Morphological Impact of a High Energy Swell Event on Caribbean Island Shorelines

Extreme waves in the Caribbean have three main origins; hurricanes, tsunami and swell. The latter have the most widespread occurrence but are the least studied. A slow-moving, low pressure system in the western Atlantic generated very large swell waves from March 20th-22nd 2008 with an approximate 1:20 yr return interval. At the peak of this event, a buoy off the US Virgin Islands recorded 14-16 ft (>4.5m) waves at 17 seconds period. Morphological impacts (coral reef damage, coral rubble deposition, beach erosion) were reported throughout the Eastern Caribbean from Guyana to Puerto Rico. In this paper we present observations of morphological impacts of the swell in the British Virgin Islands (BVI) on sand beaches, gravel beaches and coral rubble beaches. The morphological response was highly variable according to the coastal geologic setting, exposure to wave activity and nature of beach material. Sand beaches with reef protection showed little change, while others exhibited scarping, overwash and offshore sand transport, similar to that reported elsewhere for sand beaches. Although some impressive changes were noted in coarse clastic beaches (both erosion and deposition), these generally amounted to little more than surface decoration on much larger hurricane and tsunami deposits.