Large scale liquefaction is a major hazard for new cities or for extensions of cities in coastal areas. Three historic disasters are reviewed: The case of Helike, which relates to one of many repeated liquefactions, the destruction of Sibaris for which there is considerable evidence that liquefaction must have played a part, and God's wrath on Port Royal, as it was believed at the time. Three recent catastrophies are also mentioned, among many others that are left out, to show that the phenomenon is continuing. Risks are high both in cases of naturally deposited loose silty sands, and artificial uncompacted fills. Town planners should be made aware of past disasters so that mistakes can be avoided in the future. Also, building codes should include special provisions for flat coastal areas, regarding investigations and, when required, site improvement.
The splendid city of Helike is said to have disappeared under the sea, with all of its citizens, in 373 BC. The wording suggests ground subsidence, slides, and a tsunami. Judging from literary and historic references Helike must have been a big city on the coast with a famous sanctuary and a bronze statue of Poseidon. After the catastrophe, the statue remained in the sea at small depth for a long time, and became a hazard to shipping. As indicated by Stabo (67 BC – 23 AD), sacrifices were made to the God at the site of the underwater sanctuary as late as the first century A.D. References are made to Helike's catastrophe also by Ovid (43 BC – 16 AD), Plinius (23 – 79 AD) and others. There is a village called Helike in the general area mentioned by Pausanias (Fig. 1) but the relation between this modern location and the historical site is uncertain.