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The origin of barrier islands has been discussed and debated in the literature for nearly a century. Virtually all interpretations have been based on stratigraphic and geomorphic data. Two small barriers have formed in Pinellas County during the past 2 decades. Both aerial photography and field data show that these islands originated as shallow subtidal shoals. Continued accumulation of sediment occurred through normal low-energy waves and currents with assistance from occasional intense storms.

North Bunces Key became intertidal in 1957 and showed marked growth after Hurricane Donna in 1960. It is now 1.5 km long and rises more than 1 m above mean sea level. South Bunces Key was subtidal until 1974. It is 1.3 km long and rises nearly a meter above mean sea level. Anclote Key, which is 35 km north of Bunces Keys, is 4 km long and shows remarkable geomorphic similarities to North Bunces Key. Caladesi Island, located 9 km south of Anclote Key, is 6.5 km long and displays a "drumstick" configuration. Interpretation of depositional environments from 17 cores reveals that this island also originated as a shallow shoal on the inner shelf. Initial development of Caladesi Island has been dated at 5,000 to 7,000 years B.P.

Data from the modern environment and the stratigraphic record lead to the postulation that shoaling of shallow linear sand bodies has been a common mode of origin for barrier islands along the west-central peninsula of Florida.

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