MORPHOLOGIC AND SEDIMENTOLOGIC CHARACTERISTICS OF STORM DEPOSITS IN COASTAL BARRIER-ISLAND ENVIRONMENTS

Extreme energetic conditions associated with storms induce tremendous offset from equilibrium conditions and therefore result in dramatic morphologic and sedimentologic changes in coastal barrier-island environments. The extreme energy associated with coastal storms bares certain similarities to tsunamis. Valuable insights can be gained by comparing the sedimentary processes and records of these two extreme events. Storm-induced processes and subsequent sedimentary records can be classified into two general categories: erosional and depositional; both can be preserved into geological records. In terms of temporal variations of hydrodynamic energy, a storm can be separated into two phases: rapid energy increases as storm approaches and energy subsidence after storm passes. For barrier-island environments, from a general temporal point of view, erosion dominates, especially along the ocean facing side of the barrier island, when storm energy increases rapidly and peaks. Deposition tends to dominate as storm energy subsides. From a preservation-potential point of view, erosional features associated with peak storm energy and deposition occurred in the subsidence phase of the storm tend to have high probability to be preserved. Spatially, certain sub-environments in a barrier-island system, e.g., barrier interior wetlands, and back-barrier bay and wetlands tend to receive and preserve storm-induced washover deposits, without much erosion. Other sub-environments, such as backbeach, foredune, and interior dune fields, may experience erosion first as the storm energy peaks, while receiving washover deposits as storm energy subsides. Therefore, an erosional surface is expected and often identified in these sub-environments. Other sub-environments, e.g., lower foreshore and nearshore areas, tend to experience mainly erosion with little preserved post-storm deposition. Storm deposits are easily and convincingly identifiable in certain sub-environments, e.g., in wetlands and back-barrier bay and over eroded dune fields. These pre-storm sub-environments also provide relative high preservation potential. While in other areas, e.g., in the nearshore and intertidal zones, storm deposits may have lower long-term preservation potential and can also be difficult to identify.