Strong tsunami impact on the Bay of Aghios Nikolaos and its environs (NW Greece) during Classical–Hellenistic times

This paper presents, for the first time, detailed geomorphological, sedimentological, geoarchaeological, geophysical and geochemical evidence of a strong tsunami impact on the Bay of Aghios Nikolaos and its environs (NW Greece) during Classical–Hellenistic times. Tsunamigenically dislocated beachrock slabs found on top of the Santa Maura beach ridge complex are closely interrelated to adjacent coarse-grained washover fan deposits encountered in vibracores and detected by earth resistivity measurements. Based on detailed topographic surveys and geomorphometric investigations, it was possible to localize areas of high intensity overflow. Underwater studies revealed that the central and northern parts of the former Plaka beach ridge were completely destroyed by tsunami impact. Loose littoral deposits were flushed into the Bay of Aghios Nikolaos and mega blocks of the underlying beachrock structure were dislocated landwards. Tsunami landfall occurred all along the eastern and northern shores of the bay where deposits, partly weathered and associated to archaeological findings, were found. Runup was estimated to minimum values between 2–3 m and 4–6 m a.s.l. Crosschecking the results of radiocarbon analyses with archaeological ages from five sites allowed to date the strong tsunami event to the time period between 395 cal BC and 247 cal BC. Due to the funnel-like contour of the coastline, the area is extremely sensitive to tsunami events of mid to high magnitude and high frequency.