T29 Waves of Destruction: Historical and Geological Records of Tsunamis and their Effects (Posters)

THE 365 A.D. TSUNAMI DESTRUCTION OF ALEXANDRIA, EGYPT: EROSION, DEFORMATION OF STRATA AND INTRODUCTION OF ALLOCHTHONOUS MATERIAL

Paper number: T29-9
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Much of Alexandria, Egypt, the once-major Greek and Roman port in the Eastern Mediterranean, was destroyed on August 21, 365 A.D. Historic documentation includes eye-witness reports obtained at a somewhat later date by Ammianus Marcellinus. His descriptions are informative (translated from Latin, cf. Guidoboni et al., 1994, p. 267-268): “The sea was driven back, and its waters flowed away to such an extent that the deep sea bed was laid bare, and many kinds of sea creatures could be seen…Many ships were therefore stranded as if on dry land, and many people wandered freely…gathering fish and similar creatures…huge masses of water flowed back when least expected, and now overwhelmed and killed many thousands of people…Some great ships were hurled by the fury of the waves on to roof tops (as happened at Alexandria) and others were thrown up to two miles from the shore.” These phenomena and those in other reports of the time strongly point to a destructive tsunami associated with, or triggered by, major earthquake activity on the northern Mediterranean shore during early Byzantine time.

Sediment cores in the two Alexandria harbors separated by the Heptastadion (7 radiocarbon-dated cores in the Eastern Harbour, 65 closely-spaced in the Western Harbour) provide a stratigraphic, petrologic and biofacies record for identifying the 365 A.D. and subsequent events. Perhaps most useful is the major hiatus (erosion of >660 years of section) recorded in the upper part (younger than 2000 years) of all cores recovered in the Eastern Harbour, and markedly deformed Holocene strata in the Western Harbour. Also observed in cores are reversals of dated sections, and presence of coral, algae and serpulid tubes that normally occur in high-energy sectors seaward of the harbor basins. Rather than findings of unusual tsunami deposits, this geoarchaeological study documents the importance of harbor floor erosion by high-energy wave surges associated with this powerful event.