Date Thesis Awarded
Honors Thesis -- Open Access
Bachelors of Science (BS)
R. Heather Macdonald
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 research presents insights into the evolutionary and 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 illustrate that Parramore Island was three discrete islands experiencing overwash-driven retrogradation as recently as 977 ± 144 BP. Dates provided by OSL analyses indicate the progradational ridges overlying and seaward of these washovers are only 140 – 560 years old. This confirms 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 proto-barrier 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 dissected ridges in the form of so-called “Pimpled Mounds” west of the modern foredune. Lower ridges and swales have been inundated by rising sea level and are covered by thin (m), young (commonlyold) marsh that has migrated upland into the interior of the barrier island. These data indicate that Parramore has only existed in its present form for ca. 200 years. Moreover, a recent shift to rapid erosion – and consequent perceived “rotation” of the island – along much of its length (at an island-average rate ~12 m/yr since 1980), suggest that the apparent robustness and stability of Parramore are ephemeral features of a rapidly changing barrier island. The modern island may be undergoing a transition from erosion to a period of landward parallel-retreat, potentially due to a decrease in sediment supply reaching the island from sand trapping at the more northern Fishing Point. If so, Parramore may become the most southerly barrier in the Virginia Eastern Shore’s characteristic “Arc of Erosion”.
Raff, Jessica L., "Thresholds of barrier island change: A case study of Parramore Island, Virginia Eastern Shore" (2017). Undergraduate Honors Theses. William & Mary. Paper 1063.