Tsunami deposits of the Caribbean - Towards an improved coastal hazard assessment

Coasts worldwide experience considerable population pressure and the demand for reliable hazard management, such as of tsunamis, increases. Tsunami hazard assessment requires information on long-term patterns of frequency and magnitude, which are best explained by inverse power-law functions. In areas with a short historical documentation, long-term patterns must therefore be based on geological traces. The Caribbean tsunami hazard is exemplified by >80 events triggered by earthquakes, volcanic activity, or mass wasting within the region or in the far-field during the last 520 years. Most of these tsunamis had regional or local impacts. Based on two numerical hydrodynamic models of tsunamis spawning at the Muertos Thrust Belt (MTB) and the South Caribbean Deformed Belt (SCBD), which are two scenarios only marginally considered so far, we show that pan-Caribbean tsunamis can also be taken into account. We furthermore review almost 60 sites for possible geological evidence of tsunamis in the Caribbean including fine-grained subsurface deposits and subaerial coarse clasts, and re-evaluate their implications for tsunami hazard assessment against state-of-the-art models of onshore sediment deposition by tsunamis and extreme storms. The records span the mid- to late Holocene, with very few exceptions of Pleistocene age. Only a limited number of reliable palaeotsunami records with consistent and robust age control were identified, hampering inter-island or interregional correlation of deposits of the same event. Distinguishing between storm and tsunami transport of solitary boulders is very difficult in most cases, whereas those clasts arranged as ridges or incorporated into polymodal ridge complexes, which line many windward coasts of the Caribbean, can mainly be attributed to long-term formation during strong storms, overprinting potential tsunami signatures. The quantification of tsunami flooding parameters such as flow depth, inundation distance or flow velocities, by applying inverse and forward numerical models of sediment transport is still very limited and needs to be extended in the future. Likewise, sediment-derived hazard implications still await implementation in spatial planning. As extreme-wave deposits are clearly understudied in the Caribbean, there is great potential for coastal hazard assessment to be developed and improved. Thus, further studies using common standards of high-resolution methods of bedform and stratigraphical documentation and robust chronological models with independent age control, combined with refined inverse and forward models of sediment transport and deposition are required to reconstruct reliable patterns of magnitude and frequency of palaeotsunamis in the Caribbean and to map hazard-prone areas. To date, known palaeotsunami deposits from the Caribbean probably represent only a fraction of actually happened prehistoric tsunamis and, therefore, do not reflect major tsunami inundations of the past adequately. (C) 2016 Elsevier B.V. All rights reserved.