Editorials

SAN FRANCISCO — Two ancient Egyptian cities that mysteriously sank into the Mediterranean about 1,500 years ago could have fallen victim to floods or a major earthquake — or a combination of both, researchers said Sunday. 

Herakleion and Menouthis, seaports that flourished during the age of the Pharaohs and previously only known from the writings of ancient scribes, were recently uncovered by undersea archaeologists. But scientists have yet to agree on exactly how they ended up 30 feet beneath the surface of the Bay of Aboukir. 

Some experts believe an earthquake caused the land to sink up to 27 feet, submerging the shaken cities. Others point to a massive flood of the nearby Nile, which now flows farther east. Then there is the possibility of a tsunami. 

“Since that time, the land has subsided,” said Amos Nur, a geophysicist at Stanford University. “The cities have disappeared and the Nile is gone.” 

“What caused the subsidence of this entire area? Was it catastrophic subsidence or was it gradual?” he asked. “The second question is what caused the collapse of all the structures that stood in those two cities?” 

The demise of Herakleion and Menouthis was debated  

Sunday at the fall meeting of the American Geophysical Union,  

a gathering of Earth and  

planetary scientists. 

Nur, who works with the French archaeological team to uncover geologic explanations for the sinking, believes a massive earthquake played a large role in the destruction of the cities. But there’s a problem. 

The major plate boundaries, where faults capable of generating such a massive quake can be found, are hundreds of miles to the north of the port cities that once thrived about 15 miles east of Alexandria. 

There is some historical evidence of major earthquakes in the area – though not covering the time that the cities disappeared. And nobody has been able to find convincing evidence of major faults. 

“In order to get 8 meters (26 feet) of subsidence, you have to have a nearby magnitude-8.5 earthquake,” Nur said. “Is it possible that there are faults here that could generate large earthquakes but very infrequently so we miss them? 

“This makes for very exciting geophysics.” 

Egyptian engineers built the cities on unstable, silty soil. During a quake, the shaking can cause the ground to liquefy. That happens in modern times, too, including in San Francisco’s Marina district during the 1989 Loma Prieta earthquake. 

It’s also possible that the cities were destroyed by a tsunami generated by a strong earthquake elsewhere in the Mediterranean. Such a giant wave destroyed a large part of Lisbon back in 1755, killing 60,000 people. 

Though the Lisbon disaster did not result in the city sinking, it is possible elsewhere – especially if a city is built on sediments, Nur said. 

Artifacts continue to be found in the area that could shed light on the cities’ demise, said Franck Goddio, who led the original expedition to the sites. In October, previously unknown and perfectly preserved piers were found off Alexandria. 

Archaeologists also found gold coins, the most recent dating to 740 A.D., said Jean-Daniel Stanley of the Smithsonian Institution. “Coins are useful because they’re gold coins. They’re not something someone would chuck out into the sea after cities had submerged,” he said. 

On the Net: Franck Goddio Society: http://www.franckgoddio.org/