ABSTRACT
Many geologists believe that Johnson developed his classical theory relating the origin of barrier islands to shorelines of emergence by only deductive reasoning. However, he originally considered two hypotheses for the origin of barrier islands: one, in response to wave energy establishing a new profile of equilibrium on an emerging shoreline; and two, in response to longshore movement along a stable shoreline. Analysis by Johnson of 18 offshore “projected” profiles along United States and European barrier islands indicated to him that his first hypothesis was the correct one. Coastal geomorphic field studies along the Virginia-North Carolina “Outer Banks” coast by the author have suggested that parts of this barrier island chain developed in response to longshore movement. Restudy of Johnson’s bathymetric evidence seemed called for and, whereas Johnson had constructed only 3 projected offshore profiles across the barrier island portions of this coast, 16 projected bathymetric profiles were constructed. In addition, profiles were also constructed across non-barrier shorelines along this coast, including cuspate spits and headland mainland shorelines.
Analysis of the mean gradient of the offshore slope of these profiles shows that, in general, all types of shorelines along a particular segment of coast exhibit the same offshore characteristics, whether it be a barrier island, a spit, or a mainland shoreline. In addition, when quantitative values are applied to his profile geometry for the North Carolina coast, his results are both incorrect and ambigious. If Johnson had originally constructed projected profiles on both barrier and non-barrier shorelines in the testing of his hypotheses, he might have noticed this discrepancy in his theory of barrier islands as features of a shoreline of emergence.
“He who does not study the past, is doomed to repeat it.”
