The disappearance of Helike-Classsical Greece: New geological evidence

Category Climate system
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Ferentinos, George; Papatheodorou, George
Holding Date 04 October 2008

Helike was the capital of the twelve city-state alliance, "the Achean Dodecapolis" in the northern Peloponnesus, Greece. The classical city of Helike was devastated by a violent earthquake on a winter night in 373 BC. The recent discovery of architectural classical remains by the "Helike Project" team in the fan delta of the Selinous and Kerynitis rivers, combined with new geological evidence shows that Helike, after its destruction submerged and remained covered by water for a very long period.
A concise review of the sequence of events associated with the destruction of Helike as presented by the ancient writers, Diodoros, Strabo, Aelian and Pausanias, together with new research in the Gulf of Corinth regarding: (i) the onshore and offshore fault activity (Stefatos et al 2002), (ii) the causative mechanisms of coastal and submarine landslides (Papatheodorou & Ferentinos 1997) and (iii) the expected intensity of tsunami, allows us to examine the causal mechanism of its submergence. The new geological evidence suggests that: (i) tectonic activity, that is downfall of the hanging wall of the active Helike fault due to an earthquake, could not have caused enough subsidence in the coastal zone, where ancient Helike was built, for Helike to have been permanently submerged.(ii) Settlement due to grain packing caused by earthquakes could not have caused sufficient subsidence of the coastal zone for Helike to have been permanently submerged.(iii) The expected wave height of the tsunami in the Gulf of Corinth, activated by either a submarine fault or a submarine landslide would not have been high enough to invade the coastal zone as far as 2km inland and cover Helike even, temporarily by water.
The most probable causative mechanism for the submergence of Helike, based on the study of recent coastal landslides, is land subsidence caused by a translational landslide. At the head of such of landslide, where the detachment of the sliding mass occurs, a trench, due to the tensional forces which act in the sliding mass, is formed. In such a trench the sea could have invaded and permanently covered Helike. The geotechnical properties of the sediments and slope stability analysis have shown that an earthquake of 6.2 R magnitude can enhance liquefaction of subsurface horizons which can temporarily provide a failure surface for translational sliding to take place.
Papatheodorou, and Ferentinos, G. 1997. Submarine and coastal sediment failure triggered by the 1995 Ms = 6.1R Aegion earthquake, Gulf of Corinth, Greece. Marine Geology 137: 287-304.
Stefatos, A., Papatheodorou, G., Ferentinos, G., Leeder, M., and Collier, R., 2002, Seismic reflection imaging of active offshore faults in the Gulf of Corinth, Greece: Their seismotectonic significance: Basin Research, 14: 487–502.