BARRIER AND BARRIER ISLAND BEHAVIOR AT THE HISTORICAL TIMESCALE: WHAT CAN WE LEARN FROM THE OUTLIERS?

Developing geologic models of geomorphic systems involves the identification of common attributes from a variety of systems and the distillation away of local variability. Barrier and barrier island systems share many common attributes, but there is a wide range of variability that strongly influences how these systems behave at historical timescales. Much modeling work focuses on the relationship between dynamic driving forces on the one hand, and geomorphic response on the other. Some models take into account the feedback that exists between these. Less often considered are factors related to sediment volume and supply, underlying geology and the geological setting, and the self-organization that sometimes occurs.

This presentation considers several ‘unusual’ barrier island systems to highlight the role of these factors in barrier behavior. Barrier islands on bedrock in Scotland demonstrate a primary control on evolution of antecedent topography. The low volume of sand in barrier islands in Chesapeake Bay is primarily responsible for very rapid migration rates. Episodic fluvial sediment supply to some South African barriers controls their historical scale behavior while others demonstrate the influence of basement slope on migration rates. These and other examples highlight the importance of what are often considered unimportant constraints on geomorphic behavior.

The nature of ‘local variability’ in barriers and barrier islands is diverse, but its important, and even dominant role in their evolution, urges caution in the application of generic modellling approaches in predicting future shoreline behavior.