I have always found stories of the difficulties ancient civilizations have had with geohazards and disasters interesting. The story of Helike is especially interesting in this regard. Helike was an ancient Greek city located near the Corinthian Gulf that was thought to have disappeared over night into the sea. In many respects this story is quite similar to the story of the fictional Atlantis. However, the story of Helike’s demise always appeared credible due to the fact that many of the people who wrote of the demise of Helike were contemporaries.
The story goes that a massive earthquake and tsunami devastated the city in 373BC and it subsequently sunk to the bottom of the ocean. Along with the city, 10 Spartan ships which were anchored in the harbour at the time were also said to have been pulled down beneath the water. At the time this disaster was considered to be as a result of the wrath of the God of the Sea Poseidon. It was said that for centuries after this event the ruins of the city could still be seen beneath the water. Eventually the site was silted over and consequently was lost to time and forgotten. It was considered by some to be another myth, similar to Atlantis, until its rediscovery within an ancient lagoon, near a normal fault in 2001.
Excavations at the site have found significant archaeological finds going back thousands of years to the Early Bronze Age (2500-2300 BC). Investigations by Carlos A. Alvarez-Zarikian, Steven Soter and Dora Katsonopoulou into the environmental history of the area indicates that the Early Bronze Age (EBA) is overlain by clay and sandy clay with freshwater, brackish and marine microfossils. The explanation for this has been that the EBA site was submerged in a lagoon, possibly by an earthquake on a normal fault within the area. The 373BC site is overlain by silty sands and silty clays with mostly freshwater and brackish microfossils.
A working theory is that recurring earthquakes on the fault pull the land down, submerging it beneath the water, and providing an ingredient for tsunami inundation. Rapid sedimentation occurs at this site due to the Selinous, Kerynites, and Vouraikous Rivers. This sedimentation brings the land back above sea level………in preparation for the next society to come along and develop on.
Interestingly, on the same site in 1817, an earthquake followed by a tsunami swept away much of the beach. In Vostiza (now known as Aigio) 65 people lost their lives, two thirds of the buildings were ruined and 5 villages on the plain destroyed.
This provides a very interesting perspective on how the time between significant and catastrophic events are sometimes out of sync with human time scales — including the passing down of stories. What Helike has shown is that a society finds a site which looks good for development (coastal, rivers etc.), develops on it, eventually a massive earthquake and possibly a tsunami occur, the area sinks beneath sea level, rapid sedimentation occurs bringing the area above sea level, the next society comes along and thinks this is a great place to build a city…….repeat ad infinitum.
What Helike teaches us is that relying solely on anecdotal evidence is very dangerous, but such an idea is often hard to convey to those who have lived peacefully in a region without incident for their whole lives. Adequate site investigation, including an understanding of the geological history, in the quest to analyse the suitability of the building of a site is absolutely critical to future development of cities.