99. The data presented herein have shown that although islands in the 

 study area narrowed over the 130-year study period (Figures 47 and 48), they 

 did not migrate in the classic sense toward the mainland because both the 

 ocean and sound shorelines retreated toward the island. The reasons island 

 migration has ceased are not clear. Quite likely, overwash has not been an 

 important mechanism in sound shoreline progradation for the last several 

 hundred years. Today, the islands are probably too wide in most places for 

 overwash penetration across the entire island (Leatherman and Fisher 1976). 

 In addition, prior to about 1800 the islands were well vegetated with trees 

 and shrubs (Hennigar 1979) which would have either inhibited overwash or been 

 destroyed had frequent or severe overwash conditions existed. In the nine- 

 teenth and early twentieth centuries, aeolian transport may have been of some 

 local significance because poor land practices had left the island barren 

 (Hennigar 1979). However, at other times wind- transported sand probably did 

 not account for much sound shoreline progradation. If island migration oc- 

 curred in the study area between 1585 and 1850, it was probably the result of 

 inlet processes. Figure 9 shows that the number and permanency of inlets have 

 decreased in the study area from 1585 to the present time; if migration is not 

 occurring today, it is probably because the impact of inlets is too small. 

 Only Oregon Inlet now acts as a sediment trap in the study area; significantly, 

 the barriers adjacent to it are migrating in a westerly direction. 



100. The reasons for island narrowing are also not clear; nor is it 

 clear when the narrowing cycle began or when it will end. Sand losses from 

 the front and back of the islands in the recent past may have been partially 

 caused by a rise of sea level relative to land--a vertical rise of probably 

 4 mm/year in the study area since 1930 (Hicks 1981) (on a static shore slope 

 of 1:40, for example, this would translate to an apparent shore retreat of 

 0.1 m/year) . Quite likely a relative sea level rise would also have caused 

 dynamic changes in the beach that would have increased the shore retreat rate; 

 this effect cannot be quantified at present. Long-term changes in wave and 

 wind conditions also could have forced the ocean and sound shores to retreat 

 or accrete, especially if the frequency and duration of storms had changed 

 substantially. An added factor, frequently not considered, is that unconsoli- 

 dated marine coasts may retreat under "normal" conditions. Whether the rate 

 of relative sea level rise will increase or decline and whether wind and wave 

 conditions will produce more or less erosion in the future are unknown. 



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