Geologists have long reported convincing evidence that the Mediterranean Sea has dried up and refilled a few times over the last several million years as sea levels rose and fell over and under the altitude of the sill at Gibraltar (which itself has tectonically shifted up and down too). The proof lay in enormous evaporative deposits of salt under the seabed today and ancient, now-undersea stream channels extending deep into the basin. A geologist, Kenneth Hsu, even wrote a dramatic book on it 20 years ago, The Mediterranean Was a Desert, that entertained the idea of at least one stupendous waterfall at Gibraltar and perhaps more during episodes when the rising ocean refilled it.

Now, several news outlets are reporting the latest, in Nature. It sees a refilling not quite as amazing as the waterfall hypothesis, but sensational anyway. Spanish researchers report that mapping of the erosional path left by one of the refillings, the Zanclean flood of 5.33 million years ago, suggests that after a long period of low flow into the dessicated basin triggered mainly by subsidence of the natural dam, the incoming waters incised a deep enough cleft to produce a torrent. It then almost overnight carved a huge breach at Gibraltar, ran with 1000 times the volume of the Amazon, and flooded the one or two miles-deep Med valley back to sea level in almost no time – from a few months to perhaps two years. Not a waterfall exactly, but a cataract of Noachian scale.  My colleague at ksjtracker, Pere Estupinyá, got to this already today, rounding up Spain’s newspaper coverage in the next post down. He got the really snazzy artist’s picture so above is a geological one.

Here are more, from the English language press:

• Guardian (UK) Ian Sample: Mediterranean was created in Earth’s biggest deluge ; Superlatives are such tricky things – do we know this was the biggest such episode? No. But it is hard to think of any specific way to make a bigger one. Water velocities, he reports, would have been around 100 km/hr. Talk about white water. One wonders if things like whales survived the trip.
• New Scientist – Kate Ravilious: Mega-flood filled the Mediterranean in months ; Nice lede: “Eat your heart out, Noah.” Makes no sense historically or theologically, but funny and effective.
• LiveScience – Andrea Thompson: Big flood may have created Mediterranean Sea ; Ocean water cut long channel over Gibraltar Strait, study says ; The hed has no news (the flood even had a name), but the story is on target. However: conversion alert. The text says the Med may have risen at least ten meters a day. That’s obviously a very round number guesstimate. So why translate it to 33 feet? Please people, if one starts with a one-significant-figure datum, keep it that way in other units. About 30 (or, ok, even 35) feet is better.
• BBC – Victoria Gill: Ancient Mediterranean flood mystery solved ;
• AAAS ScienceNow – Phil Berardelli: A Flood, Not a Falls, Refilled the Mediterranean ;
• Science News – Lisa Grossman: The Big Spill: Flood Could Have Filled Mediterranean in Less Than Two Years ;

Grist for the Mill: Nature journal abstract ;

- Charlie Petit

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