‘A TALE OF TWO STORMS' – IMPACTS OF HURRICANES FRANCES AND JEANNE ON CARBONATE SYSTEMS, ABACOS, BAHAMAS

Hurricanes commonly are cited as being influential or even dominant controls on geomorphologic evolution of carbonate systems, and interpretations of their influence is highlighted in many interpretations of ancient platforms. Two strong tropical cyclones (Frances and Jeanne) passed directly over the oolitic tidal shoals and reefs of the Abacos, northern Bahamas, in 2004, offering a unique opportunity to explore the effects of storms on these shoals.

This study compares high-resolution (2.4 m pixels) pre- (16 November 2003) and post- (03 March 2005) storm Quickbird remote sensing images to qualitatively determine the nature and extent of geomorphologic change related to passage of the storm. Interpretations of these data suggest that storm forcing drove no major geomorphic changes or re-organization, although some low-amplitude sand waves migrated several 10s of meters. Likewise, bedform changes follow trends analogous to those that occurred between 1986 and 2005. Morphological adjustments of the past two decades suggest that the shoals adjust according to the everyday forcing of winds, waves, currents, and tides. Although the strong forces produced by the tropical cyclones are capable of impacting carbonate systems, in situ observations of flow indicate that daily tidal and wind forces may be adequate to drive geomorphic evolution.

These results illustrate that these storms were neither sufficient to drive major change nor necessary to explain geomorphic evolution of this system. This theme does not seem to be an exception; many storms had comparable impacts. These observations are consistent with quantitative wave models that show how energy is dissipated across carbonate systems with different geometries; these too document the difficulty of generating grainy ‘storm deposits' of size comparable to those interpreted in ancient successions. Collectively, these observations and models question the paradigm of storm influence on carbonate platforms.