Paper No. 8-6
Presentation Time: 2:40 PM
BARRIER ISLAND CHANGE ALONG THE EASTERN SHORE OF VIRGINIA: INSIGHTS FROM A CHRONOLOGICAL AND SEDIMENTOLOGICAL STUDY OF PARRAMORE ISLAND
The barrier islands and backbarrier marshes and bays of Virginia’s Eastern Shore are one of the largest undeveloped barrier-island systems in the US, and are currently threatened by sea-level rise, storms, and changing sediment supply. This study presents insights into the developmental history of Parramore Island, one of the largest – and commonly assumed to be most stable – of these islands. Stratigraphic (vibracores, auger cores), geospatial (historical maps, aerial imagery, t-sheets, LiDAR), and chronological (optically stimulated luminescence [OSL], radiocarbon) data reveal that Parramore has alternated between periods of landward migration and seaward progradation several times during the past 1000 years. Radiocarbon dates, stratigraphic data, and historical maps reveal that Parramore was three discrete islands undergoing overwash-driven retrogradation as recently as 977 ± 144 BP. Progradational ridges overlying these washovers, dated with OSL analyses, are only 140 – 560 years old, confirming that the progradational beach and dune ridge system forming the core of Parramore Island is much younger than those on similar barriers elsewhere along the Mid-Atlantic coast. Over the last ca. 200 years, individual islands prograded, forcing inlet closure and development of a shallow beach ridge and swale system landward of central and southern Parramore. Remnants of higher ridges are subaerially exposed and vegetated in the form of Little Beach, Revels Island, smaller ridges along the western edge of Parramore, and so-called “Pimple Mounds” west of the modern foredune. Lower ridges and swales have been inundated by rising sea level and are covered by thin (<50 cm), young (commonly <100 years old) marsh that has migrated upland into the interior of the barrier island. Although Parramore is thought to be one of the most stable of the Virginia Barrier Islands, these data indicate it has only existed in its present form for ca. 200 years. Moreover, a recent shift to rapid erosion along much of its length (~12 m/yr since 1980), suggest that the apparent robustness and stability of Parramore are ephemeral features of a rapidly changing barrier island.