PRECHT, WILLIAM F., Reef Resources and Associates, Miami, FL

ABSTRACT: The Geologic Effects of Hurricane Andrew on the Florida Reef Tract: A Preliminary Overview

On August 24, 1992, Hurricane Andrew, a small and powerful Category IV hurricane passed over south Florida leaving behind an unmatched path of destruction and devastation. The storm's eye moved rapidly (16 MPH) over the northern portion of the Florida Reef Tract. Sustained winds measured within the eyewall of the hurricane were in excess of 145 MPH. The damage to the reefs were however, not commensurate with the extensive damage observed on land. The reefs which were most affected are located between the Carysfort Light to the south and the Fowey Rocks Light to the north. In fact, the major portion of the reef tract from the Key Largo National Marine Sanctuary, south to the Dry Tortugas, sustained little or no damage.

Investigations along the length of the reef tract have revealed some important and arresting sedimentologic observations. These include: (1) most physical damage to the reefs occurred in waters of less than 15 meters; (2) branching corals, especially the Acroporids sustained the most damage; (3) although head corals were displaced and overturned, most damage to these corals was from abrasion by sediment in the water column; (4) large amounts of sediment were shifted both onto and off reef settings; and (5) most sediment smaller than the 62.5 micron fraction stayed in suspension for a long time after the storm and were removed from the surface sediment of the shallow reef facies.

In conclusion, major reef damage was localized within a relatively narrow band, less than 30 miles in width. The damage to the reefs was also less than originally predicted from hindcasting the energy of the storm. This is probably related to the Bahamas blocking and reducing the power of the largest waves.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.