An underwater “lost city” appearing to boast colonnades and courtyards has turned out to be nothing more than the aftermath of a gas leak.
When divers first spotted the structures in shallow water off the Greek island of Zakynthos in 2013 they thought they had discovered the ruins of a long-forgotten civilisation.
However, new research published today reveals the site was created by a natural geological phenomenon that took place up to five million years ago in the Pliocene era.
Scientists from the University of East Anglia joined counterparts at the University of Athens and the Ephorate of Underwater Antiquities of Greece to study the site.
They found that what superficially looked like circular column bases and courtyard floors were actually objects formed by the release of methane from cracks in the sea floor.
This natural explanation for the structures was not initially entertained because such gas escapes usually occur at far greater depths.
Professor Julian Andrews, lead author of the study, which is published in the journal Marine Petroleum Geology, said: “The disk and doughnut morphology, which looked a bit like circular column bases, is typical of mineralization at hydrocarbon seeps.
“This kind of phenomenon is quite rare in shallow waters.
“These features are proof of natural methane seeping out of rock from hydrocarbon reservoirs.
“The same thing happens in the North Sea and it is also similar to the effects of fracking.”
The column-like structures and flat 'stone' slabs were formed as a result of a prehistoric gas leak up to five million years ago.
The process, called concretion, happens when methane gas escapes from a fault and bubbles up through the sediment on the sea floor.
Bacteria living in the sediment metabolises the gas, causing a chemical reaction in the sand around them forming a natural cement known as dolomite.
This solidifies into columns, tubes and slabs and as the surrounding sediment erodes away.
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