Once upon a time there was a massive flood across the Mediterranean Sea, an in-pouring of water so huge that it excavated a canyon five kilometres deep and 20 kilometres long, and created a waterfall with a 1.5 kilometre drop.

Evidence for the great flood, long hypothesised, has now been found by a team of researchers led by geoscientist Aaron Micallef from the University of Malta.

And while several Mediterranean traditions feature great flood narratives, the earliest arising from Sumeria and already well enough known to be recorded in cuneiform by the seventeenth century BCE, this one is unlikely to have been the inspiration.

In a paper published in the journal Scientific Reports, Micallef and colleagues present geological evidence for an event known as the Zanclean megaflood, which took place around 5,300,000 years ago.

The flood was preceded by a catastrophic geologic transformation called the Messinian salinity crisis (MSC), described by the researchers as “the most abrupt, global-scale environmental change since the end of the Cretaceous”.

In the Mediterranean region, the crisis was caused by the closure of what today is known as the strait of Gibraltar, cutting the passage between the sea and the Atlantic Ocean. This occurred around six million years ago.{%recommended 5971%}

As a result, there was a drastic imbalance created between evaporation rates and replenishing water intake. The Med transformed into two giant hypersaline lakes, separated by a land-bridge running from the toe of Italy, incorporating Sicily and ending at north Africa.

Sea levels are estimated to have dropped by between 1300 and 2400 metres. Salt deposits a kilometre thick settled on the sea floor.

Geographic evidence gathered in the 1970s led to the formation of the Zanclean megaflood hypothesis. Conclusive evidence, however, was lacking, leading some researchers to suggest the MSC was ended by a flow of brackish water from the Black Sea, with Atlantic inflow resuming only later.

In the latest research, using seafloor data from offshore eastern Sicily and the islands of Malta, Micallef’s team identifies a distinct body of sediment 160 kilometres long and 95 kilometres wide that lies on top of the saline deposits, ending abruptly against an undersea limestone cliff called the Malta Escarpment off eastern Sicily, and thinning down in a wedge-shape to the east.

The wedge is 900 metres deep in places. The researchers suggest it represents debris and sediment pushed eastwards by a surge of water coming in from the Atlantic upon the reopening of the Gibraltar strait.

The mass of water, carrying the debris, crested the land-bridge and plunged down the other side creating a five-kilometre-deep trench, still around today and known as the Noto canyon. It also careened down the Malta escarpment, dropping 1.5 kilometres.

Micallef and colleagues conclude that the evidence suggests the megaflood was a Mediterranean-wide event, rather than one restricted to its eastern reaches, as the Black Sea theory holds.

So powerful was the flood, it is estimated that the Med reversed water loses incurred over 640,000 years in just two.