Introduction Parramore, like the other Virginia barrier islands, has a small sediment supply and a mesotidal range averaging 2m. Southern Parramore Island averages 0.5 km in width. Parramore Island is a typical drumstick barrier island that experiences rotation about a central point (Hayes, 1975). Southern Parramore Island is the thinner, topographically lower piece of the drumstick and is presumably receiving the bulk of geomorphic change. Sand is transposed landward over the back-barrier marsh during transgression by storm overwash processes. Erosion rates for southern Parramore have averaged at 15 m/year; northern Parramore's erosion rate are less than 5 m/year. As a result, the southern end has not had extensive time for coastal dune growth and vegetation development. The topographic differences between the northern and southern end reflect the relative age of the two sections of the island and subsequently, the length of time available for the evolution of coastal dunes. A maritime forest has gradually matured over the large, hundred-year-old+ dunes on the northern end. Dunes on the southern end are probably only tens of years in age. This research was conducted solely on the southern end during June, July, and August, 1995, therefore caution needs to be taken in extending interpretations elsewhere.

Objectives The focus of this study on southern Parramore was on the rate and the mechanisms of dune formation and included the following: 1) to identify the barrier island sub-environments that have a high potential for dune development; 2) to determine the cause of dune formation on southern Parramore Island; 3) to understand more about the relationship between the coastal dunes and other geomorphic features (e.g. berm, interdune); 4) to develop a working model for dune evolution on the southern Parramore. In order to accomplish these objectives, a number of experiments were conducted on a site located approximately .5 km south of the LTER pimple study area.

Deflation Experiment Deflation was minimal during the summer months. Berntsen (1995) also showed that in previously deflated washover locations, deflation rates were small. Overwash occurs primarily during the winter months. Following overwash, winter winds immediately begin deflation of the recently deposited overwash sediment. During the several months before the summer begins, an armour of shell lag develops on the fan due to winter deflation. By the time the summer begins, the shell lag armour appears to be sufficient to inhibit the continuance of significant deflation. High summer wind velocities are typically associated with rainfall. The effect of aeolian processes will be diminished during periods of precipitation due to increased cohesion of the sand. However, in late August, 1995, when there was virtually no rainfall, wind speeds were very high, averaging close to 4 m/s. These winds were destructive, deflating large, unprotected dunes.

Wrack Terrace One of the most significant geomorphic changes at the study site in 1995 was the development of a wrack terrace. Wrack clumps are clumps of dead Spartina grass that have been deposited by the ocean onto the edges of the washover fan during overwash events. These wrack deposits accumulate sand, attract vegetation growth, and eventually build up into terraces, particularly during the summer months. Summer winds contributed sand to the wrack terrace at a rate of 615 cm3 per m2 per day between 7/13/95 and 8/2/95. A major overwash event on 8/18/95-8/20/95, caused by Hurricane Felix, submersed the wrack terrace and deposited approximately 200000-300000 cm3 per m2 of sand by overwash processes. The results show that a large amount of overwash sediment accumulated on the former wrack terrace, a significantly higher amount than had previously accumulated through aeolian processes. Under environmental conditions devoid of a major summer overwash event, the wrack terrace would probably lead to foredune development. Other studies have focused on the occurrence and evolution of the foredune (Hesp, Thom, 1990; Carter and Wilson, 1990; Burk et.al 1981,). While the foredune is generally considered a typical part of barrier islands, the rates of island erosion, and the intensity of overwash events on Southern Parramore Island create conditions where foredune development and maintenance are not feasible. Foredune development on Southern Parramore would likely require a lull in storm activity spanning 5-10 years for a sufficient accumulation of sand to develop on the wrack terrace that could survive during future overwash. This does not seem likely given southern Parramore's lateral shoreline erosion rates. Wrack terraces also developed on the perimeter of washover fans, and on areas adjacent to the back barrier marsh. Summer observations indicated a slower rate of development for these wrack terraces due to their smaller supply of sediment. However, these wrack terraces have greater chance of longevity given their distance from potential overwash interference. The fan-margin wrack terraces appear to develop into the terraces located on the sides of the overwash fans (Berntsen, 1995).

