TSUNAMIS ON THE ABC ISLANDS – DISCREPANCIES BETWEEN THE HISTORICAL RECORD AND GEOLOGICAL ARCHIVES

The Caribbean region is disproportionally vulnerable to coastal hazards, since a relatively high percentage of the population lives right at the coasts. Based on their short recurrence intervals over the intra-Americas Seas, tropical cyclones and their associated effects of elevated storm surge, heavy wave impacts, winds, and mudflows represent the most serious hazard. However, tsunamis are responsible for the loss of lives and property as well, as indicated by (i) the variety of trigger mechanisms (strike-slip motion and oblique collision at the northern and southern Caribbean plate boundaries, subduction at the eastern plate boundary, submarine and coastal landslides, volcanism, teletsunamis), and (ii) numerous historical accounts. In contrast to almost all of the Greater Antilles and the Lesser Antilles island arc, tsunami occurrence has never been reported on the Leeward Lesser Antilles or “ABC Islands” (Aruba, Bonaire, Curaçao) off the coast of Venezuela. This lack of historical evidence stands in remarkable contrast to overwash deposits in lagoonal sediment archives and coastal boulder fields indicating wave impacts and coastal flooding events largely exceeding those of category 5 hurricanes of the recent past. We identified possible sedimentary evidence for tsunamis and explored new geoarchives for enhancing the chronology of candidate paleotsunamis by dating stratigraphical contexts using radiocarbon. Furthermore, we present a numerical study on minimum wave heights required to move the largest coastal boulders, in order to tentatively rule out hurricanes for their transport. The paper includes key results of multi-proxy investigations (grain size distribution, loss-on-ignition, XRF-ITRAX, XRD, AAS, magnetic susceptibility, macrofauna, microfauna) from coastal stratigraphies on Bonaire, aiming to infer potential Holocene tsunamis from their overwash deposits. Based on these findings, the recurrence rate for highest-magnitude coastal flooding events on Bonaire is roughly in the order of 1000 years.