Geomarkers of the 218–209 BC Atlantic tsunami in the Roman Lacus Ligustinus (SW Spain): A palaeogeographical approach

Between 218 and 209 BC, the western coasts of Iberia suffered the impact of a historical tsunami, with an epicentre probably located in the Atlantic Ocean near the Cape St. Vincent area (SW Portugal). Palaeogeographical changes in the River Guadalquivir estuary, the ancient Roman Lacus Ligustinus, have been recorded in erosional and depositional landforms, both stratigraphically and as landscape relicts. The tsunamigenic waves (run-up of ∼5 m) and their subsequent backwash eroded the previous littoral spits transversally, generating rectilinear cliffs and incisions. The littoral foredunes were also eroded and reactivated as transgressive dunes over the edge of the marshes. Former coastal sediments (∼520–100 BC) generated overwash deposits, ebb tide deltas and sand sheets within the estuary, as well as a subsequent bioclastic beach on the lagoon shore, defining the post-tsunami (130 BC–80 AD) estuarine shoreline (Roman lagoon). Some coastal pre-Roman (7th to 3rd centuries BC) human settlements were abandoned, and later, in the Roman period (1st century AD), saltworks were installed. Morphological and sedimentological changes in the coast triggered by this event were similar or greater than the changes in coastal features related to the AD 1755 Lisbon tsunami.