Evidence of late-holocene tsunami events in Lebanon

We present new evidence of megablocks left by extreme waves around the Tripoli islands and Byblos, northern Lebanon. On Ile du Palmier, megablocks have been projected a distance of 50 to 100 m from the shoreline. A Dendropoma bioconstruction was sampled from the outer part of one of the blocks, approx. 3.5 m³ in size and located 60m from the shore. It dates a mid-Holocene event (5155 ± 40 ¹⁴C years BP, or 3639-3489 cal. yr BC) deriving from the west. On the nearby island of Senani, numerous megablocks are scattered on the flat island surface. Their position again suggests projection by westerly waves. One of the blocks, approx. 30 m³ in size and 10m from the shoreline, yielded a radiocarbon age of 525 ± 40 BP (1690-1950 cal. AD). Further south, at Byblos, a 5.5 m³ block projected towards the base of the ancient sea wall, was encrusted with upper subtidal vermetid shells, constrained to 855 ± 30 yr BP (1436-1511 cal. AD). A nearby 20 m³ conglomerate block was dated 710 ± 30 yr BP (1528-1673 cal. AD). A tsunami origin seems a feasible explanation for most of the megablocks encountered. Review of the vertical movements having affected the Lebanese coast during the late Holocene shows that major uplift of coastal areas occurred around 3000 yr BP, in the 6th century AD, and possibly in the 10th to 11th centuries AD. None of these periods coincide with the megablock dates, suggesting that the tsunami waves derived from outer tsunamigenic areas.