Hazard assessment

The Caribbean region is highly vulnerable to coastal hazards since a relatively high percentage of the population lives right at the coast. Tourism, a major economic factor on many islands, is concentrated in coastal areas as well. The “traditional” hazards along the coasts of the Caribbean, as perceived some decades ago, are earthquakes, volcanism and storm surges during hurricanes. This focus is justified in the light of the devastating earthquake of Haiti in 2010, which represents a regional maximum in magnitude with a death toll of more than 230,000. The eruption of Mount Pelée on Martinique, which destroyed St. Pierre, the former principal town of the island, and killed around 28,000 inhabitants, and the Great Hurri-cane of 1780 with a similar number of fatalities along the Antilles island arc were outstanding disasters in terms of magnitude. Moreover, the frequency during the 500 years of historical documentation is high as well.
However, history tells that the Caribbean is also prone to the risk of tsunamis. One hundred twenty-seven possible tsunamis were documented during the last 500 years, of which 53 were finally considered to be real tsunamis.

Tsunami hazard on Bonaire
Since we found geological traces of potential tsunamis at almost all sites investigated along the coast of Bonaire, we consider the entire coastline to be prone to tsunami hazard. Along the windward coast, the largest boulders point to the occurrence of tsunami wave heights in the order of 8-10 m. This height estimate is similar to tsunami wave heights observed at the Venezuelan coast in historical times, e.g. at Paria in 1530 or at Puerto Tuy in 1900 [5]. The minimum inundation of such a tsunami on the carbonate platform along the windward side would be 300 m, possibly even more than 500 m. However, findings of candidate tsunami deposits in the sediment cores of the bays, bokas and saliñas, such as Boka Bartol, Saliña Tam or Lagun far inland indicate that especially these low-lying areas provide pathways for inundation and destruction by a tsunami. Thus, a low topography, as found on the entire southern part of Bonaire, is more prone to tsunami inundation.

Abstract:

We present sediment cores from seven coastal geoarchives on Bonaire, southern Caribbean, containing layers of high- energy sedimentation. Tsunami deposition is inferred for some layers based on the presence of allochthonous reefal shells including articulated specimens and a high percentage of angular fragments, planktonic foraminiferal taxa and those from the deeper shelf (below storm wave base), basal unconformities and hiatuses of >1000 a, rip-up clasts, thin depositional sequences comprising basal traction carpets overlain by normally graded sand, a proximal sediment source (littoral) in the lower part of the deposit and a broad mixture (littoral, shelfal, terrestrial) in the upper part, and the lack of deposition during recent hurricane flooding. Several tsunami layers were precisely dated to 3300-3100 cal BP, whereas the record of further candidate tsunamis is more disjunct. Additional tsunami evidence is provided by the largest coastal boulders (up to 150 t; a-axis up to 10 m).