V. BEACHES AND GEOLOGY 



The FRF, located along a barrier spit forming the eastern edge of the 

 Coastal Plain, is the northernmost part of a complex series of barrier islands 

 which extend south to Cape Lookout. Though there are currently four inlets 

 along this stretch (Oregon, Hatteras, Ocracoke, Drum), the area is dynamic and 

 includes many relic inlets (Fig. 28). 



1. Origin . 



The origin of this series of barrier islands is both complex and slightly 

 controversial. Judge (1980) provides a summary of the following significant 

 theories. De Beaumont (1845) suggested that the islands formed by bar build- 

 ing. Gilbert (1885) theorized that longshore drift and spit building were the 

 primary cause of formation. Hoyt (1967) postulated that rising sea levels (or 

 land submergence) could flood the flats behind the dunes and form a long sub- 

 aerial ridge. Hoyt and Henry (1971) noted that the capes coincided with 

 historic river deltas which were isolated by rising sea levels. Using strati- 

 graphic interpretation of core samples. Pierce and Colquhoun (1970, 1971) 

 found that 39 percent of the original 200-kiloraeter coast was primarily dune 

 and that the islands formed by shoreline submergence. Field and Uuane (1976) 

 postulated that the barriers formed on the Continental Shelf during low sea 

 levels and moved shoreward under the influence of sea level rise. Riggs 

 (1978) postulated that the islands were formed by submergence and had been 

 modified by coastal processes (waves, tides, and currents) to form their 

 present shape and alinement. 



The general consensus is that the barrier islands are comprised of recent 

 (Holocene) sediments overlying Pleistocene deposits. 



2. Shoreline Changes . 



Historically, the ocean shoreline at the FRF has been relatively stable. 

 This was documented by Wahls (1973), who found a mean annual accretion rate 

 of 0.91 meter (3 feet) per year for the period 1955 to 1971. More recently, 

 Dolan's (1979) analysis of shoreline changes north and south of the FRF showed 

 long-term stability from 1940 to 1975 (Fig. 29), and overall erosion from 1977 

 to 1979. These results are based on shoreline measurements from photos at 50- 

 meter (164 feet) intervals over the 28-kilometer (45 miles) reach. Average 

 rates of change are computed based on the rates of change for each set of suc- 

 cessive photos. The following sets of photos were used in the analysis: 



1940 to 1975 1977 to 1979 



21 October 1940 2 February 1977 



29 March 1955 11 November 1977 



3 May 1962 16 May 1978 



5 September 1975 2 December 1978 



20 September 1979 



Three rates were averaged to compute the 1940 to 1975 rates; four rates were 

 averaged to obtain the 1977 to 1979 rates. The air photo analysis procedure 

 is described in Dolan, et al. (1979). Errors can be significant, and average 

 rates of change less than 1.0 meter (3.3 feet) per year over 40 years are 

 difficult to measure. 



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