Contrasting styles of Hurricane Irene washover sedimentation on three east coast barrier islands: Cape Lookout, North Carolina; Assateague Island, Virginia; and Fire Island, New York

Abstract

Storm surge and wind-driven waves generated by Hurricane Irene, which made landfall on the U.S. east coast on August 27 2011, resulted in overwash of sandy barrier islands from North Carolina to New York State. Overwash has significant impacts on barrier island geomorphology: it represents a sediment pathway into island interiors, a component of island sediment budgets, and can cause considerable aggradation of backshore surfaces, important for potentially offsetting the effects of rising sea level. This study describes the morphology, texture and microfossil content of Hurricane Irene washover deposits at three contrasting barrier island sites: Cape Lookout, North Carolina, Assateague Island, Virginia and Fire Island, New York. At all three sites, run-up overwash occurred, wherein waves were sufficient to overtop parts of the beach system and transport sediment inland. However, at Fire Island, overwash was restricted by a higher elevational threshold to low spots in the beach system coinciding with pre-existing breaches in foredunes. The result was the formation of isolated, thinner, low-volume washover fans. At Assateague Island and Cape Lookout, lower elevational thresholds allowed waves to overtop longer continuous sections of beach systems, resulting in the formation of laterally-continuous, thicker, larger-volume washover terraces. Overall, the deposits lacked consistent trends in thickness and texture (such as thinning and fining inland, reflecting a progressive reduction in overwash competence). Thickness and texture of the deposits were both spatially variable and probably reflect infilling of low points on the former surface and the influence of beach and foredune sediment sources. All the washover deposits were essentially barren of foraminiferal microfossils, supporting the textural evidence that the adjacent beach and foredunes were the predominant sediment sources.