Underwater ‘lost city’ found to be a geological formation

Underwater ‘lost city’ found to be a geological formation

What has been considered an underwater, lost city is a geological phenomenon that occurs naturally.

Pipe-like, disc-shaped and doughnut-like structures discovered by underwater divers near the island of Zakynthos, Greece, were originally thought to be ruins of an ancient city, such as remains of paved floors, courtyards and columns.

Researchers have now discovered that the “ruins” are, in fact, geological formations, the results of a natural phenomenon that happened in the Pliocene period up to 5 million years ago.

The site is investigated by an archaeologist with the Ephorate of Underwater Antiquities in Greece, a field specialized in underwater archaeology within the Greek Ministry of Culture; no further evidence has been found that this was an ancient civilization.

The Greek Ministry had been suspecting a geological cause and studying unusual formed structures by researchers from the University of East Anglia and Athens to investigate the oddly shaped structures.

“The site was discovered by snorkelers and first thought to be an ancient city port, lost to the sea,” lead study author Julian Andrews, a professor at UEA’s School of Environmental Sciences, said in a statement.

“There were what superficially looked like circular column bases and paved floors but, mysteriously, no other signs of life — such as pottery.”

Using microscopy, X-ray techniques and chemical analyses, the researchers studied the mineral content of the underwater formations. These analyses showed that the “ruins” are likely the fossilized remains of a natural plumbing system, located beneath the seafloor, for ancient hydrocarbon seeps. Here, methane and other hydrocarbons escape from the seafloor into the water above.

While beneath the seafloor, microbes in the sediment would have used the carbon in methane as fuel, forming a natural cement around the structures. The resulting structures are known to geologists as concretion.

Erosion then exposed the underground structures to the bustling ecosystem in the modern, shallow subtidal zone, where the structures were “bored and encrusted by modern marine organisms,” Andrews and colleagues wrote in the study, which appeared today in the journal Marine and Petroleum Geology.

“The disk and doughnut morphology … is typical of mineralization at hydrocarbon seeps — seen both in modern seafloor and paleo settings,” though such formations “looked a bit like circular column bases,” Andrews said. “We found that the linear distribution of these doughnut shaped concretions is likely the result of a subsurface fault which has not fully ruptured the surface of the seabed. The fault allowed gases, particularly methane, to escape from depth.”

Though the site is not in fact an ancient, underwater city, the discovery near Zakynthos is rather uncommon geologically, Andrews said. The phenomenon is rare in shallow waters, as most similar formations can be located hundreds or thousands of meters deep underwater, he said.