HURRICANE OVERWASH DEPOSITS IN SALT PONDS OF ST. CROIX, U.S.V.I.: THEORY VS. PRACTICE

A common phenomenon on the east and gulf coasts of the United States during hurricanes and extratropical storms is the landward migration of sandy barrier islands through overwashing of beach sand into landward lagoons and marshes. These overwash events are interspersed with more quiescent time periods when fine-grained deposition of mud dominates in the back-barrier environment. Under ideal conditions, repeated overwash events through time should leave a dateable stratigraphic record consisting of alternating muds and sand.

Salt ponds of the Caribbean region, generally separated from the ocean by a sandy barrier and not directly connected to the ocean, appear to be ideal environments for the deposition and preservation of storm overwash deposits. Additionally, since the Caribbean region is largely unaffected by extratropical storms, the study of salt ponds is attractive for the paleoreconstruction of hurricane activity. Since 1886, at least 10 hurricanes have either made landfall on St. Croix or passed nearby bringing strong winds and large waves to the island. Of these hurricanes, 4 were category 3 or higher (1899, 1928, 1989 and 1998). Cores were collected from St. Croix in Southgate Pond and Westend Salt Pond within 10 m of the mangrove-covered barriers separating the salt ponds from the active beach. Analyses of these cores indicate that overwash deposits from historical hurricanes are not detectable in the stratigraphic record of the salt ponds on St. Croix. Apparent complicating factors may include a combination of protection from waves afforded by offshore reefs, trapping of landward-transported sand by dense mangroves fronting the salt ponds, the occasional presence of burrowing organisms and the potential for ephemeral connections to the open ocean. These findings suggest that sedimentary records in salt ponds with these characteristics will not be useful in the reconstruction of paleohurricane activity and that alternative proxies for hurricane landfall may be needed in the Caribbean region.