SEA-LEVEL RISE AND ISLAND BUILDING ON THE “NATURAL” CORE BANKS, NC COMPARED WITH ISLAND NARROWING ON THE “HUMAN MODIFIED” NORTHERN OUTER BANKS, NC

New ideas on the origin and evolution of the large-scale geomorphic framework and associated ecosystems, in concert with detailed process-response dynamics on the NC Outer Banks (Duck to Cape Lookout), involves integration of short- and long-term shoreline change data with geomorphic and subsurface stratigraphic mapping and chronostratigraphic analysis. Individual study sites differ in geologic framework, geomorphic character, sediment supply, physical processes, and represent both the “human modified” northern Outer Banks (includes the Cape Hatteras National Seashore) and the “natural” Core Banks (Cape Lookout National Seashore).

Major conclusions include the following. 1) Shoreline recession is storm-event driven. Short-term shoreline change data demonstrate that individual storms result in large-scale recession with only partial and temporary post-storm recovery if given enough time between storms. Since long-term recession rates integrate both low- and high-storm periods, results are a low net recession rate that is misleading. 2) Storm-driven shoreline erosion of barrier islands is intimately inter-related with sediment supply in concert with inlet and overwash dynamics, all of which determine island width, elevation, and vegetative cover through time. These processes drive island evolution and migration in response to a rising sea level. 3) Islands in which inlet and overwash dynamics are allowed to operate unimpeded tend to be healthy and display a complex, long-term evolutionary succession that is dependent upon the patterns of both storms and sea-level rise. 4) Most human modification attempts to stop or minimize normal storm impacts (shoreline recession, inlets, and overwash) severely influence the natural barrier island dynamics and cause island narrowing. Barrier-dune ridges and ocean-front development, that inhibit or prevent inlets and overwash, jeopardize the long-term health of the barrier during rising sea level, greatly increase the risk to urban development, and increase the likelihood of barrier-island collapse in response to category 3-5 storms.