Dune Nucleation Several types of potential dune nuclei were selected for observation including shell clumps, wrack piles, and paleomarsh clasts ripped up from the beach during island transgression. Two meter by two meter vegetation plots containing Cakile endulata and Spartina patens were also constructed to determine if vegetation density affected sediment accumulation. All of the potential nuclei were established on Parr 5 in May, 1995, for systematic observation and photographic documentation for the duration of the summer. Wrack deposits were the only nuclei in the experiment that were successful in the accumulation of pendant tails. However, these accumulations were temporary and were displaced during the latter half of the summer when the wind direction changed. Shell clusters accumulated nothing and paleomarsh clasts only accumulated minimal amounts of sand. The vegetation plots observed did not have the vegetation density required for significant sediment accumulation . While some sand was deposited over the plot, the amounts were dispersed over larger areas and morphologically did not resemble protodunes. A longer time interval would be required to conclude the occurrence of a preferred dune nucleus based on these observations alone.

Dune Excavation A transect of dunes adjacent to the study site across the width of the island extending from the beach to the back-barrier marsh was selected for excavation to search for evidence of dune nuclei. Augers and shovels were used to probe the dunes to determine if natural nuclei were present. Each dune cored was a hummock dune, ranging from 0.25m to 2 m in height. To ensure variety in dune age, dune size and vegetation density and diversity was discerned (Burk et al. 1981). Of the twenty-six hummock dunes cored, paleomarsh clasts were found in sixteen dunes, wrack clumps were found in two dunes, and in eight dunes the size was too large to determine if a natural nucleus was present. Paleomarsh clasts alone serving as dune nuclei undergo micro-constructive and destructive phases. During high speed winds large quantities of sand will collect in the lee of the clast; but a change in wind direction will deflate this leeward accumulation. An additional destructive component occurs when wind currents reflect off the dense paleomarsh clast, which produces a vortex scouring action. A horseshoe scour will result from the winds and will prohibit additional sand from accumulating near the clast. During the summer months Cakile Edentula tended to grow on top of the paleomarsh clasts (like the wrack terrace) because of abundant nutrient supply and high water content compared with the surrounding sand flats. Following plant growth, greater quantities of sand accumulated not only on the sides of the clasts, but sand grains were deposited on top of the clast, because the wind velocities were reduced by the vegetation roughness, not reflected. A five stage model is proposed as the tentative mechanism for dune nucleation and evolution: A. Clasts from the paleomarsh horizon are eroded during ocean transgression and deposited on fans during overwash events. B. Initially some sand will accumulate on the edges of the clast. C. Minimal sand accumulation occurs, attributed to the bi-directional wind currents and the scouring action. D. Cakile Edentula growth concentrates around the clasts due to greater water retention and nutrient supply of the paleomarsh material. Airflow- plant interaction causes reduced wind velocities, ceasing the saltation process, and resulting in sand deposition. The dune stabilized by the clast-vegetation combination, has a higher likelihood of survival. E. The dominant vegetation changes to the Spartina patens after a few years. In later dune evolution stages, the vegetation thickens and Ammophila breviligulata begins to develop on the dune.

Berntsen, Jon P., 1995. Hydrogeomorphic and Vegetative Relationships on Low Profile Barrier Islands. (on the) Virginia Coast Reserve. Senior Thesis, Bucknell University.

Burk, C. John, et. al., 1981. Dune And Vegetation: Natural Recovery on a Damaged Barrier Island. (Journal unknown). pp. 21-24.

Carter and Wilson, 1990. The Geomorphological, Ecological, and Pedological Development of Coastal foredunes at Magilligan Pt, Northern Ireland. Coastal Dunes: Form and Process. pp. 135-145.

Hayes, M. O., 1975. Morphology of sand accumulations in estuaries. Estuarine Research, v. 2: Geology and Engineering, pp. 3-22.

Hesp, Patrick A. and Bruce G.Thom, 1990. Geomorphology and evolution of active transgressive dunefields. Coastal Dunes: Form and Process. Ed. Nordstrom, Psuty, and Carter. pp. 253-284.

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