SUBMERGENCE OF GREEK COASTAL SITES IN THE MEDITERRANEAN: MORE THAN JUST RISING SEA LEVEL

Greek harbor and ship-landing facilities studied by us in the central and eastern Mediterranean, some dating back to the 8th century BC, are presently submerged at water depths to 8 m. However, Holocene sea-level curves compiled for these regions, based on results of modeling by others and our field observations (coring, geophysics), indicate very modest rates of sea-level rise (slr) during this past 2700 yr time-span. Sea levels were within -1.5 m msl for periods represented by archaeological levels. For example, sites (Herakleion and others) submerged on Egypt’s relatively stable Nile delta margin and Sybaris on Calabria’s major delta, the Crati, are now at depths ranging from 4.0 to 8.0 m beneath msl, or much lower than can be accounted for simply by slr. Diverse controlling factors for this include compaction, faulting and failure (liquifaction, slumping) of water-saturated sediment substrates at relatively shallow depths, plus isostatic lowering and shifts of thick deltaic sequences at greater depths. These result in high average long-term subsidence rates, such as 4 to 5 mm/yr for some sites on the Nile delta margin. Triggers for failure along these coasts include floods, storm surges, tsunamis and earthquakes. Moreover, there is evidence of marked episodic vertical shifts of land on highly active tectonic margins, such as those of the Calabrian Arc in southern Italy and Alexandria’s Eastern Harbor. The ~100 m rise of the ~125,000 yr old (Tyrrhenian) shoreline marker in hills behind the Ionian coast, and lowering of land beneath Greek sites of Kaulonia and Locri-Epizefiri at about the same rates (~1.0 mm/yr) offshore are measured. Rapid subsidence of land in Calabria caused a marked displacement of the coastline in a direction seaward, rather than landward, during the late Holocene. Overall, slr has played only a minor role in the submergence of sites we have examined to date and, from this, it is possible to surmise that other Greek and older coastal sites may yet be discovered by offshore exploration.