Earth's biggest flood formed Mediterranean

Catastrophic flooding caused sea levels to rise by ten metres a day, according to new research

The Mediterranean was formed by the most spectacular flood in Earth's history when water from the Atlantic Ocean breached the mountain range joining Europe and Africa with the force of a thousand Amazon rivers, scientists say.

The devastating surge lasted as long as two years and at its peak caused the level of the Mediterranean to rise by more than ten metres a day. The floodwaters moved at more than 100 kilometres per hour and created scars on the seabed that are still visible today.

The deluge was triggered 5.3m years ago by subsidence in the seabed that caused a land ridge between the Atlantic and the Mediterranean basin to collapse. The ridge linked the Betic and Rif mountain ranges that hug the coasts of modern Spain and Morocco.

As water began to pour across the strait, it eroded the ridge until the flow became a catastrophic deluge. At the time, the Mediterranean basin was an almost entirely dry expanse of low lying land, between 1.5km and 2.7km beneath today's sea level.

The surge of water created a channel several kilometres wide that would become the Strait of Gibraltar. "The flow of water increased rapidly until it was truly catastrophic," said Daniel Garcia-Castellanos, a geophysicist at the Institute of Earth Science Jaume Almera in Barcelona.

The slope to the Mediterranean was about two degrees, he reported in the magazine Nature. "The column of water going down that slope was several hundred metres deep, and in a channel like this would have reached speeds of more than 100km per hour."

A team led by Garcia-Castellanos used data from boreholes and seismic surveys in the area to reconstruct the deluge conditions in a computer model.

Subsidence in the sea floor at the strait allowed water from the Atlantic to pour slowly into the Mediterranean basin for several thousand years, before the flow became a powerful surge that filled 90% of the Mediterranean very rapidly - between a few months and two years.

The floodwater discharged around 100m cubic metres of water every second, creating a 200km-long channel across the strait. Today, the Mediterranean contains 4m cubic kilometres of water.

Source:Guardian News & Media 2009