastrophic deluge down a gigantic slope extending east from the Strait for hundreds of miles. This torrent would be fast enough to refill the Mediterranean not in centuries or even decades, but in years – or even months. A megaflood, dwarfing even the colossal Missoula Floods in modern-day Washington state at the end of the last ice age.

For understandable reasons, the Zanclean Megaflood model has proved controversial – so for the last decade, Garcia-Castellanos and his fellow researchers have been busily searching for more evidence. For example: where did all that ripped-up sediment (enough to fill “400 million olympic swimming pools”) from that 390 km-long trench go?

The coast of Sicily
The coast of Sicily

In 2018, a team led by Professor Aaron Micallef from the University of Malta published their findings from investigations off the coast of Sicily. They found a huge, chaotic mess of sediments piled at the bottom of a subterranean sea-cliff that plunges 3km to reach the eastern sea floor.

The implication? At some point in the last 6 million years, there was the mother of all waterfalls here, 1.5 km high, over which flood-waters tore at speeds up to 160 km an hour.

By comparison: Tugela Falls in South Africa, recognised since 2016 as the tallest waterfall in the world, is 983 metres high. There is no modern parallel for the Malta Escarpment waterfall, either in height, in speed or in sheer unbridled violence.

The deepest spot in the modern Mediterranean is just off Greece, where the ocean drops 5.4 km – 16,000 feet – straight down to the sea bed. Around it, the eastern Med forms a deep bowl hundreds of kilometres across. 

With that in mind, consider the team’s conclusion that during this flooding event, the water-level in the eastern sea was rising by ten metres a day.

Nevertheless, Garcia-Castellanos notes this isn’t yet scientific consensus. In 2020, he said:

“All of the evidences that have been summarized in this article may have other possible interpretations and, before convincing the scientific community it will be necessary to have other studies that consider the hypothesis from other angles.”

(However, it’s worth considering that any competing theory is going to have to work really hard to explain all these findings in other terms. It’s certainly looking like the most sensible explanation on the table.)

Could all this happen again? Quite possibly…but it’d take millions of years, so there’s not much to worry about there. 

And could this be the source of all those flood myths that every culture seems to have? This seems unlikely, because modern humans only appeared a few hundred thousand years ago, meaning those stories would have had to come from our distant primate ancestors…which were probably living in Africa at the time. Probably a safe bet that other floods are the explanation for these stories.

So – next time you’re standing on a Mediterranean beach, with the blue-green water lapping at your ankles, take a second to imagine all that water gone, so suddenly you’re at a gently sloping cliff edge, and before you is a canyon so vast that the other side is hidden over the horizon. Imagine the lost world down there that you never knew about and no human eyes have seen, because of the sheer speed at which we live…

What else is out there, waiting to be discovered?

Further Reading On The Zanclean Megaflood:

– “The Zanclean megaflood of the Mediterranean: searching for independent evidence” – Daniel Garcia-Castellanos, Aaron Micallef, Ferran Estradad, Angelo Camerlenghi, Gemma Ercilla, Raúl Periáñez, José María Abril. Earth Science Reviews Vol. 201 (2020)

– “The Mediterranean nearly dried up. A cataclysmic flood revived it.” – Maya Wei-Haas, National Geographic, March 6th 2020.

– “A Megaflood-Powered Mile-High Waterfall Refilled the Mediterranean” – Katherine Kornei, Scientific American, March 26th 2018.

Scroll to Top