Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting (13-16 March 2010)

Paper No. 7
Presentation Time: 8:00 AM-12:05 PM


WILKINS, Christopher, Environmenal Studies, Randolph-Macon College, Ashland, VA 23005, FENSTER, Michael S., Environmental Studies/Geology, Randolph-Macon College, Ashland, VA 23005, BRENNER, Owen T., Environmental Sciences, University of Virginia, Charlottesville, VA 22904, GONTZ, Allen M., Environmental, Earth and Ocean Sciences, University of Massachusetts - Boston, 100 Morrissey Boulevard, Boston, MA 02125 and MOORE, Laura J., Department of Environmental Sciences, University of Virginia, 291 McCormick Rd, Charlottesville, VA 22904,

Geophysical surveys, consisting of 274 km of seismic reflection profiles and side-scan sonograms, were obtained from the nearshore of Virginia's northern parallel beach retreat islands during July 2009 in order to answer the following questions: 1) Does a source of sediment exist that can supply Virginia's barrier islands with sand during sea-level rise? 2) What are the seismic and sedimentological characteristics of those sediment sources and in what volumes do they occur? Finally, 3) How might the inherited geology, topography, and/or bathymetry have influenced or continue to influence barrier island morphodynamics during sea-level rise? Seismic reflection profile data indicate that the upper approximate 4 m of the nearshore, over a 400 km2 area, contains approximately 1.56 billion m³ of potential sediment for supplying the islands. Bedforms visible on side-scan sonograms (average ht < 1 m; wavelength ≈ 50 m) indicate sediment mobility and an onshore migration direction. However, sediment grab samples from the seafloor in this area indicate that the average barrier island grain size (0.25 mm ± 0.05 mm) does not match the average nearshore grain size (0.14 mm ± 0.05 mm). Consequently, surficial nearshore sediments are too fine to supply the islands given the existing energetic oceanographic conditions. Finally, a seismic facies analysis reveals the presence of older stratigraphic units (Miocene – Pleistocene), which likely control the location of the present-day tidal inlets and barrier islands.