Original paper

Size and mass of shoreline boulders moved and emplaced by recent hurricanes, Jamaica

Khan, Shakira; Robinson, Edward; Rowe, Deborah-Ann; Coutou, Richard

Abstract

Using estimates of volume, bulk density and mass of shoreline boulders obtained from experiments involving water immersion of small representative samples, we provide a preliminary list of Jamaican boulders that are known to have been moved and/or emplaced by hurricanes. Storm surge, wave run-up and waves breaking over cliff tops from severe hurricanes are able to move the largest Holocene coastal boulders (up to 80 t) yet examined in Jamaica and among the largest recorded from any Caribbean coastlines. Boulders as big as 25 t have been emplaced onshore by two recent hurricanes. Some of the largest boulders may have been emplaced originally by tsunamis but no direct evidence is available.Evidence suggests that the transport history of many, perhaps most Jamaican boulders is complex, consisting of progressive movement across the coastal platforms by repeated storm and, possibly, rare tsunami events. This history probably extends back some 4,000-5,000 years, when sea level reached more or less its present elevation. Cumulative movements into zones where storm surge and inundation are reduced in intensity, and forest vegetation increasingly inhibits further movement, results in some boulders eventually being incorporated into the debris ridges characteristic of parts of the present coastline. Where they exist, these ridges and boulders provide convenient geomorphological features to guide coastal planners in delimiting areas subject to hazards associated with the impact of extreme wave events.

Keywords

bouldershurricanestsunamisjamaicacoastal management